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The interactions between aqueous humic substances (HS), the principal component of natural organic matter, and phosphorus (P), an important nutrient, are complex and poorly understood. Past research has shown that P has the potential to form complexes with HS in fresh waters. Humic complexation may change P bioavailability within such waters and, in addition, influence the transport of phosphorus within catchment settings. This project aims at examining the relationships and associations of P, HS, and iron (Fe) in Loch Meadie, Sutherland, northern Scotland, which has been assessed as reference condition with respect to P. "Reference condition" means the loch should not have been disturbed or only minimally impacted by human activities. Results will be used for identifying characteristic parameters which can enhance the performance of the model used to predict reference condition total phosphorus (TP) concentrations for highly-coloured Scottish lochs under the Water Framework Directive. Apart from Loch Meadie, samples collected from other reference condition lochs in northern Scotland and Shetland were also analysed in order to enhance our understanding of the relationship between TP and HS by including different colour types of reference condition lochs (clear water, mesohumic and polyhumic water). Significant seasonal trends in the water colour and total Fe (TFe) were observed from the Loch Meadie (Swordly) monthly samples. From mid-autumn to early winter (October-December), the water colour and TFe was typically higher than in the other seasons. The HS in Loch Meadie (Swordly) had relatively small molecular weight and low aromaticity, which was closer to fulvic acid rather than humic acid. According to the results of the 16 northern Scotland (mainland) and Shetland lochs, the total organic carbon (TOC) / dissolved organic carbon (DOC) and water colour were higher in polyhumic lochs than mesohumic lochs. The TP and total filterable P (TFP) varied in water samples collected from different lochs, whereas the TFe and total filterable Fe (TFFe) in polyhumic lochs was generally higher than that in mesohumic lochs. Ultrafiltration was used to isolate the colloidal component from loch waters, which was then fractionated by gel filtration chromatographic and centrifugal ultrafiltration methods. The gel filtration chromatographic fractionation of the colloids revealed two brown-coloured bands which had distinctive UV/Vis spectral features. The first eluting band had larger and more aromatic HS molecules than the second band, and in addition both P and Fe were primarily associated with the larger, more aromatic HS. This result demonstrated that P was able to form complexes with HS, in particular larger and more aromatic humic molecules, under the presence of Fe in the dissolved fraction of loch waters. Results from the centrifugal ultrafiltration method agreed with the gel filtration chromatographic results. The SEM-EDX results showed that P was likely bound with both the organic and inorganic particles in the particulate fraction of loch waters, however, the detailed binding mechanism between P and suspended solids was unclear and needs further investigation. Based on the main findings of this research, the current WFD models were improved by adding two new parameters, UV254nm (or SUVA254nm) and Total Suspended Solids. The new TP models, compared to the WFD non-humic model which is currently used by SEPA, gave significantly better prediction of the reference TP concentrations in most of the highly coloured Scottish lochs studied in this research.

The anthropogenic and natural input and transport of particulate organic carbon (POC) into and along stream systems from land to ocean is not yet well described (Regnier et al, 2013). Accelerated soil erosion due to changes in land use (e.g. expansion and intensification of agriculture) contribute to POC transport from land to ocean, while artificial damming of river systems, such as hydropower, trap the suspended particulate fractions and contribute to limnic storage in reservoirs. These perturbations on the landscape impact the volumes, transport and fate of suspended organic material. While mainly geomorphic processes control erosion and deposition of inorganic sediments, the mobility and transformation of POC is further subject to within-catchment stabilisation processes, sequestration by burial into sediments, and microbial fermentation which contribute to the vertical emission of potent greenhouse gases like CO2 and CH4. These sources, sinks and transformations of POC along the land-ocean aquatic continuum (LOAC) are dynamic and depend on input, transport, and deposition of suspended organic materials. Particulate organic carbon dynamics has been studied broadly in the past, both in freshwater systems, estuaries and oceans. However, its role in the global carbon cycle has been highlighted especially in recent years due to the lack of quantifiable pathways of POC sequestration, transport and mineralisation in freshwater systems. This project studied POC in two contexts: 1) POC transport and fate in a tropical reservoir was modelled and measured, and 2) the effects of flocculation on riverine DOM was measured by experiments. In the first study, erosion rates were calculated from fallout radionuclides (FRN) in a highly perturbed and largely deforested tropical catchment in Brazil. The results from these field observations were used to quantify soil erosion and sedimentation in the catchment. The results also validated modelled output with Revised Universal Soil Loss Equation (RUSLE) which was used to model soil erosion for the whole catchment. The contribution of allochthonous organic carbon from catchment soils into the reservoir was then quantified. The second study utilized the same field site, and addressed the relative inputs of allochthonous and autochthonous POC into the reservoir. Physical and chemical protection of organo-mineral aggregates and flocs determine the fate of catchment-derived POC. This second part of the study investigated whether allochthonous POC derived from terrestrial soils was more important than autochthonous POC (e.g. from macrophytes, biofilms and algae) for limnic storage in post-flooding sediments of a tropical reservoir. POC was calculated from C inventories of reservoir sediment cores collected along the delta-reservoir gradient and linked to organic matter content by loss on ignition (LOI). POC sources were determined by analysis of carbon-nitrogen ratio (C/N). Finally a POC budget was calculated for the post-flooding reservoir sediments. The third part of this project investigated flocculation dynamics of riverine organic matter in the LOAC. Flocculation experiments were undertaken to determine the effects of three treatments with coagulants on water DOM quality from eight streams draining a rural landscape with headwaters in Exmoor, UK. Through flocculation experiments stream samples were reacted with added clay and salt standards which simulated three flocculation boundaries along the LOAC. The three treatments were T1: increased input of minerogenic coagulants, such as clay, by soil erosion into streams, T2: saline mixing at the estuarine boundary, and T3: a mixture of salt and clay representing soil erosion at the estuarine boundary. Residual DOM quality by each treatment was analysed by mass spectrometry, UV-Vis absorbance and synchronous fluorescence. The results showed preferential removal of humic-like components in residual DOM and the efficiency of the chosen coagulant standards, which demonstrated the dynamics of chemical change in riverine organic matter along the LOAC.

Wastewater treatment plants (WWTP) are the primary pathway for many organic contaminants such as pharmaceuticals and persistent organic pollutants (POPs) found in domestic, industrial and hospital effluents to reach the environment. These substances can accumulate in WWPT sludges or treated biosolids, which are currently subject to limited environmental monitoring or regulation for organic contaminants. The lack of practical tools for assessing the relative quantities of organic contaminants and the potential for these to transfer into the environment presents a barrier to environmental regulators. The aim of this study was to improve understanding of the persistent organic composition of sludges and biosolids to better inform sludge treatment and disposal guidelines. The study combined conventional test methods in a novel approach to assess the leachable and non-biodegradable fraction of organic carbon in sludges and biosolids to characterise how persistent organic pollutants accumulate in these matrices, and subsequently leach when applied to land. Sludges and biosolids from four municipal WWTP were investigated for desorbable dissolved organic carbon (DDOC) using leaching tests. Leachates were then assessed for their relative quantity of persistent DDOC (PDDOC) using biodegradation experiments and optical properties of both DDOC and PDDOC were examined using UV-Vis and FTIR analysis. Sludges from primary and secondary treatment stages, from both nitrifying and non-nitrifying WWTP, and processed biosolids were compared to identify the effect of treatment on relative quantities of DDOC and PDDOC. This is one of the first studies to quantify leachable and non-biodegradable DOC in municipal WWTP sludges and biosolids, comparing results between treatment plant stages and types. The study found that there was little variability in DDOC for primary sludges but DDOC for secondary sludges varied by degree of nitrification in the WWTP, ranging from 11,760 mg.kg-1 in a nitrifying plant to 33,853 mg.kg-1 in a non-nitrifying plant. Nitrification was found to have a positive impact on reducing DDOC leached from sludges from secondary reatment stages. DDOC in biosolids undergoing thermal treatment, anaerobic digestion (AD) and dewatering were found to vary with DDOC measured at 14,422 mg.kg-1, 22,542-27,862 mg.kg-1 and 26,155-29,983 mg.kg-1 respectively. Sludge treatment was found to reduce DDOC overall, with thermal treatment having the greatest effect followed by AD. The study found that 14-39% of DDOC was found to be persistent with PDDOC values ranging from 4,096 mg.kg-1 in a partially-nitrifying secondary sludge to 7,547 of mg.kg-1 in AD treated biosolids. Concentrations of persistent mobile organic carbon at these levels warrants further consideration by environmental regulators of the potential risk associated with land application of biosolids. The levels of PDDOC were generally higher in biosolids that had undergone further treatment than in untreated primary or secondary sludges. This suggests that sludge treatment processes can result in accumulation of POPs in biosolids and may also enhance desorption potential of POPs. The analysis of optical properties of leachates revealed a similar progression in indicators of biodegradable to non-biodegradable organic compounds between DDOC and PDDOC leachates, with an increase in the ratio of high molecular weight (MW) and aromatic compounds and indicators of functional groups consistent with some common POPs (e.g. alkyl halides, alkyl benzene compounds). The comparison of WWTP type found that non-nitrifying plants had a higher proportion of high MW, aromatic compounds than the nitrifying and partially-nitrifying plants, suggesting that extended aeration and aerobic treatment can increase removal of substances such as PAHs. Overall the study indicates that sludges and biosolids may pose a risk of transfer of POPs into the environment through leaching of PDDOC. Determination of PDDOC could be used as a screening tool for assessing relative POP burden of sludges and biosolids and to assess the overall effectiveness of sludge treatment technologies for reducing POPs prior to land disposal. The novel approach overcomes many of the existing analytical and risk assessment barriers faced by environmental regulators providing an approach that is relatively low cost, accessible and provides a bulk measurement as an indicator of the mobile organic pollutant load.

Northern peatlands are a globally important soil carbon (C) store, and aquatic systems draining peatland catchments receive a high loading of dissolved and particulate forms of C from the surrounding terrestrial environment. Once incorporated into the aquatic environment, internal processes occur to modify the C pool. Of these, photo-processing preferentially targets terrestrially derived C and therefore might have a significant effect on the C budget of peatland draining aquatic systems. The overarching aim of this study was to investigate photochemical processing of C in Scottish peatland draining aquatic systems in order to determine the importance of this pathway in aquatic biogeochemical cycles. For initial laboratory experiments, water samples from a peatland headwater stream (Auchencorth Moss, SE Scotland) were collected. Laboratory based irradiation experiments were conducted at a range of temperatures, and different filtration treatments, including unfiltered samples, were employed to understand the fraction of C most susceptible to photo-processing. UV irradiation and temperature had a significant effect on DOC and gas headspace concentrations, with Q10 values of ~1.42 and ~1.65 derived for CO2 and CO photoproduction in unfiltered samples, respectively. However, filtration treatment did not induce significant changes in gaseous C production between light and dark samples, indicating that the experimental conditions favoured breakdown of DOC rather than POC to CO2 and CO. In all light treatments a small but significant increase in CH4 concentration was detected. These data were compared to results from experiments conducted in ambient light and temperature conditions. DOC normalised CO2 photoproduction was an order of magnitude lower than in laboratory conditions, although relative abundances of C species within overall budgets were similar and these experiments demonstrated that ambient exposure is sufficient to generate photo-processing of aquatic peatland C. Overall these data show that peatland C, particularly the < 0.2 μm fraction, is highly photoreactive and that this process is temperature sensitive. Further laboratory irradiation experiments were conducted on filtered water samples collected over a 13-month period from two contrasting aquatic systems. The first was the headwater stream draining Auchencorth Moss peatland with high DOC concentrations. The second was a low DOC reservoir (Loch Katrine, C Scotland) situated in a catchment with a high percentage peat cover. Samples were collected monthly from May 2014 to May 2015 and from the stream system during two rainfall events. Significant variation was seen in the photochemical reactivity of DOC between the two systems, with total irradiation induced change typically two orders of magnitude greater and DOC normalised CO2 production a factor of two higher in the headwater stream samples. This is attributed to longer water residence times in the reservoir rendering a higher proportion of the DOC recalcitrant to photo-processing. Overall the magnitude of photo-induced C losses was significantly positively correlated with DOC concentration in the headwater stream, which varied seasonally with highest concentrations detected in late autumn and winter. Rainfall events were identified as important in replenishing the stream system with photoreactive material, with lignin phenol data indicating mobilisation of fresh DOC from woody vegetation in the upper catchment during a winter rainfall event. Whilst these data clearly demonstrate that peatland catchments generate significant volumes of photoreactive DOC, the degree to which it is processed in the aquatic environment is unclear. Field investigations were undertaken to address this uncertainty. In-situ experiments with unfiltered water samples in light and dark conditions were conducted in two contrasting open water peatland pool systems. At the high DOC site (Red Moss of Balerno, SE Scotland), DOC concentrations in surface light exposed samples decreased by 18% compared to dark controls over 9 days and light treatments were enriched in CO2 and CH4. Photochemical processing was evident in δ13C-DOC and δ13C-DIC signatures of light exposed samples, which were enriched and depleted, respectively, relative to dark controls (+0.23 ‰ and -0.38 ‰) after 9 days of surface exposure. At the low DOC site (Cross Lochs, Forsinard, N Scotland) net production of DOC occurred in both light and dark samples over the experiment duration, in part due to POC breakdown. δ13C-DIC signatures indicated photolysis had occurred in light exposed samples (-1.98 ‰), whilst δ13C-DOC data suggest an absence of photo-processing, as the signatures in both treatments were similar. Accounting for light attenuation through the water column, 46 ± 4.9 and 8.7 ± 0.5 g C-CO2 eq m−2 yr−1 was processed by photochemical and microbial activity in peatland pools within the catchments at the high and low DOC sites, respectively. At both sites, light driven processing was responsible for a considerable percentage (34 and 51%) of gaseous C production when compared to equivalent estimates of microbial C processing and thus should be considered a key driver of peatland pool biogeochemical cycles. It is clear from this study that temperature, seasonal cycles, rainfall events and water residence time provide strong controls on the photoreactivity of aquatic C in Scottish peatland systems. The photo-processing pathway has the potential to alter the C balance of peatland catchments with a high percentage coverage of aquatic systems. Under climate change scenarios where light, temperature and rainfall conditions are expected to change, this process may become increasingly important in aquatic C cycling, particularly if the upward trend in DOC concentrations in northern aquatic systems continues.

The chemical speciation of trace metals controls their potential bioavailability and therefore toxicity to exposed organisms. Despite previous studies demonstrating the ameliorative effects of dissolved organic carbon (DOC) on metal toxicity, the effectiveness of ligands from varying sources and of potentially variable composition in controlling speciation has not been studied in detail in estuarine waters. In addition, the effect of DOC on radionuclide contaminants in combination with trace metals has not been investigated in any waters. This is of particular interest in the estuarine environment, where both anthropogenic and natural ligands, and contaminants that pose a potential threat to ecosystem health, can be present. Competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with complexation capacity titrations was employed to determine the speciation of dissolved Cu and Zn, two metals that possess revised environmental quality standards (EQS) which now account for potential metal bioavailability. Dissolved metal concentrations in the < 0.4 and < 0.2 μm filter fractions of samples from the Tamar Estuary were determined during seasonal transects made over a calendar year. Samples were taken over a full salinity range (0-35) and from locations thought to contain DOC from a variety of sources (e.g. terrigenous, biogenic, sewage). No seasonal trends in metal speciation were identified, but a semi-quantitative assessment of DOC type using 3-D fluorimetry showed domination of humic and fulvic type ligands in the upper estuary, and biogenic-type ligands in the lower estuary, the former appearing the most important in controlling Cu and Zn complexation. Filter size fraction differences showed a major portion of the dissolved metal is associated with the 0.2 ≥ 0.4 μm fraction, indicating an importance of larger molecule ligands in controlling potentially bioavailable metal. Sample ligand concentrations ([L_x]) ranged from 1-372 nM (Cu) and 3-412 nM (Zn), and metal-ligand conditional stability constants (log K_(ML_x )) from 10.5-13.5 (Cu) and 7.5-10 (Zn), which are similar to reported literature. Calculated free metal ion concentrations ([M2+]) of 0.3 – 109 nM (Zn) and 1.4 x 10-13 – 7.3 x 10-11 M (Cu) compared well (92% showed no significant differences (P = 0.02)) with direct measurements of [Zn2+] made for the first time in estuarine waters using “Absence of Gradients and Nernst Equilibrium Stripping” (AGNES) after optimisation for estuarine waters. AGNES fully complements CLE-AdCSV in terms of analytical capability and shows that methods are now available that are capable of directly determining [Zn2+] in estuarine waters for use in environmental monitoring studies. Calculations made using the chemical equilibrium speciation programme Visual MINTEQ (VM) showed [Cu2+] and [Zn2+] could be predicted to within one order of magnitude of measured values when log K_(ML_x ) and [L_x] are determined and input into the model. This was in contrast to poor agreement between measured and predicted [M2+] when VM was used with the NICA-Donnan complexing model, which assumes a set portion of the total DOC concentration input is fulvic acid that actively complexes metals. These results corroborate a lack of identification of a relationship between metal speciation in the Tamar samples and DOC concentration, highlighting that knowledge of DOC type, log K_(ML_x )and L_x are important when assessing environmental risk, setting EQSs and for accurate modeling of [Cu2+]. Finally, a combined chemical and biological study investigating the effects of mixtures of DOC, Zn and the radionuclide tritium (3H) on the marine mussel presents the first evidence of a protective effect of Zn on DNA damage caused by 3H. The association of 3H with DOC remains elusive and an assessment of DOC type is recommended for future research, but the study emphasises the importance of investigating mixture effects in order to avoid inaccurate risk assessment and potentially costly site remediation.

In rivers, association of organic contaminants with dissolved organic carbon may limit freely dissolved or bioavailable fractions and toxicity of organic contaminants. Consequently, assessment of toxicity of organic contaminants on the basis of their total chemical concentrations may lead to overestimation of risks to organic contaminants. Therefore, to achieve reliable and accurate risks assessment for organic contaminants, determination of bioavailability is important. The influence of humic acid on the bioavailability of organic contaminants in rivers was studied, using three chemicals with different properties as model contaminants, which at the start of the study were detected in wastewater effluents. It was hypothesized that in the presence of dissolved organic carbon, a fraction of the total concentration of an organic contaminant would not be bioavailable in river water. Therefore, the aim of the study was to determine bioavailability and its impact on toxicity. Bioavailability in the presence of humic acid was determined chemically and using a yeast estrogen screen assay. The chemical method comprised solid-phase extraction and liquid chromatography-mass spectrometry to determine freely dissolved and the fraction of the chemicals associated with dissolved organic carbon. The results indicated increased binding to dissolved organic carbon with the hydrophobicity of the test compounds except for perfluorooctane sulfonate. The dissolved organic carbon-water partition coefficient for ethinylestradiol was determined to be Log KDOC 2.36. Log KDOC values of 4.15 and 4.41 at 10 and 100 mg/L humic acid, respectively, were derived for hexabromocyclododecane indicating greater binding than ethinylestradiol due to the more hydrophobic character. The yeast estrogen screen was used as a biological method to measure the effect of humic acid on the bioavailability of ethinylestradiol and a more hydrophobic compound, dichlorodiphenyltrichloroethane. Results of the yeast estrogen screen indicated that the presence of humic acid had no effect on bioavailability of either of the chemicals.

Northern peatlands represent a significant carbon reservoir, containing approximately a third of the terrestrial carbon pool. The stability of these carbon stores is poorly understood, and processes of accumulation and degradation appear to be finely balanced. Over the last decade, it has become increasingly clear that losses of dissolved organic carbon (DOC) from peatlands can be of considerable size and this flux appears to have increased substantially over the last 20 years. Despite its significance, the chemical composition of peatland-derived DOC remains poorly understood. This study aimed to characterise dissolved organic matter (DOM) at the molecular level using a novel combination of techniques. The study site (Cors Fochno, Wales, UK) is an ombrotrophic bog on which a number of studies into carbon cycling and hydrology have been carried out, providing a useful context for this project. The size and compositions of the DOC pool was monitored over 18 months, from three banks of piezometers, sampling from depths of 15 cm to 6 m. DOM which is representative of bog runoff was also monitored. DOC concentrations varied considerably between locations, spanning an order of magnitude (11.4 to 114 mgC l-1). Several relationships between DOC concentration and environmental and physical factors were established: DOC levels near the surface of the peatland varied with temperature, those in the runoff were most affected by recent rainfall events and the apparent DOC concentration at depth was related to the hydraulic conductivity of peat at that depth. The annual flux of DOC from the site was estimated at 113 tonnes, or 17.4 gC m-2. Only a small portion of the DOC pool could be characterised by analysis of dissolved combined amino acids (DCAA) and dissolved carbohydrates (as neutral sugars). Non-protein amino acids were most abundant in runoff samples, suggesting microbial reworking of DOM on entering drainage systems. DCAA yields decreased with depth, and the DCAA pool in deeper peat layers was characterised by more hydrophobic compounds. Interpretation of semi-quantitative results from TMAH thermochemolysis GC-MS analysis suggested oxidative degradation of organic matter near the surface of the peatland and photochemical degradation where DOM entered drainage networks, and this was supported by novel interpretation of results from ultrahigh resolution mass spectrometry analysis. The deepest porewaters were dominated by nalkanes, with notable contributions from fatty acids, suggesting a plant wax source for this DOM. The highest DOC concentrations were found at intermediate depth from a site midway between the centre of the bog and the southern boundary where hydraulic conductivities were low, and DOM from these piezometers were characterised by high contributions from a suite of phenolic compounds (with mainly para-hydroxyphenyl structures). These compounds have been linked to Sphagnum species, and are known to be functionally important to the development and maintenance of the unusual chemical environment in peatlands which slows decay rates, reduces microbial activity, and allows the sequestration of the large carbon reservoir. The findings of this study highlight the dynamic nature of peatland derived DOM, both in the size of the carbon pool and its composition which change dramatically with both season and depth.

High concentrations and fluxes of dissolved organic carbon (DOC) in fluvial systems are associated with the dark brown water colour familiar in many upland, peat-dominated areas and may indicate a depletion of the terrestrial carbon store. The removal of this colour can also be problematic and expensive for water companies as well as affecting the ecological functioning of the water body through factors such as reduced light penetration through the water column. Disturbance resulting from activities such as land use change can also enhance the loss of carbon and this may manifest itself in elevated concentrations and fluxes of DOC from aquatic systems. This thesis describes and explains patterns of change in DOC quantity and quality from the Crosswater, Crosswater of Luce and Tig catchments draining Arecleoch Forest, a peatland in south Ayrshire, Scotland, from 2008 to 2010. This time period incorporates the installation of a 60-turbine wind farm built and operated by Scottish Power Renewables (SPR). Water samples were collected from Arecleoch at different spatial scales ranging from catchments to soil pore water and temporal scales ranging from daily to seasonally. Concentrations of DOC were measured and fluxes estimated at the catchment scale. DOC concentrations from all three catchments exhibited the well-established seasonal pattern with maxima in late August/early September and minima seen in February/March. The Tig catchment experienced the greatest burden of disturbance from the wind farm development and returned the highest DOC concentrations and fluxes. The Crosswater catchment, used as a control site due to its isolation from wind farm activities, had higher DOC concentrations than the Crosswater of Luce throughout the monitoring period possibly due to a greater proportion of forest cover. ii DOC flux ranged from 35.0 g C m-2 yr-1 from the Crosswater of Luce catchment in 2008 to 55.0 g C m-2 yr-1 from the Crosswater in 2009. The Tig catchment was not monitored for the whole period but returned the highest DOC fluxes of the three catchments between January and June 2010 (15.7 g C m-2). These values are considered high for UK peatlands. It is possible to make a tentative estimate of an extra 12 g C m-2 being exported from the Crosswater of Luce in 2009 that may have been a result of wind farm and/or forestry activities in the catchment. At the sub-catchment scale, “hot spots” of high DOC concentrations (up to 113.4 mg L-1) were found during the final survey of headwater streams inside the development area of the wind farm site during construction in August 2010. Further surveys are recommended to assess whether DOC concentrations have decreased since completion of the wind farm. Daily water samples were collected upstream and downstream of turbine 33 during the excavation of the turbine base. DOC concentrations were higher downstream before work began on the turbine base and although the gap between upstream and downstream DOC concentrations increased over the monitoring period, statistical comparisons of these differences before and after the start of excavation work were not significant at the 95 % confidence level. Challenges arose from the practicability of conducting robust research on a construction site and novel approaches to monitoring DOC were developed. Activity scores were used to quantify the effect of peatland disturbance on DOC concentrations at the catchment scale. The results suggest that this approach may have merit but requires comprehensive site records from the developer. The non-linear nature of the individual wind farm development and forestry activities made it impractical to disentangle the impact of each, particularly for forest harvesting. iii Activity scores could, together with other information gathered from site records, be useful to developers as an indicator of the most likely periods for peat disturbance. Knowledge of the differing disturbance potential of the various activities could also provide useful information to feed into the carbon payback calculator. DOC quality was explored using ultraviolet (UV) absorbance, specific UV absorbance (SUVA) and E4/E6 ratios. The latter metric identified changes in the composition of DOC related to disturbance with water samples from areas draining land subject to disturbance having lower E4/E6 ratios indicating a greater degree of humification of the DOC. This research provides one of only three studies to investigate concentrations and fluxes of DOC in water courses draining land subject to disturbance relating to wind farm construction. It is the only study that incorporates a period of time prior to work beginning and takes in the whole of the development phase. In this respect it provides a valuable addition to our understanding of the way in which peatlands respond to land use change and may provide useful tools to assist developers in minimising the impact of their activities on these valuable carbon stores.

Concentrations of dissolved organic carbon (DOC) measured within water bodies have been increasing on a global scale over the last two decades. Changes in temperature and rainfall have been shown to increase the production and export of DOC from catchments with peat soils in the UK (Freeman et al., 2001). However it is not clear whether increases in DOC concentrations are caused by production increases induced by temperature changes or by a greater incidence of high flows induced by rainfall changes. Increases in both temperature and rainfall have been predicted in Scotland over the next few decades (Kerr et al., 1999) which may further increase current DOC concentrations and exports. The implications of this include both a decrease in water quality and an increase in mobility of metals in upland water bodies. The overall aim of the thesis is to determine if the relationship between dissolved organic carbon (DOC) concentrations and discharge has changed over a 20 year period in small stream catchments in Scotland, in order to better understand the role of hydrology, in driving changes in DOC concentration. To achieve this streams draining two coniferous forest sites and one moorland site were monitored intensively between June 2004 and February 2006. Analysis of the relationship between DOC and discharge, within the catchments, identified the importance of the amount of precipitation falling on the catchment, antecedent precipitation and season, on the concentration of DOC that was measured within the stream. Models were then developed using variables to represent these drivers in terms of both the production (seasonal sine values and 14 day average temperatures) and movement (log of discharge (log Q), days since previous storm event and rising or falling stage) of DOC. In the Ochil Hills catchment, the best predictive model, used 4 hour average discharge and 1 day average 30cm soil temperatures (R2= 0.88). In the Duchray and Elrig catchments, the best predictive models produced used discharge and seasonal sine values; the strength of the model was greater in the Elrig (R2= 0.80) than the Duchray (R2= 0.48) catchment. The strength of the regression models produced highlighted the importance of precipitation in the movement of DOC to the stream and temperature variables representing production in the surrounding catchment. To determine if dissolved organic carbon (DOC) concentrations had changed within the three study catchments, since previous research was conducted at the same sites in the early 1980s and 1990s (Grieve, 1984a; Grieve, 1994), then regression analysis conducted in the previous research was repeated, so changes in the DOC and discharge relationship could be identified. Analysis of the Ochil Hills regression equations identified higher log of discharge and lower temperature and seasonal sine values in the present study (2004-06), when compared to the previous study (1982-83). This suggests that more DOC is now available for movement from the soil, and that the difference between winter and summer DOC production has decreased, potentially because of increasing temperatures. This would explain the limited increase in DOC concentration within the Ochil Hills stream. In the Duchray and Elrig streams, a large increase in DOC was identified at all discharges when all the models produced were compared between the two sampling periods (1989-90 and 2004-06). The increasing trend in DOC concentrations is too large to have been produced by change in temperature alone and it is suggested that the measured reduction in acidic deposition has resulted in the increased DOC concentrations measured in the Duchray and Elrig. The results from this research have identified that concentrations of DOC have increased in Scottish streams over the last 20 years and that the increases in DOC have been induced, potentially by temperature changes in climate. However, changes in temperature are not the only driver of this change as the reduction in acidic deposition is potentially more important, specifically in areas with base poor geology such as the Duchray and Elrig catchments.

Of the organic matter in soils typically < 1% by weight is dissolved in the soil solution (dissolved organic matter; DOM). DOM is a continuum of molecules of various sizes and chemical structures which has largely been operationally defined as the fraction of total organic carbon in an aqueous solution that passes through a 0.45 µm filter. Although only representing a relatively small proportion, it represents the most mobile part of soil organic carbon and is probably enriched with highly labile compounds. DOM acts as a source of nutrients for both soil and aquatic micro-organisms, influences the fate and transport of organic and inorganic contaminants, presents a potential water treatment problem and may indicate the mobilisation rate of key terrestrial carbon stores. The objective of this research was to ascertain some of the biologically relevant characteristics of soil DOM and specifically to determine: (1) the influence of method and time of extraction of DOM from the soil on its biochemical composition and concentration; (2) the dynamics of DOM biodegradation; and, (3) the effects of repeated applications of trace amounts of DOM on the rate of soil carbon mineralization. To examine the influence of method and time of extraction on the composition and concentration of DOM, soil solution was collected from a raised peat bog in Central Scotland using water extraction, field suction lysimetry, and centrifugation techniques on a bimonthly basis over the period of a year (Aug 2003 – Jun 2004). Samples were analysed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), protein, carbohydrate and amino acid content. For all of the sampled months except June the biochemical composition of DOC varied with extraction method, suggesting the biological, chemical and/or physical influences on DOC production and loss are different within the differently sized soil pores. Water-extractable DOC generally contained the greatest proportion of carbohydrate, protein and/or amino acid of the three extraction methods. Time of extraction had a significant effect on the composition of water- and suction-extracted DOC: the total % carbohydrate + protein + amino acid C was significantly higher in Oct than Dec, Feb and Jun for water-extracted DOC and significantly greater in Dec than Aug, Apr and Jun for suction-extracted DOC. There was no significant change in the total % carbohydrate + protein + amino acid C of centrifuge-extracted DOC during the sampled year. Time of extraction also had a significant effect on the % protein + amino acid N in water- and centrifuge-extracted DON: Oct levels were significantly higher than Feb for water-extracted DON and significantly higher in Aug and Apr for centrifuge-extracted DON. Concentrations of total DOC and total DON were also found to be dependent on time of extraction. DOC concentrations showed a similar pattern of variation over the year for all methods of extraction, with concentrations relatively constant for most of the year, rising in April to reach a peak in Jun. DON concentrations in water- and centrifuge-extracted DON peaked later, in Aug. There were no significant seasonal changes in the concentration of suction-extracted DON. A lack of correlation between DOC and DON concentrations suggested that DOC and DON production and/or loss are under different controls. Laboratory-based incubation experiments were carried out to examine the dynamics of DOC biodegradation. Over a 70 day incubation period at 20oC, the DOM from two types of peat (raised and blanket) and four samples of a mineral soil (calcaric gleysol), each previously exposed to a different management strategy, were found to be comprised of a rapidly degradable pools (half-life: 3 – 8 days) and a more stable pool (half-life: 0.4 to 6 years). For all soil types/treatments, excepting raised peat, the total net loss of DOC from the culture medium was greater than could be accounted for by the process of mineralization alone. A comparison between net loss of DOC and loss of DOC to CO2 and microbial biomass determined by direct microscopy suggested that at least some of the differences between DOC mineralised and net DOC loss were due to microbial assimilation and release. Changes in the microbial biomass during the decomposition process showed proliferation followed by decline over 15 days. The protein and carbohydrate fractions showed a complex pattern of both degradation and production throughout the incubation. The effects of repeated applications of trace amounts of litter-derived DOC on the rate of carbon mineralization over a 35 day period were investigated in a laboratory based incubation experiment. The addition of trace amounts of litter-derived DOC every 7 and 10.5 days appeared to ‘trigger’ microbial activity causing an increase in CO2 mineralisation such that extra C mineralised exceeded DOC additions by more than 2 fold. Acceleration in the rate of extra C mineralised 7 days after the second addition suggested that either the microbial production of enzymes responsible for biodegradation and/or an increase in microbial biomass, are only initiated once a critical concentration of a specific substrate or substrates has been achieved. The addition of ‘DOC + nutrients’ every 3.5 days had no effect on the total rate of mineralization. To date DOC has tended to be operationally defined according to its chemical and physical properties. An understanding of the composition, production and loss of DOC from a biological perspective is essential if we are to be able to predict the effects of environmental change on the rate of mineralization of soil organic matter. This research has shown that the pools of DOC extracted, using three different methods commonly used in current research, are biochemically distinct and respond differently to the seasons. This suggests some degree of compartmentalisation of biological processes within the soil matrix. The observed similarities between the characteristics of the decomposition dynamics of both peatland and agricultural DOC suggests that either there is little difference in substrate quality between the two systems or that the microbial community have adapted in each case to maximise their utilisation of the available substrate. The dependency of the concentration and biochemical composition of DOC on the seasons requires further work to ascertain which biotic and/or abiotic factors are exerting control. Published research has focussed on factors such as temperature, wet/dry cycles, and freeze/thawing. The effect of the frequency of doses of trace amounts of DOC on increasing the rate of soil organic C mineralization, evident from this research, suggests that the interval between periods of rainfall may be relevant. It also emphasises how it can be useful to use knowledge of a biological process as the starting point in determining which factors may be exerting control on DOC production and loss.

Lakes in the northeastern US are browning or increasing in dissolved organic carbon (DOC) as they recover from acidification and experience an increase in precipitation from climate change. DOC attenuates ultraviolet radiation (UV), reducing exposure of lake zooplankton to damaging wavelengths in browner lakes. Additionally, some zooplankton can detect and avoid UV. DOC’s role in the cladoceran Holopedium’s survival was tested by exposing organisms to natural solar radiation in the presence vs. absence of DOC. It was hypothesized that when exposed to natural UV, the presence of DOC would increase survival in Holopedium. Additionally, if Holopedium could behaviorally detect and avoid UV or visible light was also investigated. Survival was significantly higher in treatments exposed to UV in the presence vs. absence of DOC. There was no evidence of behavioral response to UV or visible light. These results convey the importance of DOC protecting Holopedium from UV damage as they can inhabit in the surface waters of some lakes, partially due to a defense against tactile predators. Browning may also mediate the potential for resource partitioning between Holopedium and its competitor Daphnia. Predicted increases in browning caused by climate change may continue to alter these patterns.

At 662 Pg C, the marine reservoir of dissolved organic carbon (DOC) represents the ocean’s largest pool of reduced carbon, holding over 200 times the carbon contained in marine biomass and rivaling the atmospheric carbon inventory. Recent work has suggested that the size of the DOC reservoir may respond to future changes in sea temperatures and global overturning circulation strength. Moreover, mobilization of marine DOC has been implicated in several paleoclimate change events. Despite these suggestions, however, the temporal dynamics of the marine DOC reservoir are poorly understood, and previous carbon cycle modeling work has generally assumed this reservoir to be static. In this study, we utilized an Earth system model of intermediate complexity calibrated with respect to DOC observations to assess the response of the marine DOC reservoir to climate changes representative of the last glacial maximum climate state, reduced ocean overturning circulation strength, and future warming scenarios. Our results indicate that the marine DOC reservoir is mobile in response to climate forcings and may shrink or expand depending on changes in its production rate. Moreover, variability in the ocean’s DOC reservoir was directly linked to changes in atmospheric CO2 concentrations, explaining a significant portion of CO2 drawdown or ventilation by the ocean across three sets of climate change experiments. These findings point to an integral role of marine DOC in the global carbon cycle and indicate that consideration of this reservoir is critical in improving our understanding of the connection between ocean processes and global climate of the past, present, and future.

Drier and hotter conditions linked with anthropogenic climate change increase wildfire activity which can influence terrestrial and aquatic carbon cycles at broad spatial and temporal scales. Other aspects of environmental change such as climate warming enhance soil decomposition leading to accelerated rates of sedimentation and leaching from soils into aquatic systems, a phenomenon known as “browning.” Large-scale ecological disturbances like wildfire can increase the occurrence of browning from post-fire erosion. I tested the effects of fire-treatment (burned vs. unburned plant material) and its interaction with terrestrial loading on dissolved organic carbon (DOC) composition, concentration, and degradation (biological vs. photochemical) in freshwater mesocosms. DOC concentration increased nonlinearly with added plant material in both burning treatments and degraded most rapidly at intermediate concentrations, indicating that decomposition at intermediate concentrations removes DOC at a faster rate than at higher concentrations. Excitation-Emission Matrix (EEM) fluorescence spectroscopy showed that the effect of fire and browning changed chemical signatures apparent in the EEMs, and that both mainly affected the humification index and the specific ultraviolet absorbance at 254 nm over time. Incubations showed that biodegradation contributed more to DOC decomposition than photodegradation, and that DOC decomposition was most rapid at intermediate loading levels likely because anoxia at high terrestrial input inhibited microbial activity. My thesis shows that fire and browning elicit non-linear responses in the dynamics and composition of DOC in aquatic systems, and that fire alters the chemistry of organic detritus in ways that impact its processing and role in aquatic environments.

Abstract: Presence and functions of lakes are dependent on hydrological connectivity to the terrestrial landscape. Inter-annual wet-dry periods, and their amplification through climate change, can influence hydrological connectivity and affect the delivery of water and solutes from various terrestrial sources. Altered hydrological connectivity and delivery of water to lakes influences lake water residence times and the role of within-lake processes, but can also influence the risk of a lake to contract and even completely disappear. This thesis examined the influence of inter-annual wet-dry periods and subsequent hydrologic connectivity on different ecosystem functions of 34 lakes on the Boreal Plains in Western Canada. In Chapters 2 and 3, I focused on the influence of inter-annual wet-dry periods on hydrological connectivity of terrestrial sources and subsequently the concentration and chemical composition of lake dissolved organic carbon (DOC), a key water quality parameter that influences lake ecosystem functioning. In Chapter 4, I focused on how lake extent and water level responded to inter-annual wet-dry periods and show how lakes can have different combinations of resistance and resilience to dry periods, whilst identifying watershed and lake attributes which can increase lake susceptibility to terrestrialisation. In Chapter 2, I found large spatial variability of lake DOC concentrations and aromaticity (as indicated by specific UV absorbance at 254 nm – SUVA254) that was closely linked to surficial geology and thus wetland connectivity in the watershed. The aromaticity of DOC was further influenced by lake water residence time and the extent of within-lake processing of aromatic DOC via photodegradation. Large inter-annual variability in lake DOC characteristics (concentration and composition) was attributed to interactions between surficial geology and sub-humid climate. Inter-annual variability in DOC concentration had low synchronicity among lakes, with patterns of variability linked to surficial geology and short-term precipitation shifting connectivity of terrestrial DOC sources. However, inter-annual variability in DOC composition had high synchronicity among lakes, where lake water residence time related to longer-term precipitation, and the extent of within-lake DOC degradation. This study shows that lake DOC characteristics vary spatially, but many lakes on the Boreal Plains are also highly sensitive to inter-annual wet-dry periods. In Chapter 3, end-member mixing model analysis showed that lake DOC characteristics did not conform to conservative mixing of terrestrial sources, with lower observed DOC concentrations and A254 than modelled, suggesting net DOC and A254 losses in terrestrial end-members along the soil-stream-lake continuum. Losses were associated with lakes in coarse and fine hummocky watersheds. However, we found that in fine hummocky lakes with large proportions of connected wetland and fine plains watersheds, observed DOC concentrations exceeded modelled, suggesting autochthonous production of DOC. On an inter-annual basis, losses in A254 were greater during dry years, when lake water residence times are longer and within-lake photodegradation processes enhanced. This study highlights that the DOC pool of Boreal Plains lakes reflects mixing of water from terrestrial sources, but also processes of within-lake degradation of DOC which may be influenced by inter-annual wet-dry periods, and in lakes with high nutrients and productivity, autochthonous production of DOC. In Chapter 4, I found large spatial variability in lake extent responses to dry periods, with many lakes exhibiting transient or long-term reduction in lake area. Lakes located in higher landscape positions and those with a lower proportion of connected wetland area in the watershed showed quicker responses to dry periods (i.e. shorter lag times), thus lake extent contracted relatively quickly. Resistance and resilience of lake extent to dry periods, i.e. the ability to withstand change and to return to pre-dry period extents, were highest for lakes with greater wetland connectivity and for lakes with straight-sided basin morphology. This study suggests that isolated lakes, with lower proportions of connected wetland in the watershed and lake beds that slope towards the lake centre with shallower depths of loose sediment are most susceptible to long-term terrestrialisation processes. Overall, in this thesis, I analyzed both spatial and inter-annual variability of lake ecosystem functions at a landscape scale across the Boreal Plains, my results identified watershed and lake attributes (HRA, wetland connectivity, lake water residence time, lake basin morphology) which can be used to predict lakes on the Boreal Plains where the most rapid changes in lake function can be expected.

The Huff Run Watershed, located in Mineral City, Ohio, was mined for coal, limestone, and clay from 1853 to the late 1970s. Mine spoil is left scattered on the surface of about one third of the watershed, contributing to metal leaching to the watershed. Although the mine spoil has had time to become vegetated, camouflaging itself among the native landscape, the disturbed pyrite from coal layers is exposed to water and oxygen leading to a chain of chemical reactions, resulting in the production of potentially acidic and metal-rich porewater, which can infiltrate into the groundwater and streams. Remediation efforts for this watershed have totaled around 4.5 million dollars, but most of the remediation is focused on the point sources of contamination. Runoff from the spoil is a nonpoint source of contamination, and most areas are left untreated. These untreated areas can affect the immediate area and many kilometers downstream of the leaching. For this project, soil samples were collected from a vegetated mine spoil hill and a vegetated shale hill in this watershed, to make a physical and chemical comparison of the soils and their pore water. Solid phase characterization included particle size analysis, bulk X-ray powder diffraction, and loss on ignition (LOI). Soil pore water was collected from suction lysimeters installed at different depths (10, 40, 80, and 120 cm) at the two sites. Field-based water quality analyses included pH, dissolved oxygen (DO), electrical conductivity, and temperature; collected samples were analyzed for metals by inductively coupled plasma-optical emission spectrometry (ICP-OES), anions by ion chromatography, and dissolved organic carbon (DOC). The speciation of Al, Fe, and Mn was also determined by a sequential extraction procedure. The particle size distribution showed a sandy loam, with an overall average of 4.4% clay, 47.7% silt, and 47.9% sand in the high wall (HW) and 6.3% clay, 41.8% silt, and 51.9% sand in the mine spoil (MS). The bulk mineralogy was dominated by quartz (30.6 – 43.3 % HW; 27.5 – 49% MS) and muscovite (34.9 – 42.6% HW; 29.1 – 45.0 MS). LOI values ranged from 4.27– 8.53% in the HW and 5.35– 15.48% in the MS, with the LOI being fairly uniform throughout the vertical profile in the HW and found in high percentages of the MS in areas of residual coal. DOC values were highest in the first 10 cm of the HW (91.45 ± 23.61 mg/L), 5 times higher than the first 10 cm of the MS. Although mineralogy and particle size analysis between the two sampling sites were very similar, metal leaching and mobility were different based upon whether organics were plant-derived such as the thick organic layer on the native hill, or vs. rock-derived organics from the residual coal in layers found from 50 – 100 cm in the mine spoil hill. Aqueous Al, Fe, and Cu were highest in the first 10 cm of the HW, indicating that they are readily released from soil into solution when exposed to plant-derived organic matter, and at this depth and location increased in concentration over the field season (were fairly constant at other locations). Aqueous Mn, Ni, and Zn were found in higher concentrations in the MS. Mn and Ni concentrations at both sites and all depths decreased over the field season and Zn did not show a temporal trend. Evidence of coal in the mine spoil is found through higher LOI values (approximately 10% in MS vs. 5% in HW), and extractable Fe and Mn having its highest concentrations at depths where rock-derived organics were highest, lower levels of dissolved oxygen, and overall higher concentrations of extractable Al, Fe, and Mn. Al, Fe, and Mn were all found in highest concentrations in the reducible fraction, indicating the formation of (oxy)hydroxides after pyrite dissolution in the MS. Using the results, there is potential to quantify the amount of metal leaching from non-point source mine spoil hills the and pH changes that take place during the months of May – October and evaluate the potential for metal leaching over greater lengths of time.

A substantial societal shift towards environmental awareness has focused research efforts on the impacts of pollution on natural landscapes. Improvements to pollutant regulations and technology have resulted in sizeable reductions of atmospheric deposition of anthropogenic acids, especially nitrates and sulfates, which has altered the role of these ions in the environment. As such, understandings of environmental chemistry dynamics have required regular updating. Through the National Park Service Vital Signs monitoring program, increases in precipitation pH observed in Great Smoky Mountains National Park (GRSM) has been attributed to the reduction of inorganic acid concentrations. Unfortunately, these improvements have not been uniformly reflected in stream waters across the park. As such, intra-soil and stream water chemical interactions require scrutiny for an explanation. Specifically, the dissolved organic carbon (DOC) concentrations are targeted within this research to determine their impact. GRSM stream waters were monitored on a bimonthly basis throughout the year of 2020. Ambient baseflow DOC concentrations were quantified, ranging from -1to 9.38 mg L-1, and general variations between watersheds were revealed that restrict direct comparisons from one watershed to another. Positive relationships for DOC concentrations with elevation, drainage area, and drainage density were then determined. Additionally, DOC concentrations were found to have correlations with calcium, potassium, nitrate, and acid neutralizing capacity. Stepwise regression analysis then determined a predictive model for DOC concentrations with calcium and potassium having positive relationships and nitrate having a negative relationship. Overall, this study established a foundational characterization of DOC concentrations in GRSM streams and suggests indirect consequences to reductions in inorganic acid deposition, likely through soil-based interactions. Continued analysis beyond the research presented here is best directed to DOC compositional evaluations to quantify and understand organic acids, soil solution analysis to determine contained DOC interactions, and temporal trends to enhance predictability and appropriate management.

Previous research has indicated that agricultural land-use often reduces water quality in streams. This includes: 1) an increase in total suspended solids (TSS) due to elevated soil erosion and 2) changes in dissolved organic carbon (DOC) concentrations. The goal of this study is to determine if a forested state park can mitigate these potentially negative impacts. This study examines spatial and temporal dynamics of TSS and DOC in four streams, located in an agriculturally impacted watershed in SW Ohio, as they flow from agricultural land-cover through a naturally forested state park. Eight surface water sites were sampled bimonthly over a one-year period from December 2019 to December 2020. Each water sample was processed to quantify concentrations of TSS and DOC. In addition to examining the impact of land use, this study also examined the effect of discharge and the normalized difference vegetation index (NDVI) on changes to TSS and DOC concentrations. A significant increase in TSS concentrations was found within the state park. The changes in TSS concentrations were not significantly related to stream discharge nor NDVI. A significant decrease in DOC concentrations was found in two streams within the state park. Discharge was negatively correlated with changes in DOC concentrations in three of four streams. The results suggest that small streams in the U.S. Midwest are able to reduce fluvial DOC concentrations in agricultural watersheds within naturally forested areas. Further research is needed to determine why TSS concentrations increased within the forested state park.

Dissolved organic carbon (DOC) is the largest exchangeable pool of organic carbon in the ocean, and is similar in size to atmospheric carbon. DOC is formed during surface ocean primary production by marine phytoplankton and can survive on average >6000 14C years in the deep ocean. This residence time greatly exceeds that of dissolved inorganic carbon (DIC), and indicates that a majority of DOC is refractory, or unreactive. Even though previous estimates of refractory DOC (RDOC) abundance is ~95% of total DOC, the mechanisms that facilitate its formation, cycling, and sinks are still poorly understood. A better understanding of these mechanisms is important because the ocean’s role in the global carbon cycle, and global physical climate, may link closely to the strength of the biological pump and DOC storage. This dissertation research characterizes the stable and radiocarbon isotopic compositions (13C and ∆14C) of solid-phase extracted DOC (SPE-DOC), which is representative of RDOC. First, the mass and isotopic composition of extraneous carbon (Cex) in the SPE method is analyzed. This study identifies that one SPE resin commonly used to extract DOC from seawater (Bond Elut PPL) elutes SPE-DOC with isotopic heterogeneity. Incomplete elution may exclude terrestrial-like organic matter that elutes later. An updated protocol including an extended elution is developed to ensure no fractionation of SPE-DOC occurs. This updated protocol is used to characterize SPE-DOC 13C and ∆14C values at the highest latitudinal resolution to date, using samples from three GO-SHIP Repeat Hydrography Cruises spanning the central and eastern Pacific Ocean and a portion of the western Indian Ocean. SPE-DOC 13C and ∆14C values are significantly lower than those for total DOC. Low 13C values relative to total DOC indicate preferential respiration of large biomolecules with high 13C values. An additional product of this heterotrophic respiration is carboxy-rich alicyclic matter, which is known to be extremely recalcitrant (C-rich and low in oxygen and hydrogen). These low SPE-DOC 13C and ∆14C values point to the microbial carbon pump (MCP) as a major driver of the marine carbon cycle through the removal of biomolecules with high 13C, and addition of refractory products that resist degradation. This increases DOC residence time and drives low ∆14C values. The large meridional span in this ∆14C dataset also allows for the first regional estimates of RDOC abundance. These estimates match the simple yet powerful “two-pool” model of DOC cycling proposed in 1987, in which the deep ocean is a well-mixed pool of old RDOC, and the surface is a mixture of RDOC from depth and labile DOC from recent photosynthesis. Although the importance of the MCP, and the two-pool model are not new ideas, sampling has been spatially and temporally sparse. This dissertation research provides a high-resolution isotopic perspective from under-sampled regions in the open ocean that supports these concepts.

Conventional tillage, a soil preparation practice to produce a fine seedbed, can disturb the soil profile by promoting soil compaction and soil organic matter (SOM) degradation. In contrast, conservation tillage, such as no-till and minimal tillage (30% or more crop residue) have the potential to sustain or increase soil organic carbon (SOC). Additional benefits of conservation tillage include; improvement to soil structure, reducing soil erosion, greater water retention, buffering soil temperatures, and greater crop residue retention. Conservation tillage practices promote nutrient retention in soils. Furthermore; Fe- and Mn-(oxy)hydroxide minerals play an important role in SOC stabilization and sequestration, which also promotes nutrient adsorption. This study aimed to 1) quantify SOC under varying agricultural managements, 2) qualitatively describe the degree of aromaticity and recalcitrance of SOC using fluorescence spectroscopy, 3) correlate SOC quantity with nitrogen and phosphorous retention in soils, and 4) understand the mineral phases responsible for the stabilization and sequestration of SOC, as well as phosphate and nitrate using a four-step chemical sequential extraction. Results showed that no till and minimal tillage sites consistently had greater SOC and fluorescence intensity in the humic-like acids region, when compared to conventional tilled fields. The SOC quality was obtained using relatively quick and cost-effective methods. No till and minimal tillage enhanced SOC stabilization. In addition, conservation tillage practices retained the largest total nitrogen and total phosphorous concentrations at all studied depths (0-30 cm), when compared to conventional tilled fields. Sequential extraction results showed that SOC was stabilized in the following order: crystalline Fe-oxides > amorphous Fe-oxides > Mn-oxides. Fe- and Mn-(oxy)hydroxide minerals can promote the stabilization and long-term sequestration of SOC via the formation of inner sphere complexes (e.g., ligand-exchange) within the mineral surfaces contact zone. Fe- and Mn-(oxy)hydroxide minerals adsorbed PO4-3 species to a large extent; however, NO3- was adsorbed marginally. Results indicated that PO4-3 adsorption is largely mediated by the Fe- and Mn-(oxy)hydroxide minerals, and NO3- by bulk SOM. The complex relationship between SOM, PO4-3, NO3-, and Fe- and Mn-oxides, is needed to be fully understood in order to successfully and efficiently operate an agricultural practice within a changing environment.

Solar radiation is an important contributing factor to decomposition in drylands. Research suggests that in the presence of water, previously irradiated plant litter experiences greater microbial decay than litter which was not exposed to radiation. It is unclear how exactly radiation alters litter to allow this photopriming of microbial decomposition. However, the relationship to water suggests that radiation may make litter more water-soluble, and therefore more accessible to decomposers once water enters the system. I tested the hypothesis that the abiotic impact of solar radiation on grass litter would (1) increase the production of dissolved organic carbon (DOC) when litter is subsequently extracted with water, and (2) produce DOC that stimulates more microbial activity compared to unexposed litter. Dried senesced grass litter from three species, Bromus diandrus, Avena fatua, and Hordeum murinum, were placed in sealed bags and subjected to abiotic decomposition in either an outdoor experiment or an indoor experiment. Treated litter was then soaked in water, and the extract was analyzed to determine the dissolved organic carbon concentration and its bioavailability. Exposure to radiation resulted in more DOC for all species in both the indoor and outdoor experiments, suggesting that solar radiation does enhance solubility of grass litter. During a microbial incubation, I observed a significant increase in CO2 production and a marginally significant increase in DOC consumption for samples exposed to more radiation in the indoor experiment. However, as a fraction of initial DOC available, radiation reduced these measures of microbial activity. This indicates that photodegradation produces compounds which are relatively difficult for microbes to decompose, but photodegradation can still stimulate microbial activity by increasing the total amount of available dissolved carbon. Taken together, these results suggest a possible mechanism for observed increases in mass loss due to photopriming: litter carbon is made more soluble by radiation, and is mobilized in the presence of water, allowing for increased microbial decomposition. This insight into decomposition mechanisms could aid in developing more mechanistic models of carbon cycling that include photopriming.

Projected changes in climate and urbanisation will not only impact on groundwater availability, but also its quality. Natural dissolved organic matter (DOM) character and concentration are major controls of groundwater quality, potability and treatment costs. Whilst the factors impacting DOM in surface waters are increasingly well understood, the sources, character and fate of groundwater DOM remains unclear. This thesis assesses global groundwater dissolved organic carbon (DOC) concentrations (average = 2.7 mg C / L, median = 1.0 mg C / L and σ = 15.1 mg C / L) and then quantifies variables impacting DOC concentrations on a continental scale to determine future changes. Ultra-high resolution DOM characterisation techniques combined with size exclusion chromatography and isotopic (14CDIC, 14CDOC, 18O, 2H, 3H) analyses are then used to identify groundwater DOM end-members in geographically contrasting groundwater environments in New South Wales, Australia. One of these sites was further sampled at multiple time points to determine the effects of extreme wet and dry periods on groundwater DOM character. This thesis identifies water chemistry, climate, aquifer age and land use as significant drivers of groundwater DOC concentrations. Hotspots in the United States are identified where groundwater DOC is projected to increase by almost half its current concentration by 2050 due to changes in temperature and precipitation alone. In-depth groundwater DOM analysis utilising carbon isotopes and DOM characterisation techniques in three contrasting locations in Australia revealed three major groundwater DOM end-members. These include a young terrestrial aliphatic DOM source identified at all sites, a low aromaticity, low molecular weight, aged recalcitrant by-product DOM identified at inland sites, and an aged, aromatic sedimentary DOM source identified at a coastal site. This work highlights the importance of DOM source rather than age in determining groundwater DOM character. Sampling after an extended dry period and after heavy rainfall events in the sedimentary organic carbon-rich coastal site revealed that DOM was significantly more hydrophilic and aromatic after rainfall compared to pre-rainfall samples. The findings indicate that climate change is likely to modify the character and concentration of groundwater DOM. In some areas this will make groundwater increasingly difficult and expensive to treat, requiring more efficient and cost-effective methods for groundwater treatment in the future.

In situ fluorometers have been examined for their potential to provide early warning of bloom development via the analysis of fluorescent cell pigments to give an estimate of cell biovolume. Despite the potential for monitoring algal blooms using fluorometers, there has been no in-depth study that analyses the broad spectrum of fluorescence associated with algae, from pigments through to the AOM exudates, using 3-D excitation-emission matrix (EEMs) spectroscopy. Hence, in this study, the evolution of fluorescent algal cell pigment and AOM characteristics over time for a wide variety of cyanobacterial and algal species was investigated using EEMs as a function of the growth phase, cultivation methods and simulated environmental conditions. The AOM released by key cyanobacterial and algal species were studied at lab scale throughout their growth using 3D-EEMs combined with Parallel Factor analysis (PARAFAC). Monitoring of algal population at source and drinking water treatment plant was also investigated. A six-component PARAFAC model was developed for the analysed dataset. Comparisons of the different AOM revealed that major differences in character were associated with the presence of fluorescence at wavelength pairs of 290:345 nm (tryptophan-like region) and 355:475 nm (humic-like region) which had significant correlations with DOC and dominated across the exponential and stationary phases. Distinct AOM character differences between algae and cyanobacterial species were also evident. For example, the AOM of Chlorophyll vulgaris was rich in amino acid-like materials while that of Microcystis aeruginosa was dominant with humic-like substances. Environmental variables had a significant effect on the pigment content and released AOM character during the growth phase studied. Similarly, the variability of fluorescent AOM in the field and through drinking water treatment processes was dominant within the amino acid-like region, humic-like region (Peak C) and humic-like region (Peak A). This led to the conclusion that cell pigment and AOM fluorescence vary as a function of biotic and abiotic factors and its in-depth understanding and application for real-time monitoring will help improve current monitoring tools.

Abstract: Trace metals have been estimated to be required in one-quarter to one-third of all proteins as cofactors in metalloenzymes which code for numerous crucial biological processes such as respiration, photosynthesis, DNA and RNA synthesis, nitrogen fixation, and electron transfer reactions. However, the marine bioavailability of these trace metals is affected by complexation with microbes and organic ligands. Microbial biomass is an important vector involved in the adsorption and cycling of marine biomass due to its negative surface charge at marine conditions and high surface area to volume ratio. Furthermore, the majority of trace metals in seawater are complexed with dissolved organic ligands. Most of these ligands are produced autochthonously by cyanobacteria who use these ligands to alter the bioavailability of nutrients. Therefore, studying the interplay between microbes, dissolved organic molecules, and trace metals is critical in understanding marine nutrient cycles. Gaining insights into the interplay between biomass and trace metals is also critical for understanding the evolution of metalloenzymes and long-term trace element bioavailability, since it has been hypothesized that metalloenzymes reflect marine nutrient availability at their time of evolution. Furthermore, biomass can also be a sink for trace metals, acting as a sink for trace metals into sediments with these signatures being preserved in the rock record. This study explores the surface reactivity and adsorption of the bioessential trace elements Co, Ni, Cu, and Zn to the cell wall of the marine cyanobacterium Synechococcus sp PCC 7002 and Synechococcus-derived dissolved organic carbon using a surface complexation modelling approach. Synechococcus and its lysate, an analogue for DOC, have similar surface properties as determined by FTIR analysis and titration data in conjunction with SCM. Titration data for both was modelled using a 3-site protonation model, while FTIR analysis determined the presence of carboxyl, phosphoryl, hydroxyl, and amine groups. Although the general properties of Synechococcus and its lysate were similar, the lysate exhibited lower pK¬a values as well as significantly higher site concentrations for each of the sites. Metal binding experiments were performed by means of pH edges to determine the adsorption capacity of Synechococcus, followed by surface complexation modelling of the adsorption data to calculate thermodynamic binding constants for each of the metals. These thermodynamic binding constants were then used to predict the adsorption of the metals in a competitive system, where the adsorption pattern of Zn>Cu>Ni>Co was accurately forecasted. This study aims to increase our understanding of the importance of trace metal adsorption to marine organic ligands and their influence on trace metal cycling.

Abstract: Peatlands in Canada’s western boreal forest are a major source of dissolved organic carbon (DOC) to downstream ecosystems, where DOC regulates carbon cycling, and can affect ecosystem productivity and habitat quality. Subarctic ecosystems are becoming increasingly vulnerable to the effects of climate change, particularly to disturbances such as wildfire and permafrost thaw. These disturbances have the ability to alter aboveground vegetation structure, soil thermal regimes, and hydrologic flow paths, and ultimately affect the quantity and composition of exported DOC. In high-latitude regions, the spring freshet is traditionally understudied, yet represents an important component of the annual DOC budget. To better constrain and quantify the impact of wildfire and permafrost thaw on aquatic carbon cycling in boreal peatlands I conducted a first study that comprised three in-situ incubation experiments (spring, summer, fall) with porewater collected from a partially burned peatland, investigating how wildfire and permafrost thaw affects DOC susceptibility to microbial and photochemical transformations. In spring, recently thawed sites exhibited greater microbial DOC lability (26% DOC loss) compared to unburned sites with intact permafrost (11%), while sites with mature permafrost thaw or sites that had recently burned both exhibited decreased lability (

In the western United States, elevated selenium (Se) levels in soil have resulted in documented cases of ruminant fatalities. This is due to the ingestion of Se-hyperaccumulating vegetation growing on previously reclaimed phosphate mine soils. A field-scale analysis was first conducted to examine Se bioavailability to plants. Soil and plant samples were collected from transects from five study locations in Soda Springs, Idaho. Soils were analyzed for Se speciation and geochemical phases using a sequential extraction procedure (SEP). Additionally, speciation, SEP results, and Se bioavailability in the hyperaccumulator, western aster (Symphyotrichum ascendens (Lindl.)), were related using simple linear regression. Soil speciation and the validity of this SEP were then evaluated using synchrotron-sourced X-ray absorption fine structure (XAFS) spectroscopy for both whole and a sequence of extracted soils. Lastly, competitive adsorption of Se with two dissolved organic carbon (DOC) species, citric and salicylic acid, was examined on an amorphous iron oxide mineral surface. A strong relationship was identified for western aster Se and the first two combined SEP fractions, water-soluble and PO43--extractable Se (R2 = 0.85; P =

The concentration of atmospheric carbon dioxide (CO2) is increasing at extraordinary rates (e.g. Le Quéré et al. 2016). Effectively mitigating the impacts of increasing atmospheric CO2 on climate change, the ocean has absorbed roughly 30 % of the anthropogenic CO2 produced since the Industrial Revolution (e.g. Doney et al. 2009). However, increased levels of CO2 in the surface ocean may have lasting implications for marine biogeochemical cycles (e.g. Riebesell et al. 2013). In addition to gradual increases in concentrations of CO2 in the surface ocean through rising atmospheric CO2, mixing of deep water upwards leads to the injection of elevated partial pressures of CO2 (pCO2) into the surface ocean, exposing some areas of the surface ocean to transient pulses of elevated pCO2 equivalent to those projected for the year 2100 (Feely et al. 2008, Hofmann et al. 2011). This broad range of exposure to elevated pCO2, from ephemeral pulses to gradual increases, highlights the necessity to understand the impacts of pCO2 on marine biogeochemical processes on a variety of timescales.Heterotrophic bacterioplankton play a key role in the biogeochemical cycling of carbon in the ocean through the consumption and remineralization of dissolved organic carbon (DOC). The physical mixing of DOC that accumulates in the surface ocean into the mesopelagic represents ~ 20 % of global annual organic carbon export (Hansell and Carlson 2015), making DOC export an important pathway in the biological carbon pump. Export of DOC to ocean depths removes this carbon from interaction with the atmosphere on a variety of timescales. Processes that remove or reduce the accumulation of DOC in the surface ocean can decrease the amount of DOC available for export and ultimately lessen the effectiveness of DOC export as a sink of carbon in the ocean. As the primary consumers of DOC, heterotrophic bacterioplankton can reduce the amount and rate of DOC accumulation in the surface ocean. Thus, factors that affect the ability of bacterioplankton to consume DOC can affect DOC accumulation and have implications for DOC export potential.In Chapter I, I present results from seawater culture experiments that were designed to assess the effects of pCO2 on bacterioplankton consumption of DOC. Results from these experiments provide evidence that short-term exposure to elevated pCO2 can enhance the rate of removal of photosynthetically-derived surface DOC by natural bacterioplankton communities. To evaluate potential physiological and metabolic mechanisms responsible for these enhanced rates of DOC removal by marine bacterioplankton, I present results from a metagenomic analysis in Chapter II. These results suggest that elevated pCO2 can alter the taxonomic composition and metabolic potential of natural bacterioplankton communities. Collectively, Chapters I and II contribute to a growing understanding of the effects of elevated pCO2 on bacterioplankton-mediated carbon cycling in the surface ocean. Chapter III provides the first high-resolution evaluation of key physical and biogeochemical variables controlling carbon dynamics in the oligotrophic waters surrounding the islands of Moorea and Tahiti, French Polynesia, providing the context needed to predict how short-term increases in pCO2 may alter carbon-cycling in oligotrophic gyre ecosystems.ReferencesDoney, S.C., Fabry, V.J., Feely, R.A., and Kleypas, J.A. (2009). Ocean Acidification: The Other CO2 Problem. Annual Review of Marine Science 1, 169–192.Feely, R.A., Doney, S.C., and Cooley, S.R. (2009). Ocean acidification: Present conditions and future changes in a high-CO₂ world. Oceanography 22, 36–47.Hansell D.A. and Carlson, C.A. (2015). Biogeochemistry of marine dissolved organic matter (Amsterdam; Boston: Academic Press).Hofmann, G.E., Smith, J.E., Johnson, K.S., Send, U., Levin, L.A., Micheli, F., Paytan, A., Price, N.N., Peterson, B., Takeshita, Y., et al. (2011). High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison. PLoS ONE 6, e28983.Le Quéré, C., Andrew, R.M., Canadell, J.G., Sitch, S., Korsbakken, J.I., Peters, G.P., Manning, A.C., Boden, T.A., Tans, P.P., Houghton, R.A., et al. (2016). Global Carbon Budget 2016. Earth System Science Data 8, 605–649.Riebesell, U., Gattuso, J.-P., Thingstad, T.F., and Middelburg, J.J. (2013). Preface “Arctic ocean acidification: pelagic ecosystem and biogeochemical responses during a mesocosm study.” Biogeosciences 10, 5619–5626.

Approximately 50 percent of marine primary production passes through the dissolved organic matter (DOM) pool (Myklestad 2000; Nagata 2000). The major consumers of DOM are marine bacterioplankton, which can direct DOM down three pathways: respiration to inorganic constituents, incorporation into biomass, or modification or lack of consumption leading to persistence as DOM. The aspects of DOM source and composition that determine its bioavailability, and its interactions with the clades comprising the bacterial community, are broadly understood, but many of the finer details remain to be studied. This dissertation investigates bottom-up controls on bacterial community composition (BCC) and activity through a time-series study in the Santa Barbara Channel (SBC), CA, and examines the effects of phytoplankton DOM on bacterial metabolism, in field and laboratory experiments. Chapter II describes the results of a four-year time-series study of BCC and metabolic activity in the SBC. BCC showed the greatest variability over depth; at the surface, the seasonal cycle was significantly more influential on BCC than spatial variability within cruises. Community types showed repeating patterns following the annual upwelling and phytoplankton bloom season; however, new community types appeared in the second half of the time-series, possibly in association with the Pacific warm anomaly observed in 2014. Individual operational taxonomic units (OTUs) were strongly correlated with environmental parameters, reflecting a successional pattern in OTUs following the spring upwelling. Seasonality was moderately repeatable in both the community as a whole and in individual OTUs, with long-term changes in BCC possibly linked to broader climatological phenomena. In Chapter III, interactions between dissolved organic carbon (DOC) and bacterioplankton were examined during a diatom and Phaeocystis bloom in the SBC over 5 days following an upwelling event, encompassing phytoplankton physiological states from a healthy bloom through the onset of silicon (Si) stress. DOC bioavailability, bacterial growth, and BCC responses were assessed with dilution batch-culture bioassays. In these experiments, as the bloom state progressed: bacterioplankton DOC usage increased; bacterial growth efficiencies increased; and measureable DOC that accumulated during the bloom remained unutilized in the bioassays. Thus, DOC released by the plankton community during a bloom simultaneously contributes to several DOM pools of variable longevity. In Chapter IV, the ecological role of carbon-rich DOM exuded by nutrient-stressed phytoplankton was assessed using DOM from four coastal diatoms following depletion of nitrogen (N), Si, or both N+Si. In bioassay experiments, short-term responses were affected both by diatom source species and by the nutrient stress under which the DOM was produced. Si-stress DOM was generally the most bioavailable over several days and led to higher bacterial growth efficiencies. However, the amount of diatom-derived DOC that persisted over months differed among source diatom species, with no evidence of a nutrient stress effect. The identity of the nutrient that terminates a phytoplankton bloom can therefore impact heterotrophic activity in the short term, while source phytoplankton species is more likely to influence DOC persistence in surface waters and its potential export.

Abstract: Anthropogenic climate change has affected the Canadian Arctic cryosphere, accelerating the development of retrogressive thaw slumps (RTS) across the Peel Plateau, NWT, Canada. RTS result from the thawing of ice-rich permafrost and develop due to ablation of ground ice exposed in the slump headwall. RTS provide pathways for dissolved organic carbon (DOC), previously inaccessible when stored in permafrost, to become available for biologically or photochemically-mediated degradation; creating a relatively novel input source to the global carbon cycle. The Peel Plateau, which is comprised of ice-rich glaciogenic materials and soils that are rich in inorganic materials, exhibits a high occurrence of RTS activity. RTS activity in the Peel Plateau is predicted to alter the carbon dynamics of receiving waters in ways that contrast with the effects of permafrost slumping in Arctic regions containing organic-rich soils. Here, we explore the environmental drivers and absolute magnitude of DOC delivery to impacted stream systems, and the susceptibility of this DOC to biological degradation. This work determined that temperature and precipitation are the main drivers of DOC mobilization across the Peel Plateau; environmental variables that are predicted to increase considerably across Arctic regions. Pristine streams demonstrated higher concentrations of DOC than streams impacted by slump runoff, an effect that seems likely to occur as a results of DOC adsorption to slump particles. DOC from RTS streams was more susceptible to bacterial degradation, though at lower rates than those found in other thermokarst impacted regions. Spectral and isotopic characteristics of RTS-affected and pristine streamwater were examined to explore how differences in DOC origin and composition relate to decomposition. Permafrost DOC response to climate change has been identified as one of the key knowledge gaps in predicting how integrated Arctic systems will function in the future. This work aimed to close this gap through the monitoring of the flux and fate of DOC mobilized from slump features in an understudied region.

Dissolved organic carbon (DOC) is a critical nutrient in aquatic ecosystems, but can also be a pollutant in drinking water. Controlled by a combination of catchment wide and instream processes, the bioavailability, reactivity, and concentration of DOC is readily altered by natural and anthropogenic processes within rivers and the greater watershed area. However, little is known about natural or anthropogenic controls on DOC in dryland areas where water resources are limited and increasingly endangered. To address this, we examined the major contributors of DOC within and to a dryland river—the Middle Rio Grande (MRG) in central New Mexico. This was achieved via synoptic sampling of storm event flow in an urban storm drainage system, water in agricultural conveyances, and monthly sampling of the mainstem. We measured DOC concentration, determined its source (terrestrial or instream), and explored its chemical structure (aliphatic v. aromatic) as an indicator of lability. We found that during storm events, DOC entering the river from the storm drainage system is derived from a combination of terrestrial and instream sources. The connection of the landscape to the river via storm event runoff controls when during the storm event DOC from these two sources reaches the river. We found that the agricultural system is a net DOC sink because of water loss during irrigation. The agricultural irrigation system also acts a biogeochemical hotspot where DOC is rapidly cycled. As a result labile DOC is introduced in the agricultural system’s conveyances and DOC effluent from the agricultural systems is more labile and bioavailable than DOC in the mainstem. Within the Middle Rio Grande, we find that despite the addition of DOC from storms and agricultural systems, DOC concentration and character remains largely consistent over time and as the river moves north to south. Additionally, in the MRG DOC concentration is uncoupled from discharge. Thus, we hypothesize that anthropogenic modifications of the watershed and river increase the amount of labile DOC and drive DOC concentration, overriding the influence of natural processes such as discharge. The results of this dissertation provide a framework to understand the competing influences of natural processes and anthropogenic alteration on DOC concentration, source, and character. This framework can guide future research in water treatment and reuse and nutrient dynamics in dryland regions.

Terrestrial land use is intimately connected to the amounts and characteristics of organic and inorganic carbon (C) exported to aquatic ecosystems. However, the effect of land use on the contributions of various potential C sources to headwater streams is poorly established quantitatively. In this study we examined the fluxes and δ13C and Δ14C signatures of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate organic C (POC) exported from headwater streams of six watersheds of differing land use in a long-term experimental watershed. We employed Bayesian modeling (MixSIR) to determine relative contributions of potential C sources to DIC, DOC, and POC. Agricultural activity (i.e., tilled and non-tilled corn planting) increased watershed C export fluxes by 50-400% due to a 4-9-fold greater export of terrestrial plant-derived biomass C and a 5-15-fold greater export of soil C, compared to all other land uses (i.e., pasture, mixed land use, and forested). In addition, the sources of C contributing to exports from the forested watershed differed from watersheds with both agricultural land uses and those with pasture or mixed land uses. By scaling our results to the Mississippi River Basin watershed, we estimate that historic conversion of land to tilled agricultural practices may have increased the terrestrial-aquatic C flux by 11.4 ± 0.5 Tg•C•yr-1 (nearly six-fold). If non-tilled practices were implemented across all agricultural land in the Mississippi watershed, we estimate that C exports to inland waters and subsequent CO2 release to the atmosphere could be reduced by as much as 60%.

This research was carried out in order to better understand the interactive role of vegetation and soil biogeochemistry on an ecological restoration trajectory on the West Coast of New Zealand. The Punakaiki Coastal Restoration Project (PCRP) was developed to restore degraded land to a more natural vegetation, resembling the original sandplain forest that has largely disappeared. Ecological restoration at the site, in terms of practice and research, has mainly focused on plant establishment and faunal colonization. The present study investigated whether restoration of soils is an integral part of this process. The project aimed to understand whether ecological restoration significantly modifies soils and, vice versa, whether physio-chemical variability of soils significantly influences the restoration trajectory. This research is based on a combination of laboratory, glasshouse and field-based studies. Incubation of native plant litters in soil was found to change soil chemical properties, including nitrogen (N) dynamics. It was found that two native species, Kunzea robusta and Olearia paniculata, may have the potential to ameliorate concerns associated with nitrate leaching and nitrous oxide production. Restored vegetation at the study site modified the dynamics of dissolved organic carbon (DOC) and mobile N in soil solution and increased rates of N mineralization. Interactions between vegetation and soil biota have significantly impacted these changes; changed soil conditions have also altered the composition of soil faunal communities. Study of soil pedogenesis revealed a formerly unknown spatial variability of the soil template. As soils have aged this has been reflected in a loss of soil total phosphorus (P), increase of occluded P and an increasing proportional importance of soil organic P. The dynamics of soil P fractionation on a short-term soil chronosequence across the site provided a better understanding of the response of soil biogeochemistry to the trajectory of ecological restoration on old and young soils. Key parameters were shown to be soil pH, organic matter, organic P and the variability of different P fractions. A detailed comparison of remnants of New Zealand Flax and Nikau Palm, and abandoned agricultural grassland, provided an opportunity to investigate the effects of these different types of vegetation on soil development. Multiple variables were found to be significant, including differences in plant physiology, soil organisms, hydrological gradient of an alluvial fan, and guano deposition, all of which modified soil P fractionation and secondary iron/aluminium (Fe/Al) minerals. In a glasshouse experiment, soil dehydrogenase activity and biologically based P (CaCl2-P, citrate-P and HCl-P) were significantly increased through interactions of earthworms and guano; the dynamic of soil P was modified by additional interactions with flax plants. The relationships between soil chemistry, biodiversity and plants on the restoration trajectory at PCRP were synthesized using multivariate analysis. A conceptual model was developed, elucidating changes of soil physio-chemistry on the restoration trajectory. The success of the PCRP restoration and establishment of flora and fauna are strongly influenced by soil variability, but the developing plant communities also substantially modify soil physio-chemistry. The study illustrates that a preliminary investigation of site-specific soils should be an essential part of restoration practice.

Oceans account for approximately half of global primary production, and oligotrophic gyres account for a large fraction of this production. Understanding of time-varying changes to ocean ecosystems largely derives from time-series observations. Since 1988, the Hawaii Ocean Timeseries (HOT) program has conducted near-monthly sampling at Station ALOHA (22° 45’N, 158° 00’W), providing information on the magnitude and pathways of carbon cycling in the North Pacific Subtropical Gyre (NPSG). These observations have identified microbial production and consumption of organic matter as major processes catalyzing upper ocean carbon fluxes. In this dissertation, I quantified rates of dissolved and particulate organic carbon production over daily to annual time scales in this ecosystem. Measured rates of primary production (PP) demonstrated significant depth-dependence, unlike rates of dissolved organic carbon (DOC) production. On average, depth-integrated (0–75 m) rates of DOC production were equivalent to 18 ± 10% of total (particulate and dissolved) productivity. My findings indicate that in this oligotrophic ecosystem, rates of dissolved and particulate production appear temporally decoupled over daily to monthly time scales. In addition, over a ~2-year period, I quantified rates of bacterial production (BP) at near-monthly time scales, to evaluate potential coupling between photosynthetic production of organic matter and its consumption by heterotrophic bacteria. There was no temporal correlation between rates of bacterial growth and primary production across daily to seasonal time scales, with BP lagging rates of PP by 1 to 2 months. Moreover, in the well-lit (75 m), there was no significant relationship between temperature and bacterial production. My results suggest photosynthetic production varies seasonally with changes in light, while bacterial production appears more sensitive to variations in upper ocean temperature. I also experimentally evaluated the effects of abrupt changes to the seawater carbonate system on rates of primary and bacterial production at Station ALOHA. These experiments revealed that abrupt changes in the partial pressure of seawater CO2 (pCO2) had little effect on rates of primary and bacterial production in this persistently oligotrophic ecosystem.

Climate-linked changes in hydrology and biogeochemical processes within Arctic watersheds are likely already affecting fluvial export of waterborne materials, including organic matter (OM) and dissolved inorganic nitrogen (DIN). Our understanding of Arctic watershed OM and DIN export response to climate change is hampered by a lack of contemporary baselines, as well as a dearth of seasonally comprehensive studies. This work focuses on characterizing OM and DIN concentrations and sources in six streams/rivers on the North Slope of Alaska during the entirety of the hydrologic year (May through October) in 2009 and 2010. The highest OM concentrations occurred during spring snowmelt, with results indicating that terrestrial vegetation leachates are the major source of dissolved OM, while particulate OM originates from a degraded soil source. Over the hydrologic year, soils became a progressively increasing source of dissolved OM, while autochthonous production made up a sizeable proportion of particulate OM during base flow conditions. DIN concentrations were low throughout the spring and summer and increased markedly during the late summer and fall. Our findings suggest that penetration of water into thawed mineral soils, and a reduction in nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. Although recent studies of Arctic rivers have emphasized the importance of the spring thaw period on OM export, our understanding of the mechanisms that control water chemistry observations during this time are still lacking. Experimental leaching results, from experiments conducted in 2014, suggest that aboveground plant biomass is a major source of dissolved OM in Arctic catchments during the spring, and that the timing of freezing and drying conditions during the fall may impact dissolved OM leaching dynamics on that same material the following snowmelt. Improved knowledge of OM and DIN temporal trends and the mechanisms that control seasonal concentrations is essential for understanding export dynamics of these water constituents in Arctic river systems. Perhaps more importantly, increased understanding of the seasonal controls on OM and DIN export in Arctic rivers is critical for predicting how these systems will respond under future climate change scenarios.

In June 2013, a test of sample processing steps was undertaken for limnological/oceanographic sampling of total organic carbon (TOC), particulate organic carbon (POC), dissolved organic carbon (DOC), and colored dissolved organic matter (CDOM). This was to determine the magnitude and sources of errors in the sampling of these organic carbon field measurements. Replicate Niskin rosette casts in Lake Superior (with a difference of 0.79 km in site location and 1 hour 6 min in sampling time) were found to be significantly different at both alpha= 0.05 and 0.10 for DOC, TOC, e2/e3, and CDOM, but not POC. The TOC, DOC and POC average concentration and the standard deviation of all replicates of the two casts was 2.3 +/- 0.2, 2.3 +/- 0.3, and 0.14 +/- 0.02 mg/L respectively. The variation due to sample handling within one cast for DOC and TOC is 0.1 mg/L or 5% relative standard deviation. For POC, the variation is 0.02 mg/L or 14%. Use of different Niskins from the same cast did not cause significant effects.

Geologic carbon sequestration has been proposed as a means of mitigating anthropogenic greenhouse gas emissions. At depth, supercritical CO₂ may rise above the surrounding fluid. Detecting leaks from CO₂ storage reservoirs is important to evaluate the effectiveness of carbon sequestration and address public concern for negative environmental impacts. Other attempts have been made to detect leaks, such as changes in pH, pressure and direct observation of CO₂ in the AZMI (Above Zone Monitoring Interval). Each has limitations and here we investigate dissolved organic carbon (DOC) as a potential indicator for fugitive CO₂. This study uses a series of batch experiments to evaluate the interaction between dissolved CO₂ and DOC. The batches consist of homogenized and sieved 250 micron to 425 micron matrix samples of varying mass and type, 2mL of DI water and a headspace of pure carbon dioxide or air. The three different rock samples analyzed are Buffalo River Sediment, illite and Barnett Shale. A pure CO₂ headspace results in lower amount of DOC in solution than an air headspace. All matrix samples demonstrated this effect. The proposed mechanism to describe the observed results is that a lowered pH shifts speciation of weak organic acids and protonated humic substances causing decreased solubility and increasing the adsorption of these compounds. These results suggest that a decrease in DOC concentrations could be used to detect CO₂ leakage and that CO₂ leakage would not deteriorate water quality by releasing DOC.

The incomplete combustion of biomass and fossil fuels produces black carbon (BC). BC is recalcitrant and serves as a long term holding pool for carbon, with a mean residence time of one to two orders of magnitude greater than unburnt carbon on land. Yet the known sources of BC are far larger than the known sinks, which led to studies of BC in the ocean’s dissolved organic carbon (DOC) reservoir. The goal of this dissertation was to measure the abundance and residence times of BC in sediment, sinking particles and DOC in order to understand the cycling of BC in the ocean. I found that BC in northeast Pacific sediments was older by 6,200 ± 2,200 14C years than the concurrently deposited sedimentary organic carbon, suggesting that BC ages within DOC for millennia before deposition to sediments. Sinking particulate organic carbon may provide the main transport mechanism of aged BC into sediments. A solid phase extraction (SPE) technique was modified to extract DOC from seawater, and provided the methodological basis by which BC composition, concentration and Δ14C values were determined. This SPE method isolated 43 ± 6% of the DOC from seawater. I found that the composition of SPE-BC was less aromatic in the ocean samples than those in a set of river standards. The average concentration of SPE-BC in the surface ocean samples was 1.6 ± 0.1 μM and 1.2 ± 0.1 μM in a deep ocean sample. The average 14C age of surface SPE-BC is 4,500 ± 3,000 14C years, and is much older in the deep water sample from the Sargasso Sea (23,000 ± 3,000 14C years). I calculate that the SPE-BC pool is approximately 14 ± 2 Gt C in the open ocean. This value is a minimum estimate, because it does not include the BC content in 57% of the DOC that was not isolated using SPE methods in this work. BC can explain a small part of the 4,000 – 6,500 14C years age of DOC, but is not the major cause. The range of SPE-BC structures and Δ14C values found in this work suggest that oceanic SPE-BC is not homogeneous, but that it contains several distinct pools of BC with widely ranging residence times.

Emission and uptake of greenhouse gases and the production and transport of dissolved organic matter in different wetland plant communities are key wetland functions determining two important ecosystem services, climate regulation and nutrient cycling. The objective of this dissertation was to study the variation of methane emissions, carbon sequestration and exports of dissolved organic carbon (DOC) in wetland plant communities of a subtropical climate in south Florida. The plant communities selected for the study of methane emissions and carbon sequestration were located in a natural wetland landscape and corresponded to a gradient of inundation duration. Going from the wettest to the driest conditions, the communities were designated as: deep slough, bald cypress, wet prairie, pond cypress and hydric pine flatwood. Methane fluxes from the different communities did not show a discernible daily pattern, in contrast to a marked increase in seasonal emissions during inundation. Median and mean + standard error fluxes in g CH4-C.m-2.d-1 were higher in the deep slough (11 and 56.2 + 22.1), followed by the wet prairie (9.01 and 53.3 + 26.6), bald cypress (3.31 and 5.54 + 2.51) and pond cypress (1.49, 4.55 + 3.35) communities. The pine flatwood community acted as a net sink (0.0 and -1.22 + 0.81). Seasonality in methane emissions was positively correlated with the water levels, but not with soil temperature. However, longer inundation periods did not necessarily result in higher methane emissions. The mean carbon concentration from the surface to the depth of maximum 137Cs activity between communities was similar in the deep slough, bald and pond cypress (446, 405 and 369 g-C Kg -1, respectively). However, carbon sequestration rates (g-C.m-2.yr-1) were highest in the deep slough (104 + 14), followed by the pond cypress (60 + 9), bald cypress (30 + 2), wet prairie (24 + 1) and pine flatwood (15 + 1) communities, without an apparent relationship with the duration of the inundation period. Using the latest accepted global warming potentials of methane, it was concluded that the negative effects of contemporary methane emissions from these communities is offset by their long-term carbon sequestration. The study of (DOC) export was conducted at a mesocosm scale using outflow water from the Storm Treatment Area 1W (STA-1W) of the Everglades region. Treatments dominated by. Nymphaea sp./Eleocharis sp. and Najas sp./Chara sp. functioned as temporary sinks for DOC, but, otherwise, all treatments were net sources of dissolved organic carbon, suggesting the importance of autochthonous material from within the mesocosms in the export of carbon. A two-source carbon isotope mixing model was used to estimate the contribution from inflow water and biomass into the outflow’s dissolved organic carbon in each treatment. Dissolved organic carbon from biomass was relatively higher in treatments with emergent and floating vegetation (20 - 32 %) than in treatments containing submerged aquatic vegetation (

Coral reefs are declining globally due to a combination of direct and indirect human impacts. Much of this decline can be attributed to prolonged exposure to elevated sea surface temperatures which induces coral bleaching – a process whereby corals lose their endosymbionts and/or their endosymbiotic pigments resulting in corals that appear pale or white. Corals have extremely different responses to bleaching events: some corals bleach and die, others bleach and recover, and some do not visibly bleach at all. In the absence of abundant photosynthetically fixed C, corals may rely on one or more of the following strategies to sustain themselves and promote recovery: (1) catabolize stored energy reserves, including lipids, carbohydrates, and/or proteins, (2) reduce respiration rates, (3) decrease skeletal growth, (4) increase heterotrophy or (5) shuffle or change their endosymbiont type(s). Although mounding species of coral have been shown to survive bleaching events in greater abundance than branching species, the underlying mechanism(s) for mounding coral resilience is unknown. Furthermore, controlled bleaching and recovery experiments coupled with detailed carbon budgets that incorporate autotrophy and multiple heterotrophic sources (i.e. zooplankton and dissolved organic carbon) do not exist for Caribbean corals. Therefore, two controlled tank experiments, one in Hawaii and the other in Puerto Morelos, Mexico were conducted to understand the bleaching and recovery responses in the Hawaiian coral Porites lobata and the three Caribbean corals Montastraea faveolata, Porites astreoides, and Porites divaricata. Four major findings were observed: 1) Bleaching resilience in the mounding coral P. lobata is due to it harboring a thermally tolerant endosymbiont type combined with an ability to actively metabolize zooplankton acquired C and utilize DOC as a significant fixed C source, 2) Bleached P. astreoides were capable of meeting greater than 100% of metabolic demand by increasing feeding rates, 3) All Caribbean corals took up dissolved organic carbon as a source of fixed carbon when bleached, 4) M. faveolata and P. astreoides are more resilient to single bleaching than P. divaricata. This study represents the first comprehensive assessment of the underlying traits that confer bleaching resilience in a mounding Hawaiian coral. Furthermore, these studies represent a comprehensive physiological and biogeochemical analysis of bleached and recovering Caribbean corals and the first to detail their carbon budgets. The ability for bleached corals to maintain high photosynthetic capacity coupled with the ability to utilize exogenous C sources appears to be an underlying theme in resilience to bleaching. Based on these findings, species such as P. lobata, M. faveolata, and to a lesser extent P. astreoides are more likely to survive a single bleaching event than the branching P. divaricata or the previously studied branching coral P. compressa.

Silver nanoparticles (AgNPs) are by far the most extensively used nanomaterial in general consumer products. Concurrent with this use is the major concern regarding the toxicity of AgNPs to aquatic organisms. The most persistent question regarding the toxicity of AgNPs is whether this toxicity is due to the nanoparticles (NPs) themselves or the ions they release. Two primary factors influencing the aquatic toxicity of AgNPs are the surface coating, which presumably controls the release of Ag+, and the dissolved organic carbon (DOC) of the media, which serves as a source for ligands to bind the Ag+ and reduce bioavailability to aquatic organisms. This study was conducted to investigate the role of these variables on the toxicity of AgNPs to the aquatic pelagic invertebrate, Daphnia magna and to test the hypothesis that the toxicity of AgNPs to Daphnia magna can be explained by their generation of silver ions. Acute toxicity bioassays (48h) were conducted using silver nitrate (AgNO3) as the positive control and three AgNPs with different surface coatings: gum arabic-coated (AgGA), polyethylene glycol-coated (AgPEG), and polyvinylpyrrolidone-coated (AgPVP) silver nanoparticles. Bioassays were conducted in moderately hard reconstituted water (MHW) augmented with two different concentrations of Suwannee River dissolved organic carbon (SRDOC). Measurements of the total silver and dissolved silver concentration were determined at the 48h median lethal concentration (LC50). The findings indicated that in MHW, AgNO3 was the most toxic to Daphnia magna (LC50 =1.06 μg Total Ag/L), and AgPVP was the least toxic (LC50 =14.81μg Total Ag/L). The dissolved silver concentrations at the Total Ag LC50 value were similar for all nanoparticles and AgNO3. The presence of SRDOC reduced the toxicity (48h Total Ag LC50) of AgNO3, AgGA and AgPEG while that of AgPVP was unchanged. The results also showed that there was a significant decrease in the dissolved silver concentration with all the AgNPs in SRDOC. These results supported our hypothesis that toxicity of AgNPs to Daphnia magna is a function of ionic silver concentration.

Approximately one half of terrestrial carbon runoff is processed by inland waters and released into the atmosphere as carbon dioxide (CO2) prior to reaching the oceans, and bacterial consumption of dissolved organic carbon (DOC) comprises a dominant proportion of this carbon loss. Though peatlands export more DOC per area than most other ecosystems, the sources and biodegradability of peatland DOC and their effects on downstream DOC loads and fluxes are poorly understood. Moreover, photochemical degradation plays an important role in the loss of carbon from aquatic ecosystems, especially in peatlands with high DOC concentrations rich in photochemically reactive humic and phenolic compounds, but its contribution to global CO2 evasion from inland waters has not been quantified. This dissertation focuses on predictors of biodegradable DOC (BDOC) in aquatic ecosystems, the sources and biodegradability of DOC in peatland watersheds, and the contribution of photochemical degradation of DOC to global CO2 evasion from peatlands and fluvial ecosystems. Key findings from these studies were that SUVA, a measurement broadly used in ecology and environmental engineering and fairly simple to obtain, is an excellent predictor of the amount of long-term BDOC concentrations in Minnesota lake ecosystems. The peatland bog may be the most important source of BDOC exported from peatlands annually, rather than the upland. And, photochemical enhancement of bacterial respiration in peatland and fluvial ecosystems contributes approximately 0.11-0.22 Pg C yr-1 to the total global CO2 evasion from inland waters (~1.4 Pg C yr-1), or 9-18% of all inland water CO2 evasion. The results from this dissertation will lend insight into how future changes in hydrology and surface water DOC concentrations will alter the sources, biodegradability, and photochemical enhancement of DOC in aquatic ecosystems in the northern hemisphere, especially peatlands.

Dissolved organic carbon (DOC) is the dominant form of organic matter in aquatic ecosystems and bacteria play a key role in its mobilization to higher trophic levels. The DOC pool is often divided into broad classes such as labile or recalcitrant, based on its ease of uptake by bacteria; or as autochthonous and allochthonous, based on its production within or outside the ecosystem. In this dissertation, I examined the relationship between the composition of the DOC pool and bacterial community structure and function. The three research chapters address this relationship in different freshwater ecosystems. In the first research chapter, the effect of presence or absence of Microcystis, a dominant primary producer in the western basin of Lake Erie as well as an autochthonous DOC source, on bacterial community structure and heterotrophic productivity was studied. This study revealed that bacterial responses were independent of the presence of the dominant primary producer. In second research chapter, the effect of compositional diversity of DOC within labile and recalcitrant categories, on stream bacterial community structure and denitrification rates was investigated. Use of different compounds within each category, administered individually and in mixtures, contributed to the heterogeneity. Results of this study suggest molecular heterogeneity of DOC can lead to differences in bacterial structure and denitrification potential. In my final research chapter, bacterial responses to differences in proportion of autochthonous and allochthonous DOC between a river and reservoir ecosystem were compared. The findings of this study demonstrated that, rather than the proportion of the two DOC sources, each source, considered individually, played a more important role in determining bacterial response. Regardless of the study, in all cases bacterial community structure was not linked to function, emphasizing the requirement to study both. The results indicate that differences in DOC quality, rather than the quantity, may play a greater role in determining bacterial responses and that structure and function can be decoupled.

Carbon (C), nitrogen (N), and calcium (Ca) cycling in forest ecosystems is controlled largely by the recycling of organic matter by biota and by the balance of new inputs and losses. In the northeastern U.S., the availability of these elements has been dramatically altered by human activities. Acid deposition has increased N inputs and caused declines in soil Ca concentrations. Concurrently, atmospheric carbon dioxide concentrations are rising. My dissertation research focused on understanding how individual tree species influence ecosystem C, N, and Ca cycling, and how increasing soil Ca by liming affects C and N pools, fluxes, and dissolved organic matter retention. In chapter 1, I show how Norway spruce, red oak, and sugar maple planted in a common garden influence soil C, N, and Ca pools. Norway spruce had the largest C and N stocks in the forest floor and upper mineral soils. No differences among species were observed in soil exchangeable Ca availability. Red oak plots displayed the highest foliar litter lignin concentrations, the shortest residence time for C and N in the forest floor, and the highest earthworm densities. This suggests that leaf litter recalcitrance is not the dominant driver of decomposition in this forest and that other factors, such as the presence of earthworms, can influence organic matter turnover in ways that are unexpected when only considering litter chemistry. In chapters 2 and 3, I discuss the long-term effects of liming on ecosystem C and N dynamics. Twenty years after lime addition, there was no evidence of a tree response. Within the forest floor, C and N stocks in limed soils were double that found in controls. I observed reductions in both soil basal respiration and net N mineralization, indicating that liming has altered C and N cycling within this ecosystem. I also investigated how soil exchangeable Ca concentrations influence dissolved organic C and N retention. Soils higher in exchangeable Ca tended to release less C and N, suggesting that liming may facilitate Ca-organic matter bridging, thereby reducing C and N losses from the upper mineral soils.

The natural abundance radiocarbon and stable isotopic distributions of bulk dissolved organic carbon (DOC), particulate organic carbon (POC), dissolved inorganic carbon (DIC), zooplankton, size-fractionated organic matter, and biochemical compound classes were used to investigate the sources, biogeochemical cycling, and fate of organic matter in the water column of Lake Superior. DIC pool appears to reset rapidly, showing radiocarbon values similar to atmospheric values from approximately 3 years previous to sampling. DIC concentrations and isotopic compositions were mostly homogeneous across the entire lake. POC was generally more depleted in stable carbon isotopic values than concurrent DOC. POC was also consistently depleted in radiocarbon (thus, older) relative to DOC and DIC. Radiocarbon ages of POC was spatially heterogeneous (range, modern to 2,840 year BP), and appear to be related to total water depth, exhibiting more older and more variable ages in the deepest basins of the lake. The ages and reactivity of bulk DOC did not change radically across the lake. DOC pool appears to be semi-reactive, recycling over up to 60 years in the entire water column. The radiocarbon signatures of the various DOC size fractions show that they recycle on similar time scales, with consistently modern (post 1950) radiocarbon values. Radiocarbon and Nuclear Magnetic Resonance (NMR) data show most of the high molecular weight dissolved organic matter (HMW DOM) originates from contemporary origin and was dominated by carbohydrates, aliphatic compounds, and acetate, with little aromatic compounds. Total hydrolyzable free carbohydrates and amino acids within HMW DOM exhibited modern radiocarbon signatures and recycled rapidly in the lake. In contrast, extractable lipid was pre-aged (20 to 2,320 years BP) due to older sources and/or general long term persistence in the lake. Coupled radiocarbon and stable carbon isotopic values indicate multiple sources, and variable formation pathways for the acid insoluble organic fraction within HMW DOM in the lake. Radiocarbon and stable isotopic values show zooplankton in Lake Superior selectively feed on within-lake produced organic matter even though other organic carbon sources represented a considerable portion of the available food resource.

In this research, five different coagulants were evaluated to determine their effectiveness at removing turbidity, color and dissolved organic carbon (DOC) from a surface water in Sarasota County, Florida. Bench-scale jar tests that simulated conventional coagulation, flocculation, and sedimentation processes were used. Iron-based coagulants (ferric chloride and ferric sulfate) and aluminum-based coagulants (aluminum sulfate, polyaluminum chloride (PACl) and aluminum chlorohydrate (ACH)) were used to treat a highly organic surface water supply (DOC ranging between 10 and 30 mg/L), known as the Cow Pen Slough, located within central Sarasota County, Florida. Isopleths depicting DOC and color removal efficiencies as a function of both pH and coagulant dose were developed and evaluated. Ferric chloride and ACH were observed to obtain the highest DOC (85% and 70%, respectively) and color (98% and 97%, respectively) removals at the lowest dose concentrations (120 mg/L and 100 mg/L, respectively). Ferric sulfate was effective at DOC removal but required a higher concentration of coagulant and was the least effective coagulant at removing color. The traditional iron-based coagulants and alum had low turbidity removals and they were often observed to add turbidity to the water. PACl and ACH had similar percent removals for color and turbidity achieving consistent percent removals of 95% and 45%, respectively, but PACl was less effective than ACH at removing organics. Sludge settling curves, dose-sludge production ratios, and settling velocities were determined at optimum DOC removal conditions for each coagulant. Ferric chloride was found to have the highest sludge settling rate but also produced the largest sludge quantities. Total trihalomethane formation potential (THMFP) was measured iv for the water treated with ferric chloride and ACH. As with DOC removal, ferric chloride yielded a higher percent reduction with respect to THMFP.

Dissolved organic carbon (DOC) poses many challenges for drinking water treatment plants (WTP) as its reaction with chlorine produces disinfection by-products (DBP) which are undesirable because if their harmful effect on humans and is also regulated by the United States Environmental Protection Agency (U.S. EPA). Parallel factor (PARAFAC) analysis, fluorescence regional integration (FRI), excitation-emission matrices (EEM) maximum peaks and ultra-violet absorbance (UVA) are all optical analysis methods used to characterize DOC and its contribution to disinfection by-product (DBP) formation. Multifactor linear regression models were developed from these optical analysis methods to predict DOC concentrations and DBP formation from raw water and coagulated water collected from a WTP. This comprehensive study utilized 492 total samples collected from January 2010 to July 2011that were used in the DOC analysis while 88 total samples (September 2010 to July 2011) were used for the DBP analysis. The models were evaluated statistically to determine which of the optical analysis techniques performed the best in predicting DOC concentration and DBP formation. PARAFAC analysis had the highest linear correlations of all the models tested and had statistically significant components characterizing the nature of DOC and the precursors to DBP formation. The speed, sensitivity and low cost of PARAFAC analysis shows great promise for incorporation of PARAFAC components into a WTP operation helping them make more informed and science-based decisions to treatment train processes.

An environmentally friendly method for the disposal of scrap tires is currently unavailable; as a result, ultimate disposal of used vehicle tires continues to be a major challenge around the world. In the United States (US), during the past two decades, scrap tires have been generated at the rate of approximately one tire per person per year (i.e., approximately 290 million new scrap tires every year). It is estimated that there are currently 2 billion tires stockpiled in the US. Due to various problems involved in the disposal of scrap tires, different alternatives for recycle and reuse have been examined; however, one concern is the leaching of different tire constituents (organic and inorganic) with time, and their subsequent potential harmful impacts on the environment. The main objective of this study was to perform a systematic investigation to examine the leaching of dissolved organic carbon and selected inorganic constituents from crumb rubber and tire chips under different water chemistry conditions: at three different pH values (4.0, 7.0 and 10.0) in distilled and deionized water, and in the stimulants of acidic rain water (pH 3.0), hard groundwater (pH 8.3) and soft groundwater (pH 6.3) These are the water chemistry conditions that are likely to be encountered during scrap tire (crumb rubber or tire chips) reuse applications. One hundred grams of crumb rubber (8x14 mesh size) or tire chips (1'_1', 2'_2', 4'_2' and 6'_2') were soaked and mixed in each leaching solution with a solid to solution ratio of 1:20 at room temperature for one month period. Samples were periodically collected and analyzed for selected inorganic constituents (sulfur (S), zinc (Zn), cadmium (Cd), chromium (Cr), arsenic (As), potassium (K), phosphorus (P), sodium (Na), manganese (Mn), iron (Fe), calcium (Ca), magnesium (Mg), aluminum (Al), copper (Cu), lead(Pb), selenium (Se), molybdenum (Mo) and nickel (Ni)), dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and dissolved nitrogen (DN). Toxicity Characterization Leaching Procedure test was also performed to assess the toxicity of the leachates. Results showed that the best condition for using scrap tire chips in environmental reuse applications was around the neutral pH conditions. Leaching of dissolved organic carbon and selected elements was minimal around the neutral pH values. pH was a more important parameter than conductivity of the solution in controlling the leaching of DOC and selected elements from scrap tires. The changes in conductivity did not have a significant impact on the leaching of organics or inorganics. When tire chips were exposed to acidic conditions, Fe by far was the most significant metal leaching from tires at very large quantities (up to ~800 mg/ 100 g tire). The presence of organics significantly increased the Fe concentrations in water (e.g., ~ 20 mg/L at pH 4) above its solubility. Mn was the second metal observed leaching at acidic conditions; however at amounts (2-5 mg/ 100 g tire) significantly lower than Fe. When the tire chips were exposed to basic conditions, the leaching of DOC significantly increased (reaching 27 mg/ 100 g tire). For crumb rubber, leaching of DOC reached up to ~120 mg/ 100 g tire, indicating that organic components in tires are more prone to leaching under basic conditions. Under the basic conditions, the leaching of inorganics, including Fe ( The SUVA254 values of the leaching solutions remained in the range of 1.5 to 3.0 L/mg-m during the experiments. A gradual increase in the SUVA254 values after the first week was observed, indicating an increase in the fraction of aromatic carbons leaching from the tires over time. The presence of some aromatic compounds in the leachate solutions was confirmed with gas chromatograph coupled with tandem mass spectrometer scans. Some of these compounds (e.g., aniline, benzothiazole, benzothiazolone) have been also reported in previous studies. Analysis of DOC leaching data showed that the mass of DOC leached during the first 12 hr consisted of 40-50% of the leaching during the first week and 20-25% of the leaching during the four weeks of experiments. Although the cumulative DOC mass leached from tires depended on tire size and leaching solution, the leaching rate remained constant regardless of tire type and leaching solution composition. Analysis of leaching rate of four metals (Zn, Fe, Al, Mn) at acidic conditions showed a rapid initial leaching rate for Zn, followed by a slower but constant rate, while there was a constant rate of leaching for Fe, Mn and Al from the beginning of the experiments without showing any sign of slowing down. This observation was attributed to the release of the Zn from the rubbery portion of the tires due to the relatively similar leaching patterns observed for DOC and Zn. On the other hand, Fe, Al and Mn are probably coming from the wires in tire chips and showed a continuous and constant rate of dissolution. Crumb rubber showed significantly higher degree of leaching than tire chips for all detected constituents except Fe, since the main source of the iron in tire chip was the wires that were removed prior to preparing the crumb rubber. Among the tire chips that were within the particle size range of practical applications, leaching from 1'_1' size tire chips, in general, was higher than the other particle sizes. The difference in leaching among other particle sizes (2'_2', 4'_2' and 6'_2') was relatively small or negligible for most of the parameters monitored.

We use remote sensing and geographic information system (GIS) tools to develop simple predictive models to define relationships between watershed variables known to influence lake DOC concentrations and lake water color in the Absaroka-Beartooth Wilderness in Montana and Wyoming, USA. Variables examined include watershed area, topography, and vegetation cover. The resulting GIS model predicts DOC concentrations at the lake watershed scale with a high degree of accuracy (R2 = 0.92; p =

Ferrate (VI) has been studied as an alternative chemical to disinfect water and wastewater in recent years. The disinfection effectiveness of two different wet oxidation ferrate (VI) synthesis formulas in wastewater and Econlockhatchee River water was evaluated. Ferrate (VI) is synthesized by addition of ferric chloride to a mixture of sodium hydroxide and calcium hypochlorite (refer to U.S. Patent 6,790,429). One ferrate (VI) synthesis formula uses below the stoichiometric requirement of hypochlorite (Low Chlorine Formula) while the other ferrate (VI) synthesis formula uses more than the stoichiometric requirement of hypochlorite (Standard Chlorine Formula). For applications requiring low chlorine residual effluent quality, the Low Chlorine Formula intuitively is a more suitable disinfectant than the Standard Formula. For applications where chlorine residual is of little or no significance, the Standard Formula is logically a more suitable disinfectant due to lower production cost and production of higher ferrate (VI) concentrations than the Low Chlorine Formula. The total chlorine concentration, unfiltered and filtered ferrate (VI) concentration, and dissolved organic carbon concentration before and after treatment using both ferrate (VI) formulas in wastewater and Econ River water was measured at a contact time of 30 minutes. Disinfection capabilities were measured by comparing the quantity of Heterotrophic bacteria, Total Coliform, Escherichia coli, and Enterococcus bacteria pre-ferrate (VI) to post-ferrate (VI) at dosages of 2, 4, and 7.5 mg/L as ferrate (VI) using both ferrate (VI) formulas. The rate of disappearance of both ferrate (VI) formulas in wastewater at an unadjusted pH and pH of 6.0-6.35 was determined. In addition the total oxidant absorbance and total chlorine concentration were measured over a 30-minute period. Both ferrate (VI) formulas were effective at inactivating Total Coliform, E. Coli, Enterococcus, and heterotrophic bacteria at a 30-minute contact time and lowering DOC concentrations in Econlockhatchee River water and secondary wastewater. The Standard Formula demonstrated better disinfection at lower dosages than the Low Chlorine Formula. In both ferrate (VI) formulas, there was a presence of an instantaneous demand of ferrate (VI) and a first-order reaction rate of ferrate (VI) over 30 minutes. The chlorine residual of 7.5 mg/L ferrate (VI) dose in wastewater at a 30-minute contact time was 0.2 to 0.6 mg/L Cl2 for the Low Chlorine Formula and 0.8 to 1.4 mg/L Cl2 for the Standard Formula. These experiments indicate that both ferrate (VI) formulas can serve as effective environmentally friendly disinfectants for wastewater and Econ River water.

A simple, mechanistic hydrochemical model for DOC export was developed and tested for a small, old-growth forested watershed on the Chiloe island in southern Chile. Despite the important roles of DOC in both terrestrial and aquatic ecosystems, there are few tested watershed scale DOC models published to date and, in general, they have had modest success in reproducing observed stream DOC fluxes. The model developed here coupled a simple Boussinesq-type hydrological model of lateral subsurface flows from two soil layers and an Arrhenius-type model for DOC production in soil water. One unique aspect of this model is that DOC production is scaled to account for soil saturation. The streamflows were well simulated (r2=0.86). Simulated stream water DOC concentrations also agreed well with observed values (r2=0.80). Simulated soil water DOC concentrations were generally underestimated for the shallow soil layer and overestimated for the deep layer compared to observed values. Lysimeter sampling errors, lack of agreement between modeled and actual soil layers and the relative position of the lysimeters in the watershed are discussed as the possible causes of these deviations. In general, the model presented here captured the DOC stream water trends in this old-growth forest better than similar models used in other ecosystems. The simple structure of this DOC model may offer a good platform to gradually and accurately increase its intricacy, providing a better understanding of the inherent complexity of the processes regulating the carbon dynamics in forested ecosystems.