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Our current knowledge of the chemical composition of ocean dissolved organic matter (DOM) is limited, mainly because of its extreme molecular diversity, low concentration of individual compounds and the elevated ionic strength of ocean waters. As a result, many analytical methods require a previous extraction step. The efficiency and selectivity of the extraction method defines the representativeness of the extracted DOM fraction. Nowadays, the most widespread procedure for concentrating DOM is solid phase extraction (SPE) using styrene divinyl benzene polymer cartridges (PPL). Here, we investigate the effect of SPE-PPL on DOM elemental and optical properties to assess the efficiency and selectivity of this extraction method on water samples from the main intermediate and deep water masses of Arctic, Mediterranean and Antarctic origin present in the Cape Vert Frontal Zone (CVFZ, NW Africa). Furthermore, North and South Atlantic Central waters converge in this area and coastal DOM is injected by the giant upwelling filament of Cape Blanc. On one side, the colored fraction of DOM (CDOM) presented extraction efficiencies comparable to that of the bulk dissolved organic carbon (DOC), but decreased significantly with increasing wavelength, suggesting an affinity of PPL cartridges for low molecular weight organic compounds. While the protein-like fluorescent fraction of DOM (FDOM) was also extracted with the same efficiency than DOC, the extraction efficiency of the humic-like fraction was comparatively much higher. On the other side, dissolved organic nitrogen (DON) extraction efficiencies were about half that of DOC. These contrasting extraction efficiencies of the different DOM pools indicated that the extracts were enriched in N-poor, low molecular weight and recalcitrant DOM, therefore showing less variability than the corresponding bulk DOM. Furthermore, DOC, DON, CDOM and FDOM extracted were not homogeneous through the water column but displayed certain significant differences among water masses in both efficiency and selectivity.

Abstract The impact of submarine hydrothermal systems on organic carbon in the ocean—one of the largest fixed carbon reservoirs on Earth—could be profound. Yet, different vent sites show diverse fluid chemical compositions and the subsequent biological responses. Observations from various vent sites are to evaluate hydrothermal systems' impact on the ocean carbon cycle. A response cruise in May 2009 to an on‐going submarine eruption at West Mata Volcano, northeast Lau Basin, provided an opportunity to quantify the organic matter production in a back‐arc spreading hydrothermal system. Hydrothermal vent fluids contained elevated dissolved organic carbon, particulate organic carbon (POC), and particulate nitrogen (PN) relative to background seawater. The δ13C‐POC values for suspended particles in the diffuse vent fluids (−15.5‰ and −12.3‰) are distinct from those in background seawater (−23 ± 1‰), indicative of unique carbon synthesis pathways of the vent microbes from the seawater counterparts. The first dissolved organic nitrogen concentrations reported for diffuse vents were similar to or higher than those for background seawater. Enhanced nitrogen fixation and denitrification removed 37%–89% of the total dissolved nitrogen in the recharging background seawater in the hydrothermal vent flow paths. The hydrothermal plume samples were enriched in POC and PN, indicating enhanced biological production. The total “dark” organic carbon production within the plume matches the thermodynamic prediction based on available reducing chemical substances supplied to the plume. This research combines the measured organic carbon contents with thermodynamic modeled results and demonstrates the importance of hydrothermal activities on the water column carbon production in the deep ocean.

The impact of submarine hydrothermal systems on organic carbon in the ocean—one of the largest fixed carbon reservoirs on Earth—could be profound. Yet, different vent sites show diverse fluid chemical compositions and the subsequent biological responses. Observations from various vent sites are to evaluate hydrothermal systems' impact on the ocean carbon cycle. A response cruise in May 2009 to an on‐going submarine eruption at West Mata Volcano, northeast Lau Basin, provided an opportunity to quantify the organic matter production in a back‐arc spreading hydrothermal system. Hydrothermal vent fluids contained elevated dissolved organic carbon, particulate organic carbon (POC), and particulate nitrogen (PN) relative to background seawater. The δ13C‐POC values for suspended particles in the diffuse vent fluids (−15.5‰ and −12.3‰) are distinct from those in background seawater (−23 ± 1‰), indicative of unique carbon synthesis pathways of the vent microbes from the seawater counterparts. The first dissolved organic nitrogen concentrations reported for diffuse vents were similar to or higher than those for background seawater. Enhanced nitrogen fixation and denitrification removed 37%–89% of the total dissolved nitrogen in the recharging background seawater in the hydrothermal vent flow paths. The hydrothermal plume samples were enriched in POC and PN, indicating enhanced biological production. The total "dark" organic carbon production within the plume matches the thermodynamic prediction based on available reducing chemical substances supplied to the plume. This research combines the measured organic carbon contents with thermodynamic modeled results and demonstrates the importance of hydrothermal activities on the water column carbon production in the deep ocean. Plain Language Summary: External energies fuel the production of organic carbon and nitrogen by living organisms. Exploring the organic compounds' concentrations and characteristics help reveal the energy flow and biogeochemical processes. Here, we investigate the marine organic matter in the submarine hot springs (hydrothermal fluids) generated by deep seawater interacting with uplifting magma caused by spreading seafloor. We surveyed the organic carbon and nitrogen contents with samples collected during a cruise in May 2009, in response to an on‐going submarine eruption at West Mata Volcano, northeast Lau Basin. The submarine hot spring water, relative to background seawater, had elevated organic carbon and nitrogen with unique characters. The amount of elevated organic carbon meets our calculated values based on the energy that the hot spring brings to marine life. We conclude that the underwater hot springs fuel "dark" organic carbon production via unique carbon fixation pathways in the deep ocean. Key Points: Unique stable carbon isotope of suspended particulate organic carbon is indicative of unique carbon fixation pathway by vent biomesWe estimated first dissolved organic nitrogen for hydrothermal vent fluids and observed enhanced nitrogen fixation and/or denitrificationTotal dark organic carbon production within the plume matches thermodynamic prediction based on available, reducing chemical substances [ABSTRACT FROM AUTHOR]

Previous research has focused on dissolved organic carbon (DOC) as a surrogate for soluble microbial products (SMPs) and found that temperature has a significant influence on the production of SMP-based DOC (SDOC) during biological processes. Little is known about the SMP-based dissolved organic nitrogen (SDON), although some nitrogenous organic matter has been identified as an important part of SMPs. This study investigated the effect of temperature (8 °C, 15 °C and 25 °C) on the characterization of SMPs in an activated sludge system with special emphasis on SDON. Results showed the positive effect of reduced temperature on SDON production. Fluorescence spectroscopy and ultrahigh-resolution mass spectrometry showed the produced SDON at 8 °C and 15 °C exhibits more lability than at 25 °C. This was also supported by the algal bioassay, indicating the SDON produced at low temperature is highly bioavailable and prone to stimulate algae and microorganisms. In addition, principal component analysis demonstrated that the effect of temperature on the chemical characterization of SDON is different from that of SDOC. Overall, this study highlights the importance of SDON control during biological processes at a low temperature to reduce the potential impact of effluent SMPs on receiving waters or wastewater reuse. Image 1 • The effect of temperature on the characterization of SDON was investigated. • Results showed the positive effect of reduced temperature on SDON production. • SDON produced at low temperature was highly bioavailable. • The effect of temperature on the characterization of SDON was different from that of SDOC. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effects of freezing and cold storage at 4 °C on bulk dissolved organic carbon (DOC) and nitrogen (DON) concentration and SEC fractions determined with size exclusion chromatography (SEC), as well as on spectral properties of dissolved organic matter (DOM) analyzed with fluorescence spectroscopy. In order to account for differences in DOM composition and source we analyzed storage effects for three different sample types, including a lake water sample representing freshwater DOM, a leaf litter leachate of Phragmites australis representing a terrestrial, ‘fresh’ DOM source and peatland porewater samples. According to our findings one week of cold storage can bias DOC and DON determination. Overall, the determination of DOC and DON concentration with SEC analysis for all three sample types were little susceptible to alterations due to freezing. The findings derived for the sampling locations investigated here may not apply for other sampling locations and/or sample types. However, DOC size fractions and DON concentration of formerly frozen samples should be interpreted with caution when sample concentrations are high. Alteration of some optical properties (HIX and SUVA 254 ) due to freezing were evident, and therefore we recommend immediate analysis of samples for spectral analysis. [ABSTRACT FROM AUTHOR]

Urban grasslands not only provide a recreational venue for urban residents, but also sequester organic carbon in vegetation and soils through photosynthesis, and release carbon dioxide through respiration, which largely contribute to carbon storage and fluxes at regional and global scales. We investigated organic carbon and nitrogen pools in subtropical turfs and found that dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were regulated by several factors including microbial activity which is indicated by soil enzymatic activity. We observed a vertical variation and different temporal patterns in both soil DOC, DON and enzyme activities, which decreased significantly with increasing soil depths. We further found that concentration of soil DON was linked with turf age. There were correlations between grass biomass and soil properties, and soil enzyme activities. In particular, soil bulk density was significantly correlated with soil moisture and soil organic carbon (SOC). In addition, DOC correlated significantly with DON. Significant negative correlations were also observed between soil total dissolved nitrogen (TDN) and grass biomass of Axonopus compressus and Zoysia matrella . Specifically, grass biomass was significantly correlated with the soil activity of urease and β-glucosidase. Soil NO 3 -N concentration also showed negative correlations with the activity of both β-glucosidase and protease but there were no significant correlations between cellulase and soil properties or grass biomass. Our study demonstrated a relationship between soil C and N dynamics and soil enzymes that could be modulated to enhance SOC pools through management and maintenance practices. [ABSTRACT FROM AUTHOR]

The release of dissolved organic matter (DOM) in forest floors is a dynamic component of organic carbon transformations in forest soils. The biogeochemical processes driving the production and release of dissolved organic carbon and nitrogen (DOC and DON) in forest floors are strongly affected by hydroclimatic conditions during rainfall events. We conducted an exhaustive percolation experiment to examine the pool size and sustained production of mobilizable DOC and DON in Oi, Oe and Oa layers of spruce, larch and beech forest floors. The percolation experiment with small reconstructed soil columns was conducted at 5 and 15 °C for 25 days with a percolation volume equal to 36 mm d − 1 , adding up to a total percolation volume of 900 mm. Percolates were collected at an interval of 5 days and analyzed for DOC and DON. Simultaneously to the periodic analysis of percolates, the CO 2 release was measured. The sustained release of DOM during the last leaching period from day 20 to 25, after 720 mm of percolation, was defined as the production rate of DOM . The cumulative release of DOM was large: in case of the 15 °C treatment, the total amount of DOM extracted for 25 days was on average 1.6% and 2.2% of the total C and N stock, respectively. The largest cumulative release of DOM and CO 2 was observed for the beech samples. The ratio of cumulative CO 2 /cumulative DOC release ranged from 1 to 3 for Oi and Oe samples but was < 0.2 for spruce Oa. No changes in DOC/DON ratios as a result of percolation amount were detected. The production rates indicated a rapid replenishment of DOM pools after leaching. The Q 10 values for the DOM production rates ranged from 2 to 4 and were similar to those for CO 2 production. The positive correlation between DOM and CO 2 production rates in Oi and Oe samples highlights the importance of microbial activity for DOM release. The pool of mobilizable DOM in forest floors seems large enough to provide a sustained rate of DOM release throughout precipitation events under field conditions although the actual rate of mobilization may vary in the field, depending on antecedent conditions and the duration and intensity of the rainfall event. [ABSTRACT FROM AUTHOR]

Plastic debris is accumulating in agricultural land due to the increased use of plastic mulches, which is causing serious environmental problems, especially for biochemical and physical properties of the soil. Dissolved organic matter (DOM) plays a central role in driving soil biogeochemistry, but little information is available on the effects of plastic residues, especially microplastic, on soil DOM. We conducted a soil-incubation experiment in a climate-controlled chamber with three levels of microplastic added to loess soil collected from the Loess Plateau in China: 0% (control, CK), 7% (M1) and 28% (M2) (w/w). We analysed the soil contents of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH 4 + , NO 3 − , dissolved organic phosphorus (DOP), and PO 4 3− and the activities of fluorescein diacetate hydrolase (FDAse) and phenol oxidase. The higher level of microplastic addition significantly increased the nutrient contents of the DOM solution. The lower level of addition had no significant effect on the DOM solution during the first seven days, but the rate of DOM decomposition decreased in M1 between days 7 and 30, which increased the nutrient contents. The microplastic facilitated the accumulation of high-molecular-weight humic-like material between days 7 and 30. The DOM solutions were mainly comprised of high-molecular-weight humic-like material in CK and M1 and of high-molecular-weight humic-like material and tyrosine-like material in M2. The Microplastic stimulated the activities of both enzymes. Microplastic addition thus stimulated enzymatic activity, activated pools of organic C, N, and P, and was beneficial for the accumulation of dissolved organic C, N and P. [ABSTRACT FROM AUTHOR]

The bioavailabilities of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were examined in eight sampling stations of the Heilongjiang watershed, located in Heilongjiang Province, northeast China. Water samples were incubated for 55 days at 20 °C, and the decreases in the DOC and DON concentrations were measured during the laboratory incubations. The experiments showed that bioavailable DOC (BDOC) accounted for 15–30 % of DOC and bioavailable DON (BDON) accounted for 29–57 % of DON. DOM bioavailability was higher for DON compared to DOC, suggesting that DON was more bioavailable and had a faster turnover than DOC in the Heilongjiang watershed. Furthermore, the percent of bioavailable DOC (%BDOC) was significantly related to SUVA254, not the DOC concentration, suggesting that the chemistry composition of DOM played a more important role in affecting its bioavailability compared to the DOM concentration. In addition, significant negative correlations were observed between the initial DOC/DON ratios and the percent of bioavailable DOM fractions (%BDOC and %BDON), especially for %BDON, implying that low C/N molecules or N-rich compounds may be preferentially utilized by microbes. [ABSTRACT FROM AUTHOR]

Mediterranean fluvial systems are subject to severe drought/rewetting cycles. These extreme periods modify the direction and magnitude of the water fluxes between the stream surface water and the riparian ground water, enabling exploration of the abrupt changes affecting dissolved organic matter (DOM). We investigated the variability in DOM concentration and composition over a drying and rewetting period in a stream– riparian groundwater system. We analyzed dissolved organic C (DOC) and N (DON), and bioavailable DOC (BDOC) in whole water and 3 molecular-weight (MW) fractions (high [HMW]: >10 KDa, medium: 1–10 KDa, low [LMW]: <1 KDa) in surface water and riparian ground water. The quantitative differences in DOM between surface water and riparian ground water were minimal during the drying period, but were greater during the rewetting period because of notable flushing of DOC (>6 mg/L) and DON (>0.4 mg/L) in stream water. Asynchronous inputs of DOC and DON were detected in stream water during rewetting: an abrupt and brief increase (up to 32%) in DOCHMW contribution, and a strong and persistent increase (up to 70%) in DONLMW contribution. Average BDOC values were 18% in stream water and 13% in riparian ground water. BDOC was not correlated with DOC MW, but was positively correlated with DON (r = 0.59, df = 17, p < 0.01). During rewetting, BDOC increased by up to 49%, DONLMW input occurred, and the DOCLMW:DONLMW ratio decreased to values <15:1, suggesting that small, nitrogenous organic compounds contributed to DOM bioavailability. The rewetting period occurred in the brief span of only 2 wk, but it had major biogeochemical implications for DOM and generated a pulse of potentially bioavailable DOM to the stream–riparian interface and downstream communities. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation of haloacetamides function of DON/DOC, SUVA254 and bromide. [•] DON/DOC may act as an indicator of HAcAm yields during chlorination. [•] More formation during chloramination in low-SUVA waters with no bromide. [•] More formation of dihalogenated species than tri- or mono-halogenated species. [•] Bromine incorporation increased with increasing bromide with either disinfectant. [Copyright &y& Elsevier]

Abstract: The gradual increase of salt concentration (0 to 35g-NaCl/L) on the performance of membrane bioreactor (MBR) was studied. The uptake rate of dissolved organic carbon and ammonia decreased from around 17.0mg-DOC/g-MLVSS.d to 1.8mg-DOC/g-MLVSS.d and from 8.2mg-NH4-N/g-MLVSS.d to 0mg-NH4-N/g-MLVSS.d respectively when salt concentration reached to 35g-NaCl/L. Similarly the specific oxygen uptake rate (SOUR) reduced from 8 to 9 to around 0.3mg-O2/g-MLVSS.h. The removal of bio-polymers, humic acids, building blocks and low molecular weight neutral decreased with increase in salt concentration. The concentration of dissolved organic nitrogen (DON) in bio-polymer increased from 0.05 to 3.31mg/L when the salt concentration reached to 35g-NaCl/L. This study provides good information for understanding the effect of continuous increase of salt concentration in treating saline wastewater in a MBR process. [Copyright &y& Elsevier]

We present the results of a full year of high-resolution monitoring of hydrologic event-driven export of stream dissolved organic matter (DOM) from the forested Bigelow Brook watershed in Harvard Forest, Massachusetts, USA. A combination of in situ fluorescent dissolved organic matter (FDOM) measurement, grab samples, and bioassays was utilized. FDOM was identified as a strong indicator of concentration for dissolved organic carbon (DOC, r = 0.96), dissolved organic nitrogen (DON, r = 0.81), and bioavailable DOC (BDOC, r = 0.81). Relationships between FDOM and concentration were utilized to improve characterization of patterns of hydrological event-driven export and the quantification of annual export. This characterization was possible because DOM composition remained relatively consistent seasonally; however, a subtle shift to increased fluorescence per unit absorbance was observed for summer and fall seasons and percent BDOC did increase slightly with increasing concentrations. The majority of export occurred during pulsed hydrological events, so the greatest impact of bioavailable exports may be on downstream aquatic ecosystems. Export from individual events was highly seasonal in nature with the highest flow weighted mean concentrations (DOC) being observed in late summer and fall months, but the highest total export being observed for larger winter storms. Seasonal trends in DOC export coincide with weather driven changes in surface and subsurface flow paths, potential for depletion and rebuilding of a flushable soil organic matter pool, and the availability of terrestrial carbon sources such as leaf litter. Our approach and findings demonstrate the utility of high frequency FDOM measurement to improve estimates of intra-annual temporal trends of DOM export. [ABSTRACT FROM AUTHOR]

In forested ecosystems, the quality of dissolved organic matter (DOM) produced by freshly senesced litter may differ by litter type and species, and these differences may influence the amount of DOM that is respired versus that which may either contribute to soil organic matter accumulation or be leached from the ecosystem. In this study, we investigated the effect of litter type (including freshly senesced fine root, leaf, fine woody, and reproductive litter) and species (5 species of leaf litter) on several measures of the quality of DOM produced at a site along a primary successional chronosequence at Mt. Shasta, California. We measured differences in solid litter chemistry (C, N, and P concentration) and differences in the concentration of dissolved organic C, N, and P (DOC, DON, and DOP, respectively), water-soluble monomeric carbohydrates, polyphenols, proteins, fractions of DOC, as well as UV absorbance. For several aspects of DOC quality, DOM from fine roots was less labile than DOM from leaf litter. In contrast to DOC quality, soluble material originating from fine roots was high in labile forms of dissolved N and P in comparison to leaf litter. We also found that leaf litter with greater total %N or %P in solid litter had higher DON or DOP concentration (and higher total soluble P concentration). A very high percentage, on average 72% (up to 89%) of the total P in leaf litter was water-soluble and mostly inorganic P. Concen-trations of soluble polyphenols were strongly related to DOC, and concentrations of soluble proteins were significantly related to DON in leaf litter of different species. During primary succession at the Mt. Shasta site, an increasing ratio of root to leaf litter production and shifting species composition has been found to occur, and the results of this study suggest that some aspects of DOC quality reflect a decrease in labile forms of DOC originating from both above and belowground litter. In contrast, dissolved N and P reflect an increase in labile forms with increasing inputs of root litter. In particular, our study has demonstrated important differences in the quality of inputs of DOM from freshly senesced root and leaf litter, and these differences have implications for C and nutrient cycling. [ABSTRACT FROM AUTHOR]

Surface and subsurface litter fulfil many functions in the biogeochemical cycling of C and N in terrestrial ecosystems. These were explored using a microcosm study by monitoring dissolved inorganic nitrogen (DIN) (NH-N + NO-N), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) concentrations and fluxes in drainage water under ambient outdoor temperatures. Subsurface litter remarkably reduced the DIN concentrations in winter, probably by microbial N uptake associated with higher C:N ratio of added litter compared with soil at 10-25 cm depth. Fluxes of DIN were generally dominated by NO-N; but NH-N strongly dominated DIN fluxes during freeze-thaw events. Appreciable concentrations of NH-N were observed in the drainage from the acid grassland soils throughout the experiment, indicating NH-N mobility and export in drainage water especially during freeze-thaw. Litter contributed substantially to DOC and DON production and they were correlated positively ( p < 0.01) for all treatments. DOC and DON concentrations correlated with temperature for the control ( p < 0.01) and surface litter ( p < 0.001) treatments and they were higher in late summer. The subsurface litter treatment, however, moderated the effect of temperature on DOC and DON dynamics. Cumulative N species fluxes confirmed the dominance of litter as the source of DON and DOC in the drainage water. DON constituted 42, 46 and 62% of cumulative TDN flux for control, surface litter and subsurface litter treatments respectively. [ABSTRACT FROM AUTHOR]

There is sufficient evidence to support the idea that organic matter (OM) in plants converts to inorganic matter during a fire. However, it is still unclear whether plant burning can also produce enough dissolved organic matter (DOM) to affect the regional environment. In order to investigate this issue, we analyzed the contents of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and dissolved organic nitrogen (DON) in plant ash derived from simulated burning. The results showed that the ash of wetland plants contained a certain amount of DOM. The DOC contents in plant ash ranged from 48.6 ± 13.1 mg·kg-1 to 232.3 ± 62.6 mg·kg-1, and DON contents in plant ash ranged from 18.7 ± 3.6 mg·kg-1 to 232.3 ± 6.7 mg·kg-1. In addition, the contents of DOC, DIC and DON in ash varied with the vegetation species in wetland ecosystem. There were greater DIC and DON in the shrub plant ash than in the herbage plant ash, while the ratio of DOC and TC was lower than in the shrub plant ash. There was a reason to believe that plant ash derived from fire did play an important role in nutrient cycling in wetland ecosystems, and DOM in plant ash did contribute to the regional and global environmental changes. [ABSTRACT FROM AUTHOR]

Intensively managed grasslands are occasionally chemically killed with herbicide and ploughed in order to grow an arable crop. After this management, large N mineralization rates with large losses to the environment are commonly observed. However, it remains to be determined to what extent the chemical killing contribute to increased N mineralization. In this study the potential nitrogen (N) mineralization from grasslands, that were killed with herbicides but otherwise undisturbed, was investigated in a laboratory experiment with undisturbed soil columns. Subsequently we assessed the predictive value of several laboratory indices for N mineralization after chemically killing of the grass. Mineralization rates varied from 0.5 to 3.0 g N m−2 wk−1. The contents of total N, total C, dissolved organic carbon (DOC) and hot-KCl extractable NH were best related to N mineralization rates (R2 = 50, 48, 38 and 47%, respectively). In combination with information on the N content of the roots and stubble and the age of grassland at destruction, up to 62% of the variation in N mineralization rates could be explained. Although previous studies suggested that dissolved organic nitrogen (DON) is a good indicator for mineralization rates, this was not the case after chemically killing grass in the current study. [ABSTRACT FROM AUTHOR]

Abstract: There is little understanding about the role eastern US forested headwater riparian areas play in protecting aquatic habitats and water quality from impacts of side slope forest harvest. To better understand this important riparian area function, we selected three sites from management units with a 2-age regeneration silvicultural prescription located on the Nantahala National Forest, North Carolina, USA. Each site was harvested and a riparian buffer was left uncut along the stream. Buffer widths were 10m and 30m; we included a 0m buffer to experimentally determine nutrient and riparian zone responses to forest cutting under extreme conditions. A fourth site was selected to serve as an uncut reference. Transects were established perpendicular to a 200m stream reach, from streamside to 50m upslope for intensive study. Forest cutting increased extractable NO3 − at both 0–10cm and 10–30cm soil depths compared to pre-treatment concentrations. Soil solution NO3 − concentrations increased only in harvested areas, on all sites; increases were greater in sites with narrow riparian buffers. Stream water NO3 − concentration increased significantly following site harvest only on the 0m buffer site. Dissolved organic C and N did not respond to harvesting in either soil solution or stream samples. Our results suggest that riparian buffers are effective in removing NO3 − from soil solution prior to its entering the stream. [Copyright &y& Elsevier]

Dissolved organic matter (DOM) plays several important roles in forest ecosystem development, undergoing chemical, physical and/or biological reactions that affect ecosystem nutrient retention. Very few studies have focused on gross rates of DOM production, and we know of no study that has directly measured DOM production from root litter. Our objectives were to quantify major sources of total potentially water-soluble organic matter (DOMtps) production, with an emphasis on production from root litter, to quantify and compare total potentially soluble organic C, N, and P (DOCtps, DONtps, and DOPtps) production, and to quantify changes in their production during forest primary succession and ecosystem development at the Mt. Shasta Mudflows ecosystem chronosequence. To do so, we exhaustively extracted freshly senesced root and leaf and other aboveground litter for DOCtps, DONtps, and DOPtps by vegetation category, and we calculated DOMtps production (g m−2 y−1) at the ecosystem level using data for annual production of fine root and aboveground litter. DOM production from throughfall was calculated by measuring throughfall volume and concentration over 2 years. Results showed that DOMtps production from root litter was a very important source of DOMtps in the Mount Shasta mudflow ecosystems, in some cases comparable to production from leaf litter for DONtps and larger than production from leaf litter for DOPtps. Total DOCtps and DONtps production from all sources increased early in succession from the 77- to the 255-year-old ecosystem. However, total DOPtps production across the ecosystem chronosequence showed a unique pattern. Generally, the relative importance of root litter for total fine detrital DOCtps and DONtps production increased significantly during ecosystem development. Furthermore, DOCtps and DONtps production were predominantly driven by changes in biomass production during ecosystem development, whereas changes in litter solubility due to changes in species composition had a smaller effect. We suggest that DOMtps production from root litter may be an important source of organic matter for the accumulation of SOM during forest ecosystem development. [ABSTRACT FROM AUTHOR]

We identify and assess the relative importance of the principal factors influencing the release of dissolved organic carbon (DOC) and dissolved forms of nitrogen (N) from a small upland headwater dominated by podzolic soils during a sequence of autumn runoff events. We achieve this by subjecting high-resolution hydrometeorological and hydrochemical data to an R-mode principal component factor analysis and a stepwise multivariate regression analysis, We find that the release of DOC and N is influenced by four principal factors, namely event magnitude, soil water flow through the Bs horizon, the length of time since the soil profile was last flushed, and rewetting of the H horizon, The release of DOC and dissolved organic nitrogen (DON) is most strongly influenced by the combination of event magnitude and soil water flow through the Bs horizon, and to a lesser extent by the length of time since the soil profile was last flushed. Rewetting of the H horizon also influences the release of DOC, but this is not the case for DON. The release of nitrate (NO3-N) is most strongly influenced by the combination of the length of time since the soil profile was last flushed and rewetting of the H horizon, and to a lesser extent by event magnitude. Soil water flow through the Bs horizon does not influence the release of NO3-N. We argue that the mechanisms by which the above factors influence the release or DOC and N are probably strongly associated with moisture-dependent biological activity, which governs the turnover of organic matter in the soil and limits the availability of NO3-N in the soil for leaching. We conclude that the release of DOC and N from upland headwaters dominated by podzolic soils is largely controlled by the variable interaction of hydrometeorological factors and moisture-dependent biological processes, and that a shift in climate towards drier summers and wetter winters may result in the release of DOC and N becoming increasingly variable and more episodic in the future. [ABSTRACT FROM AUTHOR]

Porewater equilibration samplers were used to obtain porewater inventories of inorganic nutrients (NH, NO x , PO), dissolved organic carbon (DOC) and nitrogen (DON), sulfate (SO), dissolved inorganic carbon (DIC), hydrogen sulfide (H2S), chloride (Cl−), methane (CH4) and reduced iron (Fe2+) in intertidal creek-bank sediments at eight sites in three estuarine systems over a range of salinities and seasons. Sulfate reduction (SR) rates and sediment particulate organic carbon (POC) and nitrogen (PON) were also determined at several of the sites. Four sites in the Okatee River estuary in South Carolina, two sites on Sapelo Island, Georgia and one site in White Oak Creek, Georgia appeared to be relatively pristine. The eighth site in Umbrella Creek, Georgia was directly adjacent to a small residential development employing septic systems to handle household waste. The large data set (>700 porewater profiles) offers an opportunity to assess system-scale patterns of porewater biogeochemical dynamics with an emphasis on DOC and DON distributions. SO depletion (SO)Dep was used as a proxy for SR, and (SO)Dep patterns agreed with measured (35S) patterns of SR. There were significant system-scale correlations between the inorganic products of terminal metabolism (DIC, NH and PO) and (SO)Dep, and SR appeared to be the dominant terminal carbon oxidation pathway in these sediments. Porewater inventories of DIC and (SO)Dep indicate a 2:1 stoichiometry across sites, and the C:N ratio of the organic matter undergoing mineralization was between 7.5 and 10. The data suggest that septic-derived dissolved organic matter with a C:N ratio below 6 fueled microbial metabolism and SR at a site with development in the upland. Seasonality was observed in the porewater inventories, but temperature alone did not adequately describe the patterns of (SO)Dep, terminal metabolic products (DIC, NH, PO), DOC and DON, and SR observed in this study. It appears that production and consumption of labile DOC are tightly coupled in these sediments, and that bulk DOC is likely a recalcitrant pool. Preferential hydrolysis of PON relative to POC when overall organic matter mineralization rates were high appears to drive the observed patterns in POC:PON, DOC:DON and DIC:DIN ratios. These data, along with the weak seasonal patterns of SR and organic and inorganic porewater inventories, suggest that the rate of hydrolysis limits organic matter mineralization in these intertidal creek-bank sediments. [ABSTRACT FROM AUTHOR]

Despite growing attention to the role of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in forest nutrient cycling, their monthly concentration dynamics in forest ecosystems, especially in subtropical forests only were little known. The goal of this study is to measure the concentrations and monthly dynamics of DOC and DON in precipitation, throughfall and stemflow for two plantations of Schima superba (SS) and Chinese fir ( Cunninghamia lanceolata, CF) in Jianou, Fujian, China. Samples of precipitation, throughfall and stemflow were collected on a rain event base from January 2002 to December 2002. Upon collection, all water samples were analyzed for DOC, NO3 −−N, NH4 +−N and total dissolved N (TDN). DON was calculated by subtracting NO3 −−N and NH4 +−N from TDN. The results showed that the precipitation had a mean DOC concentration of 1.7 mg·L−1 and DON concentration of 0.13 mg·L−1. The mean DOC and DON concentrations in throughfall were 11.2 and 0.24 mg·L−1 in the SS and 10.3 and 0.19 mg·L−1 in the CF respectively. Stemflow DOC and DON concentrations in the CF (19.1 and 0.66 mg·L−1 respectively) were significantly higher than those in the SS (17.6 and 0.48 mg·L−1 respectively). No clear monthly variation in precipitation DOC concentration was found in our study, while DON concentration in precipitation tended to be higher in summer or autumn. The monthly variations of DON concentrations were very similar in throughfall and stemflow at both forests, showing an increase at the beginning of the rainy season in March. In contrast, monthly changes of the DOC concentrations in throughfall of the SS and CF were different to those in stemflow. Throughfall DOC concentrations were higher from February to April, while relatively higher DOC concentrations in stemflow were found during September–November period. [ABSTRACT FROM AUTHOR]

The impact of atmospheric N deposition on the dynamics of dissolved organic carbon and nitrogen were investigated in a microcosm study of two Scots pine forest soils (cambisol, podzol) from northern Germany receiving different atmospheric nitrogen inputs. The soils were fertilized with two different nitrogen doses (45 kg N ha-1 a-1, 90 kg N ha-1 a-1) in order to simulate the impacts of further increasing nitrogen inputs. On both sites, the nitrogen treatment showed no response to the DOC and DON leachate concentrations in all soil layers. In contrast, water-soluble organic carbon (WSOC) and water-soluble organic nitrogen (WSON) contents decreased in most of the investigated top soil layers of the podzol, while these parameters remained almost unchanged in the cambisol. The nitrogen induced changes of the WSOC and WSON contents were well correlated to other hot- and cold-water-extractable carbon and nitrogen fractions in the mineral soil, while correlations in the organic layers were mostly nitrogen independent. The results show, that the impacts of increasing nitrogen inputs on the WSOC and WSON dynamics are much more pronounced on the N stressed podzol than on the cambisol, while no differences were detected for the DOC and DON dynamics on both sites. The reasons for this might be differences in the composition of the microorganism populations and differences in the carbon and nitrogen sources for the WSOC and the WSON as well as the DOC and DON. [ABSTRACT FROM AUTHOR]

A direct comparison has been made for the measurement of total dissolved nitrogen (TDN) in seawater using high temperature combustion (HTC) instruments. A side-by-side comparison in one laboratory (Lewes exercise) was made with two hybrid total organic carbon (TOC) instruments linked to chemiluminescence detectors (CLD), a combined TOC total nitrogen (TN) instrument, and two stand-alone TN instruments. Later, a series of field samples was run in home laboratories of the participants (Homelab exercise) using four hybrid TOC–CLD systems, the combined TOC/TN instrument, and three stand-alone TN instruments. In the Lewes and Homelab exercises, samples were also run by the more established persulfate oxidation method. There was fairly good agreement (group precision) among all the HTC methods; average %CV of ±12.0% for five nitrogen compounds and average %CV of ±7.7% for five natural samples in the Lewes exercise and %CV of ±10.7% for 14 field samples in the Homelab exercise. In both cases, the persulfate method values were similar to those of the HTC instruments.On a finer scale of evaluation, the stand-alone TN instruments, operating at higher combustion temperatures, gave considerably more scatter and more divergent values than the set of HTC instruments that used a singular combustion environment with a lower temperature. The five hybrid systems, with Shimadzu TOC instruments combined with five different CLD systems and employing individual integration programs, gave a group precision of ±5.8% for the field samples. These systems also provided simultaneous dissolved organic carbon (DOC) concentrations, and the DOC group precision for the 14 samples was ±5.9%. Our conclusion is that the five Shimadzu instrument systems provide more accurate TDN measurements than the stand-alone instruments. However, when subtracting inorganic nitrogen (DIN) to calculate dissolved organic nitrogen (DON), there is not good agreement, especially for deep ocean samples. The persulfate method gave slightly higher TDN concentrations for the field samples than the Shimadzu HTC averages, indicating a possibility of incomplete conversion of some nitrogen compounds by the HTC instruments and/or peak integration problems. The inequity with persulfate oxidation and the scatter with the HTC methods require further investigation. A new broad community DON comparison is currently underway which includes TDN and DIN analyses. In addition, several of us are informally collaborating to improve and evaluate routine analysis with HTC instrumentation. [Copyright &y& Elsevier]

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters. [Copyright &y& Elsevier]

The increased use of plastic films and pesticides on agricultural soil leads to the accumulation of plastic debris and pesticide residues in soil. This accumulation has become a serious environmental issue, as it threatens life of earthworms, inhibits the enzyme activities and microbial diversity, and contributes to the loss of soil microbial carbon and nitrogen. However, little information is available regarding the effects of pesticides on soil dissolved organic matter (DOM). It is also unknown how plastic debris, especially small-sized particles called microplastics, influences the effects of pesticides on soil DOM. In this study, we performed a 30-day soil incubation experiment. Three levels of the common herbicide glyphosate were applied to soil: 0 (control, CK), 3.6 kg ha−1 (G1) and 7.2 kg ha−1 (G2). We also tested four levels of glyphosate and microplastics (homopolymer polypropylene powder) co-addition: 3.6 kg ha−1 + 7% (w/w) (M1G1), 3.6 kg ha−1 + 28% (w/w) (M2G1), 7.2 kg ha−1 + 7% (w/w) (M1G2), and 7.2 kg ha−1 + 28% (w/w) (M2G2). Glyphosate addition slightly increased soil fluorescein diacetate hydrolase (FDAse) and phenol oxidase (PO) activities. Although the glyphosate addition significantly promoted the accumulation of dissolved organic phosphorus (DOP) within the first 14 days, the M2 treatment decreased DOP at day 30. M2G1 and M2G2 increased soil FDAse activity and promoted the accumulation of DOC and DOP relative to G1 and G2 respectively while M1G1 and M1G2 benefited DON accumulation. Our results highlighted that the interaction between glyphosate and low microplastics content negatively affected DOC and DOP dynamics, leading to the loss of bioavailable C and P loss. The interaction between glyphosate and high content microplastics negatively affected DON compared with glyphosate addition, possibly decreasing DON. Unlabelled Image • Glyphosate addition transitorily increased the nutrient contents in DOM. • Interaction between glyphosate and high content microplastic enhanced FDAse. • Interaction between glyphosate and high content microplastic decreased DON. • Interaction between glyphosate and low content microplastic decreased DOC and DOP. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) and nitrogen (DON) represent an important part of the C and N cycles in forest ecosystems. Little is knownabout the controls on fluxes and concentrations of these compounds in soils under field conditions. Here we compiled published data on concentrations and fluxes of DOC and DON from 42 case studies in forestecosystems of the temperate zone in order to evaluate controls on a larger temporal and spatial scale. The focus was on annual fluxes andconcentrations in throughfall, forest floor leachates and soil solutions. In all compartments considered, concentrations and fluxes differed widely between the sites. Highest concentrations of DOC and DON were generally observed in forest floor leachates and in A horizons. Highest fluxes occurred in forest floor leachates. The fluxes of DOC and DON in forest floor leachates increased with increasing annual precipitation and were also positively related to DOC and DON fluxes with throughfall. Variation in throughfall fluxes could explain 46% and 65% of the variation in DOC and DON fluxes from the forest floor, respectively. No general difference in DOC and DON concentrations and fluxes in forest floor leachates was found when comparing coniferous and hardwood sites. Concentrations of DOC in forest floor leachates were positively correlated to the pH of the forest floor. Furthermore, there was no relationship between organic C and N stocks, soil C/N, litterfall or mineral N inputs and concentrations and fluxes of DOC andDON in forest floor leachates. Including all compartments, fluxes ofDOC and DON were highly correlated. Ratios of DOC to DON calculated from fluxes from the forest floor were independent of the amount of annual precipitation, pointing to a similar response of DOC and DON toprecipitation conditions. A decrease in the ratio of DOC to DON withsoil depth as observed on a plot-scale, was not confirmed by data analysis on a large scale. The controls observed on annual fluxes and concentr [ABSTRACT FROM AUTHOR]

We measured DOM fluxes from the O horizon of Hawaiian soils that varied in nutrient availability and mineral content to examine what regulates the flux of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) from the surface layer of tropical soils. We examined DOM fluxes in a laboratory study from N, P and N+P fertilized and unfertilized sites on soils that ranged in age from 300 to 4 million years old. The fluxes of DOC and DON were generally related to the % Cand % N content of the soils across the sites. In general, CO2 and DOC fluxes were not correlated suggesting that physical desorption, dissolution and sorption reactions primarily control DOM release from these surface horizons. The one exception to this pattern was at the oldest site where there was a significant relationship between DOC and CO2, flux. The oldest site also contained the lowest mineral and allophane content of the three sites and the DOC-respiration correlation indicates a relationship between microbial activity and DOC flux at this site. N fertilization increased DON fluxesby 50% and decreased DOC:DON ratios in the youngest, most N poor site. In the older, more N rich sites, N fertilization neither increasedDON fluxes nor decreased DOM C:N ratios. Similarly, short term changes in N availability in laboratory-based soil N and P fertilization experiments did not affect the DOM C:N ratios of leachate. DOM C:N ratios were similar to soil organic matter C:N ratios, and changes in DOM C:N ratios with fertilization appeared to have been mediated through long term effects on SOM C:N ratios rather than through changes in microbial demand for C and N. There was no relationship between DON and inorganic N flux during these incubations suggesting that the organic and inorganic components of N flux from soils are regulated by different factors and that DON fluxes are not coupled to immediate microbial demand for N. In contrast to the behavior of DON, the net flux of [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) and nitrogen (DON) derived from aquatic and terrestrial vascular plants provide a major energy and nutrient source for freshwater and coastal marine biota. The bioavailabilityof this material may to a large extent depend on plant species. In this study, we have compared the bioavailability of DOC and DON sampled in two distinct stands of Typha domingensis and Eleocharis mutata in a coastal tropical lake and in the adjacent ocean in the state of Rio de Janeiro, Brazil. Bioavailability of organic matter was assessedby regrowth bioassays using natural bacterial inocula. Nutrients were added to achieve carbon or nitrogen limitation. At all sampling sites, DON comprised over 95% of the total bioavailable nitrogen, suggesting its dominant role as a nitrogen source. The bioavailability of lacustrine DON (22% in the Typha stand and 34% in the Eleocharis stand) exceeded the bioavailability of DOC (8 and 10%, respectively) and exhibited a larger difference between the stands. 3H-leucine incorporation studies showed that lake bacterioplankton had a well balanced supply of C, N and P. Therefore, an accumulation of labile DON due to an excess nitrogen supply is not probable. We propose that a substantial part of the lake DON was newly formed within the macrophyte stands, while DOC was predominantly of terrestrial origin and more diagenetically changed. [ABSTRACT FROM AUTHOR]

In forest ecosystems, organic solutes play prominent roles in pollutant and nutrient transport. This study, conducted in subalpine forested Humaquepts in Switzerland, investigated the influence of redox conditions and flow processes on dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). In the mineral soil, concentrations of DOC were higher under reduced than under oxidized conditions. They averaged 1.2 mmol DOC L-1 in the reduced mineral soil at a 100-cm depth. A close correlation between DOC and dissolved Fe concentrations (r2 = 0.83; p < 0.001) suggests that reductive dissolution of Fe-oxides was the major reason for the low retention. However, during aerobic sampling of soil solution from the reduced mineral soil, DOC coprecipitated with Fe. This suggests that the DOC inputfrom reduced mineral soils to aerobic stream water is lower than expected from the high DOC concentrations in the soil. Organic N was themajor form of total dissolved N at all soil depths. In the reduced subsoil, dissolved N was completely organically bound. This was probably due to both an immobilization of inorganic N and a low retention of DON. During storms, DOC concentrations increased rapidly with increasing discharge in the subsurface flow. At peak flow, DOC concentrations were doubled, compared with base flow. The molar UV absorptivity of DOC in the subsurface flow corresponded closely to that of the topsoil. These findings suggest that DOC concentrations and properties are sensitive to flow velocities, and that DOC is preferentially transported to the subsoil at high discharge. [ABSTRACT FROM AUTHOR]

The influence of liming on leaching and distribution of dissolved organic carbon (DOC) and nitrogen (DON) in mineral soil was investigated in a leaching experiment with soil columns. Soil samples from separate horizons (O, A and B horizons) were collected from control and limed plots in a field liming experiment in a spruce forest in southernSweden. The field liming (0.88 kg m-2) had been carried out 8 years before sampling. To minimize the variation among replicates, soil profiles were reconstructed in the laboratory so that the dryweight was the same for each individual soil horizon regardless of treatment. Two soil column types were used with either the O+A horizons or the O+A+B horizons. One Norway spruce seedling (Picea abies (L.)Karst) was planted in each soil column. Average pH in the leachate water was greater in the limed treatment than in the control treatment(5.0 versus 4.0 for O+A columns and 4.3 versus 3.8 for O+A+B columns). After reaching an approximate steady state, the leaching of DOC was 3-4 times greater from the limed O+A and O+A+B columns than from the corresponding control columns but the leaching of DON increased (3.5 times) only in the limed O+A columns. There was a significant correlation between DOC and DON in the leachates from all columns except for the control O+A+B columns, which indicated a decoupling of DOC andDON retention in the B horizon in the control treatment. This might be explained by a selective adsorption of nitrogen poor hydrophobic compounds (C/N ratio: 32-77) while there was a lower retention of nitrogen rich hydrophilic compounds (C/N ratio: 14-20). Proportionally more hydrophobic compounds were leached from the limed soil compared tothe unlimed soil. These hydrophobic compounds also became more enriched in nitrogen after liming so in the limed treatment nitrogen mightbe adsorbed at nearly the same proportion as carbon, which might explain the fact that there was no decoupling of leached DOC and DON from the B [ABSTRACT FROM AUTHOR]

Chronic N deposition has been hypothesized to affect DOC production in forest soils due to the carbon demand exerted by microbial immobilization of inorganic N. We tested this hypothesis in field experiments at the Harvard Forest, Petersham, Massachusetts, USA. During four years of sampling soil solution collected beneath the forest floor in zero-tension lysimeters, we observed little change in DOC concentrations (10-30 % increase, not statistically significant) associated withelevated N inputs, but did observe significant increases in DON concentrations. Both DOC and DON varied seasonally with highest concentrations in summer and autumn. Mean DON concentrations increased 200-300% with the highest rate of inorganic N fertilization, and concentrations of DON were highest in samples with high inorganic N concentrations, We conclude that the organic chemistry of soil solution undergoes qualitative changes as a result of long-term N amendment at this site, with small changes in DOC, large increases in DON, and a decline in the C:N ratio of dissolved organic matter. [ABSTRACT FROM AUTHOR]