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Further development of the bioeconomy, the substitution of bioresources for fossil resources, will lead to an increased pressure on land and water resources in both agriculture and forestry. It is important to study whether resultant changes in land management may in turn lead to impairment of water services. This paper describes the Nordic Bioeconomy Pathways (NBPs), a set of regional sectoral storylines nested within the global Shared Socioeconomic Pathways (SSP) framework developed to provide the BIOWATER research program with land management scenarios for projecting future developments to explore possible conflicts between land management changes and the Water Framework Directive (WFD). The NBPs are a set of narrative storylines capturing a range of plausible future trajectories for the Nordic bioeconomy until 2050 and that are fit for use within hydrological catchment modelling, ecosystem service studies and stakeholder dialogue about possible changes in agricultural and forestry management practices.

Plants release carbon-based exudates from their roots into the rhizosphere to increase phosphorus (P) supply to the soil solution. However, if more P than required is brought into solution, additional P could be available for leaching from riparian soils. To investigate this further, soil columns containing a riparian arable and buffer strip soil, which differed in organic matter contents, were sown with three common agricultural and riparian grass species. The P loads in leachate were measured and compared with those from unplanted columns, which were 0.17 ± 0.01 and 0.89 ± 0.04 mg kg -1 for the arable and buffer strip soil, respectively. A mixture of ryegrass and red fescue significantly (p ≤ .05) increased dissolved inorganic P loads in leachate from the arable (0.23 ± 0.01 mg kg -1 ) and buffer strip soil (1.06 ± 0.05 mg kg -1 ), whereas barley significantly reduced P leaching from the buffer strip soil (0.53 ± 0.08 mg kg -1 ). This was dependent on the dissolved organic C released under different plant species and on interactions with soil management history and biogeochemical conditions, rather than on plant uptake of P and accumulation into biomass. This suggested that the amount and forms of P present in the soil and the ability of the plants to mobilize them could be key factors in determining how plants affect leaching of soil P. Selecting grass species for different stages of buffer strip development, basing species selection on root physiological traits, and correcting soil nutrient stoichiometry in riparian soils through vegetative mining could help to lower this contribution., (© 2019 The Authors. Journal of Environmental Quality © 2019 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Estuarine sediments are a reservoir for faecal bacteria, such as E. coli , where they reside at greater concentrations and for longer periods than in the overlying water. Faecal bacteria in sediments do not usually pose significant risk to human health until resuspended into the water column, where transmission routes to humans are facilitated. The erosion resistance and corresponding E. coli loading of intertidal estuarine sediments was monitored in two Scottish estuaries to identify sediments that posed a risk of resuspending large amounts of E. coli . In addition, models were constructed in an attempt to identify sediment characteristics leading to higher erosion resistance. Sediments that exhibited low erosion resistance and a high E. coli loading occurred in the upper- and mid-reaches of the estuaries where sediments had higher organic content and smaller particle sizes, and arose predominantly during winter and autumn, with some incidences during summer. Models using sediment characteristics explained 57.2% and 35.7% of sediment shear strength and surface stability variance respectively, with organic matter content and season being important factors for both. However large proportions of the variance remained unexplained. Sediments that posed a risk of resuspending high amounts of faecal bacteria could be characterised by season and sediment type, and this should be considered in the future modelling of bathing water quality.

Microbiological water quality monitoring of bathing waters does not account for faecal indicator organisms in sediments. Intertidal deposits are a significant reservoir of FIOs and this indicates there is a substantial risk to bathers through direct contact with the sediment, or through the resuspension of bacteria to the water column. Recent modelling efforts include sediment as a secondary source of contamination, however, little is known about the driving factors behind spatial and temporal variation in FIO abundance. E. coli abundance, in conjunction with a wide range of measured variables, was used to construct models to explain E. coli abundance in intertidal sediments in two Scottish estuaries. E. coli concentrations up to 6 log 10 CFU 100 g dry wt -1 were observed, with optimal models accounting for E. coli variation up to an adjusted R 2 of 0.66. Introducing more complex models resulted in overfitting of models, detrimentally affected the transferability of models between datasets. Salinity was the most important single variable, with season, pH, colloidal carbohydrates, organic content, bulk density and maximum air temperature also featuring in optimal models. Transfer of models, using only lower cost variables, between systems explained an average deviance of 42%. This study demonstrates the potential for cost-effective sediment characteristic monitoring to contribute to FIO fate and transport modelling and consequently the risk assessment of bathing water safety., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Vegetated buffer strips (VBS) between agricultural areas and surface waters are important retention areas for eroded particulate P through which they may obtain critically high degrees of P saturation imposing high risk of soluble P leaching. We tested topsoil removal and three harvesting frequencies (once, twice, or four times per year) of natural buffer vegetation to reduce P leaching with the aim to offset erosional P accumulation and high degrees of P saturation. We used a simple numerical time-step model to estimate changes in VBS soil P levels with and without harvest. Harvesting offset erosional deposition as it resulted in an annual ammonium oxalate-extractable P reduction of 0.3 to 2.8% (25-cm topsoil content) in soils of the VBS and thus, with time, reduced potential P leaching below a baseline of 50 μg L. Topsoil removal only marginally reduced potential leaching at two sites and not anywhere near this baseline. The harvest frequency only marginally affected the annual P removal, making single annual harvests the most economical. We estimate 50 to 300 yr to reach the P leaching baseline, due to substantial amounts of P accumulated in the soils. Even in high-erosion-risk situations in our study, harvesting reduced soil P content and the P leaching risk. We suggest harvesting as a practical and efficient management to combat P leaching from agricultural VBS, not just for short-term reductions of dissolved P, but also for reductions of the total soil P pool and for possible multiple benefits for VBS., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The extent of pathogen transport to and within aquatic systems depends heavily on whether the bacterial cells are freely suspended or in association with suspended particles. The surface charge of both bacterial cells and suspended particles affects cell-particle adhesion and subsequent transport and exposure pathways through settling and resuspension cycles. This study investigated the adhesion of Faecal Indicator Organisms (FIOs) to natural suspended intertidal sediments over the salinity gradient encountered at the transition zone from freshwater to marine environments. Phenotypic characteristics of three E. coli strains, and the zeta potential (surface charge) of the E. coli strains and 3 physically different types of intertidal sediments was measured over a salinity gradient from 0 to 5 Practical Salinity Units (PSU). A batch adhesion microcosm experiment was constructed with each combination of E. coli strain, intertidal sediment and 0, 2, 3.5 and 5 PSU. The zeta potential profile of one E. coli strain had a low negative charge and did not change in response to an increase in salinity, and the remaining E. coli strains and the sediments exhibited a more negative charge that decreased with an increase in salinity. Strain type was the most important factor in explaining cell-particle adhesion, however adhesion was also dependant on sediment type and salinity (2, 3.5 PSU > 0, 5 PSU). Contrary to traditional colloidal (Derjaguin, Landau, Vervey, and Overbeek (DLVO)) theory, zeta potential of strain or sediment did not correlate with cell-particle adhesion. E. coli strain characteristics were the defining factor in cell-particle adhesion, implying that diverse strain-specific transport and exposure pathways may exist. Further research applying these findings on a catchment scale is necessary to elucidate these pathways in order to improve accuracy of FIO fate and transport models., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Reactive nitrogen (N) and phosphorus (P) inputs to surface waters modify aquatic environments, affect public health and recreation. Source controls dominate eutrophication management, whilst biological regulation of nutrients is largely neglected, although aquatic microbial organisms have huge potential to process nutrients. The stoichiometric ratio of organic carbon (OC) to N to P atoms should modulate heterotrophic pathways of aquatic nutrient processing, as high OC availability favours aquatic microbial processing. Heterotrophic microbial processing removes N by denitrification and captures N and P as organically-complexed, less eutrophying forms. With a global data synthesis, we show that the atomic ratios of bioavailable dissolved OC to either N or P in rivers with urban and agricultural land use are often distant from a "microbial optimum". This OC-deficiency relative to high availabilities of N and P likely overwhelms within-river heterotrophic processing. We propose that the capability of streams and rivers to retain N and P may be improved by active stoichiometric rebalancing. Although autotrophic OC production contributes to heterotrophic rates substantial control on nutrient processing from allochthonous OC is documented for N and an emerging field for P. Hence, rebalancing should be done by reconnecting appropriate OC sources such as wetlands and riparian forests that have become disconnected from rivers concurrent with agriculture and urbanisation. However, key knowledge gaps require research prior to the safe implementation of this approach in management: (i) to evaluate system responses to catchment inputs of dissolved OC forms and amounts relative to internal production of autotrophic dissolved OC and aquatic and terrestrial particulate OC and (ii) evaluate risk factors in anoxia-mediated P desorption with elevated OC scenarios. Still, we find stoichiometric rebalancing through reconnecting landscape beneficial OC sources has considerable potential for river management to alleviate eutrophication, improve water quality and aquatic ecosystem health, if augmenting nutrient source control., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Citrate and phytase root exudates contribute to improved phosphorus (P) acquisition efficiency in Nicotiana tabacum (tobacco) when both exudates are produced in a P deficient soil. To test the importance of root intermingling in the interaction of citrate and phytase exudates, Nicotiana tabacum plant-lines with constitutive expression of heterologous citrate (Cit) or fungal phytase (Phy) exudation traits were grown under two root treatments (roots separated or intermingled) and in two soils with contrasting soil P availability. Complementarity of plant mixtures varying in citrate efflux rate and mobility of the expressed phytase in soil was determined based on plant biomass and P accumulation. Soil P composition was evaluated using solution 31 P NMR spectroscopy. In the soil with limited available P, positive complementarity occurred in Cit+Phy mixtures with roots intermingled. Root separation eliminated positive interactions in mixtures expressing the less mobile phytase (Aspergillus niger PhyA) whereas positive complementarity persisted in mixtures that expressed the more mobile phytase (Peniophora lycii PhyA). Soils from Cit+Phy mixtures contained less inorganic P and more organic P compared to monocultures. Exudate-specific strategies for the acquisition of soil P were most effective in P-limited soil and depended on citrate efflux rate and the relative mobility of the expressed phytase in soil. Plant growth and soil P utilization in plant systems with complementary exudation strategies are expected to be greatest where exudates persist in soil and are expressed synchronously in space and time., (This article is protected by copyright. All rights reserved.)

Aims: Intercropping can improve plant yields and soil phosphorus (P) use efficiency. This study compares inter- and intra-species intercropping, and determines whether P uptake and shoot biomass accumulation in intercrops are affected by soil P availability., Methods: Four barley cultivars ( Hordeum vulgare L.) and three legume species ( Trifolium subterreneum, Ornithopus sativus and Medicago truncatula ) were selected on the basis of their contrasting root exudation and morphological responses to P deficiency. Monocultures and barley-barley and barley-legume intercrops were grown for 6 weeks in a pot trial at very limiting, slightly limiting and excess available soil P. Above-ground biomass and shoot P were measured., Results: Barley-legume intercrops had 10-70% greater P accumulation and 0-40% greater biomass than monocultures, with the greatest gains occurring at or below the sub-critical P requirement for barley. No benefit of barley-barley intercropping was observed. The plant combination had no significant effect on biomass and P uptake observed in intercropped treatments., Conclusions: Barley-legume intercropping shows promise for sustainable production systems, especially at low soil P. Gains in biomass and P uptake come from inter- rather than intra-species intercropping, indicating that plant diversity resulted in decreased competition between plants for P.

The degradation of aquatic ecosystems by multiply-acting stressors is a key threat requiring new approaches to identify impairment processes and restoration targets. Heterotrophic respiration of C-substrates can be an integrative indicator of how aquatic ecosystems respond to pollution. We utilised sixteen C-substrates (simple metabolites to dissolved organic matter (DOM)) to characterise substrate induced respiration (SIR) for sediments from sixteen NE Scotland streams covering a range of land use-related pollution pressures. Pollution explanatory variables were as assessed from GIS-derived land cover areas, dissolved water chemistry (N, P, base cations and trace elements) and sediment trace metals (by aqua-regia digest). Large inter-site variation in dissolved and sediment chemical concentrations was strongly significantly correlated with land cover: dissolved N, Ca, Mg, K, Na positively with agriculture and urban, negatively with semi-natural land areas; sediment As, Ba, Co, Zn with agriculture, Cu, Pb, Zn with urban areas. Simple linear regression modelling was used to explore the influences across land cover, dissolved and sediment chemistry with C-substrate responses, both individually and using principal components-derived SIR 'fingerprints'. The data supported the hypothesis that pollution pressures altered water and sediment quality, in turn affecting sediment microbes and their respiration responses to a range of C-substrates, especially discriminating the DOM respiration. Since headwater DOM is a dominant pool of C driving ecosystem processes downstream then any loss of ability to utilise DOM should be further explored in terms of possible connections to pollution processes., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Phosphorus (P) and nitrogen (N) use efficiency may be improved through increased biodiversity in agroecosystems. Phenotypic variation in plants' response to nutrient deficiency may influence positive complementarity in intercropping systems. A multicomponent screening approach was used to assess the influence of P supply and N source on the phenotypic plasticity of nutrient foraging traits in barley (H. vulgare L.) and legume species. Root morphology and exudation were determined in six plant nutrient treatments. A clear divergence in the response of barley and legumes to the nutrient treatments was observed. Root morphology varied most among legumes, whereas exudate citrate and phytase activity were most variable in barley. Changes in root morphology were minimized in plants provided with ammonium in comparison to nitrate but increased under P deficiency. Exudate phytase activity and pH varied with legume species, whereas citrate efflux, specific root length, and root diameter lengths were more variable among barley cultivars. Three legume species and four barley cultivars were identified as the most responsive to P deficiency and the most contrasting of the cultivars and species tested. Phenotypic response to nutrient availability may be a promising approach for the selection of plant combinations for minimal input cropping systems., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Concerns about the sustainability of inorganic fertilizers necessitate the characterization of alternative P source materials for agronomic P-efficiencies and P losses via leaching. Firstly, this study examined nutrient compositions including P speciation of seven soil amendments: sewage sludge (SS), anaerobic digestate (AD), green compost (GC), food waste compost (FWC), chicken manure (CM), biochar, and seaweed. Secondly, soil P leaching and availability was studied on a subset of four materials (SS, AD, GC, and CM). Sorption of extracts onto columns of a test soil showed strong P retention for SS and compost, but weak P sorption for CM and especially AD, suggesting short-term leaching risks for soil applied AD. Limited P desorption with water or citrate indicated sorbed P was strongly fixed, potentially limiting crop availability. These data indicate that variation in P forms and environmental behavior should be understood to maximize P usage, but minimize leaching and soil P accumulation. Hence, different alternative P source materials need differing recommendations for their agronomic management.

The fate of dissolved organic matter (DOM) exported from headwaters is a large uncertainty in global carbon models and catchment biogeochemical process understanding. We examined the biodegradability of stream DOM collected during different flow conditions (n = 12) from a heather-dominated moorland headwater in NE Scotland. Freeze-dried DOM isolates were characterised, re-dissolved to 10 mg C L(-1), inoculated with indigenous stream sediment microbes and incubated, with and without added nutrients, to assess decomposition rates at different times up to 41 days. Biodegradable DOM ranged from 5.0 to 19% of the total transported DOM, representing 8.54 kg C ha(-1) yr(-1) (11.1% of the total DOC flux, calculated as 77.2 ± 39.0 kg C ha(-1) yr(-1)). No simple patterns with flow rate were apparent but accumulated antecedent rainfall, specific UV absorbance of DOM and (15)N content were significant predictors of the proportion of organic matter decomposed. In headwater streams draining organic-rich catchments, in-stream DOM decomposition processes act as a secondary control on the spatial variability of carbon species, and are important for establishing accuracy of aquatic carbon fluxes and cycling budgets. Moreover, biologically-mediated DOM decomposition represents a net 'climate forcing effect' via the soil-stream-atmosphere pathway, drives downstream ecosystem metabolism and should be incorporated in carbon predictive modelling and ecosystem process studies., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Variation in the organic matter content associated with suspended particulate matter (SPM) is an often overlooked component of carbon cycling within freshwater riverine systems. The potential biogeochemical reactivity of particulate organic carbon (POC) that affect its interactions and fate, i.e. respired and lost to the atmosphere along river continua or ultimately exported to estuarine and oceanic pools was assessed. Eleven contrasting sites draining nested catchments (5-1837 km(2)) in the River Dee basin, NE Scotland were sampled during summer 2008 to evaluate spatio-temporal variations in quantity and quality (biogeochemical reactivity) of SPM during relatively low flow conditions. Mean SPM concentrations increased from 0.21 to 1.22 mg L(-1) between the uppermost and lowest mainstem sites. Individually, POC concentrations ranged from 0.08 to 0.55 mg L(-1) and accounted for ca. 3-15% of total aqueous organic carbon transported. The POC content was partitioned into autotrophic (2.78-73.0 mg C g(-1) SPM) and detrital (119-388 mg C g(-1) SPM) biomass carbon content. The particulate respired CO(2)-C as a % of the total carbon associated with SPM, measured by MicroResp™ over 18 h, varied in recalcitrance from 0.49% at peat-dominated sites to 3.20% at the lowermost mainstem site. Significant (p<0.05) relationships were observed between SPM biogeochemical reactivity measures (% respired CO(2)-C; chlorophyll α; bioavailable-phosphorus) and arable and improved grassland area, associated with increasing biological productivity downstream. Compositional characteristics and in-stream processing of SPM appear to be related to contributory land use pressures, that influence SPM characteristics and biogeochemistry (C:N:P stoichiometry) of its surrounding aqueous environment. As moorland influences declined, nutrient inputs from arable and improved grasslands increasingly affected the biogeochemical content and reactivity of both dissolved and particulate matter. This increases the potential for recycling of the organic matter that is either transported from upstream or entering further along the riverine continuum., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Diffuse pollution remains a major threat to surface waters due to eutrophication caused by phosphorus (P) transfer from agricultural land. Vegetated buffer strips (VBSs) are increasingly used to mitigate diffuse P losses from agricultural land, having been shown to reduce particulate P transfer. However, retention of dissolved P (DP) has been lower, and in some cases VBSs have increased delivery to surface waters. The aims of this review were (i) to develop a conceptual model to enhance the understanding of VBS functioning in terms of DP, (ii) to identify key processes within the model that affect DP retention and delivery, and (iii) to explore evidence for the controls on these processes. A greater understanding in these areas will allow the development of management strategies that enhance DP retention. We found evidence of a surface layer in buffer strip soils that is enriched in soluble P compared with adjacent agricultural land and may be responsible for the reported increased DP delivery. Through increased biological activity in VBSs, plants and microorganisms may assimilate P from particulates retained in the VBSs or native soil P and remobilize this P in a more soluble form. These conclusions are based on a limited amount of research, and a better understanding of biogeochemical cycling of P in buffer strip soils is required., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The retention of nutrients in narrow, vegetated riparian buffer strips (VBS) is uncertain and underlying processes are poorly understood. Evidence suggests that buffer soils are poor at retaining dissolved nutrients, especially phosphorus (P), necessitating management actions if P retention is not to be compromised. We sampled 19 buffer strips and adjacent arable field soils. Differences in nutrient retention between buffer and field soils were determined using a combined assay for release of dissolved P, N, and C forms and particulate P. We then explored these differences in relation to changes in soil bulk density (BD), moisture, organic matter by loss on ignition (OM), and altered microbial diversity using molecular fingerprinting (terminal restriction fragment length polymorphism [TRFLP]). Buffer soils had significantly greater soil OM (89% of sites), moisture content (95%), and water-soluble nutrient concentrations for dissolved organic C (80%), dissolved organic N (80%), dissolved organic P (55%), and soluble reactive P (70%). Buffer soils had consistently smaller bulk densities than field soils. Soil fine particle release was generally greater for field than buffer soils. Significantly smaller soil bulk density in buffer soils than in adjacent fields indicated increased porosity and infiltration in buffers. Bacterial, archaeal, and fungal communities showed altered diversity between the buffer and field soils, with significant relationships with soil BD, moisture, OM, and increased solubility of buffer nutrients. Current soil conditions in VBS appear to be leading to potentially enhanced nutrient leaching via increasing solubility of C, N, and P. Manipulating soil microbial conditions (by management of soil moisture, vegetation type, and cover) may provide options for increasing the buffer storage for key nutrients such as P without increasing leaching to adjacent streams., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Catchment riparian areas are considered key zones to target mitigation measures aimed at interrupting the movement of diffuse substances from agricultural land to surface waters. Hence, unfertilized buffer strips have become a widely studied and implemented "edge of field" mitigation measure assumed to provide an effective physical barrier against nitrogen (N), phosphorus (P), and sediment transfer. To ease the legislative process, these buffers are often narrow mandatory strips along streams and rivers, across different riparian soil water conditions, between bordering land uses of differing pollution burdens, and without prescribed buffer management. It would be easy to criticize such regulation for not providing the opportunity for riparian ecosystems to maximize their provision for a wider range of ecosystem goods and services. The scientific basis for judging the best course of action in designing and placing buffers to enhance their multifunctionality has slowly increased over the last five years. This collection of papers aims to add to this body of knowledge by giving examples of studies related to riparian buffer management and assessment throughout Europe. This introductory paper summarizes discussion sessions and 13 selected papers from a workshop held in Ballater, UK, highlighting research on riparian buffers brought together under the EU COST Action 869 knowledge exchange program. The themes addressed are (i) evidence of catchment- to national-scale effectiveness, (ii) ecological functioning linking terrestrial and aquatic habitats, (iii) modeling tools for assessment of effectiveness and costs, and (iv) process understanding enabling management and manipulation to enhance pollutant retention in buffers. The combined understanding led us to consider four principle key questions to challenge buffer strip research and policy., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The Tarland Catchment Initiative is a partnership venture between researchers, land managers, regulators, and the local community. Its aims are to improve water quality, promote biodiversity, and increase awareness of catchment management. In this study, the effects of buffer strip installations and remediation of a large septic tank effluent were appraised by water physico-chemistry (suspended solids, NO, NH, soluble reactive P) and stream macroinvertebrate indices used by the Scottish Environmental Protection Agency. It was done during before and after interventions over an 8-yr period using a paired catchment approach. Because macroinvertebrate indices were previously shown to respond negatively to suspended solid concentrations in the study area, the installation of buffer strips along the headwaters was expected to improve macroinvertebrate scores. Although water quality (soluble reactive P, NH) improved downstream of the septic tank effluent after remediation, there was no detectable change in macroinvertebrate scores. Buffer strip installations in the headwaters had no measurable effects (beyond possible weak trends) on water quality or macroinvertebrate scores. Either the buffer strips have so far been ineffective or ineffectiveness of assessment methods and sampling frequency and time lags in recovery prevent us detecting reliable effects. To explain and appreciate these constraints on measuring stream recovery, continuous capacity building with land managers and other stakeholders is essential; otherwise, the feasibility of undertaking sufficient management interventions is likely to be compromised and projects deemed unsuccessful., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Medium to small scale point sources continue to threaten river ecosystems through P loadings. The capacity and timescales of within-river processing and P retention are a major factor in how rivers respond to, and protect downstream ecosystems from, elevated concentrations of soluble reactive P (SRP). In this study, the bio-geochemical response of a small river (approximately 40 km(2) catchment area) was determined before, during and after exposure to a fourteen day pulse of treated sewage effluent using an upstream reach as a control. A wide array of approaches (batch and column simulations to in-situ whole stream metabolism) allowed independent comparison and quantification, of the relative contribution of abiotic and biotic processes in-river P cycling. This enabled, for the first time, separating the relative contributions of algae, bacteria and abiotic sorption without the use of labelled P (radioisotope). An SRP mass balance showed that the ecosystem switched from a P sink (during effluent inputs) to a P source (when effluent flow ceased). However, 65-70% of SRP was retained during the exposure time and remained sequestered two-weeks after-effluent flow ceased. Batch studies treated with biocide gave unrealistic results, but P uptake rates derived by other methods were highly comparable. Downstream of the effluent input, net P uptake by algae, bacteria and sediment (including the biofilm polysaccharide matrix) were 0.2 (+/-0.1), 0.4 (+/-0.3), and 1.0 (+/-0.9) mmol m(-2) day(-1) during effluent exposure. While autotrophic production did not respond to the effluent exposure, heterotrophic production increased by 67% relative to the control and this translated into a 50% increase in biological P uptake rate. Therefore, both biological and abiotic components of stream ecosystems uptake P during exposure to treated sewage effluent P inputs, and maintain a long 'memory' of this input in terms of P storage for considerable timescales after loading., ((c) 2010 Elsevier Ltd. All rights reserved.)

Establishing vegetated buffer strips (VBS) between cropland and watercourses is currently promoted as a principal control of diffuse pollution transport. However, we lackthe mechanistic understanding to evaluate P retention in VBS and predict risks of P transport to aquatic ecosystems. We observed that VBS establishment led to enhanced rates of soil P cycling, increasing soil P solubility and the potential amount leached to watercourses. Soil in VBS, relative to adjacentfields, had increased inorganic P solubility indices, dissolved organic P, phosphatase enzyme activity, microbial diversity, and biomass P. Small relative increases in the pool of soil P rendered labile had disproportionate effects on the P available for leaching. We propose a mechanism whereby the establishment of VBS on previous agricultural land causes a diversifying plant-microbial system which can access previous immobilized soil P from past fertilization or trapped sediment P. Laboratory experiments suggested that sediment-P inputs to VBS were insufficient alone to increase P solubility without biological cycling. Results showthat VBS management may require strategies, for example, harvesting vegetation, to offset biochemical processes that can increase the susceptibility of VBS soil P to move to adjoining streams.

Within-river cycling of P is a crucial link between catchment pollution sources and the resulting ecological impacts and integrates the biogeochemistry and hydrodynamics of river systems. This study investigates benthic sediment P sorption in relation to river soluble reactive phosphorus (SRP) concentrations during high- to low-flow changes in a major mixed land use river system in NE Scotland. We hypothesised that sediments comprised P sinks during moderate to higher flows but became P saturated with loss of buffering function during prolonged baseflow. Sediment characteristics were evaluated and equilibrium P concentrations (EPC(0)) calculated using a standardised batch adsorption method (EPC(0) values 0.04-1.75 micromol Pl(-1)). Pollution-impacted tributaries (32-69% catchment agricultural land cover) had increased SRP concentrations (0.19-2.62 micromol Pl(-1)) and maintained EPC(0)SRP values during summer baseflow so that sediments were indicated as P sources. This deviation from a geochemical sediment-water P equilibrium was attributed to biological accumulation of P from the water column into the sediments. In particular, large stores of sediment P accumulated in main stem reaches below agricultural tributaries and this may be consequential for sensitive downstream ecosystems. Hence, biogeochemical processes at the river bed may strongly influence river SRP cycling between geochemical and biotic pools. The nature of this internal reservoir of river P and its ecosystem interactions needs better understanding to enable best results to be attained from catchment mitigation actions designed to maintain/improve ecological status under the Water Framework Directive.

This study evaluates water quality, suspended and bed sediment, ecological and catchment land use data for 13 catchments of the mixed land use River Dee, NE Scotland, where pollution point sources are limited. Samples were collected at key times of biological activity (early and late summers). Mean river water concentrations were smaller in main stem and upland sites and greater in tributaries where agricultural pressures were greater and were 2-41 microgPO(4)-Pl(-1), 8-58 microg total dissolved Pl(-1) and 1-6 mg l(-1) of suspended particulate matter (SPM). SPM was 7-372 times enriched in biologically available P (BAP; determined using an FeO paper strip method) and 2-122 times in organic C relative to bed sediments. Ratios in river water concentrations of BAP attributed to the SPM (0.1-1.0 microgPl(-1)) to PO(4)-P had the greatest range at baseflow (0.01-0.80) with larger values for low land use intensity catchments. During May chlorophyll a concentrations were related to SPM BAP (p<0.001), but later in summer to PO(4)-P, and there was a corresponding change in the organic composition of SPM observed by IR spectroscopy. SPM concentrations and SPM BAP were better related to intensive grassland land use (p<0.001) than was PO(4)-P concentration (p<0.01) and also predicted abundances of filter feeding macroinvertebrates (p<0.001). Within this river system SPM quantity and composition proved to be an indicator of river biogeochemical functioning and requires further investigation as a potentially sensitive monitoring tool and to increase our understanding of chemical ecological links.

A chemical model (constructed in the ORCHESTRA modeling framework) of an organic soil horizon was used to describe soil solution data (10 cm depth) and assess if seasonal variations in soil solution dissolved organic carbon (DOC) could be explained by purely abiotic (geochemical controls) mechanisms or whether factors related to biological activity are needed. The NICA-Donnan equation is used to describe the competitive binding of protons and cations and the charge on soil organic matter. Controls on organic matter solubility are surface charge and a parameter, gamma, that accounts for the distribution of humic molecules between hydrophobic and hydrophilic fractions. Calculations show that the variations in solute chemistry alone are not sufficient to account for the observed variations of DOC, but factors that alter gamma, such as biological activity, are. Assuming that DOC in organic soils is derived from soluble humic material and that gamma is modified seasonally due to biological activity (with monthly soil temperature used as a surrogate for biological activity) we are able to model the observed seasonality of soil solution DOC over a 10-year period. Furthermore, with modeled DOC coupled to other geochemical processes we also model soil solution pH and Al concentrations.