Search

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Pesticide losses from agricultural land to water can result in the environmental deterioration of receiving systems. Mathematical models can make important contributions to risk assessments and catchment management. However, some mechanistic models have high parameter requirements which can make them difficult to apply in data-poor areas. In addition, uncertainties in pesticide properties and applications are difficult to account for using models with long run-times. Alternative, simpler, conceptual models are easier to apply and can still be used as a framework for process interpretation. Here, we present a new conceptual model of pesticide behaviour in surface water catchments, based on continuous water balance calculations. Pesticide losses to surface waters are calculated based on the displacement of a limited fraction of the soil pore water during storm events occurring after application. The model was used to describe the behaviour of metaldehyde in a small (2.2 km2) under-drained catchment in Eastern England. Metaldehyde is a molluscicide which has been regularly detected at high concentrations in many drinking water supply catchments. Measured peak concentrations in stream water (to about 9 micro g L-1) occurred in the first few storm events after application in mid-August. In each event, there was a quasi-exponential decrease in concentration during hydrograph recession. Peak concentrations decreased in successive events - responding to rainfall but reflecting an effective exhaustion in soil supply due to degradation and dissipation. Uncertain pesticide applications to the catchment were estimated using land over-analysis of satellite data, combined with a Poisson distribution to describe the timing of application. Model performance for both the hydrograph (after calibration of the water balance) and the chemograph was good and could be improved via some minor adjustments in assumptions which yield general insights into the drivers for pesticide transport. The use of remote sensing offers some promising opportunities for estimating catchment-scale pesticide applications and associated losses.

Greenhouse gas (GHG) fluxes from livestock grazed pasture soils are highly variable in both space and time but the quantitative importance of the factors regulating this variation remain poorly understood. Our aim was to explore this variability on contrasting extensively (low input) and intensively managed sheep-grazed ‘case-study’ pastures. We quantified (through standard and spatially-informed regressions) the statistical relationships between GHG fluxes (nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4)) and a range of soil, field and management characteristics. Fluxes of these three GHGs at two study sites were highly variable, but spatial structure (i.e. autocorrelation) was only observed in the variability of N2O fluxes across the intensive site and CO2 fluxes across the extensive site. The regression analyses identified significant GHG predictor variables for the extensive site as: NO3- (p < 0.001) and vegetation-type (p < 0.01) for N2O (R2 = 0.57; p = 0.000); NH4+ (p < 0.05), slope (p < 0.05) and elevation (p < 0.01) for CO2 (R2 = 0.34; p = 0.000); and NO3- (p < 0.01), NH4+ (p < 0.05) and soil moisture (p < 0.05) for CH4 (R2 = 0.25; p = 0.005). Significant GHG predictor variables for the intensive site were soil moisture (p < 0.01) and bulk density (p < 0.01) for N2O (R2 = 0.27; p = 0.005); soil moisture (p < 0.001) for CO2 (R2 = 0.31; p = 0.001); while none were found for CH4 (R2 = 0.10; p = 0.655). Key factors driving GHG variation were both site- and GHG-specific, with fluxes controlled by local conditions leading to differences in limiting factors (possibly even at the within-site scale). Our statistical analyses suggest a larger range of driving variables (e.g. air and soil temperature or other soil chemical properties such as total extractable N) may be required to more fully capture the observed variability in the GHG processes considered here, and that it may also be fruitful for future analyses to consider non-linear, non-stationary and interacting relationships across space- and time-scales. Adequacies of each site’s sample design also played a key interpretive role in the GHG processes, requiring further evaluation through additional sampling campaigns.

Nitrogen behaviour in domestic wastewater was investigated to develop a mechanistic understanding of ammonia dynamics in Floating Treatment Wetlands (FTWs) and to improve design and operation. A critical FTW design (full coverage of the floating mat and maximum plant density) was evaluated to optimize treatment performance of a pilot-scale system in removing ammonia under different operational volumes. A system dynamics approach as a framework was employed for robust understanding of the treatment mechanisms and system performance in removing ammonia. The results revealed that ammonia removal was enhanced in FTWs and the magnitude of removal was controlled by the design examined. Findings suggest that a design code of full coverage of water surface with mat material, high plant density, and low water volume can be considered as a critical design for FTW system to remove ammonia from domestic wastewater. This design promoted nitrification as principal ammonia removal process even when plants were present. The contribution of nitrification to overall ammonia removal was estimated to be between 81 and 85%. Plant uptake contributed to 14-19% of the total N loss. Ammonia loss via volatilization was determined to be negligible in examined system. Kinetics parameters for ammonia removal were between 0.14-0.22 day-1 in FTWs compared to 0.01-0.02 day-1 in controls. Understanding the contribution of removal processes of N could be useful to improve treatment system design, and enhance treatment performance.

Rising nitrate concentrations in rivers and groundwater in regions with intensive agriculture have been of concern for several decades. Long records of nitrate concentration are rare; in the UK, few pre-date 1974. Records from the River Stour from 1937 are analysed using "moving-windows", to explore the effects of window width on trend detection and process inference. Nitrate concentrations rose sharply from the late 1950s in response to widespread ploughing of grassland, but have fallen since the early 1980s, suggesting that widespread nitrogen control measures, which were introduced after the start of the downward trend, may not be the principal driver for recent change. Short windows (5 years) are too noisy; longer windows (10, 15 and 30 years) identify signals (i.e. trends) more reliably. Since system response times can be of the order of 20–30 years, management decisions made on shorter data sets (even up to 15 years) could be misleading.

A dynamic multi-media model that includes temperature-dependency for partitioning and degradation was developed to predict the behaviour of petroleum hydrocarbons during biopiling at low temperature. The activation energy (Ea) for degradation was derived by fitting the Arrhenius equation to hydrocarbon concentrations from temperature-controlled soil mesocosms contaminated with crude oil and diesel. The model was then applied to field-scale biopiles containing soil contaminated with diesel and kerosene at Casey Station, Antarctica. Temporal changes of total petroleum hydrocarbons (TPH) concentrations were very well described and predictions for individual hydrocarbon fractions were generally acceptable (disparity between measured and predicted concentrations was less than a factor two for most fractions). Biodegradation was predicted to be the dominant loss mechanism for all but the lightest aliphatic fractions, for which volatilisation was most important. Summertime losses were significant, resulting in TPH concentrations which were about 25% of initial concentrations just 1 year after the start of treatment. This contrasts with the slow rates often reported for hydrocarbons in situ and suggests that relatively simple remediation techniques can be effective even in Antarctica.

Cyclic volatile methylsiloxanes (cVMS) are used in personal care products and emitted to aquatic environments through wastewater effluents, and their bioaccumulation potential is debated. Here, a new bentho-pelagic version of the ACC-HUMAN model was evaluated for polychlorinated biphenyls (PCBs) and applied to cVMS in combination with measurements to explore their bioaccumulation behavior in a subarctic lake. Predictions agreed better with measured PCB concentrations in Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) when the benthic link was included than in the pelagic-only model. Measured concentrations of decamethylcyclopentasiloxane (D5) were 60 ± 1.2 (Chironomidae larvae), 107 ± 4.5 (pea clams Pisidium sp.), 131 ± 105 (three-spined sticklebacks: Gasterosteus aculeatus), 41 ± 38 (char), and 9.9 ± 5.9 (trout) ng g-1 wet weight. Concentrations were lower for octamethylcyclotetrasiloxane (D4) and dodecamethylcyclohexasiloxane (D6), and none of the cVMS displayed trophic magnification. Predicted cVMS concentrations were lower than measured in benthos, but agreed well with measurements in fish. cVMS removal through ventilation was an important predicted loss mechanism for the benthic-feeding fish. Predictions were highly sensitive to the partition coefficient between organic carbon and water (KOC) and its temperature dependence, as this controlled bioavailability for benthos (the main source of cVMS for fish). This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

Pesticide pollution of surface water is a major concern in many agricultural catchments The development of rapid and accurate methods for determining pesticide concentrations in water samples is, therefore, important. Here we describe a method for the simultaneous analysis of six pesticides (metaldehyde, quinmerac, carbetamide, metazachlor, propyzamide and pendimethalin) in natural waters by direct aqueous injection with liquid chromatography-tandem mass spectrometry. The method validation showed good linearity from 0.2 to 50.0 µg/L with correlation coefficients between 0.995 and 0.999. Method accuracy ranged from 84 to 100% and precision Relative standard deviation (RSD) from 4 to 15%. The limits of detection for the targeted pesticides ranged from 0.03 to 0.36 µg/L. No significant matrix effects on quantification were observed (t-test). The method was tested on water samples from a small arable catchment in eastern England. Peak concentrations for the determinands ranged from 1 to 10 µg/L.

Phosphorus (P) is one of the most limiting macronutrients for crop productivity and P deficiency is a common phenomenon in agricultural soils worldwide. Despite long-term application of phosphate fertilizers to increase crop yields, P availability is often low, due to the high affinity of phosphate for the soil solid phase. It has been suggested that the accumulated (surplus) P in agricultural soils is sufficient to sustain crop yields worldwide for about 100years. In this paper, we try to clear up the potential for making use of legacy P in soils for crop growth potentially alleviating the global P resource shortage. Specifically, we try to clear up the potential of soil "P activators" for releasing fixed P. P activators accelerate and strengthen process which transform P into bio-available forms via a range of chemical reactions and biological interactions. They include phosphate solubilizing microorganisms, phosphatase enzymes and enzyme activators, low molecular weight organic acids, humic acids, lignin, crop residues, biochar and zeolites. Although reported performance is variable, there is growing evidence that P activators can promote the release of phosphate from soil and, hence, have potential for mitigating the impending global P crisis. Further basic and applied research is required to better understand the mechanisms of interaction of P activators with natural soils and to maximize activator efficacy.

The behaviour of cyclic volatile methyl siloxanes (cVMS) in lakes was explored using a fugacity-based steady-state non-equilibrium multimedia fate and transport model (a modified version of QWASI). Three substances were investigated: Octamethylcyclotetrasiloxane (D4), Decamethylcyclopentasiloxane (D5) and Dodecamethylcyclohexasiloxane (D6) in two contrasting North American lakes: Lake Ontario and Lake Pepin (a natural shallow lake on the Mississippi river between Minnesota and Wisconsin). Values for the principal partition coefficients and the hydrolysis rate constant were adjusted for the mean annual temperatures of each lake. Hydrolysis rate constants were also adjusted for the fraction of chemical calculated to be in the freely dissolved phase. Half-lives in sediment were calculated from partitioning theory, assuming hydrolysis can occur only in the dissolved phase. Best estimates of substance-specific emissions were obtained by combining current per capita approximations of usage and fraction lost to domestic waste water, the population of the lake catchment and cVMS removal in waste water treatment. Concentrations were generally lower and chemical residence times longer in Lake Ontario than in Lake Pepin, owing to greater depth, a higher hydraulic retention time and a higher degree of dilution. Overall persistence in Lake Pepin is significantly influenced by the high rate of sediment burial assumed in the model, as well as by a relatively high rate of water discharge. Despite the many similarities of the compounds considered, the dominant loss mechanisms vary significantly and are not the same in each lake system. This highlights the pitfalls of subjective evaluation of chemical fate and illustrates the important role which models have to play in providing a quantitative framework for assessing chemical behaviour objectively under the influence of a complex and interacting set of factors.

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus (P) behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2&plus; and HPO42− when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg L−1 to 0.061 mg L−1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

An ultra performance liquid chromatography method coupled to a triple quadrupole mass spectrometer was developed to determine nonylphenol and 15 of its possible precursors (nonylphenol ethoxylates and nonylphenol carboxylates) in aqueous and particulate wastewater matrices. Final effluent method detection limits for all compounds ranged from 1.4 to 17.4 ng l(-1) in aqueous phases and from 1.4 to 39.4 ng g(-1) in particulate phases of samples. The method was used to measure the performance of a trickling filter wastewater treatment works, which are not routinely monitored despite their extensive usage. Relatively good removals of nonylphenol were observed over the biological secondary treatment process, accounting for a 53 % reduction. However, only an 8 % reduction in total nonylphenolic compound load was observed. This was explained by a shortening in ethoxylate chain length which initiated production of shorter polyethoxylates ranging from 1 to 4 ethoxylate units in length in final effluents. Modelling the possible impact of trickling filter discharge demonstrated that the nonylphenol environmental quality standard may be exceeded in receiving waters with low dilution ratios. In addition, there is a possibility that the EQS can be exceeded several kilometres downstream of the mixing zone due to the biotransformation of readily degradable short-chained precursors. This accentuates the need to monitor 'non-priority' parent compounds in wastewater treatment works since monitoring nonylphenol alone can give a false indication of process performance. It is thus recommended that future process performance monitoring and optimisation is undertaken using the full suite of nonylphenolic moieties which this method can facilitate.

Summary This paper compares the fluvial flux of nitrate at the UK’s tidal limit with an estimate of losses from the terrestrial biosphere at the point of entry to the river system to estimate in-stream losses across the UK’s entire river network between 1925 and 2007. These estimates were used to support interpretation of the current trend in the fluvial flux of nitrogen from the UK, and to give an assessment of the fluvial component of the total nitrogen budget of UK. The release of nitrate to the point at which it enters the stream network is estimated, using a Monte-Carlo framework, from a description of annual soil N mineralisation and immobilisation combined with an export coefficient model. Long-term records of land use (including – agricultural, forestry and urban uses); livestock; human population and atmospheric deposition are used. The study shows that: (i) The flux of nitrate from UK soils in the period since 1925 varied between 420 and 1463 ktonnes N yr −1 , with two peaks, one in 1944 and one in 1967. The first of these peaks was caused by mineralisation of soil organic matter following radical land use change in the 1940s, and the second was a multifactorial response to land use change and agricultural intensification in the 1960s. (ii) The current trend in N release from soils appears to be downward but the current fluvial flux at the tidal limit is slowly increasing. It is possible that in the near future nitrate–N losses at the tidal limit will, in some years, exceed N losses from soils implying a net N gain into the fluvial network. This apparent gain can be explained by the breakthrough of high nitrate groundwater into surface waters. (iii) The predicted export from UK soils at source as water enters the stream network implies that the UK will soon become a net source of total reactive N species, as the capacity for in-stream removal becomes exhausted by the ingress of N-rich groundwater to the river system.

Phospholipid fatty acid (PLFA) analysis is an informative method for characterising and quantifying changes in the phenotypic profile of the soil microbial community when soils are exposed to chemical toxicants and other xenobiotics. However, where such materials are lipophilic, a range of non-polar compounds can be co-extracted with PLFAs and can consequently mask PLFA chromatograms. We found this to be the case with the lipophilic anti-microbial compound triclosan, which can enter the soil via the addition of sewage sludge. A simple method of washing soil in solvent prior to extraction was developed in order to remove triclosan without altering the relative abundance of PLFAs. Three contrasting soils were spiked with 500 mg kg −1 of triclosan before being washed with methanol (MeOH), dichloromethane (DCM), hexane or aqueous solutions of these solvents. PLFAs were then extracted and analysed. All treatments were found to remove triclosan effectively, allowing all peaks to be identifiable. Whilst the polar solvents MeOH and DCM significantly altered the relative abundance of extracted fatty acids in most of the soils tested, soil washing with a small quantity of hexane was able to remove triclosan whilst best preserving the fidelity of the PLFA profiles.

Summary A model of catchment-scale nitrate transport is presented for a small, rural headwater basin (Alton Pancras: 2 ) in Dorset, UK, for the period 1930–2007. Estimates of annual nitrogen (N) loading were based on parish land-use data, held in the UK’s National Archives, and previously reported figures of typical UK N loadings from livestock, fertiliser, ploughing of permanent pasture, atmospheric deposition, biological fixation and crop uptake. Loading calculations were performed within an uncertainty framework to allow for the reliance on literature data sources. Loading calculations show that all significant sources must be included not just fertiliser application which, at most, contributes 50% of N input in any given year. A simple algorithm was used to transform estimated catchment N loading (1930–2007) into a river nitrate response (observed data: 1980–2004). This assumed N-loads were delayed by some catchment mean travel time (MTT), t a , attenuated according to a Peclet number, P e , converted into solute concentrations by a factor, α , to increase some initial baseline river concentration, C b . Simple graphical translation of estimated catchment N loading to the river concentration data suggested a MTT of around 37 years. As P e → ∞ , the transport model simplified to a linear relationship between catchment N load and river nitrate concentration response lagged by the MTT. Hence, the model results suggest that, in this catchment, advection is the dominant mechanism for transport of diffuse pollution from land to river: there is little or no dispersion present. The MTT ( t a ) was then reconsidered using an estimated distribution of unsaturated zone depths in the Alton Pancras catchment. Conclusions suggest that, in modelling of long-term nutrient transport, a detailed source term is of much greater importance than a complex hydrogeological model. Implications of epistemic uncertainty, long-term prediction and management of diffuse agricultural pollution are discussed.

Anaerobic digestion (AD) is becoming increasingly popular for treating organic waste. The methane produced can be burned to generate electricity and the digestate, which is high in mineral nitrogen, can be used as a fertiliser. In this paper we evaluate potential losses of ammonia via volatilisation from food waste anaerobic digestate using a closed chamber system equipped with a sulphuric acid trap. Ammonia losses represent a pollution source and, over long periods could reduce the agronomic value of the digestate. Observed ammonia losses from the experimental system were linear with time. A simple non-steady-state partitioning model was developed to represent the process. After calibration, the model was able to describe the behaviour of ammonia in the digestate and in the trap very well. The average rate of volatilisation was approximately 5.2 g N m −2 week −1 . The model was used to extrapolate the findings of the laboratory study to a number of AD storage scenarios. The simulations highlight that open storage of digestate could result in significant losses of ammonia to the atmosphere. Losses are predicted to be relatively minor from covered facilities, particularly if depth to surface area ratio is high.

We investigated variations in the biochemical composition and biodegradation of Scots pine (Pinus sylvestris) needles and litter on four soils with different cation exchange characteristics, ranging from 7 to 92% base saturation. Trends in cellulose, non-crystalline holocellulose concentrations (as measured by a trifluoracetic acid (TFA) hydrolysis technique) and ratios of lignin-to-cellulose and lignin-to-N in needles and litters varied significantly between sampling sites and reflected trends in soil base status under P. sylvestris stands. Although these relationships need to be tested rigorously on a more extensive sample set, clearly the biochemical quality of needles and litter within the same tree species is not uniform. Detailed analysis of the carbohydrate composition of TFA extracts from plant tissues showed that the ratios of selected hexoses (predominantly of microbial origin) to pentoses (mainly from plant cell wall constituents) were between 1 and 15 times lower in decomposing litter than needles. The hexose-to-pentose ratios also increased from 0.117:1 to 0.136:1 (as rhamnose+fucose-to-arabinose+xylose) and from 1.32:1 to 1.67:1 (as galactose+mannose-to-arabinose+xylose) with increasing base saturation of soils. It is concluded that the former ratio most clearly differentiated between the contrasting sites, whereas the latter ratio was more diagnostic of biotransformations during litter decomposition and associated development of microbial biomass. The study highlights a need to further clarify intraspecific differences in tree leaf and litter biochemistry in relation to soil characteristics and challenges the conventional definition of litter quality in terms of C-to-N or lignin-to-N ratio without consideration for the biochemical quality and spatial patterns of a “holocellulose” fraction. The determination of constituent carbohydrates in TFA extracts may provide a useful diagnostic for the potential decomposition of litter and the depolymerisation of structural carbohydrates.

Intact Pinus sylvestris needles and litter from the soil surface were sampled from several stands in SW England growing on soils with different chemical characteristics. The intrinsic chemical and biochemical characteristics of needle and litter samples were measured. The total concentration of lignin, measured by proximate analysis, and the chemical characteristics of the lignin-polymer in P. sylvestris needles and litter, varied between soil types. Lignin concentrations increased from 180 to 316 mg litter g −1 with increasing soil base saturation, although no similar trends in the concentration of lignin in needles were observed. The total concentration of phenylpropanoid moieties, released on CuO-oxidation, increased from 65.6 to 96.1 mg lignin g −1 in needles and 35.3–83.6 mg lignin g −1 in litters, which followed a trend of increasing soil base saturation under P. sylvestris stands. The concentration of NaOH-extractable moieties in needles increased from 1.79 to 2.35 μg sample g −1 with soil base saturation, as did the acid to aldehyde ratios of phenylpropanoid moieties in NaOH-extracts from litters. We conclude that the quality of lignin in needles and litter, as measured by its phenylpropanoid characteristics, varied significantly in P. sylvestris stands. In the light of the evidence from other studies that phenylpropanoid moieties have significantly different rates of microbial decomposition, this aspect of lignin quality should be considered when modelling the rate of litter mass loss and organic matter accumulation in forest soils. Furthermore, we have shown that by combining the CuO-oxidation technique with a NaOH-extraction procedure, phenylpropanoid signatures of a ‘bound’ and a relatively ‘labile’ lignin derived fraction in needles and litters can be more accurately monitored. A more extensive study is required to clarify the apparent relationships between the soil chemical characteristics beneath stands and the quality of lignin in plant materials.

The anti-microbial substance triclosan can partition to sewage sludge during wastewater treatment and subsequently transfer to soil when applied to land. Here, we describe the fate of triclosan in a one-year plot experiment on three different soils receiving sludge. Triclosan and methyl-triclosan concentrations were measured in soil samples collected monthly from three depths. A large fraction of triclosan loss appeared to be explained by transformation to methyl-triclosan. After 12 months less than 20% of the initial triclosan was recovered from each soil. However, the majority was recovered as methyl-triclosan. Most of the chemical recovered at the end of the experiment (both triclosan and methyl-triclosan) was still in the top 10 cm layer, although there was translocation to lower soil horizons in all three soils. Between 16.5 and 50.6% of the applied triclosan was unaccounted for after 12 months either as a consequence of degradation or the formation of non-extractable residues.

The application of sewage sludge to land can expose soils to a range of associated chemical toxicants. In this paper we explore the effects of the broad spectrum anti-microbial compound triclosan on the phenotypic composition of the microbial communities of three soils of contrasting texture (loamy sand, sandy loam and clay) using phospholipid fatty-acid (PLFA) analysis. Each soil type was dosed and subsequently re-dosed 6 weeks later with triclosan at five nominal concentrations in microcosms (10, 100, 500, 1000 mg kg −1 and a zero-dose control). PLFA profiles were analysed using multivariate statistics focussing on changes in the soil phenotypic community structure. Additionally, ratios of fungal:bacterial PLFA indicators and cyclo:mono-unsaturated PLFAs (a common stress indicator) were calculated. It was hypothesised that triclosan addition would alter the community structure in each soil with a particular effect on the fungal:bacterial ratio, since bacteria are likely to be more susceptible to triclosan than fungi. It was also hypothesised that the PLFA response to re-dosing would be suppressed due to acclimation. Although the microbial community structure changed over the course of the experiment, the response was complex. Soil type and time emerged as the most important explanatory factors. Principal component analysis was used to detect phenotypic responses to different doses of triclosan in each soil. As expected, there was a significant increase in the fungal:bacterial ratio with triclosan dose especially in treatments with the highest nominal concentrations. Furthermore, the PLFA response to re-dosing was negligible in all soils confirming the acclimation hypothesis.

[1] Widespread pollution of groundwater by nutrients due to 20th century agricultural intensification has been of major concern in the developed world for several decades. This paper considers the River Thames catchment (UK), where water-quality monitoring at Hampton (just upstream of London) has produced continuous records for nitrate for the last 140 years, the longest continuous record of water chemistry anywhere in the world. For the same period, data are available to characterize changes in both land use and land management at an annual scale. A modeling approach is used that combines two elements: an estimate of nitrate available for leaching due to land use and land management; and, an algorithm to route this leachable nitrate through to surface or groundwaters. Prior to agricultural intensification at the start of World War II, annual average inputs were around 50 kg ha−1, and river concentrations were stable at 1 to 2 mg l−1, suggesting in-stream denitrification capable of removing 35 (±15) kt N yr−1. Postintensification data suggest an accumulation of 100 (±40) kt N yr−1 in the catchment, most of which is stored in the aquifer. This build up of reactive N species within the catchments means that restoration of surface nitrate concentrations typical of the preintensification period would require massive basin-wide changes in land use and management that would compromise food security and take decades to be effective. Policy solutions need to embrace long-term management strategies as an urgent priority.

The behaviour of decamethylcyclopentasiloxane (D5) in river water was evaluated by measuring concentration changes in open beakers. Effective values for the partition coefficient between organic carbon and water (K(OC)) were derived by least-squares optimisation of a dynamic model which accounted for partitioning between the sorbed and dissolved phases of D5, and for losses via volatilisation and hydrolysis. Partial mass transfer coefficients for volatilisation were derived from model fits to controls containing deionised water. Effective values of log (K(OC)) were between 5.8 and 6.33 (mean 6.16). These figures are higher than some other experimentally-derived values but much lower than those estimated from the octanol: water partition coefficient using single-parameter linear free energy relationships (LFERs). A poly-parameter LFER gave a predicted log (K(OC)) of 5.5. Differences in partitioning are believed to be due to the nature of the organic matter present. The new value for effective K(OC) was employed in a simple model of D5 behaviour in rivers to ascertain the extent to which a higher affinity for organic carbon would depress volatility. The results suggest that despite the revised K(OC) value, volatilisation of D5 remains a significant removal mechanism in surface waters.

Human activity has doubled the loading of biologically available nitrogen to the terrestrial biosphere compared to pre-industrial levels (Vitousek et al., 1997; Galloway et al., 2004; Schlesinger et al., 2006; Seitzinger et al., 2006). This has led to a sixfold increase in global fluxes of fluvial dissolved inorganic nitrogen (Green et al., 2004) contaminating surface- and groundwater as terrestrial ecosystems become increasingly nitrogen-saturated (Foster et al., 1982; Meybeck, 1982; Aber et al., 1998; Bouwman et al., 2005; Mulholland et al., 2008; Ju et al., 2009; Qiu, 2009; Worrall et al., 2009). Nitrate is one of the most problematic and widespread of water contaminants (Howden and Burt, 2008, 2009): it has been regulated on the basis of its alleged toxicity to humans (Sandor et al., 2001; Addiscott and Benjamin, 2004), but elevated fluvial nitrate concentrations and fluxes are detrimental to both river and marine ecology (Burt et al., 1993). Nitrate originates from land-based, diffuse (spatially distributed) agricultural sources due to land management (e.g. fertilizer application; Goolsby and Battaglin, 2001) or changes in land use (e.g. long-term release of soil nitrogen (N) resulting from ploughing of permanent grassland; Whitmore et al., 1992), and from discharges of sewage effluent direct to rivers (Howden et al., 2009). Inputs may also occur from nitrogen fixation in the soil, atmospheric deposition and bedrock weathering (Holloway et al., 1998). It is essential that we understand the mechanisms controlling the movement of nitrate through river basins to the oceans, such that likely impacts on river ecology, potable water supply and marine tropic status may be identified. A key and poorly understood component is identification of the timescales over which river basin-scale nitrate transport occurs. This is of interest because modelling studies (Young et al., 1976; DOE, 1986; Howden and Burt, 2008) have suggested that changes in land use could be responsible for elevated mean fluvial concentrations persisting for some decades after initial land use change.

[1] Long-term records of the concentration of nitrogen species from British rivers were compiled in order to assess temporal change in the total fluvial nitrogen flux compared to the other inputs to, and outputs from, the UK terrestrial biosphere. The following nitrogen species are considered: ammoniacal N, nitrate, nitrite, dissolved organic nitrogen, and particulate organic nitrogen. Concentration and flow records were reconstructed from 1974 to 2005 for ammoniacal N, nitrate, nitrate, and dissolved organic nitrogen (DON) and from 1992 for particulate organic nitrogen (PON). The reconstructed fluvial nitrogen time series was compared to records for inorganic fertilizer, atmospheric emissions, industrial and sewage effluent, and imports. The results show that (1) the total dissolved nitrogen flux over the study period, after flow correction, varied from 470 to 980 kt N a−1, which, on average, comprised 69% nitrate N; 26% dissolved organic N; 4% ammoniacal N; and 1% nitrite N; (2) the total nitrogen flux including PON varied from 504 to 1004 kt N a−1; (3) the flux of ammoniacal N shows a significant decline over the study period, but significant increases in both nitrate N and dissolved organic N mean that the total dissolved nitrogen flux still shows a significant increase at a rate of 6.3 kt N a−1; and (4) the dissolved nitrogen flux record shows both a steady increase over the period 1974 to 2005 and sharp discrete rises in response to severe droughts. Flux increases (up to 69% increase compared to the 4 years prior to the drought) in response to severe droughts are not consistent with a storage effect caused by reduced flows but, instead, appear to represent enhanced production in the year of the drought. The long-term rise of fluvial nitrogen flux from British rivers is in contrast to declines in inputs and other N outputs.

A method is described for the analysis of decamethylcyclopentasiloxane (D(5)) in river water and treated waste water using headspace gas chromatography/mass spectrometry. Internal standard addition to samples and field blanks was carried out in the field to provide both a measure of recovery and to prevent any exposure of samples to laboratory air, which contained background levels of D(5). Measured levels of D(5) were typically in the range10-29ngL(-1) in the River Great Ouse (UK) with slightly higher levels in the River Nene (UK). The measured concentration of D(5) in treated waste water varied between 31 and 400ngL(-1), depending on the type of treatment process employed.

The behaviour of the cyclic volatile methyl siloxane (cVMS) decamethylcyclopentasiloxane (D5) in surface waters is explored using a combination of laboratory experimentation and mathematical modelling. In the laboratory experiment, changes were observed in the concentration of radiolabelled D5 in open stirred beakers containing mineral medium with different concentrations of added Aldrich humic acid over 120 h. Although D5 is very volatile, its strong affinity for dissolved organic carbon (DOC) reduced the rate of water to air transfer significantly. The data were well described using a simple partitioning model which accounted for hydrolysis and for depth and DOC changes resulting from sampling and evaporation, although there was some evidence for the formation of a hypothetical bound residue with increasing time. The model was used to derive effective values for the partition coefficient between DOC and water [log(K(DOC))]. These values were relatively consistent across five treatments and varied between 5.04 and 5.40 log(L kg(-1)), with no systematic treatment bias. These values are significantly higher than previously published experimental estimates of K(OC) for D5 but more than two orders of magnitude lower than some K(OC) estimates based on the octanol:water partition coefficient (K(OW)). The data confirm that volatilisation will be an important loss mechanism from surface waters for D5, although the rate of loss will decrease with increasing DOC concentration.

Direct discharge of untreated sewage to surface waters is a common practice in many parts of the world. However, relatively little is known about the behaviour of synthetic organic pollutants under these conditions. This paper describes a sampling campaign designed to track changes in water quality in a surface water system in Vientiane (Lao PDR) receiving significant quantities of untreated waste water. The study was based on following in-channel transport using a fluorescent tracer injected as a pulse, with a focus on the anionic surfactant linear alkylbenzene sulphonate (LAS) and ammonia. Water samples were collected at a number of stations with sampling times estimated to coincide with solute time-of-travel. The reduction in LAS concentration with flow-time could be approximated by first-order kinetics with a half life of about 7 h. Free ammonia concentrations decreased more slowly than LAS and remained above the level believed to be toxic for sensitive aquatic species along the entire channel. Changes in the ratios of LAS alkyl chain homologues to total LAS concentrations suggest a preferential removal of longer chain lengths. The role of biodegradation in the removal of LAS was confirmed by the presence of LAS metabolites (sulphophenylcarboxylates, SPCs) which increased systematically (as a fraction of LAS remaining) with flow-time.

Chemicals present in domestic wastewater can adsorb to solid phase materials during sewage treatment. If biosolids (or sewage sludge) are applied to land, these chemicals can be transferred to soil. Under some circumstances they can also be transferred to surface waters during storm events either in solution or attached to sediment. In this paper we describe the utility of the SWAT 2000 model to estimate diffuse-source surface water exposure to “down-the-drain” chemicals. The model was applied hypothetically to predict the behaviour of linear alkylbenzene sulphonate (LAS), an anionic surfactant commonly used in household detergents, in a small catchment in Bedfordshire, UK, where it has previously been successfully validated for stream flow, sediments and pesticides. LAS transfers were estimated for two scenarios: (1) realistic and (2) reasonable worst case, based on assumptions on sludge application rates and the concentration of LAS in sludge. In addition, the sensitivity of the model output to the proportion of the catchment to which sludge is applied was established. Soil wetness and the total quantity of biosolids applied were the biggest determinants of chemical transport from the catchment. The potential of SWAT as a higher-tier tool in environmental risk assessments is discussed.

Volatile methyl siloxanes break down in the atmosphere by reacting with OH radicals to form OH-substituted silanols. As the silanols become increasingly OH substituted they are increasingly likely to be removed from the atmosphere by wet and dry deposition. A simple equilibrium partitioning model was constructed to explore the relative rates of removal by different mechanisms (reaction vs. deposition) for siloxanes and their resultant silanols. A mass balance is calculated for the parent siloxane molecule and for each silanol, characterised by the number of OH substitutions. The model includes the effect of incomplete equilibrium between the vapour, adsorbed and dissolved phases of silanols in the atmosphere using a non-equilibrium factor (epsilon) expressing relative departure from equilibrium. Model results show: (1) maximum vapour-phase concentrations for non-substituted siloxanes and single-OH-substituted silanols; (2) maximum dissolved-phase and adsorbed-phase concentrations for two-OH-substituted silanols; (3)99% of the original material will be removed in wet deposition and1% in dry deposition as silanols. For increasing OH-substitutions, the decreasing concentration of precursor molecules (as a consequence of combined removal processes) means that concentrations are negligible, in all phases, beyond three or four substitutions. Predictions were relatively insensitive to assumed departures from phase equilibrium. Predictions of silanol hydrolysis in liquid water droplets suggest that the mix of diol chain lengths in precipitation may not be in thermodynamic equilibrium and will depend on atmospheric residence time and pH.

One problem with many mechanistic models of soil organic matter decomposition and nitrogen MIT is that the conceptual pools used to represent fractions of material which decompose at different rates are not easy to measure directly. A range of biochemical techniques for fractionating soil organic matter and the microbial biomass are presented in this paper and their potential for inclusion in models of carbon and nitrogen turnover discussed. These techniques include analysis of lignin de-polymerisation, a quantification of total and labile carbohydrate and a fractionation of the microbial biomass between fungi and bacteria using phospholipid and ergosterol analysis. Preliminary comparisons between the biochemical signatures of different soil types under different land uses are discussed in relation to the physical and biological factors affecting decomposition rates.

1. Soil profiles developed under beech woodland, spruce woodland, pasture and arable cropping were analysed for total organic C and lignin derivatives extracted by CuO oxidation. This reaction primarily releases lignin-derived phenylpropanoid moieties from soil organic matter(SOM). The amount and composition of the moieties obtained provided a signature that was related to the origin of organic matter from particular soil horizons. 2. There were clear differences between the lignin-derived phenylpropanoid signatures from similar depth horizons of soils developed under beech, spruce and pasture. This was characterized by: equal amounts of syringyl and vanillyl residues; a low syringyl:vanillyl ratio; and high concentration of ferulic acid, respectively, in the surface soil layers. The arable soil profile showed little differentiation in phenylpropanoid signature with depth (0-18 cm), presumably because of annual tillage. 3. Further investigation into the degradation rates of individual phenylpropanoid moieties in soils and their adsorption onto soil fractions is required. A more extensive survey, characterizing the 'lignin'-derived fraction in soils with a well documented land use history is also needed to establish a time scale for the translocation and degradation of the phenylpropanoid signatures of soils. Once calibrated, however, temporal changes in the composition of the lignin-phenylpropanoid SOM fraction will be potentially useful in monitoring the effects of vegetation and land management change on soil C cycling.