Demonstration Test Catchments programme: phase 2, funded by the UK Department of Environment, Food and Rural Affairs (Defra)

The impact of riparian wetlands on the cycling, retention and export of nutrients from land to water varies according to local environmental conditions and is poorly resolved in catchment management approaches. To determine the role a specific wetland might play in a catchment mitigation strategy, an alternative approach is needed to the high-frequency and spatially detailed monitoring programme that would otherwise be needed. Here, we present a new approach using a combination of novel and well-established geochemical, geophysical and isotope ratio methods. This combined approach was developed and tested against a 2-year high-resolution sampling programme in a lowland permeable wetland in the Lambourn catchment, UK. The monitoring programme identified multiple pathways and water sources feeding into the wetland, generating large spatial and temporal variations in nutrient cycling, retention and export behaviours within the wetland. This complexity of contributing source areas and biogeochemical functions within the wetland were effectively identified using the new toolkit approach. We propose that this technique could be used to determine the likely net source/sink function of riparian wetlands prior to their incorporation into any catchment management plan, with relatively low resource implications when compared to a full high-frequency nutrient speciation and isotope geochemistry-based monitoring approach.

A detailed analysis of temporal and spatial trends in nitrogen (N) speciation and phosphorus (P) fractionation in the Wylye, a lowland Chalk sub-catchment of the Hampshire Avon, UK is presented, identifying the sources contributing to nutrient enrichment, and temporal variability in the fractionation of nutrients in transit from headwaters to lower reaches of the river. Samples were collected weekly from ten monitoring stations with daily sampling at three further sites over one year, and monthly inorganic N and total reactive P (TRP) concentrations at three of the ten weekly monitoring stations over a ten year period are also presented. The data indicate significant daily and seasonal variation in nutrient fractionation in the water column, resulting from plant uptake of dissolved organic and inorganic nutrient fractions in the summer months, increased delivery of both N and P from diffuse sources in the autumn to winter period and during high flow events, and lack of dilution of point source discharges to the Wylye from septic tank, small package Sewage Treatment Works (STW) and urban Waste Water Treatment Works (WwTW) during the summer low flow period. Weekly data show that contributing source areas vary along the river with headwater N and P strongly influenced by diffuse inorganic N and particulate P fluxes, and SRP and organic-rich point source contributions from STW and WwTW having a greater influence in the lower reaches. Long-term data show a decrease in TRP concentrations at all three monitoring stations, with the most pronounced decrease occurring downstream from Warminster WwTW, following the introduction of P stripping at the works in 2001. Inorganic N demonstrates no statistically significant change over the ten year period of record in the rural headwaters, but an increase in the lower reaches downstream from the WwTW which may be due to urban expansion in the lower catchment.

Diffuse water pollution from agriculture (DWPA) is a major environmental concern, with significant adverse impacts on both human and ecosystem health. However, without an appropriate understanding of the multiple factors impacting on water, mitigation measures cannot be targeted. Therefore, this paper addresses this gap in understanding, reporting the hydrochemical monitoring evidence collected from the UK Government's Demonstration Test Catchments (DTC) programme including contrasting chalk and clay/mudstone catchments. We use data collected at daily and sub-daily frequency over multiple sites to address: (1) How does the behaviour of the full range of nitrogen (N) species and phosphorus (P) fractions vary? (2) How do N species and P fractions vary inter- and intra-annually? (3) What do these data indicate about the primary pollution sources? And (4) which diffuse pollution mitigation measures are appropriate in our study landscapes? Key differences in the rates of flux of nutrients were identified, dependent on catchment characteristics. Full N speciation and P fractionation, together with dissolved organic carbon (DOC) enabled identification of the most likely contributing sources in each catchment. Nitrate (NO3-N) was the dominant N fraction in the chalk whereas organic and particulate N comprised the majority of the load in the clay/mudstone catchments. Despite current legislation, orthophosphate (PO4-P) was not found to be the dominant form of P in any of the catchments monitored. The chalk sub-catchments had the largest proportion of inorganic/dissolved organic P (DOP), accompanied by episodic delivery of particulate P (PP). Contrastingly, the clay/mudstone sub-catchments loads were dominated by PP and DOP. Thus, our results show that by monitoring both the inorganic and organic fractions a more complete picture of catchment nutrient fluxes can be determined, and sources of pollution pin-pointed. Ultimately, policy and management to bring nutrient impacts under control will only be successful if a multi-stressor approach is adopted.

Diffuse pollution of watercourses from agriculture represents a complex and persistent environmental problem in the UK. This paper provides insights into why UK policy interventions have had limited success to date, drawing on the disciplines of psychology, sociology and behavioural economics to more thoroughly understand farmer attitudes and behaviours towards pollution mitigation. Our analysis is based on eliciting the opinions of commercial farmers through a series of surveys and discussion groups in three catchments: the grassland dominated River Eden catchment; the arable dominated River Wensum catchment and the mixed farming area of the Hampshire River Avon catchment. Results strongly suggest that a fundamental shift in identities, normative behavioural beliefs and social norms is required within the farming community before mitigation behaviours become embedded. Simply offering financial incentives or imposing regulatory penalties is unlikely to achieve the desired results. Double loop learning has the potential to enable farmers to migrate from a productivist to a multifunctional outlook where pollution mitigation becomes internalised within a farm management system. Expert farm advisors will be required to facilitate this process.

The role that hydrology plays in governing the interactions between dissolved organic carbon (DOC) and nitrogen in rivers draining lowland, agricultural landscapes is currently poorly understood. In light of the potential changes to the production and delivery of DOC and nitrate to rivers arising from climate change and land use management, there is a pressing need to improve our understanding of hydrological controls on DOC and nitrate dynamics in such catchments. We measured DOC and nitrate concentrations in river water of six reaches of the lowland river Hampshire Avon (Wiltshire, southern UK) in order to quantify the relationship between BFI (BFI) and DOC : nitrate molar ratios across contrasting geologies (Chalk, Greensand, and clay). We found a significant positive relationship between nitrate and BFI (p < 0. 0001), and a significant negative relationship between DOC and BFI (p < 0. 0001), resulting in a non-linear negative correlation between DOC : nitrate molar ratio and BFI. In the Hampshire Avon, headwater reaches which are underlain by clay and characterized by a more flashy hydrological regime are associated with DOC : nitrate ratios > 5 throughout the year, whilst groundwater-dominated reaches underlain by Chalk, with a high BFI have DOC : nitrate ratios in surface waters that are an order of magnitude lower (< 0.5). Our analysis also reveals significant seasonal variations in DOC : nitrate transport and highlights critical periods of nitrate export (e.g. winter in sub-catchments underlain by Chalk and Greensand, and autumn in drained, clay sub-catchments) when DOC : nitrate molar ratios are low, suggesting low potential for in-stream uptake of inorganic forms of nitrogen. Consequently, our study emphasizes the tight relationship between DOC and nitrate availability in agricultural catchments, and further reveals that this relationship is controlled to a great extent by the hydrological setting.

The European Water Framework Directive (WFD) is a main driver for enhancing water management policies and increasing infrastructure investment to improve all water bodies to good ecological status. This requires scientists, managers and regulators to develop an effective evidence base for understanding which strategies maximise the cost-benefit associated with water quality improvements. Such evidence is underpinned by national monitoring and predictions of change are often quantified through the application of computer models. This paper is associated with understanding how observations of water quality within river systems at different temporal resolutions and types of monitoring strategies enable us to understand and detect changes over and above the natural variability. Therefore we explore the inter- and intra-annual variabilities of water quality data in the form of concentrations and loads to benchmark the expected variability and uncertainty under different sampling regimes. Recent research has investigated the effects of sampling designs on commonly used metrics for assessing nutrient fluxes, such as the estimation of annual pollutant loads in catchments. However, there have been significantly fewer studies which have considered the effect of sampling frequencies on the detection of inter- and intra-annual variability in water quality time-series and which include the uncertainty estimates in such data. This is important as it determines both the resolution of sampling which is needed for effective monitoring schemes and also the length of dataset which is necessary to characterise baseline and post-remediation behaviours adequately. Without this, we do not have an effective evidence base that enables us to quantify changes in pollutants when improving water quality management plans and associated infrastructure investment. The study uses a Monte-Carlo based approach to generate deviate sample sets of varying time resolutions from measured continuous time-series of paired discharge and nitrate concentrations. These deviate datasets are used to calculate conventional metrics including annual loads, peak pollutant concentrations and pollution event frequencies. We provide an assessment of the uncertainty associated with these metrics, including the determination of variance and probability distributions. The approach is applied to a number of different datasets of varying length and sampling resolution, including a 40-year weekly resolution dataset from the River Frome, UK and a 4-year daily resolution dataset from the Hampshire Avon, UK. The results will be used to benchmark current water quality status for the Hampshire Avon Demonstration Test Catchment (DTC) project before a range of mitigation experiments are implemented (see http://www.avondtc.org.uk/).

The European Water Framework Directive (WFD) requires that all water bodies should be maintained at, or raised to, good ecological status, driven by improved integrated catchment management. Therefore, it is necessary to implement cost-effective mitigation strategies to reduce pollution from nutrients and improve overall water quality. If successful mitigation strategies are to be designed then it is imperative that catchment scale responses to environmental and anthropogenic changes are better understood. Against this background, this presentation investigates changes in hysteretic behaviours of nutrients in response to different environmental drivers using high resolution monitoring techniques. Observations of hysteretic behaviour can provide insights into the dominant flow pathways of pollutants. Therefore, monitoring changes in nutrient hysteresis can provide a useful tool for detecting regime differences or changes within and between catchments. In the UK, the Demonstration Test Catchment (DTC) project has been set up to monitor evidence for improving water quality problems arising specifically from diffuse pollution from agriculture using targeted mitigation experiments and high resolution monitoring. This research platform provides an opportunity to compare storm-driven nutrient behaviour between catchments which have differing geologies, as well as how these behaviours evolve on a seasonal and annual basis. The monitoring to date has included a period of drought, directly followed by extreme wet conditions in the UK and therefore offers opportunities to assess the effect of differences in antecedent conditions on monitored nutrient response to rainfall events. The study compares the hysteretic behaviour of nutrients, including nitrogen and phosphorus species as well as sediment from a number of storm events of varying magnitudes throughout the 2011-2012 monitoring period in the Hampshire Avon catchment as part of the DTC programme. The investigation focuses on four of the monitored sub-catchments which are all mainly agricultural and underlain by differing geologies. Two sub-catchments are predominately underlain by chalk (Brixton Deverill, River Wylye and Ebbesbourne Wake, River Ebble) and two are underlain by clay (Prior's Farm and Cool's Cottage, River Sem). Existing metrics such as loop size, shape and area are being used to assess changes in the hysteretic responses through time and in conjunction with varying antecedent conditions, including the recent post-drought period. The study is also examining changes in annual hysteresis patterns from individual storms in order assess catchment responses to longer-term climatic variabilities. Overall, the work considers the importance of understanding hysteresis in quantifying nutrient loads and estimating the uncertainty and variability in this behaviour. This work therefore provides key insights for future adaption, planning and water quality management in the UK and continental Europe.

The Water Framework Directive (WFD) requires continued reporting of the water quality status of all European waterbodies, with this status partly determined by the time a waterbody exceeds different pollution concentration thresholds. Routine water quality monitoring most commonly takes place at weekly to monthly time steps meaning that potentially important pollution events can be missed. This has the potential to result in the misclassification of water quality status. Against this context, this paper investigates the implications of sampling design on a range of existing water quality status metrics routinely applied to WFD compliance assessments. Previous research has investigated the effect of sampling design on the calculation of annual nutrient and sediment loads using a variety of different interpolation and extrapolation models. This work builds on this foundation, extending the analysis to include the effects of sampling regime on flow- and concentration-duration curves as well as threshold-exceedance statistics, which form an essential part of WFD reporting. The effects of sampling regime on both the magnitude of the summary metrics and their corresponding uncertainties are investigated. This analysis is being undertaken on data collected as part of the Hampshire Avon Demonstration Test Catchment (DTC) project; a DEFRA funded initiative investigating cost-effective solutions for reducing diffuse pollution from agriculture. The DTC monitoring platform is collecting water quality data at a variety of temporal resolutions and using differing collection methods, including weekly grab samples, daily ISCO autosamples and high resolution samples (15-30 min time step) using analysers in situ on the river bank. Datasets collected during 2011-2013 were used to construct flow- and concentration-duration curves. A bootstrapping methodology was employed to resample randomly the individual datasets and produce distributions of the curves in order to quantify the uncertainty associated with the different sampling temporal resolutions and collection methods. This analysis was repeated using temporally degraded versions of the high-resolution dataset to assess specifically the impact of temporal resolution alone on the estimated distributions. Threshold- exceedance statistics were also calculated for each experimental dataset. The principal outcome of the ongoing work to date is a quantification of the impact that sampling design decisions have on well-used water quality metrics and the uncertainty associated with their calculation, which, in turn, is vital if accurate evaluations of water quality status and compliance are to be made.

The role that hydrology plays in governing the interactions between dissolved organic carbon (DOC) and nitrogen in rivers draining lowland, agricultural landscapes is currently poorly understood, yet important to assess given the potential changes to production and delivery of DOC and nitrate arising from climate change. We measured DOC and nitrate concentrations in river water of six reaches of the lowland River Hampshire Avon (Wiltshire, southern UK) in order to quantify the relationship between Baseflow Index (BFI) and DOC : nitrate molar ratios across contrasting geologies (Chalk, Greensand and clay). We found a significant positive relationship between nitrate and Baseflow Index (p 5 throughout the year, whilst groundwater-dominated reaches underlain by Chalk, with a high Baseflow Index have DOC : nitrate ratios in surface waters that are an order of magnitude lower (

Mitigation of diffuse water pollution from agriculture is a key national environmental policy objective in England. With the recent introduction of the new agri-environment scheme, Countryside Stewardship, there is an increased emphasis on the macro-spatial targeting of on-farm mitigation measures to reduce pollutant pressures, and a concomitant need to forecast the technically feasible impacts of on-farm measures detailed in current policy and their associated costs and benefits. This paper reports the results of a modelling application to test these limits in the context of the associated costs and benefits for the reduction of diffuse water pollution from agriculture for each Water Framework Directive (WFD) water management catchment (WMC) and nationally. Four mitigation scenarios were modelled, including pollutant source control measures only (SC), mobilisation control measures only (MC), delivery control measures only (DC) and measures for source, mobilisation and delivery control (SMDC) combined. Projected impacts on nitrate, phosphorus and sediment export to water, ammonia, methane and nitrous oxide emissions to the atmosphere, together with the associated costs to the agricultural sector were estimated for each WFD WMC and nationally. Median WMC-scale reductions (with uncertainty ranges represented by 5th–95th percentiles) in current agricultural emissions, were predicted to be highest for the SMDC scenario; nitrate (18%, 11–23%), phosphorus (28%, 22–37%), sediment (25%, 18–43%), ammonia (26%, 17–32%), methane (13%, 7–18%) and nitrous oxide (18%, 16–20%). The median benefit-to-cost ratios (with uncertainty ranges represented by 5th–95th percentiles) were predicted to be in the following order; DC (0.15, 0.09–0.65), MC (0.19, 0.09–0.95), SMDC (0.31, 0.20–1.39) and SC (0.44, 0.19–2.48). Of the four scenarios simulated, the SC and SMDC suites of measures have the greatest potential to deliver reductions in BAU emissions from agriculture, and the best benefit:cost ratio.

The European Water Framework Directive (WFD) is a main driver for enhancing water management policies and increasing infrastructure investment to improve all water bodies to good ecological status. This requires scientists, managers and regulators to develop an effective evidence base for understanding which strategies maximise the cost-benefit associated with water quality improvements. Such evidence is underpinned by national monitoring and predictions of change are often quantified through the application of computer models. This paper is associated with understanding how observations of water quality within river systems at different temporal resolutions and types of monitoring strategies enable us to understand and detect changes over and above the natural variability. Therefore we explore the inter-and intra-annual variabilities of water quality data in the form of concentrations and loads to benchmark the expected variability and uncertainty under different sampling regimes. Recent research has investigated the effects of sampling designs on commonly used metrics for assessing nutrient fluxes, such as the estimation of annual pollutant loads in catchments. However, there have been significantly fewer studies which have considered the effect of sampling frequencies on the detection of inter-and intra-annual variability in water quality time-series and which include the uncertainty estimates in such data. This is important as it determines both the resolution of sampling which is needed for effective monitoring schemes and also the length of dataset which is necessary to characterise baseline and post-remediation behaviours adequately. Without this, we do not have an effective evidence base that enables us to quantify changes in pollutants when improving water quality management plans and associated infrastructure investment. The study uses a Monte-Carlo based approach to generate deviate sample sets of varying time resolutions from measured continuous time-series of paired discharge and nitrate concentrations. These deviate datasets are used to calculate conventional metrics including annual loads, peak pollutant concentrations and pollution event frequencies. We provide an assessment of the uncertainty associated with these metrics, including the determination of variance and probability distributions. The approach is applied to a number of different datasets of varying length and sampling resolution, including a 40-year weekly resolution dataset from the River Frome, UK and a 4-year daily resolution dataset from the Hampshire Avon, UK. The results will be used to benchmark current water quality status for the Hampshire Avon Demonstration Test Catchment (DTC) project before a range of mitigation experiments are implemented (see http://www.avondtc.org.uk/).

A multi-pollutant modelling framework for England and Wales is described. This includes emissions of nitrate, phosphorus and sediment to water and ammonia, methane and nitrous oxide to air, and has been used to characterise baseline (no uptake of on-farm measures) and business-as-usual (BAU) annual pollutant losses, comparing these with the loss under a range of new policies aimed at increasing the uptake of relevant source control measures to 95% across England and Wales. Model outputs, including uncertainty ranges, evaluated using national water and air quality data layers have been summarised at both farm (Robust Farm Type) and water management catchment(WMC) scale. Nationally, across allfarm types, the median annual reductions in pollutant losses under the new scenario, relative to BAU in 2010, were predicted to range between 9 and 16% for nitrate, 13–37% for phosphorus, 12–21% for sediment, 2–57% for methane and 10–17% for nitrous oxide. For ammonia, the range was −2–28%, indicating the potential for pollution swapping and an increase in ammonia emissions under scenarios designed to reduce nitrogen flux to waters. Increased uptake of pollution source control measures would result in a wide range of annualtotal(capital and operational) costs (per farm)for the major farm types, with median estimates ranging from £635 yr−1 (Less Favourable Areas (LFA) with grazing livestock) to £15,492 yr−1 (Cereals) in Nitrate Vulnerable Zone (NVZ) areas, compared with a range of £23 yr−1 to £13,484 yr−1 for the same respective farm types in non-NVZ areas. The estimated median annual load reductions for all WMCs relative to BAU, were predicted to be 16% for nitrate, 20% for phosphorus, 16% for sediment, 16% for ammonia, 15% for methane and 18% for nitrous oxide. These predictions suggest that almost perfect (95% uptake) implementation of source control measures will not deliver substantial improvements in pollutant emissions