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Robust understanding of the fine-grained sediment cascades of temperate agricultural catchments is essential for supporting targeted management for addressing the widely reported sediment problem. Within the UK, many independent field-based measurements of soil erosion, sediment sources and catchment suspended sediment yields have been published. However, attempts to review and assess the compatibility of these measurements are limited. The data available suggest that landscape scale net soil erosion rates (∼38 t km−2 yr−1 for arable and ∼26 t km−2 yr−1 grassland) are comparable to the typical suspended sediment yield of a UK catchment (∼44 t km2 yr−1). This finding cannot, however, be reconciled easily with current prevailing knowledge that agricultural topsoils dominate sediment contributions to watercourses, and that catchment sediment delivery ratios are typically low. Channel bank erosion rates can be high at landscape scale (27 km−2 yr−1) and account for these discrepancies but would need to be the dominant sediment source in most catchments, which does not agree with a review of sediment sources for the UK made in the recent past. A simple and robust colour-based sediment source tracing method using hydrogen peroxide sample treatment is therefore used in fifteen catchments to investigate their key sediment sources. Only in two of the catchments are eroding arable fields likely to be important sediment sources, supporting the alternative hypothesis that bank erosion is likely to be the dominant source of sediment in many UK catchments. It is concluded that the existing lines of evidence on the individual components of the fine sediment cascade in temperate agricultural catchments in the UK are difficult to reconcile and run the risk of best management interventions being targeted inappropriately. Recommendations for future research to address paucities in measured erosion rates, sediment delivery ratios and suspended sediment yields, validate sediment source fingerprinting results, consider the sources of sediment-associated organic matter, and re-visit soil erosion and sediment cascade model parameterisation are therefore made. • Net soil erosion rates are approximately equal to catchment suspended sediment yields. • This is incompatible with most sediment originating from topsoils and low sediment delivery. • High bank erosion source contributions close the gap in sediment budgets. • The sources of mineral sediment were traced in 15 UK catchments. • Arable fields were suggested to be important sediment sources in only two of these. [ABSTRACT FROM AUTHOR]

The need for improved abatement of agricultural diffuse water pollution represents cause for concern throughout the world. A critical aspect in the design of on-farm intervention programmes concerns the potential technical cost-effectiveness of packages of control measures. The European Union (EU) Water Framework Directive (WFD) calls for Programmes of Measures (PoMs) to protect freshwater environments and these comprise ‘basic’ (mandatory) and ‘supplementary’ (incentivised) options. Recent work has used measure review, elicitation of stakeholder attitudes and a process-based modelling framework to identify a new alternative set of ‘basic’ agricultural sector control measures for nutrient and sediment abatement across England. Following an initial scientific review of 708 measures, 90 were identified for further consideration at an industry workshop and 63 had industry support. Optimisation modelling was undertaken to identify a shortlist of measures using the Demonstration Test Catchments as sentinel agricultural landscapes. Optimisation selected 12 measures relevant to livestock or arable systems. Model simulations of 95% implementation of these 12 candidate ‘basic’ measures, in addition to business-as-usual, suggested reductions in the national agricultural nitrate load of 2.5%, whilst corresponding reductions in phosphorus and sediment were 11.9% and 5.6%, respectively. The total cost of applying the candidate ‘basic’ measures across the whole of England was estimated to be £450 million per annum, which is equivalent to £52 per hectare of agricultural land. This work contributed to a public consultation in 2016. [ABSTRACT FROM AUTHOR]

Mitigation of diffuse water pollution from agriculture is of concern in the United Kingdom, so that freshwater quality can be improved in line with environmental objectives. Targeted on-farm mitigation is necessary for controlling sources of pollution to rivers; a positive impact must also be delivered at the subcatchment and catchment scales before good ecological status can be achieved. A farm on the River Sem in the Hampshire Avon Demonstration Test Catchment was selected for monitoring due to its degraded farmyard, track, and drainage ditch, which was targeted by the Demonstration Test Catchment programme for improvement using a treatment train of interventions. The river was monitored before and after, upstream and downstream, of the potential sources of pollution and subsequent mitigation, both locally at farm scale, and downstream at the subcatchment scale. Sediment was obtained from the riverbed using a conventional disturbance technique, and source samples were collected from across the subcatchment. Samples were analysed for geochemistry, mineral magnetism, and environmental radionuclide activity using the <63-μm fraction, before sediment source fingerprinting was conducted to apportion sources. Source tracing revealed that, although the degraded farm track was experiencing channelized flow and erosion in the pre-mitigation period, it was not a major sediment source even at farm scale. Repeat source apportionment during the pre- and post-mitigation periods showed that the targeted treatment train did not result in statistically significant decreases in predicted contributions from the farm track sources at either scale. Sediment sources must be determined at a range of spatial scales to support effective mitigation. [ABSTRACT FROM AUTHOR]

The classification of sediment source groups is often the least thoroughly considered part of a sediment fingerprinting methodology; however, the use of inappropriate source groups can be the cause of significant uncertainty. In many catchments, source groups based on land use or geology are a poor fit for their geomorphological processes and the nature of the tracers used. Against this context, this study directly compared the average percentage difference in the standardised concentrations of all tracers between a sediment sample and each individual source sample, to map the similarity between the properties of sources and sediment in 3 study catchments. The environmental significance of individual tracers and their similarity between individual samples were also examined in order to identify functionally important source groups. In the River Nene, UK, the mean percentage differences between source and sediment tracer concentrations were primarily controlled by the presence of distinctive ironstone and urban sources, which had very dissimilar properties to the target sediment. However, a generally consistent trend of certain source samples having more similar properties to multiple target sediment samples than others was also found; a finding that could not be identified when using conventional source groups. In the Sywell reservoir catchment, UK, sediment originated from throughout its catchment, apart from in the case of damaged road verges, and there was little indication of any major change in sediment sources through recent time. In the Vuvu catchment, South Africa, there was a larger contribution from distal igneous sources during high-flow events. The trialled method, however, provided little advantage over the standard fingerprinting approach in this case, due to the existing good fit between catchment geomorphology, the tracers used, and the geological source groups. The method trialled herein can provide distinct advantages over the conventional fingerprinting approach and, although it should not replace it, provides a useful supplement by permitting an assessment of whether potential source groupings make best environmental sense and providing increased resolution of sediment provenance. [ABSTRACT FROM AUTHOR]

The effective management of sediment losses in large river systems is essential for maintaining the water resources and ecosystem services they provide. However, budgetary, and logistical constraints often mean that the understanding of catchment sediment dynamics necessary to deliver targeted management is unavailable. This study trials the collection of accessible recently deposited overbank sediment and the measurement of its colour using an office document scanner to identify the evolution of sediment sources rapidly and inexpensively in two large river catchments in the UK. The River Wye catchment has experienced significant clean-up costs associated with post-flood fine sediment deposits in both rural and urban areas. In the River South Tyne, fine sand is fouling potable water extraction and fine silts degrade salmonid spawning habitats. In both catchments, samples of recently deposited overbank sediment were collected, fractionated to either <25 μm or 63-250 μm, and treated with hydrogen peroxide to remove organic matter before colour measurement. In the River Wye catchment, an increased contribution from sources over the geological units present in a downstream direction was identified and was attributed to an increasing proportion of arable land. Numerous tributaries draining different geologies allowed for overbank sediment to characterise material on this basis. In the River South Tyne catchment, a downstream change in sediment source was initially found. The River East Allen was identified as a representative and practical tributary sub-catchment for further investigation. The collection of samples of channel bank material and topsoils therein allowed channel banks to be identified as the dominant sediment source with an increasing but small contribution from topsoils in a downstream direction. In both study catchments, the colour of overbank sediments could quickly and inexpensively inform the improved targeting of catchment management measures. • Overbank sediment colour showed its source evolution along two large rivers. • Hydrogen peroxide mitigated organic matter enrichment related uncertainties. • In the River Wye contributions were associated with an increasing arable land use. • In the River South Tyne river bank erosion dominated throughout its length. • Targets for management were rapidly and inexpensively determined. [ABSTRACT FROM AUTHOR]

The growing awareness of the environmental significance of fine-grained sediment fluxes through catchment systems continues to underscore the need for reliable information on the principal sources of this material. Source estimates are difficult to obtain using traditional monitoring techniques, but sediment source fingerprinting or tracing procedures, have emerged as a potentially valuable alternative. Despite the rapidly increasing numbers of studies reporting the use of sediment source fingerprinting, several key challenges and uncertainties continue to hamper consensus among the international scientific community on key components of the existing methodological procedures. Accordingly, this contribution reviews and presents recent developments for several key aspects of fingerprinting, namely: sediment source classification, catchment source and target sediment sampling, tracer selection, grain size issues, tracer conservatism, source apportionment modelling, and assessment of source predictions using artificial mixtures. Finally, a decision-tree representing the current state of knowledge is presented, to guide end-users in applying the fingerprinting approach. [ABSTRACT FROM AUTHOR]

The ingress of particulate material into freshwater spawning substrates is thought to be contributing to the declining success of salmonids reported over recent years for many rivers. Accordingly, the need for reliable information on the key sources of the sediment problem has progressed up the management agenda. Whilst previous work has focussed on apportioning the sources of minerogenic fine sediment degrading spawning habitats, there remains a need to develop procedures for generating corresponding information for the potentially harmful sediment-bound organic matter that represents an overlooked component of interstitial sediment. A source tracing procedure based on composite signatures combining bulk stable 13C and 15N isotope values with organic molecular structures detected using near infrared (NIR) reflectance spectroscopy was therefore used to assess the primary sources of sediment-bound organic matter sampled from artificial spawning redds. Composite signatures were selected using a combination of the Kruskal–Wallis H-test, principal component analysis and GA-driven discriminant function analysis. Interstitial sediment samples were collected using time-integrating basket traps which were inserted at the start of the salmonid spawning season and extracted in conjunction with critical phases of fish development (eyeing, hatch, emergence, late spawning). Over the duration of these four basket extractions, the overall relative frequency-weighted average median (±95% confidence limits) source contributions to the interstitial sediment-bound organic matter were estimated to be in the order: instream decaying vegetation (39±<1%; full range 0–77%); damaged road verges (28±<1%; full range 0–77%); septic tanks (22±<1%; full range 0–50%), and; farm yard manures/slurries (11±<1%; full range 0–61%). The reported procedure provides a promising basis for understanding the key sources of interstitial sediment-bound organic matter and can be applied alongside apportionment for the minerogenic component of fine-grained sediment ingressing the benthos. The findings suggest that human septic waste contributes to the interstitial fines ingressing salmonid spawning habitat in the study area. [ABSTRACT FROM AUTHOR]

Although traditional sediment tracing approaches provide valuable information for characterising key generic sediment sources, Catchment Officers working as part of the Catchment Sensitive Farming initiative frequently require more detailed evidence to permit improved targeting of mitigation. Accordingly, a novel framework combining conventional sediment source fingerprinting and a dual signature tracking method has recently been used to improve sediment source information for the River Glaven (~115 km2) priority catchment in eastern England. Conventional geochemical tracing incorporating a number of recent refinements to the mass balance modelling, including the combined use of local and genetic algorithm optimisation, was used to provide information on the average median relative contributions (±95% confidence limits) of generic sediment sources in three sub-catchments, categorised as grassland (1 ± 1%-12 ± 1%) or arable (25 ± 1%-46 ± 1%) surface soils, damaged road verges (2 ± 1%-50 ± 1%) and channel banks/subsurface sources (20 ± 1%-50 ± 1%) and to provide a framework for the spatial extrapolation of tracking data. Particle tracking using fluorescent-magnetic grains was used to provide preliminary sub-catchment scale information on sediment loss from key components of the primary arable topsoil and channel bank generic sources, characterised, respectively, as wheelings (18 ± 1%-33 ± 1%) or inter-wheelings (7 ± 1%-13 ± 1%) and poached (19 ± 1%-47 ± 1%) or fluvially eroded (1 ± 1%-3 ± 1%) channel margins. The insertion of high-strength magnets in watercourses ensured that the tracking component of the novel framework links sediment loss from labelled areas to river channels as opposed to providing information to edge-of-field only. Uncertainty and prior information on source contributions are explicitly recognised by the framework. This study represents the first in the UK to link wheeling sediment losses to river channels. The findings underpin the importance of compacted areas used for trafficking as sources of, and conduits for, sediment delivery in the lowland agricultural landscape of the UK. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Agricultural diffuse pollution is a significant contributor to water and air quality in many catchments and the need to control harmful emissions remains paramount for government policy. In England, the Demonstration Test Catchments (DTCs) have been established to provide a basis for testing on-farm mitigation measures using collaborative multi-partner research and some of this work is targeting the Hampshire Avon (∼1700km2) catchment. To help provide integrated farm advice across England and Wales, a new Excel-based tool, FARM Scale Optimisation of Pollutant Emission Reductions (FARMSCOPER), has recently been developed for characterising diffuse agricultural pollutant emissions from representative farm types and quantifying the expected impacts of control options on those losses to the environment. Against this background, this paper describes the application of FARMSCOPER in the Hampshire Avon DTC in order to assess its utility at catchment scale and the potential benefits of relevant and practical mitigation options. Spatial datasets and the Agricultural Census returns for 2009 specific to the River Avon catchment were integrated to produce a collection of representative farm types which capture the characteristics of the local physical environment, land use patterns and farm management practices. FARMSCOPER was used to estimate the annual emissions of nitrate, phosphorus, sediment, nitrous oxide, methane and ammonia for each representative farm type. The scenarios investigated comprised baseline losses with no mitigation measures implemented, current emissions using information on the present implementation of options under existing schemes and initiatives and, the maximum potential reduction possible on the basis of implementing all available and relevant options. Model outputs suggested that reductions in pollutant loads in response to the existing uptake of mitigation methods are small (e.g. 10% for phosphorus, 7% for sediment, 4% for nitrate and 5% for nitrous oxide). FARMSCOPER suggested that technically feasible pollutant reductions on the basis of the implementation of more mitigation options could be of the order of 47% for phosphorus, 66% for sediment, 22% for nitrate and 16% for nitrous oxide. This work represents the first catchment scale application of the FARMSCOPER tool. [Copyright &y& Elsevier]

Abstract: Catchment erosion, soil losses and resulting sediment pressures continue to represent cause for concern with respect to the ecological vitality and amenity value of riverine systems, including those in the agricultural catchments of southern England. Given that the sources of fine-grained sediment are typically diffuse in nature, it is essential to adopt a catchment-wide perspective to corresponding management strategies and sediment source tracing procedures have proved useful in assisting such planning. There remains, however, scope for further refining sediment sourcing procedures and on that basis, a recent study in the upper River Kennet (~214km2) catchment in southern England, provided an opportunity for designing and testing a refined statistical procedure for sediment source discrimination with composite fingerprints using Genetic Algorithm (GA)-driven Discriminant Function Analysis, the Kruskal–Wallis H-test and Principal Components Analysis. The revised statistical verification of composite signatures was combined with numerical mass balance modelling using recent refinements including a range of tracer weightings and both local and GA optimisation. Comparison of the local and global optimisation increased confidence in the outputs of local optimisation and the goodness-of-fit for the predicted source contributions using the optimum composite signatures selected from the revised statistical testing ranged from 0.914 to 0.965. Overall relative frequency-weighted average median source type contributions were estimated to be 4% (agricultural topsoils; predicted deviate median inputs 1–19%), 55% (unmetalled farm track surfaces; predicted deviate median inputs 9–91%), 6% (damaged road verges; predicted deviate median inputs 4–42%), 31% (channel banks/subsurface sources; predicted deviate median inputs 5–41%) and 4% (urban street dust; predicted deviate median inputs 0–20%). The study provides further evidence of the importance of eroding farm tacks as a catchment scale sediment source and confirms the utility of tracing for assembling information on sediment inputs from both the agricultural and urban sectors. [Copyright &y& Elsevier]

Abstract: Sediment fingerprinting techniques provide a means of assembling valuable reliable information on the principal sources of sediment problems at catchment scale. However, there is a need to refine existing approaches to take account of a variety of sources of uncertainty and to incorporate prior information. To address this need, a modified mass balance model incorporating a Monte Carlo approach for representing the uncertainty surrounding source and sediment sampling, as well as weightings to take account of the within-source variability and discriminatory power of individual tracer properties and prior information on bank erosion, was used to apportion recent sediment sources in sub-catchments of the Somerset Levels, south west UK. Sensitivity tests confirmed that the precision of source apportionment was improved by incorporating the weightings and prior information into the mixing model. Estimates of the overall mean contributions from individual source types, bounded by 95% confidence limits, were assessed to be 42±2% (pasture topsoils), 22±2% (cultivated topsoils), 22±1% (channel banks/subsurface sources), 12±2% (damaged road verges) and 2±1% (STWs). Respective estimates of net sediment delivery to watercourses, provided by integrating the source ascription results with estimated sediment yield ranges and sub-catchment or land use areas, ranged between 33–829kgha−1 yr−1, 30–1995kgha−1 yr−1, 2–315kgha−1 yr−1, 0–217kgha−1 yr−1, and 0–28kgha−1 yr−1. Sediment fingerprinting should always include uncertainty analysis but on the understanding that the latter will be conditional on the assumptions used. [Copyright &y& Elsevier]

Abstract: In association with a major initiative aimed at identifying policy packages for inclusion in the Programmes of Measures (POM''s) comprising EU Water Framework Directive (WFD) River Basin Management Plans (RBMP''s), recent work has evaluated the gap between current and compliant suspended sediment losses due to farming across England and Wales. The work required national scale sediment source apportionment to assess the current contributions of diffuse agricultural and urban sector losses, channel bank erosion and point source discharges to the total suspended sediment loads delivered to all rivers. Results suggested that the agricultural sector dominates present day (year 2000) sediment inputs to rivers (1929 kt=76%) compared to eroding channel banks (394 kt=15%), diffuse urban sources (147 kt=6%) and point source discharges (76 kt=3%). Projected change in farming by 2015, represented by the Business as Usual forecast of structural developments and predicted uptake of sediment mitigation methods, suggested an overall 9% reduction in sediment loss from the agricultural sector across England and Wales. The projected reduction is unlikely to deliver sediment compliance in all catchments. Key limitations of the integrated modelling approach are discussed. [Copyright &y& Elsevier]

The absence of guidelines for pre-selecting the most effective combination of properties for inclusion in a composite fingerprint represents a key methodological uncertainty hampering the wider adoption of the fingerprinting approach for identifying suspended sediment sources. This contribution reports a preliminary attempt to address this issue by testing the discrimination of potential sediment sources within a number of contrasting river basins in the UK and Africa, afforded by a range of sediment properties. Statistical analysis confirms that there is no single diagnostic property capable of discriminating the range of potential suspended sediment sources in the study basins. The use of composite fingerprints based on several constituents drawn from a single group of properties consistently improves sediment source discrimination. However, the level of discrimination afforded by a particular combination of properties is not consistent between the study catchments. Composite fingerprints incorporating constituents selected from several groups of properties using a stepwise statistical selection procedure consistently provide the most robust discrimination of potential sediment sources. Whilst it is not possible to identify a universally applicable optimum composite fingerprint, the results suggest that at present, the most effective means of optimising sediment source discrimination is to identify a number of groups of properties for subsequent use in the establishment of a composite fingerprint. More specifically, this study suggests that measurements of a combination of acid and pyrophosphate–dithionite extractable metals, base cations and organic constituents should provide an effective basis for establishing composite fingerprints for discriminating individual sediment source types. Radiometric properties can also provide useful information for improving sediment source discrimination. The final choice of the groups of properties will necessarily reflect the laboratory facilities available. [Copyright &y& Elsevier]

Soil erosion and sediment losses are likely to increase with projected climate change and increasing storm intensity, causing detrimental impacts to agriculture and the degradation of aquatic ecosystems. Agri-environment initiatives aim to mitigate these losses through farmer engagement and incentivisation for best practice. There is, however, limited evidence regarding the impacts of their delivery and their capacity to deliver resilience to extreme wet weather. As such, the aim of this study was to determine how fine-grained sediment provenance changes with flow condition in eight high priority English catchments targeted through a strategic agri-environment initiative and to compare the estimated sediment source proportions to the targeted advice being delivered to farmers. The provenance of fine-grained sediment was determined using sediment source fingerprinting over low flow conditions and the winter of 2019–2020 which was characterised by severe flooding. Details on the advice delivered to farmers through the Catchment Sensitive Farming initiative were obtained from a delivery agency database and interviews with catchment officers. Dominant sediment sources varied considerably between catchments and were not easily predicted based upon their characteristics meaning that targeting on-farm advice effectively is challenging. Critically, however, changes in sediment sources rarely occurred with the extreme wet winter of 2019–2020. It is recommended that the greater availability of empirical catchment-specific evidence could significantly improve the delivery of such agri-environment initiatives. In the current absence of this evidence an assumption that riparian woodland is effective at preventing sediment losses and the targeting of advice to sediment sources proportionally based upon the area of the catchment they cover may improve the benefits of such initiatives. • Dominant sediment sources varied considerably between catchments. • No significant change in sediment sources occurred with an extreme wet winter. • Targeting on-farm advice efficiently without empirical evidence is challenging. • Agri-environment initiatives can provide future resilience if guided by evidence. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ investigations of fine sediment ingress in gravel-bed rivers remain limited. • Ingress rates and directional mechanisms of accumulation were investigated across a range of flow conditions. • Three designs of sediment traps (>250 traps in total) were used. • Linear mixed effects models showed that the ingress of cohesive particles were well explained by mean hydro-sedimentological parameters. • Observed results have important implications on the legacy effects that can originate from ingressed particles. Most studies investigating fine sediment ingress in gravel-bed rivers have been conducted at the laboratory scale, and even fewer have explored the ingress processes of flocculated particles. Here, an extensive in-situ sampling programme was undertaken to investigate hydro-sedimentological drivers of interstitial fine sediment accumulation and to evaluate fine sediment ingress directional mechanisms in a gravel-bed river located on the eastern slopes of the Rocky Mountains in southern Alberta. Three sediment trap designs were installed across seven deployment cycles at four sites along the river. Instantaneous discharge, suspended solids concentration, and particle size distributions (of suspended and ingressed particles) were measured, while relevant hydraulic parameters were modelled with a flow model (MOBED). Distinct patterns of ingress dynamics between non-cohesive and cohesive fractions of fine sediment were observed. While the assessed hydro-sedimentological parameters did not statistically explain the ingress rates of non-cohesive 0.5 – 2 mm particles, the opposite was observed for < 0.5 mm particles, which were mostly transported in flocculated form. For flocculated sediment, horizontal ingress accounted for ∼ 60 % of interstitial accumulation. Directional ingress mechanisms, however, were dependent on flow conditions for both particle size fractions, with vertical and horizontal accumulations becoming more important during higher and lower energy flows, respectively. Our observations demonstrate the importance of ingress for the interstitial accumulation of fine sediment, even during events with flow above the critical threshold conditions for fine sediment gravitational deposition. Despite the comparable ingress rates to other studies, no interstitial clogging was observed in this study, demonstrating the channel potential storage capacity, which has implications for legacy impacts from landscape disturbances in the Crowsnest River catchment. [ABSTRACT FROM AUTHOR]

Diffuse pollutant transfers from agricultural land often constitute the bulk of annual loads in catchments and storm events dominate these fluxes. There remains a lack of understanding of how pollutants move through catchments at different scales. This is critical if the mismatch between the scales used to implement on-farm management strategies, compared to those used for assessment of environmental quality, is to be addressed. The aim of this study was to understand how the mechanisms of pollutant export may change when assessed at different scales and the corresponding implications for on-farm management strategies. A study was conducted within a 41 km2 catchment containing 3 nested sub-catchments, instrumented to monitor discharge and various water quality parameters. Storm data over a 24-month period were analysed and hysteresis (HI) and flushing (FI) indices calculated for two water quality variables that are typically of environmental significance; NO 3 –N and suspended sediment (SSC). For SSC, increasing spatial scale had little effect on the mechanistic interpretation of mobilisation and the associated on-farm management strategies. At the three smallest scales NO 3 –N was chemodynamic with the interpretation of dominant mechanisms changing seasonally. At these scales, the same on-farm management strategies would be recommended. However, at the largest scale, NO 3 –N appeared unaffected by season and chemostatic. This would lead to a potentially very different interpretation and subsequent on-farm measures. The results presented here underscore the benefits of nested monitoring for extracting mechanistic understanding of agricultural impacts on water quality. The application of HI and FI indicates that monitoring at smaller scales is crucial. At large scales, the complexity of the catchment hydrochemical response means that mechanisms become obscured. Smaller catchments more likely represent critical areas within larger catchments where mechanistic understanding can be extracted from water quality monitoring and used to underpin the selection of on-farm mitigation measures. • Nested hydrochemical monitoring undertaken in a headwater catchment. • HI and FI indices calculated for NO 3 –N and suspended sediment (SSC) for all sites. • NO 3 –N was chemodynamic at most scales and displayed seasonal variability. • SSC was chemodynamic but consistent across spatial and temporal scales. • Mechanistic understanding informs mitigation but is affected by scale of assessment. [ABSTRACT FROM AUTHOR]

Highlights: [•] Highlights principle data issues for change detection in hydrochemistry. [•] An extensive assessment of detection methods and their assumptions is presented. [•] Provides an evaluation of statistical power of the change detection methods. [•] Conceptual framework for choosing a robust change detection methodology is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Deposition and storage of fine sediment on channel beds can represent an important component of catchment sediment budgets and can therefore have implications for particulate phosphorus (PP) transfers. Accordingly, spatial and temporal variations in the phosphorus (P) content of fine (<63 μm) bed sediment and associated P storage have been studied in three UK lowland permeable catchments, the Pang and Lambourn (Berkshire) and the Tern (Shropshire). These catchments were chosen because of their contrasting geologies. Fine bed sediment was sampled in representative reaches on a bi-monthly basis using a re-suspension technique, and analysed for total P, a range of P fractions and particle size. The results demonstrate significant spatial and temporal variability in PP concentrations and storage both between and within the study catchments, with concentrations and storage of PP higher in the Tern catchment than in the Pang and Lambourn, mainly due to the contrasting geologies and different land management practices in the catchments. Maximum and minimum PP concentrations and storage occurred in late summer and winter, respectively. It was concluded that geology played an important role in P storage associated with fine bed sediments. [Copyright &y& Elsevier]

There is a need to model and predict the transfer of phosphorus (P) from land to water, but this is challenging because of the large number of complex physical and biogeochemical processes involved. This study presents, for the first time, a ‘limits of acceptability’ approach of the Generalized Likelihood Uncertainty Estimation (GLUE) framework to the Soil and Water Assessment Tool (SWAT), in an application to a water quality problem in the Newby Beck catchment (12.5 km 2 ), Cumbria, United Kingdom (UK). Using high frequency outlet data (discharge and P), individual evaluation criteria (limits of acceptability) were assigned to observed discharge and P loads for all evaluation time steps, identifying where the model was performing well/poorly and to infer which processes required improvement in the model structure. Initial limits of acceptability were required to be relaxed by a substantial amount (by factors of between 5.3 and 6.7 on a normalized scale depending on the evaluation criteria used) in order to gain a set of behavioral simulations (1001 and 1016, respectively out of 5,000,000). Of the 39 model parameters tested, the representation of subsurface processes and associated parameters, were consistently shown as critical to the model not meeting the evaluation criteria, irrespective of the chosen evaluation metric. It is therefore concluded that SWAT is not an appropriate model to guide P management in this catchment. This approach highlights the importance of high frequency monitoring data for setting robust model evaluation criteria. It also raises the question as to whether it is possible to have sufficient input data available to drive such models so that we can have confidence in their predictions and their ability to inform catchment management strategies to tackle the problem of diffuse pollution from agriculture. [ABSTRACT FROM AUTHOR]

Excessive sediment pressure on aquatic habitats is of global concern. A unique dataset, comprising instantaneous measurements of deposited fine sediment in 230 agricultural streams across England and Wales, was analysed in relation to 20 potential explanatory catchment and channel variables. The most effective explanatory variable for the amount of deposited sediment was found to be stream power, calculated for bankfull flow and used to index the capacity of the stream to transport sediment. Both stream power and velocity category were highly significant ( p ≪ 0.001), explaining some 57% variation in total fine sediment mass. Modelled sediment pressure, predominantly from agriculture, was marginally significant ( p < 0.05) and explained a further 1% variation. The relationship was slightly stronger for erosional zones, providing 62% explanation overall. In the case of the deposited surface drape, stream power was again found to be the most effective explanatory variable ( p < 0.001) but velocity category, baseflow index and modelled sediment pressure were all significant ( p < 0.01); each provided an additional 2% explanation to an overall 50%. It is suggested that, in general, the study sites were transport-limited and the majority of stream beds were saturated by fine sediment. For sites below saturation, the upper envelope of measured fine sediment mass increased with modelled sediment pressure. The practical implications of these findings are that (i) targets for fine sediment loads need to take into account the ability of streams to transport/retain fine sediment, and (ii) where agricultural mitigation measures are implemented to reduce delivery of sediment, river management to mobilise/remove fines may also be needed in order to effect an improvement in ecological status in cases where streams are already saturated with fines and unlikely to self-cleanse. [ABSTRACT FROM AUTHOR]