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Excess fine sediment is a global cause of lotic ecosystem degradation. Despite historic interest in identifying sediment sources and quantifying instream dynamics, tackling fine sediment problems remains a key challenge for river managers and a continued focus of international research. Accordingly, a national meeting of the British Hydrological Society brought together those working on fine sediment issues at the interface of hydrology, geomorphology, and ecology. The resulting collection of papers illustrates the range of research being undertaken in this interdisciplinary research arena, by academic researchers, environmental regulators, landowners, and consultants. More specifically, the contributions highlight key methodological advancements in the identification of fine sediment sources, discuss the complexities surrounding the accurate quantification of riverbed fine sediment content, demonstrate the potential utility of faunal traits as a biological monitoring tool, and recognize the need for improved mechanistic understanding of the functional responses of riverine organisms to excess fine sediment. Understanding and mitigating the effects of fine sediment pressures remains an important and multifaceted problem that requires interdisciplinary collaborative research to deliver novel and robust management tools and sustainable solutions. [ABSTRACT FROM AUTHOR]

Accessible sediment provenance information is highly desirable for guiding targeted interventions for reducing excess diffuse agricultural sediment losses to water. Conventional sediment source fingerprinting methods can provide this information, but at high cost, thereby limiting their widespread application for catchment management. The use of sediment colour measured using an office document scanner represents an easy, fast, and inexpensive alternative method to trace sediment sources. However, the potential for poor source discrimination and its non-conservatism due to enrichment in sediment organic matter content during sediment transport represent possible limitations to its use. As such, the treatment of samples using hydrogen peroxide to remove organic matter can potentially improve source discrimination based upon geology or soil type, and the mapping of differences in colour between source and sediment samples removing the need for a priori source groups, were trialled in a new colour-based tracing framework. The River Avon in southwest England and Holbeck/Wath Beck in northeast England were studied as they have been identified as being of high priority for the targeting of on-farm advice delivered through a long-running agri-environment initiative. In both catchments, colour was effective at identifying that a small proportion of each which would be considered as being low erosion risk was the dominant source of the sampled sediment. This was due to poor connectivity between fields deemed to be at high risk of erosion and stream channels. The hydrogen peroxide sample treatment confirmed that sediment colour was not significantly altered by enrichment in organic matter content. This treament and the mapped comparison between source and suspended sediment colour improved source discrimination allowing for the more spatially-refined identification of critical sediment source areas. It is argued that this new inexpensive procedure can potentially deliver more precise and reliable information to catchment managers than costly quantitative sediment source fingerprinting methods. This method can greatly increase the availability of catchment-specific sediment source data and therefore the robust targeting of management efforts on a national scale. • Colour was effective at tracing sediment sources in both catchments. • Hydrogen peroxide treatment significantly improved source discrimination. • Sediment losses were from a small part of each catchment with a low erosion risk. • The proposed method can out perform quantiative fingerprinting methods. • The inexpensively generated data can improve catchment management support. [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: 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]

Abstract: There is increasing recognition that fine sediment represents an important diffuse source pollutant in surface waters, due to its role in governing the transfer and fate of many substances, including nutrients, heavy metals, pesticides and other organic contaminants, and because of its impacts on aquatic ecology. Catchment management strategies therefore frequently need to include provision for the control of sediment mobilisation and delivery. The sediment budget concept provides a valuable framework for assisting the management and control of diffuse source sediment pollution and associated problems, by identifying the key sources and demonstrating the importance of intermediate stores and the likely impact of upstream mitigation strategies on downstream suspended sediment and sediment-associated contaminant fluxes. Accordingly, the utility of the sediment budget concept for catchment management is further discussed, by introducing examples from several contrasting river basins. [Copyright &y& Elsevier]

Summary: Information on suspended sediment and particulate P (PP) sources is an important requirement in many catchment-based diffuse source pollution studies, in order to assist with model validation and to provide information to support the development of effective sediment and phosphorus control strategies. Such information is, however, frequently unavailable or difficult to assemble. In the study reported, source fingerprinting procedures were successfully used to assemble this information for seven sub-catchments in the Hampshire Avon catchment and five sub-catchments in the Middle Herefordshire Wye catchment. The results provide important new information on the relative importance of the contributions from surface and channel/subsurface sources to the suspended sediment and PP fluxes from the catchments. In the Wye sub-catchments channel/subsurface sources contributed 40–55% of the overall suspended sediment flux and 21–43% of the PP flux from the catchments. Equivalent values for the Avon were 1–41% and 1–54%, respectively. Combination of the information on the relative importance of surface and channel/subsurface sources with measured suspended sediment fluxes has provided the first estimates of the specific fluxes of sediment and PP attributable to channel/subsurface sources for UK catchments. The former are as high as 15–20tkm−2 year−1 in some of the Wye sub-catchments, whereas the latter exceeded 0.1kgPha−1 year−1 in the same sub-catchments. The results emphasize the need to take account of potential contributions from channel/subsurface sources when using measured suspended sediment and PP flux data to validate predictions derived from models incorporating only surface contributions. [Copyright &y& Elsevier]

Abstract: Groundwater-fed, lowland permeable catchments in the UK are particularly susceptible to fine sediment accumulation on the bed of their main channel systems. Appropriate catchment management solutions are therefore required. Accurate targeting of sediment abatement strategies is, however, hampered by the dearth of reliable information on the principal sediment sources involved. In view of this, a composite fingerprinting technique, incorporating uncertainty analysis, has been used to investigate the primary sources of fine sediment samples recovered from a total of 18 individual sampling sites on the channel bed of the rivers Frome (∼ 437 km2) and Piddle (∼ 183 km2), Dorset, UK. In the Frome study catchment, mean relative contributions from areas of woodland, pasture and cultivation, and from channel banks/subsurface sources ranged between 1±1%–6±2%, 10±2%–42±2%, 44±4%–81±2% and 7±2%–19±4%, respectively. The corresponding mean relative contributions in the Piddle study area were 1±1%–11±4% (woodland), 10±2%–28±4% (pasture), 44±2%–80±2% (cultivated) and 7±2%–21±2% (channel banks and subsurface sources). These findings have important implications for establishing a scientific basis for assisting the targeting of sediment management and control policies. [Copyright &y& Elsevier]

Summary: An integrated approach to data collection, combining the use of 137Cs measurements, sediment source fingerprinting, bed sediment surveys and conventional river monitoring, has been successfully employed to establish the fine-grained sediment budgets of two lowland groundwater-fed catchments in the UK. Gross surface erosion is higher on cultivated land (Pang: 55263tyr−1 or 507tkm−2 yr−1; Lambourn: 79997tyr−1 or 437tkm−2 yr−1) than on pasture (Pang: 1960tyr−1 or 140tkm−2 yr−1; Lambourn: 1425tyr−1 or 95tkm−2 yr−1) in both study areas and a substantial proportion of the mobilized sediment is sequestered within the fields (Pang: 28058tyr−1 or 228tkm−2 yr−1; Lambourn: 55575tyr−1 or 281tkm−2 yr−1) and between the individual fields and the river channel network (Pang: 28672tyr−1 or 233tkm−2 yr−1; Lambourn: 24782tyr−1 or 125tkm−2 yr−1). The sediment contribution from banks and subsurface sources is relatively low and typically ca. 5tyr−1 in the Pang and ca. 11tyr−1 in the Lambourn, representing only about 1% of the suspended sediment output from each study catchment. The mean level of fine-grained sediment storage in the main channel system is equivalent to 38% (Pang) and 21% (Lambourn) of the respective mean annual suspended sediment yields of the two catchments. The estimated sediment delivery ratio for both study catchments is ca. 1%. [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]

Fine sediments are known to be an important cause of increased mortality in benthic spawning fish. To date, most of the research has focussed on the relationship between embryo mortality and the quantity of fine sediment accumulated in the egg pocket. However, recent evidence suggests a) that the source of fine sediment might also be important, and b) that fitness of surviving embryos post-hatch might also be impacted by the accumulation of fine sediments. In this paper, we report an experiment designed to simulate the incubation environment of brown trout ( Salmo trutta ) and Atlantic salmon ( Salmo salar ). During the experiment, the incubating embryos were exposed to different quantities of fine (< 63 μm) sediment derived from four different sources; agricultural topsoils, damaged road verges, eroding river channel banks and tertiary level treated sewage. Results showed that mass and source are independently important for determining the mortality and fitness of alevin. Differences between species were observed, such that brown trout are less sensitive to mass and source of accumulated sediment. We demonstrate for the first time that sediment source is an additional control on the impact of fine sediment, and that this is primarily controlled by the organic matter content and oxygen consumption of the catchment source material. [ABSTRACT FROM AUTHOR]