Damaged Road Verges Research Articles

Are source groups always appropriate when sediment fingerprinting? The direct comparison of source and sediment samples as a methodological step

AbstractThe 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.

Fingerprinting source contributions to bed sediment‐associated organic matter in the headwater subcatchments of the River Itchen SAC, Hampshire, UK

AbstractExcessive accumulation of sediment‐associated organic matter in river beds has detrimental impacts on aquatic ecology, including fish. Sediment and source samples were collected from 3 headwater tributaries of the River Itchen, in southern England. Near infrared spectra and bulk stable carbon and nitrogen isotopes were employed as fingerprint properties to quantify the relative contributions from catchment‐based (farmyard manures/slurries, damaged road verges, and septic tanks) and channel‐based (decaying instream vegetation, watercress farms, and fish farms) sources. The findings suggested that over the duration of the sampling period, the final estimated median relative contributions in the Candover Stream subcatchment were in the order: farmyard measures/slurries 74% > decaying instream vegetation 15% > watercress farms 6% > septic tanks 3% > damaged road verges 2%. For the River Arle subcatchment, corresponding estimated median relative contributions were in the order: watercress farms 40% > farmyard manures/slurries 28% > decaying instream vegetation 21% > fish farms 7% > damaged road verges and septic tanks 2% each. Similar contributions were estimated for the Tichborne Stream subcatchment: watercress farms 36% > farmyard manures/slurries 26% > decaying instream vegetation 26% and damaged road verges and septic tanks at 6% each. These source apportionment estimates will contribute to stakeholder engagement and targeted management interventions.

Sediment-associated organic matter sources and sediment oxygen demand in a Special Area of Conservation (SAC): A case study of the River Axe, UK.

Oxygen demand in river substrates providing important habitats for the early life stages of aquatic ecology, including lithophilous fish, can arise due to the oxidation of sediment‐associated organic matter. Oxygen depletion associated with this component of river biogeochemical cycling, will, in part, depend on the sources of such material. A reconnaissance survey was therefore undertaken to assess the relative contributions from bed sediment‐associated organic matter sources potentially impacting on the River Axe Special Area of Conservation (SAC), in SW England. Source fingerprinting, including Monte Carlo uncertainty analysis, suggested that the relative frequency‐weighted average median source contributions ranged between 19% (uncertainty range 0–82%) and 64% (uncertainty range 0–99%) for farmyard manures or slurries, 4% (uncertainty range 0–49%) and 35% (uncertainty range 0–100%) for damaged road verges, 2% (uncertainty range 0–100%) and 68% (uncertainty range 0–100%) for decaying instream vegetation, and 2% (full uncertainty range 0–15%) and 6% (uncertainty range 0–48%) for human septic waste. A reconnaissance survey of sediment oxygen demand (SOD) along the channel designated as a SAC yielded a mean SOD5 of 4 mg O2 g−1 dry sediment and a corresponding SOD20 of 7 mg O2 g−1 dry sediment, compared with respective ranges of 1–15 and 2–30 mg O2 g−1 dry sediment, measured by the authors for a range of river types across the UK. The findings of the reconnaissance survey were used in an agency (SW region) catchment appraisal exercise for informing targeted management to help protect the SAC.

Does fine sediment source as well as quantity affect salmonid embryo mortality and development?

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 (<63μm) 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.

High‐temporal resolution fluvial sediment source fingerprinting with uncertainty: a Bayesian approach

ABSTRACTThis contribution addresses two developing areas of sediment fingerprinting research. Specifically, how to improve the temporal resolution of source apportionment estimates whilst minimizing analytical costs and, secondly, how to consistently quantify all perceived uncertainties associated with the sediment mixing model procedure. This first matter is tackled by using direct X‐ray fluorescence spectroscopy (XRFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses of suspended particulate matter (SPM) covered filter papers in conjunction with automatic water samplers. This method enables SPM geochemistry to be quickly, accurately, inexpensively and non‐destructively monitored at high‐temporal resolution throughout the progression of numerous precipitation events. We then employed a Bayesian mixing model procedure to provide full characterization of spatial geochemical variability, instrument precision and residual error to yield a realistic and coherent assessment of the uncertainties associated with source apportionment estimates. Applying these methods to SPM data from the River Wensum catchment, UK, we have been able to apportion, with uncertainty, sediment contributions from eroding arable topsoils, damaged road verges and combined subsurface channel bank and agricultural field drain sources at 60‐ and 120‐minute resolution for the duration of five precipitation events. The results presented here demonstrate how combining Bayesian mixing models with the direct spectroscopic analysis of SPM‐covered filter papers can produce high‐temporal resolution source apportionment estimates that can assist with the appropriate targeting of sediment pollution mitigation measures at a catchment level. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.

Catchment source contributions to the sediment-bound organic matter degrading salmonid spawning gravels in a lowland river, southern England

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.

Contemporary fine‐grained bed sediment sources across the River Wensum Demonstration Test Catchment, UK

AbstractBecause the sources of fine‐grained sediment problems in river systems are diffuse, it is essential to assemble catchment scale information for informing management strategies. Sediment source‐tracing procedures have increasingly been adopted in this respect. Accordingly, a recently refined composite tracing procedure was used to investigate contemporary sources of fine‐grained channel bed sediment in 11 sub‐catchments (364 km2) of the River Wensum Demonstration Test Catchment, in the eastern UK. The procedure incorporated a combination of statistical tests for discriminating source end members, plus numerical mass balance modelling incorporating weightings for within‐source tracer variations and tracer‐specific discriminatory power, as well as a combination of local and genetic algorithm optimisation coupled with Monte Carlo uncertainty analysis. Replicate Monte Carlo runs demonstrated the convergence of the modelling outputs within ±1% of the average medians. Relative frequency‐weighted average median source type contributions were estimated to range between 27%–69% (agricultural topsoils; predicted deviate median inputs 0%–98% and 9%–100%), 0%–38% (damaged road verges; predicted deviate median inputs 0%–58% and 0%–100%) and 21%–48% (channel banks/subsurface sources; predicted deviate median inputs 0%–50% and 4%–50%). The study provides further evidence of the importance of channel banks and damaged road verges as sediment sources and the need to include such areas in catchment sediment management strategies. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Using a novel tracing‐tracking framework to source fine‐grained sediment loss to watercourses at sub‐catchment scale

AbstractAlthough 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 &amp; Sons, Ltd.

Sediment source tracing in a lowland agricultural catchment in southern England using a modified procedure combining statistical analysis and numerical modelling

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.

Quantifying fine‐grained sediment sources in the River Axe catchment, southwest England: application of a Monte Carlo numerical modelling framework incorporating local and genetic algorithm optimisation

AbstractIncreasing recognition of the deleterious environmental effects of excessive fine sediment delivery to watercourses means that reliable sediment source assessment represents a fundamental component of catchment planning targeting the protection of freshwater resources and their ecological integrity. Sediment tracing or fingerprinting approaches have been increasingly used to provide catchment scale sediment source information, but there is a need to continue refining existing procedures especially with respect to uncertainty analysis during mass balance modelling. Consequently, an updated Monte Carlo numerical modelling framework was devised and tested, incorporating both conventional and robust statistics coupled with random and Latin Hypercube Sampling (LHS) together with local and genetic algorithm (GA) optimisation. A sediment sourcing study undertaken in the River Axe catchment, southwest England, suggested that the use of robust statistics and LHS with GA optimisation generated the best performance with respect to predicting measured bed sediment geochemistry in six out of eight model applications. On this basis, the catchment‐wide average median sediment source contributions were predicted to be 38 ± 1% (pasture topsoils), 3 ± 1% (cultivated topsoils), 37 ± 1% (damaged road verges) and 22 ± 1% (channel banks/subsurface sources). Using modelling frameworks which provide users with flexibility to compare local and global optimisation during uncertainty analysis is recommended for future sediment tracing studies. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment, southern United Kingdom

AbstractDiffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub‐catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time‐integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub‐catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub‐catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02–27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub‐catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub‐catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15–20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Apportioning catchment scale sediment sources using a modified composite fingerprinting technique incorporating property weightings and prior information

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 33–829 kg ha − 1 yr − 1 , 30–1995 kg ha − 1 yr − 1 , 2–315 kg ha − 1 yr − 1 , 0–217 kg ha − 1 yr − 1 , and 0–28 kg ha − 1 yr − 1 . Sediment fingerprinting should always include uncertainty analysis but on the understanding that the latter will be conditional on the assumptions used.

Particulate organic carbon sources and delivery to river channels in the Somerset Levels ECSFDI priority catchment, southwest UK

Soil erosion and sediment delivery represent an important transport pathway for particulate organic carbon (POC) in fluvial systems. Catchment management strategies designed to protect soil resources therefore require reliable information on the significance of key sediment sources for POC transfers. Within this context, a composite fingerprinting procedure, incorporating uncertainty and prior understanding of catchment processes, was used to investigate the significance of eroding pasture or cultivated topsoils, damaged road verges, channel banks/subsurface sources and point source discharges as POC sources and the associated net delivery to river channels across the Somerset Levels, southwest UK. Overall mean relative contributions of POC from the five individual sediment sources were estimated at 41 ± 2% (pasture topsoils), 18 ± 1% (STWs), 15 ± 2% (cultivated topsoils), 14 ± 1% (damaged road verges) and 12 ±2% (channel banks/subsurface sources). Respective estimates of net sediment‐associated POC delivery to watercourses, provided by integrating sediment source ascription 50th percentiles bounded by 95% confidence limits, organic carbon content, sediment yield ranges and sub‐catchment or land use areas, ranged between 2.4–48.5 kg ha−1 yr−1, 0–16.5 kg ha−1 yr−1, 1.7–119.2 kg ha−1 yr−1, 0–13.8 kg ha−1 yr−1 and 0–7.4 kg ha−1 yr−1.