Fine Sediment Accumulation Research Articles

The magnitude and significance of sediment oxygen demand in gravel spawning beds for the incubation of salmonid embryos

AbstractGlobally, salmon populations are under pressure and in those where numbers are severely depleted, density independent factors such as the accumulation of fine sediment and subsequent mortality of incubating embryos are critical factors in their conservation. Although progress has been made in identifying the processes by which fine sediment can lead to embryo mortality, this has focussed on the physical blockage of gravel pores. This paper presents new knowledge on the role of sediment‐associated organic matter in controlling the supply of dissolved oxygen to incubating salmon embryos within gravel river beds. We report a new approach to the measurement of sediment oxygen demand (SOD) from interstitial sediments accumulated within salmon redds and demonstrate this across a range of salmon river types. The effects of varying SOD on dissolved oxygen supply to incubating salmon embryos are quantified for the first time, using the physically based Sediment Intrusion and Dissolved Oxygen (SIDO‐UK) model. The results reveal the importance of the mass of accumulating sediment and sediment consumption rates (sediment oxygen consumption [SOC]), which constitute the overall SOD over time for a particular sediment sample. Higher SOC result in reductions in dissolved oxygen that are deleterious to salmonids; however, these are subordinate to the effects of sediment mass. Larger quantities of sediment accumulating within the redd not only create a higher SOD but also physically block the pores within the gravels, leading to a more drastic decline in oxygen supply through the combined effects of reduced seepage velocity and dissolved oxygen concentration. We seek to generalize the results by exploring the influence of catchment characteristics on field measures of SOD and SOC. This work makes a significant and novel contribution to improving our fundamental understanding of hyporheic processes within salmonid spawning gravels whilst providing resource managers with evidence of the deleterious effects of sediment‐associated organic matter on salmon recruitment.

The complexities of measuring fine sediment accumulation within gravel‐bed rivers

AbstractFine sediment storage within gravel beds is a key component of catchment sediment budgets and affects the health of benthic and hyporheic habitats. Here, we assess the performance of two substrate infiltration traps for the characterization of fine sediment (<2 mm) accumulation. One design, the vertically extending sediment trap, permits both lateral and vertical exchange in the sediment column, whereas the second type, a more traditional fixed‐area sediment trap with impermeable side walls, permits only vertical exchange. Traps were deployed at three sites on the River Tame, Birmingham (UK), over varying installation periods (14–401 days). Results indicate that the facilitation of multiple pathways of exchange within the vertically extending sediment traps (vertical and lateral) resulted in a significantly greater amount of fine sediment being accumulated than in adjacent fixed‐area sediment traps. This suggests that lateral transport is an important component contributing to fine sediment accumulation. However, there are notable and inherent problems associated with the use of different types of sediment trap and in the way the data should be presented and interpreted. This paper discusses the practical implications of the study findings and reflects on the complexities of undertaking accurate sediment deposition measurements in the field.

Subsurface flow in lowland river gravel bars

AbstractGeomorphic and hydraulic processes, which form gravel bars in large lowland rivers, have distinctive characteristics that control the magnitude and spatial patterns of infiltration and exfiltration between rivers and their immediate subsurface environments. We present a bedform‐infiltration relation together with a set of field measurements along two reaches of the San Joaquin River, CA to illustrate the conditions required for infiltration and exfiltration of flow between a stream and its undulating bed, and a numerical model to investigate the factors that affect paths and residence times of flow through barforms at different discharges. It is shown that asymmetry of bar morphology is a first‐order control on the extent and location of infiltration, which would otherwise produce equal areas of infiltration and exfiltration under the assumption of sinusoidal bedforms. Hydraulic conductivity varies by orders of magnitude due to fine sediment accumulation and downstream coarsening related to the process of bar evolution. This systematic variability not only controls the magnitude of infiltration, but also the residence time of flow through the bed. The lowest hydraulic conductivity along the reach occurred where the difference between the topographic gradient and the water‐surface gradient is at a maximum and thus where infiltration would be greatest into a homogeneous bar, indicating the importance of managing sand supply to maintain the ventilation and flow through salmon spawning riffles. Numerical simulations corroborate our interpretation that infiltration patterns and rates are controlled by distinctive features of bar morphology.

How to assess the impact of fine sediments on the macroinvertebrate communities of alpine streams? A selection of the best metrics

Excessive fine sediment accumulation (i.e., siltation) in streams and rivers originates from several human activities and globally results in heavy alterations of aquatic habitats and biological communities. In this study the correlation between fine sediment and several benthic invertebrate community metrics was tested through a manipulative approach in alpine streams, where siltation mainly results as a physical alteration (i.e., the clogging of substrate interstices) without the influence of co-occurring confounding factors. We selected 12 candidate metrics, belonging to three different categories: compositional, structural and functional. We first carried out a manipulative experiment where artificial substrates were used to provide standardized conditions of siltation. All candidate metrics were calculated for each artificial substrate and the selection of the best combination of metrics was statistically performed with an information-theoretic approach. All candidate metrics were calculated both at family level and also at a mixed level (family and genus) in order to account for the systematic resolution. Then, data from a field study on alpine streams affected by mining activities were used as independent dataset for testing the performance of the selected metrics. We found that the total taxa richness, the EPT (Ephemeroptera, Plecoptera and Trichoptera) richness and the abundance of benthic invertebrates associated to rheophilous conditions and coarse mineral substrates were the most sensitive metrics. When these metrics were aggregated into a multimetric index in the validation dataset, we observed high and significant correlations between index values and the quantity of fine sediment for both taxonomic levels, especially for the mixed level. The findings of this study provide useful tools for biomonitoring the effects of fine sediment in low order, mountainous streams and contribute to improve our diagnostic ability on stressor-specific alterations.

Key hydraulic drivers and patterns of fine sediment accumulation in gravel streambeds: A conceptual framework illustrated with a case study from the Kiewa River, Australia

Fine sediment processes in gravel beds may have significant impacts to overall river ecosystem function. In addition to gravitational deposition, horizontal intragravel transport has been recognized to influence fine sediment accumulation. However, the specific hydraulic mechanisms and origin of fine sediment movement are not clearly identified. The purpose of this study was to investigate key hydraulic drivers and patterns of fine sediment accumulation. Using a conceptual framework to set the scene, we implemented an experimental setup in a gravel lateral bar subject to irregular flow fluctuations in the Kiewa River (Australia). We installed nine sets of sediment collector pairs and piezometers into the gravel. Each pair included one horizontally and one horizontally-vertically perforated collector. Mid-range, rather than peak flows, covering the site in water drove fine sediment deposited in the collectors. We estimated horizontal contribution to final deposition as 59%. Such contribution resulted from shear stresses >3Nm−2 promoting streamwise near-bed turbulence at the water-sediment interface during flooded conditions. Despite high subsurface hydraulic gradients, intragravel transport in the lower sediment layers via Darcy flow did not show any influence to fine sediment deposition. Our findings contribute to an improved understanding of fine sediment accumulation processes, key for overall river ecosystem functioning, particularly in regulated rivers.

The pernicious problem of streambed colmation: a multi‐disciplinary reflection on the mechanisms, causes, impacts, and management challenges

The accumulation of fine sediments in rivers is a pernicious problem with wide‐ranging consequences for the healthy functioning of rivers throughout the world. It is linked to a range of landuse changes and human activities that have increased sediment inputs leading to elevated fine sediment loads that exceed the sediment transport capacities of rivers. Surficial deposits of fine material can also create the conditions for fine sediment to move into and accumulate within the coarser bed substrate, a process known as colmation and the focus of this review. Colmation, also referred to as clogging, fine sediment infiltration, fine sediment deposition, ingress, infilling, intrusion of fines, siltation, and the surface–subsurface exchange of particles, is particularly damaging to river habitats and ecosystems. It causes degradation through the physical effects of reduced porosity and flow connectivity and the biogeochemical changes arising from the hydraulic and hydrological impacts and the effects of sediment‐bound contaminants, all of which can impact on river ecology. Different aspects of the phenomenon of colmation have been studied across a number of disciplines and over several decades and this paper synthesizes this wide literature to provide a multidisciplinary perspective on the mechanisms, causes, and impacts of colmation and discusses some key management challenges. WIREs Water 2017, 4:e1231. doi: 10.1002/wat2.1231This article is categorized under: Water and Life > Stresses and Pressures on Ecosystems Science of Water > Water Quality

Disrupted carbon cycling in restored and unrestored urban streams: Critical timescales and controls

AbstractCarbon fixation and respiration in flowing waterways play significant roles in global and regional carbon budgets, yet how land use and watershed management interact with temporal disturbances (storms) to influence metabolism remains poorly understood. Here, we combine long‐term with synoptic sampling of metabolism and its variable controls in neighboring watersheds of the Chesapeake Bay to resolve limiting factors and critical timescales associated with recovery from disturbance. We found that, relative to predictions of the river continuum concept, focal streams have “disrupted” carbon cycles, with carbon balances closer to zero, and, in some cases, tighter coupling between gross primary production (GPP) and ecosystem respiration (ER), attributable to carbon limitation. Carbon became limiting to ER where flashy storm hydrographs and simplified channel geomorphology inhibited accumulation of fine sediment. Shannon entropy analysis of timescales revealed that fine sediment served as a time‐release capsule for nutrients and carbon over 4–6 months, fueling biogeochemical transformations. Loss of fines through hydraulic disturbance had up to 30‐d impacts on GPP and 50‐d impacts on ER in the stream with carbon limitation. In contrast, where GPP and ER were not tightly coupled, recovery occurred within 1 d. Results suggest that a complex interplay between nutrient and carbon limitation and mechanical and chemical disturbance governs patterns and consequences of disrupted carbon cycling in urban streams. Carbon limitation and tight GPP/ER coupling enhance the vulnerability of stream ecosystem functions, but best management practices that target stormflow reduction and channel geomorphic diversity can break that coupling and minimize carbon cycle disruptions.

Trophic availability buffers the detrimental effects of clogging in an alpine stream

Clogging, the streambed colmation by fine sediments, is an important widespread source of impact affecting freshwaters. Alterations in stream morphology and hydrology, added to the effects of global climate change, are responsible for this phenomenon, that is particularly pernicious in mountainous lotic systems naturally characterized by coarse substrates. Among the studies investigating this issue some were descriptive, while others used artificial substrates to compare ongoing fine sediment accumulation and macroinvertebrate assemblage recruitment. Other studies used from the outset artificial substrates arranged with different levels of clogging. Our study fits into this line, but adding an innovative element simulating different availability of coarse particulate organic matter, i.e. the main trophic input in low-order, mountainous stream. To investigate how clogging and CPOM can influence macroinvertebrate communities, we placed 135 artificial substrates in the upper Po river (NW Italy). We set up a three way factorial design with three different levels of sedimentation and terrestrial leaf material. Artificial substrates were removed on three different dates. Benthic invertebrates were identified and classified according to their bio-ecological traits. We also measured macroinvertebrate dry mass and CPOM degradation in the different trap types. Our findings show that clogging acts as a selective filter influencing taxa richness, density, functional composition and biomass of benthic assemblage. Moreover, fine sediments affect the energetic dynamics in the river ecosystem, decreasing the mass loss rate of terrestrial leaves. Interestingly, our results clearly demonstrate that high availability of CPOM can buffer the negative effect of clogging, suggesting that an adequate input of allochthonous organic matter may lessen the impact of fine sediment deposition. Because land use transformation and removal of wooded riparian areas increase clogging and simultaneously reduces the input of CPOM, our findings stress the importance to include the management of river basins in the conservation strategies of mountainous streams.

Effects of vegetation on turbulent flow structure in groyne fields

ABSTRACTFlow recirculation in groyne fields promotes accumulation of fine sediments and development of riparian and aquatic vegetation. Although flow hydrodynamics in groyne fields is subject of intensive ongoing research, knowledge of vegetation effects on recirculating flow remains lacking. This paper reports the results of field experiments in a natural river comprising large-scale groyne models populated with rigid and flexible artificial vegetation. In the experimental runs population density, submergence ratios, and vegetation types were varied. The results show that vegetation rearranges twin-circulation flow into slow backwater flow. The magnitude of backwater flow is controlled by the bio-mechanical properties of vegetation. The hydrodynamics of the flow interface between the main river and groyne fields was only slightly altered by vegetation. Analytical models of flow at the interface and inside vegetated areas agree well with these experimental results.

Mapping the combined risk of agricultural fine sediment input and accumulation for riverine ecosystems across England and Wales

Fine sediment inputs from agricultural sources are a potential threat to freshwater ecosystems and may impact on the ability of EU members⿿ states to achieve environmental targets under the Water Framework Directive (WFD).An index (the Agricultural Sediment Risk index or ASR) representing the risk of agricultural fine sediment accumulation in rivers was produced using estimates of sediment inputs from the process-based PSYCHIC model and predictions of fine sediment accumulation using River Habitat Survey data. The ASR was mapped across the entire river network of England and Wales.The ASR map and index were combined with a national dataset of fisheries surveys using logistic regression to test its relevance to freshwater biota. The ASR was strongly associated with a group of species sensitive to fine sediment inputs including salmon and trout. Another group of species including roach and perch showed a positive association with low levels of agricultural sediment inputs potentially due to their impacts on predators and competitors.The proposed approach demonstrates how existing national monitoring data and sediment pressure models can be combined to produce an assessment of risk to aquatic ecosystems from agricultural fine sediment sources at a national scale that can be used alongside WFD classification tools to identify potential causative pressures and design remedial actions.

Effects of invasive crayfish on fine sediment accumulation, gravel movement, and macroinvertebrate communities

AbstractCrayfish are one of the most prolific freshwater invaders, yet the role of crayfish as ecosystem engineers that structure benthic substrates in their nonnative habitat is rarely studied. We used an in situ experimental manipulation to document changes in sediment dynamics and macroinvertebrate density and richness caused by the presence or absence of invasive rusty crayfish (Orconectes rusticus). Rusty crayfish reduced fine-sediment accumulation and increased pit and mound structures in the river bed by moving gravels at the bed surface. We predicted that this omnivorous species would directly reduce macroinvertebrate density and richness, but we found that macroinvertebrate density was higher in treatments with rusty crayfish present and that macroinvertebrate richness did not differ between treatments with and without crayfish. Our findings suggest that rusty crayfish, which are spreading throughout the northeast USA, are probably important engineers of physical habitat structure in stream ecosy...

Fine sediment deposition and interstitial flow effects on macroinvertebrate community composition within riffle heads and tails

The distribution of macroinvertebrates in the heads and tails of riffles were examined in an in situ field experiment under stable baseflow conditions. Paired colonisation cylinders were used to examine the influence of vertical hydraulic exchange (upwelling and downwelling) and horizontal interstitial flow on the patterns of sedimentation and invertebrate colonisation. Sedimentation rates were greatest in cylinders permitting vertical and horizontal flow (VHE cylinders), and were significantly lower (29%) in cylinders where only vertical flow and ingress of fine sediment were possible (VE cylinders). The results demonstrate that horizontal interstitial flows represent an important pathway for fine sediment transport. Differences in fine sediment accumulation were also observed between riffle heads and tails. Significantly higher sedimentation rates were recorded in riffle tails, with the macroinvertebrate communities characterised by larger proportions of fine sediment tolerant taxa. In contrast, riffle head communities were characterised by greater proportions of sediment sensitive taxa, and in the case of VHE cylinders, shredders and EPT taxa. The results demonstrate that spatial differences in fine sediment deposition are evident at the riffle scale as a function of vertical and horizontal subsurface flows and that these factors play a key role in the distribution of macroinvertebrate fauna.

Benthic macroinvertebrate communities response on the fine sediment accumulation in mountain stream

Benthic macroinvertebrate communities response on the fine sediment accumulation in mountain stream

Phosphorus decreases in Lake Geneva but climate warming hampers the recovery of pristine oligochaete communities whereas chironomids are less affected

<p>In response to the decrease of phosphorus concentrations in Lake Geneva (France and Switzerland), the mean percentage of individuals belonging to oligochaete species sensitive to low oxygen concentrations has increased in the profundal from 8% in 1983 to 31% in 2003. But these species decreased anew from 17% in 1999 to 2% in 2009 in the western basin of Lake Geneva (the Small Lake). This shallow basin is more exposed to the effects of warming observed since 1989 than the rest of the lake. To demonstrate these effects, the response of the main species to the increase of organic sedimentation was analysed in the gradient of fine sediment accumulation (FSA), observed in 1999 in the Small Lake. As expected, the abundance of four species classified as sensitive to low oxygen concentrations - <em>Stylodrilus lemani</em>, <em>Embolocephalus velutinus, Bichaeta sanguinea, Paracladopelma nigritula gr. </em>- decreased with the increase of FSA whereas the inverse relationship was observed for four species classified as tolerant <em>Potamothrix vejdovskyi </em>or very tolerant <em>P. hammoniensis, P. heuscheri</em>, and <em>Tubifex tubifex</em>. In contrast, the abundance of three species was not correlated with FSA:<em> Stylodrilus heringianus</em> and<em> Micropsectra contracta</em> both classified as sensitive, <em>Limnodrilus hoffmeisteri </em>as tolerant. The first component of a principal component analysis, based on the mean abundance per transect of the above species, was correlated with FSA. The second component could reflect the long-term increase of water temperature which has been advantageous for <em>Limnodrilus</em> and <em>Micropsectra</em> but disadvantageous for the sensitive oligochaete species less adapted to warm water lakes. Indeed, the abundance of the sensitive oligochaete species and of <em>P. vejdovskyi</em> has decreased from 1994 to 2009 in the Small Lake whereas the abundance of <em>Limnodrilus</em> has increased. <em>Micropsectra </em>and <em>Paracladopelma</em> became more abundant than sensitive oligochaete species. In addition to the effects of temperature, the recovery of the pristine oligochaete community was perhaps impeded in 2009 because the transfer of organic matter to the sediment was increased by the impact of fish (mostly<em> Coregonus</em>) feeding selectively on zooplankton. Finally, many micro pollutants (pesticides, drugs, and other substances) which are present in the lake could have negatively affected sensitive oligochaete species. </p><p> </p>

Mobilising fine sediment in a highly regulated upland snowmelt river using hydrological scaled experimental floods

Significant water diversion, flow variability, and the lack of high flow events can result in altered channel surfaces and morphology through the accumulation of fine sediments within the riverbed. Mitigation of this issue using environmental water often involves single large annual flushing floods as peak discharge is often regarded as the critical hydrological metric for river habitat recovery. We assess the performance of a hydrological scaled flow strategy of five intra-annual experimental floods to mobilise fine sediment below a large reservoir in the Snowy River, Australia. Suspended sediment was measured using a high frequency sampling regime; before, during and post-flood along a longitudinal gradient of 2.2, 24 and 92km. Substantial sediment loads and high peak total suspended solid (TSS) concentrations were produced by the five experimental floods. The first (61.7m3s–1) and fourth (largest at 148.5m3s–1) experimental floods were by far the most effective, producing more than 70% of the total sediment load at each site. The effectiveness of each experimental flood was related to the peak discharge rate, time since flood, and the magnitude increase from the previous event. This study illustrates how a hydrological scaled flood regime can produce effective fine sediment mobilisation within the channel of a highly regulated lotic system.

An Approach to Simulate Interstitial Habitat Conditions During the Incubation Phase of Gravel‐Spawning Fish

AbstractThe incubation period represents an important development phase for successful reproduction of gravel‐spawning fish, whereby colmation processes can affect the quality of the interstitial habitat. From a sedimentary perspective, the infiltration and accumulation of fine sediments can result in a reduction of the pore space and limit the transport of oxygen‐rich surface water in the interstitials of riverbeds. From a biogeochemical perspective, the increased surface area for microbial growth can lead to an increase of respiration rates, which additionally limits the oxygen supply. The assessment and prediction of such processes on interstitial habitat quality represents a challenging task given their complex dynamic interacting processes and their high spatio‐temporal variability. This study presents a new habitat‐based modelling approach, which simulates interstitial habitat suitability (IHS) to evaluate dynamically the quality of interstitial habitat conditions during incubation. For this purpose, three key parameters (hydraulic conductivity, interstitial temperature and hyporheic respiration) are linked to the habitat requirements of different developmental stages during the incubation period (egg, hatching, larvae) via a multivariate fuzzy approach. The proposed modelling concept has been developed on the River Spoel in Switzerland, whereby results of a numerical 3D sediment transport model, together with supplementary measurements, deliver the spatio‐temporal variations of the required input data. The fuzzy approach provides results in form of maps and time series of IHS values to allow for an identification of abiotic bottlenecks during the incubation period. Hence, this approach represents a significant contribution for the restoration of reproduction areas of gravel‐spawning fish. Copyright © 2016 John Wiley & Sons, Ltd.

Spatial distribution of major and trace elements in a mining dam: sources and relationships among elements of environmental concern

The concentration of major and trace elements have been determined in sediments samples taken from a mining dam, located in the upper area of the Tinto River basin (SW Spain). This dam, built to fulfil water needs for mining operations, is now completed clogged by accumulation of fine sediments. The results obtained for vertical and horizontal distribution of chemical elements showed highest average concentrations of Fe and Al, both with 10 %, and S (about 4 %). Toxic elements, such as As and Pb occur also with high concentrations (2515 and 5172 mg/kg, respectively). Determination of Enrichment Factors (EF) showed that sediments are enriched in elements related with the massive sulphide ore bodies and subsequent acid mine drainage processes. The elements Pb and As are that of major environmental concern, with enrichment factors higher than 10. Application of cluster analysis put in evidence the main sources of elements, allowing for the modelling of the origin of the accumulated matter. Therefore, in addition to contributions from sulphide (Fe, S) and gangue (Al, Mg), there are grouping of elements mobilized from phyllosilicates and feldspars, (e.g. Ca and K) as well as a specific group that reflects the geochemical affinity of rare earth elements in such acidic environment. Moreover, the way how elements are grouped testify the heterogeneity of geological contributions as well as the mining cycles over 4000 years of mining history in this worldwide known river basin.

Transport and bottom accumulation of fine river sediments under typhoon conditions and associated submarine landslides: case study of the Peinan River, Taiwan

Abstract. A combination of a three-dimensional Eulerian ocean circulation model (Princeton ocean model, POM) and a Lagrangian particle-tracking model (Surface-Trapped River Plume Evolution, STRiPE) is used to study the fate of fine river sediments discharged by the Peinan River at the southeastern coast of the island of Taiwan. The composite model is verified against in situ measurements and applied to simulate primary sediment deposition under freshet and typhoon discharge conditions of the Peinan River. It is shown that local wind plays a crucial role in sediment transport and settling in the coastal area through its influence on the river plume dynamics and turbulent mixing in the upper layer. Wind forcing conditions generally determine the location of the sediment deposit area, while its final pattern is defined by coastal circulation as modulated by the geometry of the coast and local bathymetry. In the study, region river-borne sediments are deposited to the sea floor, mainly in the shallow shelf areas. A significant portion of discharged fine sediments is moved offshore to the deeper ocean where it is further advected and dispersed by strong coastal circulation, mainly governed by the Kuroshio Current.The performed numerical experiments showed that sediment accumulation rate under typhoon conditions is about 2 orders of magnitude greater compared to freshet conditions. Based on the simulation results, we identified areas of continental shelf and continental slope adjacent to the Peinan River estuary which exhibit a high risk of formation of submarine landslides during and shortly after the typhoon events.

An investigation into the effects of particle texture, water content and parallel plates׳ diameters on rheological behavior of fine sediment

Siltation, a phenomenon resulted from the presence of fine particles in an aqueous environment, dominated by silt and clay, is a known and common environmental issue worldwide. The accumulation of fine sediments engenders murky water with low oxygen levels, which leads to the death of aquatic life. Thus, investigating the physical and mechanical properties of fine sediment by rheological methods has expanded. Rheology is the science of deformation and flow of matter in stress. This survey investigates the rheological behavior of six samples of soil as the fine particles structure (D<63µm) from different regions of Malaysia by using a rotational rheometer with a parallel-plate measuring (using two sizes: 25mm and 50mm) device to explore the flow and viscoelastic properties of fine particles. The samples were examined in two rheological curve and amplitude sweep test methods to investigate the effect of water content ratio, texture, and structure of particles on rheological properties. It was found that the content of fine sand, clay, and silt had an effect on the stiffness, structural stability, and shear behavior. Thus, the pseudoplastic and viscoelastic behavior are respectively shown. Moreover, the amount of fine sediments present in water i.e. the concentration of these particles, has a direct effect on the rheological curve. A reduction in viscosity of samples with higher concentrations of water has been observed. As a consequence, a considerable quantity of fine sediments are distributed within the water body and remain suspended over the time. As a result, the sedimentation rate slows down. It needs to be asserted that the storage modulus G′, loss modulus G″, and yield point can vary depending on particle type. The G′ and G″ were instigated for samples (70% and 45% concentrations) that demonstrated viscoelastic characteristics using the same rotational rheometer with a parallel-plate measuring device.

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.