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Sediment System (sediment + system)
Selected AbstractsUnderstanding ,hot-spot' problems in catchments: the need for scale-sensitive measures and mechanisms to secure effective solutions for river management and conservationAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2010Malcolm Newson Abstract 1.Regulatory progress in controlling point sources of chemical river pollution has progressively thrown the attention of public policy towards anthropogenic physical impacts, many of which are scaled to the catchment via the runoff/sediment system. At the same time, concern over diffuse chemical pollution has reinforced ,catchment consciousness': land-use and land-management planning and control must be considered to conserve or restore river ecosystem integrity. 2.The scientific, political and legal elements of this scale change are, however, complex and uncertain: ,myths' abound. Landscape-scale consideration of ,pressures' suggests an unequal distribution of regulatory costs and benefits and large uncertainties in the evidence from a ,land-use hydrology' and fluvial geomorphology perspective. 3.,Hydrological connectivity' brings together a number of knowledge themes about catchment spatial organization which facilitate applying mitigation measures to much smaller areas, helping to offset uncertainty and reduce costs. 4.Instead of blanket ,remedies', more practical use is needed of process evidence from hydrology and fluvial geomorphology; this tends to suggest that ,hot-spots' dominate risks and impacts of factors such as leaching, surface flow generation and silt entrainment. 5.Set in a realistic policy framework, from strategic spatial planning to grant-aided best practice, a ,catchment acupuncture' approach to measures provides a cost-effective contribution to improving ecological status and may also increase resilience to the impacts of climate change. 6.The European Union's Water Framework Directive (WFD) encourages ,joined-up thinking' on this issue but it remains to be seen whether spatial scales, structures and concepts already enshrined in the WFD and the relevant UK national policies for land use and nature conservation can be exploited to permit the much-needed practical uptake of this new riparianism. Copyright © 2010 John Wiley & Sons, Ltd. [source] Sediment budget for an eroding peat-moorland catchment in northern EnglandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2005Martin Evans Abstract This paper describes a detailed contemporary sediment budget from a small peat-covered, upland catchment in Upper Teesdale, northern England. The sediment budget was constructed by measuring: (1) sediment transfers on slopes, (2) sediment flux on the floodplain and through the main stream channel and (3) sediment yield at the catchment outlet. Measurements were taken over a four-year monitoring period between July 1997 and October 2001 when interannual variations in runoff were relatively small. Three sites were selected to represent the major erosion subsystems within the catchment: an area of bare peat flats, a pair of peat gullies, and a 300 m channel reach. Collectively the sites allow detailed characterization of the main patterns of sediment flux within the catchment and can be scaled up to provide an estimate of the sediment budget for the catchment as a whole. This constitutes the first attempt to provide a complete description of the functioning of the sediment system in eroding blanket peatlands. Results demonstrate that fluvial suspended sediment flux is controlled to a large degree by channel processes. Gully erosion rates are high but coupling between the slopes and channels is poor and therefore the role of hillslope sediment supply to catchment output is reduced. Consequently contemporary sediment export from the catchment is controlled primarily by in-channel processes. Error analysis of the sediment budgets is used to discuss the limitations of this approach for assessing upland sediment dynamics. A 60 per cent reduction in fluvial suspended sediment yield from Rough Sike over the last 40 years correlates with photographic evidence of significant re-vegetation of gullies over a similar period. This strongly suggests that the reduced sediment yields are a function of increased sediment storage at the slope,channel interface, associated with re-vegetation. Copyright © 2005 John Wiley & Sons, Ltd. [source] Metabolism of uniconazole-P in water-sediment systems under illuminationENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2006Rika Kodaka Abstract Aerobic soil metabolism of uniconazole-P ([S]- E -1-[4-chlorophenyl]-4,4-dimethyl-2-[1,2,4-triazole-1-yl]-penten-3-ol) and the effect of illumination on metabolic profiles were studied in the water,sediment system when spiked to water. Uniconazole-P was gradually partitioned to the sediment with an aquatic half-life of 6.9 d in darkness with formation of bound residues. Illumination of the system from a xenon lamp (>290 nm) greatly accelerated the degradation of uniconazole-P via photoinduced isomerization between E- and Z-isomers with a subsequent intramolecular cyclization, and its aquatic half-life was greatly reduced to 0.6 d. Kinetic analysis based on compartment models suggested the possible contribution of photodegradation at the water-sediment interface, leading to more formation of the cyclized derivative in the sediment. [source] The sedimentary records in Mediterranean rockshelters and caves: Archives of environmental changeGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2001Jamie C. Woodward It is important to develop rigorous methods and robust conceptual models for the interpretation of rockshelter and cave sediment records so that the cultural sequences they contain can be considered in their proper environmental context. Much of what we know about the prehistory of the Mediterranean region and adjacent areas has largely been pieced together from materials excavated from sedimentary sequences in these environments. The rockshelters and caves of the region form important environmental and sedimentary archives. Recent work has begun to consider if the remarkable climatic variability evident in the high resolution lacustrine and ice core records is manifest in the rockshelter and cave sediment records of the area. In this context, the two main characteristics of a rockshelter or cave site which control its usefulness as an archive of environmental change are the temporal resolution of the sedimentary record and the environmental sensitivity of the site. Many rockshelters and caves can be described as either Active Karst Settings (AKS) or Passive Karst Settings (PKS) and site type is an important influence on climatic sensitivity with a direct influence upon the usefulness of the sedimentary sequence as a proxy record of climate change. It is now clear that some sites may preserve detailed paleoclimatic records and the climatic signal may be represented by distinctive suites of micromorphological features, by variations in the input of allogenic sediment, or by fluctuations in the mineral magnetic properties of the fine sediment fraction. It can be argued that data derived from the analysis of bulk coarse-grained samples often lacks the stratigraphic resolution and environmental sensitivity that can be obtained from other approaches. The most favorable sites for detailed paleoclimatic reconstruction appear to be in active karst settings such as Theopetra Cave (Greece) and Pigeon Cave (Morocco) where micromorphological analyses offer insights into the stratigraphic record that are not otherwise obtainable. The temporal resolution of a site can only be established through a rigorous stratigraphic analysis and a comprehensive dating program. These are fundamental considerations in the study of rockshelter sediment records, especially when attempting to correlate between sites and draw comparisons with other proxy records of environmental change derived from sedimentary environments with rather different characteristics. Rockshelters and caves are part of a wider sediment system, and their investigation must be accompanied by detailed geomorphological, sedimentological, paleoecological, and geochronological studies of the off-site Quaternary record. © 2001 John Wiley & Sons, Inc. [source] Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basinsHYDROLOGICAL PROCESSES, Issue 9 2002J. C. Woodward Abstract Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in-stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by in-stream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Partitioning, bioavailability, and toxicity of the pyrethroid insecticide cypermethrin in sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2002Steve J. Maund Abstract The partitioning, bioavailability, and toxicity of cypermethrin in water,sediment systems was investigated. Cypermethrin adsorbed extensively and rapidly, with an overall mean organic carbon (OC) adsorption partition coefficient (Koc) of 350,000, and approximately 99% adsorption occurred within 24 h. Bioavailability was measured via body burdens of Daphnia magna and Chironomus tentans. Mean biota,sediment accumulation factors (BSAFs), that is, the concentration in the organism as a proportion of the concentration in the sediment, decreased with increasing OC content. The BSAF values were 0.31, 0.14, and 0.08 for D. magna and 0.63, 0.19, and 0.08 for C. tentans, in 1, 3, and 13% OC sediments, respectively. The 10-d median lethal sediment concentrations (LC50s) of cypermethrin were 3.6, 18, and 32 mg/kg for Hyalella azteca and 13, 67, and 62 mg/kg for C. tentans in 1, 3, and 13% OC sediments, respectively. Predictions of aqueous concentrations at the LC50 in sediments (based on Koc) compared well to each other and to effect concentrations from studies in water alone, suggesting that equilibrium partitioning theory could be used reasonably to predict and normalize the toxicity of cypermethrin across sediments of differing OC content. [source] Cd, Cu, Pb, and Zn coprecipitates in Fe oxide formed at different pH: Aging effects on metal solubility and extractability by citrateENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2001Carmen Enid Martínez Abstract Coprecipitates of heavy metals with Fe oxides may form in contaminated soil, water, and sediment systems, particularly when oxidation-reduction processes are occurring. Once formed, coprecipitates with ferrihydrite could limit heavy metal mobility, solubility, toxicity, and bioavailability in geochemical systems. In this study, Cd, Cu, Pb, and Zn were coprecipitated with Fe by titration to pHs 6 and 7. Metal solubility was monitored during the coprecipitation process to pH 7 and after aging of the product. In the coprecipitate formed at pH 6, metal solubility was determined after the system reached pH 6 and at subsequent time intervals. We also reacted the coprecipitates with citrate and evaluated potential metal availability at increased aging times. The pH of coprecipitate formation had little effect on the long-term solubility of Cu and Zn, whereas soluble Cd was greater in the coprecipitate formed at pH 6. Soluble percentages of metals were low at both pH 6 and 7 for Cu and Pb but averaged 1.5 to 3% for Zn and greater than 40% for Cd. Hysteresis was observed in the coprecipitation curves for Zn and Cd, revealing reduced solubility after adsorption or coprecipitation. Lead and Cu failed to show hysteresis, with strong retention in the solid phase at pH greater than 6. The citrate-extractable fraction was greatest for Cd and Zn, less for Cu, and least for Pb. Citrate-extractable metal was higher for the coprecipitate formed at pH 7 than at pH 6, suggesting increased potential availability from coprecipitates formed at higher pH. [source] Laboratory persistence and fate of fluoxetine in aquatic environmentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2006Jeong-Wook Kwon Abstract The persistence and fate of fluoxetine, a selective serotonin reuptake inhibitor, has been investigated in laboratory-scale experiments, including studies with various aqueous solutions, water/sediment systems, and activated sludge-amended medium. The samples were placed in the dark and/or in a growth chamber fitted with fluorescent lamps simulating the ultraviolet output of sunlight. Over a period of 30 d, fluoxetine was hydrolytically and photolytically stable in all aqueous solutions except synthetic humic water (pH 7), in which the degradation rate was increased by approximately 13-fold in comparison with buffered solutions at the same pH. Fluoxetine rapidly dissipated from the aqueous phase in water/sediment systems, primarily because of distribution to sediments. The dissipation rate from the aqueous phase was similar between light and dark systems, indicating a low contribution of photodegradation to the dissipation of fluoxetine in this system. The potential impact of fluoxetine in aquatic environments would be decreased because of adsorption to sediments. Based on results of ready-biodegradability investigations, fluoxetine would not be expected to rapidly biodegrade in wastewater treatment plants. A photoproduct was detected only in a sample of synthetic humic water and was identified as norfluoxetine formed by demethylation. Results indicate that fluoxetine is relatively recalcitrant to hydrolysis, photolysis, and microbial degradation and that it is rapidly removed from surface waters by adsorption to sediment, where it appears to be persistent. [source] | |||||||||||||