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Titel |
Source tracing of fluvial suspended sediments by magnetic and geochemical particle characterization: example of the Canche watershed (Nord-Pas-de-Calais, France) |
VerfasserIn |
Edouard Patault, Claire Alary, Christine Franke, Arnaud Gauthier, Nor-Edine Abriak |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250126445
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Publikation (Nr.) |
EGU/EGU2016-6167.pdf |
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Zusammenfassung |
In France, erosion by water run-off is estimated to 1.5 t ha−1yr−1 and can exceed 10 t
ha−1yr−1 in large growing areas, such as the North of France (Nord-Pas-de-Calais). In this
region, the Canche watershed (1294 km2) sustains heavy loss of fertile soils. The land use is
mainly dominated by arable lands (80%) and in 2013, 104 kt of suspended sediment transited
to the estuary. As demonstrated in literature, agricultural soil erosion leads to the gradual
disappearance and depletion of fertile soil, which constitute a non-renewable resource at
human time scale. Additionally, water erosion can significantly damage the aquatic
habitat and can be responsible for the input of nutrients, bacteria, pesticides, heavy
metals and radionuclides into surface waters. Conscious of these effects, many
programs have emerged in the Nord-Pas-de-Calais to reduce erosion. This study
presents a combination of environmental magnetic proxy parameters and geochemical
analyses on sediments and suspended particulate matter. The aim is to develop
effective tools to trace erosion by water run-off and quantify this process. In order to
identify the respective sediment sources in the Canche watershed, sediment trap
samples of suspended particulate matter were recovered at key positions along the
Canche watershed. The preliminary results show that magnetic concentration (Mrs)
shows typical values for the agricultural soils in the region, but these variations in
magnetic concentrations and total irons concentrations are not always correlated, which
may be explained by the iron speciation. In calculating the so-called S-ratio for
each sample we can distinguish changes in magneto-mineralogy (and thus iron
speciation) from magnetite-dominated assemblages in the mainstream Canche (naturel
background signal) to high-coercivity-dominated assemblages in the tributaries, typical for
soil erosion material rich in hematite/goethite. In combination with the element
concentrations from ICP analyses, this proxy parameter may give valuable insight
into the tracing of the suspended sediment sources. In perspective, the seasonal
variability and the discharge in the Canche watershed have to be taken into account. |
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