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Titel |
Evaluating the provenance of fine sediment in degraded Freshwater Pearl Mussel habitats. |
VerfasserIn |
Will Blake, Steve Haley, Rupert Goddard, Peter Stone, Kat Broadhead |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250110954
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Publikation (Nr.) |
EGU/EGU2015-11001.pdf |
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Zusammenfassung |
Freshwater Pearl Mussels (FWPM), Margaritifera margaritifera, are among the most
critically threatened freshwater bivalves worldwide. In addition to their important roles in
particle processing, nutrient release, and sediment mixing, they also serve as an
ideal target species for evaluation of aquatic ecosystem functioning especially in
the context of their symbiotic relationship with Atlantic salmon Salmo salar and
brown or sea trout Salmo trutta. Poor water quality, particularly eutrophication, and
siltation are considered major contributory factors in the decline of the species
hence management of diffuse water pollution from agriculture (DWPA) is a key
priority in catchments that host FWPM habitats. Against this background, this study
adopted a combined monitoring, surveying and sediment fingerprinting approach to
determine the principal sources of fine sediment impacting FWPM habitats in the
River Clun, a Special area of Conservation (SAC) for FWPMs in central western
UK.
Potential sediment production hotspot areas in the ca 200 km2 catchment area upstream
of FWPM habitats were initially evaluated using the SCIMAP risk mapping tool. Suspended
sediment monitoring was undertaken on the main stem channel where FWPM habitats
are located and wet weather catchment walkover surveys undertaken along the
upstream river and stream network. Within this monitoring framework, sediment
fingerprinting was undertaken at two levels. The first level aimed to link primary
catchment sources (cultivated and uncultivated soil, channel bank erosion, and material
transported via roads and tracks) to suspended sediment output from each main
tributary upstream of the FWPM beds. The second level linked silt in the FWMP beds
to the main tributaries, as integrated source end-members, with the inclusion of
main channel bank erosion, a notable feature of walkover surveys as an additional
source.
Geochemical fingerprints, determined by XRF spectroscopy, were dominated
by conservative mineral-bound elements and results indicated the importance of
mainstem channel bank erosion as a sediment source to the FWMP beds, in line with
catchment walkover observations. In addition, broad subcatchment discrimination and
subsequent sediment apportionment showed agreement with SCIMAP risk analysis for
more intensively farmed areas. Fingerprinting results also suggested, however, an
unexpected contribution from upland grazed areas, categorised as lower risk by SCIMAP.
Detailed evaluation of primary sources in these areas was undertaken to evaluate this
discrepancy and test the hypothesised importance of channel bank erosion at the
subcatchment scale. The results highlight the benefits of adopting a combined monitoring,
modelling and tracing approach to support targeted management of fine sediment
problems.
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