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| Titel |
Impact of upland erosion and sediment transport on macroinvertebrate communities: An interdisciplinary pressure-impact study in the Kharaa catchment (Mongolia) |
| VerfasserIn |
Michael Schaeffer, Melanie Hartwig, Philipp Theuring, Michael Rode, Dietrich Borchardt |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054535
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| Zusammenfassung |
| Sediment erosion and transport pathways towards and within rivers are complex as they are
dependent on many catchment properties, in particular hydrology and land use. Moreover,
fine sediments are a key constraint for aquatic ecosystem functions at the riverbed that
potentially alter for example the regulation of biogeochemical processes, habitat suitability
for benthic organisms or primary production. Consequently, the understanding of this
pressure-impact chain is challenging in order to suggest effective catchment management
strategies.
This interdisciplinary study aims to assess system understanding of the interactions of
terrestrial sediment transport and the aquatic ecosystem. Therefore, a linked model and
monitoring system was developed for the simultaneous analysis of sediment erosion,
sediment transport and aquatic ecosystem impacts.
The study area is the catchment of the Kharaa River in Northern Mongolia. This region is
influenced by harsh continental climate and because of the long time of nomadic dominated
land use, most of the running waters show significantly less anthropogenic influences when
compared to Middle Europe. However, analyses of matrix sedimentation traps and
macroinvertebrate communities revealed increased fine sediment intrusion in certain river
sections. In particular, fine sediment infiltration rates into the river bed and general metrics of
the macroinvertebrate community were negatively correlated, i.e. Shannon diversity, Taxa
richness, Percentage of EPT individuals (Ephemeroptera, Plecoptera, Trichoptera),
whereas a positive correlation was detected for the Percentage of fine sediment
colonisers.
Once fine sediment immission was identified as being one of the main stressors for
benthic organisms, open questions remained. Namely, these were questions concerning the
sources of fine sediment in the catchment, its delivery pathways to the river and its impact on
especially the hyporheic zone. To answer these questions a model and monitoring framework
was established. Geochemical and fallout isotope (137Cs, 210Pb and 7Be) sediment source
fingerprinting is used for spatial sediment source discrimination and to gain information on
the importance and proportions of surface-, stream bank and gully erosion in the catchment.
Further, two different models are tested to describe the sediment transport in the catchment.
The HYPE model is used to model runoff and the associated fine sediment transport in
the catchment, and the SedNet for sediment budget calculation. In addition, a two
compartment river water quality model including submodels for the hydraulics,
fine sediment transport and oxygen balance was conceptualized. Based on that, an
intensive monitoring program was developed and applied to investigate across a
gradient of impact and for distinct hydrological settings at riffle scale. First results
suggest that only a small part of the catchment contributes considerably to the total
sediment load and that gully and bank erosion might be the dominating sources in the
catchment. Also the erosion behaviour between spring and autumn was found to be
different. Data on surface water and subsurface settings showed limited primary
production as well as increased fine sediment fractions at the downstream site.
The observed decrease of water exchange at that interface needs to be investigated
further.
This study results contribute to an IWRM (Integrated Water Resource Management)
approach and delivers important information for environmental assessment, management
demands and suitable mitigation measures. |
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