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| Titel |
The impact of papyrus wetland encroachment on the spatial and temporal variability of stream flow and sediment export in the upper Rwizi catchment, Southwest Uganda |
| VerfasserIn |
Nick Ryken, Matthias Vanmaercke, Joshua Wanyama, Jozef Deckers, Moses Isabirye, Jean Poesen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094855
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| Publikation (Nr.) |
 EGU/EGU2014-10287.pdf |
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| Zusammenfassung |
| During the past 30 years, human activities in the Lake Victoria basin are responsible for
eutrophication of Lake Victoria via sediment-bound nutrients. This affects food security for
millions on people. Addressing this problem in this densely populated region will
require adequate catchment management strategies. However, sediment yield and
runoff data to develop such a strategy are currently unavailable. Also in general,
sediment yields for catchments in tropical environments are very scarce, especially in
East-Africa.
Therefore, runoff discharge and sediment export measurements were conducted in the
upper Rwizi, a representative catchment for the Lake Victoria basin which is located in
Southwest Uganda. Land use in this catchment is characterized by grazing area on the high
plateaus, banana cropping on the slopes and Cyperus papyrus L. wetlands in the river
valleys. These papyrus wetlands are currently encroached and transformed into
cropland. Eight subcatchments (99 km2 - 2120 km2), with different degrees of
wetland encroachment, were monitored during the hydrological year June 2009 - May
2010.
Temporal and spatial variations in runoff discharge give strong indications that papyrus
wetlands are crucial for buffering runoff and sediment discharge towards Lake Victoria.
Subcatchments with intact wetlands show a slower runoff response to rainfall, smaller peak
runoff discharges and lower runoff coefficients. Yearly runoff depths of subcatchment with
intact wetlands are three to four times smaller compared to subcatchments with encroached
wetlands. Suspended sediment concentrations (SSC) show a similar result, with significant
smaller SSC in the subcatchments having intact papyrus wetlands. In the subcatchments
where no encroachment occurred, annual area-specific suspended sediment yields (SSY)
varied between 0,26 ton ha-1 yr-1and 0,33 ton ha-1 yr-1 , while the SSY of the
encroached subcatchments varied between 1,20 ton ha-1 yr-1and 2,61 ton ha-1
yr-1.
This study demonstrates that papyrus wetlands are crucial for buffering runoff and
sediment discharges to Lake Victoria. Hence, measures should be taken to protect these
wetlands. |
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