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| Titel |
Phosphorus transport and retention in a channel draining an urban, tropical catchment with informal settlements |
| VerfasserIn |
P. M. Nyenje, L. M. G. Meijer, J. W. Foppen, R. Kulabako, S. Uhlenbrook |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 3 ; Nr. 18, no. 3 (2014-03-12), S.1009-1025 |
| Datensatznummer |
250120304
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| Publikation (Nr.) |
 copernicus.org/hess-18-1009-2014.pdf |
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| Zusammenfassung |
| Urban catchments in sub-Saharan Africa (SSA) are increasingly becoming a major
source of phosphorus (P) to downstream ecosystems. This is primarily due to
large inputs of untreated wastewater to urban drainage channels, especially
in informal settlements (or slums). However, the processes governing the
fate of P in these catchments are largely unknown. In this study, these
processes are investigated. During high runoff events and a period of base
flow, we collected hourly water samples (over 24 h) from a primary
channel draining a 28 km2 slum-dominated catchment in Kampala, Uganda,
and from a tertiary channel draining one of the contributing slum areas
(0.54 km2). The samples were analysed for orthophosphate (PO4-P),
particulate P (PP), total P (TP), suspended solids (SS) and hydrochemistry.
We also collected channel bed and suspended sediments to determine their
geo-available metals, sorption characteristics and the dominant phosphorus
forms. Our results showed that the catchment exported high fluxes of P
(0.3 kg km2 d−1 for PO4-P and 0.95 for TP), which were several
orders of magnitude higher than values normally reported in literature. A
large proportion of P exported was particulate (56% of TP) and we
inferred that most of it was retained along the channel bed. The retained
sediment P was predominantly inorganic (> 63% of total
sediment P) and consisted of mostly Ca and Fe-bound P, which were present in
almost equal proportions. Ca-bound sediment P was attributed to the
adsorption of P to calcite because surface water was near saturation with
respect to calcite in all the events sampled. Fe-bound sediment P was
attributed to the adsorption of P to iron oxides in suspended sediment during
runoff events given that surface water was undersaturated with respect to
iron phosphates. We also found that the bed sediments were P-saturated and
showed a tendency to release P by mineralisation and desorption. During rain
events, there was a flushing of PP which we attributed to the resuspension
of P-rich bed sediment that accumulated in the channel during low flows.
However, first-flush effects were not observed. Our findings provide useful
insights into the processes governing the fate and transport
of P in urban slum catchments in SSA. |
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