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Long-Term Water Quality Patterns of a Flow Regulated Tropical Lowland River

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Water Research Group, Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa
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Department of Zoology, University of Johannesburg, Auckland Park 2006, South Africa
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Animal Ecology, Global Change and Sustainable Development, Department of Biology, University of Leuven, 32 Charles Deberiotstraat, 3000 Leuven, Belgium
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Author to whom correspondence should be addressed.
Water 2020, 12(1), 37; https://doi.org/10.3390/w12010037
Received: 4 November 2019 / Revised: 12 December 2019 / Accepted: 13 December 2019 / Published: 20 December 2019
(This article belongs to the Section Water Quality and Ecosystems)
Floodplain ecosystems in Africa are under threat due to direct anthropogenic pressure and climate change. The lower Phongolo River and associated floodplain is South Africa’s largest inland floodplain ecosystem and has been regulated by the Pongolapoort Dam since the 1970s. The last controlled flood release from the dam occurred in December 2014, after which a severe drought occurred and only a base flow was released. The central aims of this study were to determine the historic and present water quality state of the middle and lower Phongolo River and assess the possible effects of the most recent drought may have had. Historic water quality data (1970s to present) were obtained from monitoring stations within the Phongolo River catchment to assess the long-term water quality patterns. Using multivariate statistical analyses as well as the Physicochemical Driver Assessment Index (PAI), a water quality index developed for South African riverine ecosystems, various in situ and chemical water variables were analysed. Key findings included that the water quality of the middle and lower Phongolo River has degraded since the 1970s, due to increased salinity and nutrient inputs from surrounding irrigation schemes. The Pongolapoort Dam appears to be trapping nutrient-rich sediments leading to nutrient-depleted water entering the lower Phongolo River. The nutrient levels increase again as the river flows through the downstream floodplain through input from nutrient rich soils and fertilizers. The drought did not have any significant effect on water quality as the PAI remained similar to pre-drought conditions. View Full-Text
Keywords: anthropogenic effects; drought; dams; floodplain system; sediment retention; salinization; Southern Africa; South Africa anthropogenic effects; drought; dams; floodplain system; sediment retention; salinization; Southern Africa; South Africa
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de Necker, L.; Neswiswi, T.; Greenfield, R.; van Vuren, J.; Brendonck, L.; Wepener, V.; Smit, N. Long-Term Water Quality Patterns of a Flow Regulated Tropical Lowland River. Water 2020, 12, 37.

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