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Impact of a large tropical reservoir on riverine transport of sediment, carbon, and nutrients to downstream wetlands
Author(s) -
Kunz Manuel J.,
Wüest Alfred,
Wehrli Bernhard,
Landert Jan,
Senn David B.
Publication year - 2011
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2011wr010996
Subject(s) - biogeochemical cycle , environmental science , hydrology (agriculture) , wetland , sediment , floodplain , drainage basin , ecosystem , nutrient , nutrient cycle , hypolimnion , eutrophication , ecology , geology , geography , geotechnical engineering , biology , paleontology , cartography
Large dams can have major ecological and biogeochemical impacts on downstream ecosystems such as wetlands and riparian habitats. We examined sediment removal and carbon (C), nitrogen (N), and phosphorus (P) cycling in Itezhi‐Tezhi Reservoir (ITT; area = 364 km 2 , hydraulic residence time = 0.7 yr), which is located directly upstream of a high ecological value floodplain ecosystem (Kafue Flats) in the Zambezi River Basin. Field investigations (sediment cores, sediment traps, water column samples), mass balance estimates, and a numerical biogeochemical reservoir model were combined to estimate N, P, C, and sediment removal, organic C mineralization, primary production, and N fixation. Since dam completion in 1978, 330 × 10 3 tons (t) of sediment and 16 × 10 3 , 1.5 × 10 3 , 200 t of C, N, and P, respectively, have accumulated annually in ITT sediments. Approximately 50% of N inputs and 60% of P inputs are removed by the reservoir, illustrating its potential in decreasing nutrients to the downstream Kafue Flats floodplain. The biogeochemical model predicted substantial primary production in ITT (∼280 g C m −2 yr −1 ), and significant N‐fixation (∼30% for the total primary production) was required to support primary production due to marginal inputs of inorganic N. Model simulations indicate that future hydropower development in the reservoir, involving the installation of turbines driven by hypolimnetic water, will likely result in the delivery of low‐oxygen waters to downstream ecosystems and increased outputs of dissolved inorganic N and P by a factor of ∼4 and ∼2 compared to current dam management, respectively.