Premium
Nutrient release from sediments and biological nitrogen fixation: Advancing our understanding of eutrophication sources in Lake Victoria, Tanzania
Author(s) -
Shayo Salome,
Limbu Samwel M.
Publication year - 2018
Publication title -
lakes and reservoirs: research and management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.296
H-Index - 39
eISSN - 1440-1770
pISSN - 1320-5331
DOI - 10.1111/lre.12242
Subject(s) - bay , eutrophication , water column , environmental science , sediment , nutrient , nitrate , water quality , nitrogen , hydrology (agriculture) , oceanography , environmental chemistry , geology , ecology , chemistry , biology , paleontology , geotechnical engineering , organic chemistry
Intensification of anthropogenic activities in the three riparian countries bordering the shoreline of Lake Victoria is exacerbating eutrophication in the main body of the lake. The present study evaluated the importance of sediments and biological nitrogen fixation as sources of nutrient enrichment into Lake Victoria in Magu, Mwanza and Kayenze bays influenced by different anthropogenic activities, over a period of 7 months. Kayenze Bay is a relatively pristine site, while higher anthropogenic activities occur in the Magu Bay and Mwanza North Bay areas. Sediment cores were retrieved from each sampling site and transported to the laboratory for nutrient concentrations and flux analyses. In situ nitrogen fixation rates also were measured in the water column. The results indicated the sediment–water interface in Magu Bay exhibited significantly higher concentrations of nitrate‐N and a net release of nitrate‐N, compared to Mwanza North Bay and Kayenze Bay ( p < 0.001). The sediment–water interface in Magu Bay also exhibited a significant net release of total phosphate towards the water column, compared to Mwanza Bay ( p < 0.001). The sediment–water interface in Mwanza North Bay exhibited higher ammonium‐N concentrations, and net release of ammonium‐N and total nitrogen than did Magu and Kayenze Bays ( p < 0.001). The sediment–water interface in Mwanza and Magu Bays exhibited higher total nitrogen and soluble reactive phosphate concentrations than Kayenze Bay ( p < 0.001). Their sediments also released net fluxes of soluble reactive phosphate to the water column than did Kayenze Bay ( p < 0.001). In contrast, the Kayenze Bay sediments acted as a sink of ammonium‐N from the water column, compared to Mwanza North and Magu Bays ( p < 0.001). Biological nitrogen fixation rates were significantly higher during the rainy season than the dry season ( p < 0.05), although no spatial variations in biological nitrogen fixation existed among the three sites ( p > 0.05). The present study indicated the water column and sediments in Magu Bay and Mwanza North Bay, characterized by high anthropogenic activities are rich in nitrate‐N, ammonium‐N, total nitrogen and soluble reactive phosphate, compared to the relative pristine Kayenze Bay. Anthropogenic activities and sediments may well be important sources of nutrients enrichment to the overlaying waters, thereby enhancing eutrophication of Lake Victoria. Management strategies are required to reduce external releases and internal nutrient fluxes to enhance the lake ecosystem health.