Trace-element behaviour in sediments of Ugandan part of Lake Victoria: results from sequential extraction and chemometrical evaluation

Lake Victoria is the second largest freshwater lake and the largest tropical lake in the world. The transboundary lake has the fastest growing population in its catchment, which can impact the water and sediment quality. To determine the extent of anthropogenic effects on sediment quality in the Ugandan part of Lake Victoria, the contents and binding behaviour of trace elements were analysed, as well as organic matter and phosphorus in different sediment layers of both deep and coastal sediments near the coastal cities of Entebbe, Kampala and Jinja. The data were assessed using the German LAWA criteria for trace-element pollution, the Geo-Index, Cluster- and Factor analyses. Mostly, no critical trace-element contamination in the sediments of the investigated area was observed. However, changes in element distributions caused by anthropogenic influences from around the lake were detected, like higher contents of Cu, Ti and V in near shore sediments with urban surrounding. Near Jinja, industrial wastewaters caused particularly elevated contents of Cu in the sediments (70–121 mg/kg, 3.5–6 times the geogenic background), exceeding the LAWA criteria and potentially harming the aquatic habitat. In addition, temporally growing organic matter contents in the lake sediments near the estuary of River Nzoia (from 4.2 to 17.6% in around 60 years) due to increased soil erosion in the river’s catchment area and blooms of the water hyacinth became visible. This study demonstrates that the whole catchment area is responsible to ensure a healthy aquatic ecosystem in Lake Victoria.