Significance of wetlands for sediment and nutrient reduction in Lake Tana Sub-Basin, Upper Blue Nile Basin, Ethiopia

Sedimentation from agricultural fields and seasonal eutrophication from non-point source inorganic nutrients (N, P and OM) on the lakes and reservoirs are the main problems in the Tana sub-basin, Ethiopia. The objective of this study was to quantify the amount of suspended sediment concentration and sediment fixed nutrients in the wetland. Two wetlands were selected purposefully to quantify how much sediment and nutrient trapped by the wetlands and 26 runoff events were sampled for each wetland at inlet and outlet points. All runoff samples were filtered by a filter paper and measured after air dried using sensitive balance to determine sediment amount in g/L. Only 10 representative samples were subjected to nutrient analysis in the laboratory. Averagely, 7 g/L (86%) and 3 g/L (80%) suspended sediment was absorbed by wetlands in site 2 and site 1 respectively. Regarding to nutrient loss, 53, 50 and 49% nitrogen, phosphorus and organic matter (OM) was absorbed by wetland in site 2 respectively. Whereas, it was 33, 29 and 31% in site 1. Thus, wetlands have crucial role to catch suspended sediment load and associated nutrients entering into downstream reservoirs and lakes.