Impacts of dam on characteristics of tropical rainforest soils and sediments in south central Nigeria

The effects of Dam on soil erosion were examined in Ekpoma, Edo State of Nigeria with decrease in silt and clay contents, organic matter, phosphorus and ECEC in lands cleared of vegetation. The pH of the sediment in upstream Ukhun dam areas were strongly acidic with effective cation exchange capacity (ECEC) of 4.24cmol/kg as compared to moderately acidic sediment with ECEC of 6.37cmol/kg in the downstream Ibiekuma dam areas. The upstream sediments of clay and silt recorded 4.5% and 6.2% in Ukhun dam but 3.0% and 4.2% in down streams whereas 5.0% and 6.7% of clay and silt in upstream of Ibiekuma dam and 3.0% and 4.7% in down streams indicating the effects of downstream erosion. The velocity of ftow in Ukhun and Ibiekuma up streams was 0.30 m/s but 0.35 m/s and 0.96 m/s in down streams respectively. The reduced water flow in the upstream have a negative effect on the communities downstream as they have to spend exira fertilizers to boost their crop yield.