ESTIMATION OF POLLUTANT FLOWS IN THE SÔ AND DJONOU RIVERS TRIBUTARY TO LAKE NOKOUE IN WEST AFRICA.

The aim of this study is to estimate the pollution flow of the tributaries (Sô and Djonou) of Lake Nokoué in Benin in West Africa. To achieve this, the pollutants influencing the two tributaries were quantified monthly for 12 months at the lake's entry points by molecular absorption spectrometry (chemical elements) and atomic absorption spectrometry (ETM). Daily flow records were obtained from Benin Institute for Fisheries and Oceanographic Research (IRHOB) and from water level sensors, in addition to long-term gauging data from the ADCP and the current meter. The flow was estimated using the method developed by the United States Environmental Protection Agency (1986). The result is that the Djonou river is subject to: a high organic load with average annual flows of ammonium, Biochemical Oxygen Demand and Chemical Oxygen Demand estimated at 462.47 Kg/d, 4225.73 Kg/d and 10595.79 Kg/d respectively; metallic pollution with an average annual flow of lead estimated at 18.20 Kg/d, and nitrogen pollution with average annual flows of nitrates and nitrites at 462.47 Kg/d and 276.55 Kg/d respectively. As for the river Sô, it is subject to nitrogen and metal pollution, with average annual flows of nitrates, ammonium, toatal nitrogen and cadmium estimated at 6029.10 kg/d, 7746.81 kg/d, 19764.43 kg/d and 328.47 kg/d respectively. Measures to mitigate these pollutants must therefore be taken in the short, medium and long term to save Lake Nokoué from environmental disaster