ORGANIC POLLUTION INDEX IN THE EVALUATION OF THE QUALITY OF LAKE DOHOU, A SOURCE OF DRINKING WATER SUPPLY IN THE CITY OF DUEKOUE (WEST COTE DIVOIRE)

The abiotic typology of the different sampling stations based on physico-chemical parameters and the assessment of the nutrient load and the relative contributions of the different nutrient sources to this surface water were analysed. Five physical and chemical parameters (temperature, dissolved oxygen, transparency, pH and conductivity) were measured in situ at each sampling campaign in Lake Dohou over a period of one year, once a month at seven (7) selected stations. Water samples were taken for subsequent determination of dissolved solids, biological oxygen demand for 5 days and nutrient salts (nitrite, nitrate, phosphate, ammonium).Thephysico-chemical characterisation revealed weakly mineralised water with average conductivities varying from 12.38 ±16.33 µS.cm-1 to 39.63 ±45.28 µS.cm-1 with high temperatures in the dry season. A hierarchical ascending classification (HAC) was used to group the stations into 3 groups. Group I (stations 6), due to its exposure to domestic discharges and leaching from agricultural land, is heavily loaded with organic matter and nutrients. The values of the pollution index express a high organic pollution at all the sampling stations. The water of Lake Dohou is highly loaded with organic matter and receives a very high amount of pollutant from the environment.