Eutrophication of a River Impacted by Agricultural Activities (N’zi River, Côte D’ivoire)

Abstract

Water eutrophication is a global environmental problem. In Côte d'Ivoire, no data is available to predict this phenomenon in rivers. The purpose of this study is to evaluate the impact of agricultural activities on the eutrophication phenomenon of the N'zi River in Côte d'Ivoire. The approach used focused on two points. The first one was to determine the different dissolved forms of phosphorus and nitrogen in the water of the N'zi River using AFNOR methods. The second focused on the mobility of phosphorus in sediments using the sequential extraction procedure of Williams. Results show that the inorganic phosphorus concentrations (IP) in sediments decrease in favor of contents in the water. Moreover, nitrate ions (NO3-) quantitatively dominates the nitrogenous forms in water. These results are attributable to the intensive use of fertilizers in agriculture, the leaching of cropland and/or contamination by human or animal waste. The phosphorus sequential extraction shows that 29 to 72% of the iron-bound bioavailable P (Fe-P) in sediments is likely to be mobilized into the water column and contributes to the N'zi River eutrophication. Therefore, an awareness and monitoring program must be put in place to reduce the nutrients inputs in the N'zi River upstream.