Nitrogen and phosphorus spatio-temporal distribution and fluxes intensifying eutrophication in three tropical rivers of Côte d'Ivoire (West Africa)

Abstract

Nutrient contamination assessments in the three West African tropical Comoé, Bandama, and Bia Rivers (Côte d'Ivoire) were performed from March 2016 to March 2018. Five stations per river were sampled. Nutrients spatio-temporal distributions were mapped and showed nitrogen concentrations (nitrite 0.001 to 0.025 mg/L NO2−-N, and nitrate 0.26 to 3.60 mg/L NO3−-N) increased significantly with rainfall contrary to phosphorus (0.01 to 0.12 mg/L P). The Chl-a and TSItsr data revealed the hypereutrophic status of rivers. Moreover, N:P mass ratio suggests nitrogen as the main limiting factor of primary production during the low (March) and high flow periods (October–November), while phosphorus is the limiting factor in June, at the high flow beginning. The land uses around watersheds were the main sources of phosphorus and nitrogen enhancing the rivers' eutrophication. Phosphorus and nitrogen fluxes were related to leaching river catchments and were significant sources of nutrients to the Atlantic Ocean.