Assessment of Hydrologic Alteration within Ecosystem in a Sahalian Shallow Lake: Lake Guiers, Senegal

Sambou Djiby, B. Diekkruger, A. Gaye and A. Th. Gaye

University of Abomey Calavi, Benin, University of Bonn, Germany, Lake Guiers Authority, Senegal, UCAD, Senegal

Abstract: In this study, daily streamflow data of 35 years records and water quality data were investigated to determine Lake Guiers hydrologic alteration within its ecosystem. The Range of Variability Approach (RVA) was used to quantify the modification of the Indicators of Hydrologic Alteration (IHA) and the trophic State Indices (TSIs) was calculated to characterize the eutrophication level. Results show that the flow pattern at Lake Guiers is reversed from the pre-impact with high alteration on most of indicators. These changes on flow have greater impacts on the lake ecological functioning and on water quality. The trophic State Indices (TSIs) of Nitrogen (N) and Phosphorus (P) indicate respectively a eutrophic and hypereutrophic state. Lake Guiers hydrological alteration

endangers its ecological integrity. Its restoration requires more than ever reconciling economic needs and ecological requirement.

Key words: environmental flow, hydrologic alteration, indicator, Lake Guiers, Senegal, streamflow