Abstract
Abstract. Tropical moist ecosystems, such as Ahémé lake, south-west Benin, are increasingly marked by water degradation, linked with the activities of increasing riparian populations. The objective of this study is to analyze sedimentary dynamics and its influence on the changing ecosystem of Ahémé lake from 1961–2010. Data used to carry out the study are records of precipitation, flows, turbidity, suspended sediment, mineral elements and bathymetry. Grain size data from the sieving of sediment samples were used to interpret suspended solids distribution in the lake. Linear correlation coefficients were used to assess the degree of dependence between rainfall and runoff inputs to the lake. Lake depth measurements in some areas of the lake serve to determine the rate of infilling. The sorting index was used to highlight the distribution and origin of sediments in the lake. The results show a degradation of the lake Ahémé ecosystem characterized by infilling of its bed, a high correlation (r=0.90) between rainfall and runoff, seasonal change in physicochemical parameters (total suspended sediment decrease by −91 %) and decrease in fish production by 135.8 t yr−1. The highest mean suspended sediment concentrations in lake inputs occur during high water periods (123 mg L−1) compared to low water periods (11.2 mg L−1).
Highlights
Ahémé lake, in Benin western Africa, and its biodiversity attract enormous interest from people, local residents and scientists in particular (Amoussou et al, 2016)
This study aims to analyze the evolution of sedimentary and environmental parameters from 1961 to 2010 and their impacts on the ecosystem of Ahémé lake
Linear correlation coefficient were calculated between mean monthly rainfall at Athiémé, Grand Popo, Bopa, Allada and Rainfall Flows of Couffo river (m 3S -1 ) Flows of Mono river (m 3S-1)
Summary
In Benin western Africa, and its biodiversity attract enormous interest from people, local residents and scientists in particular (Amoussou et al, 2016). The riparian population interest is in the supply of fish resources but the ecosystem of Ahémé lake is in constant degradation. Eutrophication of Ahémé lake (Oyédé, 1991; Amoussou, 2004) leads to siltation, excessive concentration of chemical elements, resulting in sometimes a significant presence of algae or aquatic plants, and absence of certain plant species along the lake shores inducing hydraulic erosion. These combined pressure factors could lead to destruction of the ecological habitats of fish species and disrupt socio-economic activities. This work brings together hydrometric, sedimentary and water quality information to help understand ecosystem changes and its impacts in Ahémé lake
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