Dynamics of the optical water quality parameters in the Lake Nokoué and Cotonou Channel complex (Benin)

Abstract

The use of satellite imagery to develop models for detecting lake water quality requires a good knowledge of the optical parameters of the water. This study aims to characterise spatiotemporal variations in chlorophyll-a (Chl-a) and turbidity for future remote sensing applications. To achieve this, data from the Lake Nokoué Cotonou Channel (LNCC) lagoon complex in the Republic of Benin, which has an annual productivity 16 times higher than that of lakes in the West African sub-region, was used for the period from December 2019 to November 2022. The research approach is based on statistical analyses, including Principal Component Analysis (PCA), Pearson correlation, mixed regression, clustering analysis and analysis of the influence of seasonality on the variation of the various parameters. The results clearly show that Chl-a concentrations vary considerably (0 to 75.5 µg/L) depending on the hydrological regime. During periods of high water (HW), concentrations are high, while during periods of low water (LW), they are more moderate. Similarly, turbidity shows a fairly wide range of variation, from 0.8 to 326.02 NTU, with peaks during the HW period due to land-based nutrient inputs. Cluster analysis allowed us to divide the lake into four distinct zones, characterised by similar variations in the different parameters. The diversity in the outcomes obtained could prove to be of paramount importance in the context of ecosystem monitoring. Moreover, these results could serve as a foundational basis for the future development of water quality detection models using remote sensing, a field that remains under-explored within the LNCC complex.