Water Quality Assessment in part of Lagos Lagoon Using Sentinel-2A and Landsat-8 Multispectral Imagery

Remote sensing provides a cost-effective alternative to conventional in-situ techniques for monitoring surface water quality over large spatial extents. This study evaluates the performance of Landsat-8 Operational Land Imager (OLI) and Sentinel-2A Multispectral Instrument (MSI) data for assessing key water quality parameters in Lagos Lagoon, Nigeria, during wet and dry seasons. Laboratory-based in-situ measurements of chlorophyll-a, turbidity, dissolved oxygen, pH, total carbon, and electrical conductivity collected from ten sampling stations were correlated with atmospherically corrected satellite reflectance using empirical multivariate regression models. Results indicate that Sentinel-2A exhibited stronger correlations for chlorophyll-a during the dry season (r = 0.83), while Landsat-8 performed more consistently for turbidity across both seasons, achieving correlations up to r = 0.99. Dissolved oxygen, pH, and electrical conductivity showed moderate to strong relationships with selected spectral bands for both sensors, with Landsat-8 generally outperforming Sentinel-2A. Elevated turbidity and altered physicochemical conditions observed during the wet season reflect increased runoff and anthropogenic influence. Although the findings demonstrate the utility of multispectral satellite imagery for comparative water quality assessment, the results are indicative and highlight the need for expanded sampling and validation. The study underscores the complementary strengths of Landsat-8 and Sentinel-2A for monitoring water quality dynamics in tropical lagoon environments.