The objective of this study was to assess the seasonal contamination of the Lobo River by pesticide residues from surrounding crops. Water samples were taken eight times, in the dry and wet seasons, at the exit of agricultural plots (upstream) and in the watercourse (downstream). These samples were analyzed using a SHIMAZU liquid chromatograph. The analyses revealed the presence of nine different pesticides in the samples. Mancozeb, 2, 4-D and deltamethrin were the most detected at respective mean concentrations of 0.767 µg/L; 9.437 µg/L; 10.953 µg/L upstream and 0.326 µg/L; 8.579 µg/L; 9.160 µg/L downstream. Furthermore, the measured concentrations generally exceeded the international standards recommended by WHO, both for the total pesticides and for most individual molecules. The results also showed that agricultural activities exerted significant pressure on the water quality of the Lobo River, especially during the rainy season. Pesticides used in crops were drained by runoff into the watercourse, contaminating the aquatic ecosystem.

The water of the Issia reservoir is used to supply drinking water to the local population. Unfortunately, the various anthropogenic pressures in the Lobo watershed threaten the quantity of water flows entering the Issia reservoir. The objective of this study is to assess the impact of the combined actions of anthropization and climate change on the water flows entering the Issia reservoir. The approach implemented was based on the coupling of remote sensing and agro-hydrological modeling with SWAT. The diachronic analysis of Landsat 7 ETM+ (2008 and 2013) and Sentinel-2 (2019) images through the method of supervised classification by maximum likelihood has allowed to discriminate five (05) classes of land use that are: forest, degraded forest, habitat and bare soil, crop and fallow, and water bodies. The overall accuracies obtained for the 2008, 2013 and 2019 classified images are 90%; 92% and 95.33% respectively. The Kappa indices of the confusion matrix for the three classified images are 0.88; 0.9 and 0.94 for 2008, 2013 and 2019 respectively. From 2008 to 2019, dense forest, degraded forest, and crops and fallow had overall regressions of 13.70%, 10.49%, and 1.29% respectively. In addition, bare soil and habitats and water bodies increased by 75.50% and 57.09% respectively. The graphical and statistical criteria of the SWAT model (NS and R2, greater than 0.5) showed good model performance for both calibration and validation. The water balance analysis for the 2050 time horizon indicates that water flows into the reservoir will decrease by 52% compared to current flows. This decrease could constitute a real threat for the population of the Issia locality in the years to come.