seasonal eutrophication dynamics in ahmed el hansali reservoir, morocco: a multivariate statistical approach

In morocco, dams are essential for supplying drinking water, supporting agriculture, and regulating watercourses, but these aquatic ecosystems face increasing pressures, particularly eutrophication, which degrades water quality and threatens biodiversity. this study analyzed the seasonal dynamics of eutrophication in the ahmed el hansali reservoir (moroccan middle atlas) between 2019 and 2023, utilizing multivariate statistical analysis (principal component analysis and multiple linear regression). a limitation was quarterly data collection, which might not capture short-term fluctuations. results revealed a significant correlation between phytoplankton biomass and nutrient levels, especially total kjeldahl nitrogen (ntk) (r=0.656 p<0.01). ntk was the most significant predictor, positively impacting chlorophyll-a (chl-a) in surface waters (for each unit increase in ntk, chl-a increased by 15.16 µg/l). other parameters had minimal effects. marked seasonal variability in water quality was observed, ranging from oligotrophic in winter and autumn to mesotrophic in spring and summer. maximum productivity (15.73 µg/l chl-a) was in summer, while the lowest (5.92 µg/l chl-a) was in winter. excessive nutrient inputs from agricultural runoff during the rainy season were recorded, highlighting the need for continuous monitoring, especially during peak productivity, to mitigate eutrophication risks. recommendations include optimizing agricultural practices to reduce nutrient inputs and implementing integrated water resource management strategies to preserve the reservoir's ecological quality. this research provides valuable information for decision-makers and environmental managers aiming to improve water quality and protect aquatic biodiversity in morocco.