Recent hydrogeochemical disturbance and human impact in Lake Afourgagh (Middle Atlas, Morocco)

This study objectively assesses the recent hydrogeochemical disturbances affecting Lake Afourgagh in the Moroccan Middle Atlas Mountains. The lake system has experienced intense degradation since the 1970s. This degradation is evident in the drastic reduction of the water level, leading to the lake's total drying and significant erosion at the watershed level. These disturbances coincide with recurring drought episodes and the implementation of intensive agriculture, which relies on groundwater pumping for irrigation. By 2006, when the lake dried up, its brackish waters were bicarbonate chloro-sodic magnesian, strongly hard, slightly oxygenated, and relatively turbid. Salinity increased significantly due to high evaporation after the tributaries dried up, with total dissolved solids (TDS) reaching an average of 6 g/L by the end of 2006. The Mg/Ca ratio also rose dramatically, from 25.5 to 92 by the end of 2006. The lake saw significant precipitation of endogenic carbonates (calcite, aragonite, and dolomite). The advanced trophic state of the lake is characterized by phosphate enrichment, mainly of anthropogenic origin. The sediment dynamics of Lake Afourgagh suggest rapid basin infill due to substantial changes in the underlying basin. The exogenous detrital fraction is dominated by dolomite, while the authigenic fraction consists of aragonite, calcite, and gypsum, resulting from intense water evaporation. The abundance of clay minerals, particularly illite and kaolinite, is related to soil hydrolysis under seasonal climatic thermal and rainfall contrasts.