Given that reservoirs contain most of the leached materials from soils, we have
studied the sediments accumulated in the bottom of two groups of reservoirs developed under different climatic conditions and thus with contrasting rates of weathering/erosion regimes. Through detailed comparative study of clay minerals of the parent rocks and soils with the clay fractions of the dam sediments, we have concluded that, during cycles of erosion-transport-deposition, the leached materials have complex transformation mechanisms, making them much more active in the environment. All clay-mineral groups are well represented in the reservoir sediments, including abundant mixed-layer and partly disordered minerals. Moreover, the sediments are nutrient-rich and potentially useful as agricultural fertilizers and hence in reversing the declining soil productivity in some regions.