The natural process of soil erosion gives rise to sediments in water. Sediments include soil, sand and mineral particles washed into aquatic environment by flood waters. In addition, large deposits of sewage sludge, pulverized coal ash and various industrial solids are disposed off into waters. Suspended solid loadings reaching natural waters are about 700 times as large as solid loading from sewage discharge. Soil erosion gets enhanced 10 times as a result of agricultural development and about 100 times due to construction activities. Bottom sediments are subjected to anaerobic conditions and have the ability to exchange metals, e.g. Cr, Cu, Co, Mn, Ni etc.
Detrimental Effects of Sediments.
Sediments destroy aquatic organism. Bottom sediments decrease fish population by blanketing fish nests, spawn and food supplies. Suspension may cause thickening of fish gills which may lead to asphyxiation of the fish. Toxic metals like Hg, Cd and Pb present in sediments attack sulphur bonds in enzymes causing immobilizing effect and transportation through cell membrane.
Reduces light penetration in water. Sediments reduce direct penetration of sunlight which lowers photosynthesis in aquatic plants. Sediments result in less food availability and plant biomass.
Water gets clouded. Sediments increase the cost of water treatment used for culinary purpose. Sediments passing through power plant turbines make serious abrasion and wear. Due to turbid water, the hunting ability of fish gets curtailed. The amounts of suspended solids, which are greater from surface, run off than that of sewage discharge deteriorate the water quality broadly.
Water bodies get easily flooded. Sediments make the rivers, streams, channels and reservoirs to overflow. They also change the flow rates and depths of water systems as well as destroy the life of reservoirs. However, expensive treatments are needed to counteract these effects.