Water Quality and Sediment Management in Brahmaputra Basin of India: Impact of Agricultural Land Use

In Brahmaputra basin of India, the social sanctions and belief system maintained a balance between resource potential and their utilization for a long time but due to the increase in the demographic pressure and indiscriminate use of natural resources, imbalance has been created. Socio-economic constraints like shifting cultivation, land tenure system, small size of land holdings, unabated deforestation, free range grazing and undulating terrain have affected the sediment yield and, quantity and quality of available water. The mean annual sediment yield per ha from the Brahmaputra basin constitutes, 23.2 tonnes of soil and, 26.1, 4.2, 19.4, 0.93, 0.58, 2.3 and 1.79 kg of N, P₂O₅, K₂O, Mn, Zn, Ca and Mg, respectively. The Brahmaputra river in India has more than 100 tributaries of which 15 in the north and 10 in the south are fairly large. It was estimated that about 660 m³ km⁻² of sediment load is brought by the northern and 100 m³ km⁻² by the southern tributaries to the main river channel, annually. To evolve eco-friendly and sustainable farming systems to replace sediment encouraging practice of shifting cultivation, a multidisciplinary, long-term study was undertaken with seven land use systems on micro watersheds viz.; livestock based (grasses and fodders), forestry, agro-forestry, agriculture, agri-horti-silvi-pastoral, horticulture and shifting cultivation, to monitor their comparative efficacy with regard to in-situ retention of rain water, water quality and sediment yield. The sediments emanating from the farming systems affected the surface and groundwater quality, the magnitude of which was highly related to the use of amount of fertilizers and other agricultural chemicals in the basin.