Characterization of bottom sediments and phosphorus fractions in hyper-eutrophic Krishnagiri reservoir located in an agricultural watershed in India

The hyper-eutrophicated Krishnagiri reservoir is situated in hot tropical and semiarid climate zone in South India. There are 16 villages in the command area, which are directly benefited by this reservoir, and water from the reservoir is used for irrigation, fish rearing, livestock rearing and recreation purposes. The reservoir is located in an agricultural watershed, and the rate of soil erosion in the catchment area is very high. Thus, the reservoir is severely affected by sedimentation, and half of its capacity was reduced. Previous studies in Krishnagiri reservoir clearly indicate the lack of information on the quality of sediments and dynamics of nutrient in the reservoir. Hence, the present study was conducted on bottom sediments, and it included the assessment of physicochemical characteristics and nutrients, such as composition, redox potential, moisture content, organic carbon, organic matter, total iron, manganese, calcium carbonate, different phosphorus fractions and total phosphorus. The increasing trend in organic matter and also the significant change from positive to high negative values of redox potential clearly indicate the inflow of high organic load which may result from the disposal of sewage and industrial waste water in the upstream catchment side. The high concentration of inorganic phosphorus fractions at the inflow point of the reservoir obviously implies that there was a significant input of nutrients into the reservoir. Hence, the study concludes that the rainfall, soil erosion and runoff are the major environmental factors for the input and accumulation of large quantities of nutrients in the bottom sediments of Krishnagiri reservoir during the study period. The present study clearly suggests for a careful investigation into sediment nutrients in Krishnagiri reservoir, and it is also necessary to assess the role of sediments in the phosphorus dynamics and its significant effect on eutrophication. This study demonstrates that the examination of physicochemical characteristics and nutrients in the bottom sediments is a helpful tool to identify the sources of nutrients to the reservoir. The baseline data provided in this paper will be helpful for the policy makers to frame better policies for the sustainable management of water quality in Krishnagiri reservoir.