Trophic Status of Shanti Sagara Reservoir: Implications on Nutrient Management in Reservoir Catchment

Abstract

Water quality assessment of Shanti Sagara reservoir for drinking water supply and for water allocation to meet the demands in the semiarid climate is aimed. Seasonal water sampling (Pre monsoon, December 2021 & Post monsoon, May 2022) at 2 depths to investigate physico-chemical parameters and assess the Water Quality index based on IS 10500: 2012 is found to be poor in pre monsoon, December 2021 and very poor in post monsoon, May 2022. Trophic status of the reservoir assessed based on Carlson’s Trophic State Classification (Secchi Depth, Total Nitrogen and Total Phosphorous) indicated that the reservoir is Hypereutrophic for Post Monsoon. This calls for assessment of internal nutrient load (silt characteristics) and external loading from the reservoir catchment (fertilizer from agriculture land) and the domestic water and the sewage water has contributed to high concentration of phosphorous (P) in Rudrapura and Jakli near Somalapura.
 Soil texture (sandy clay, silty loam, silty clay and sandy clay loam) in the reservoir catchment compliments high concentration of suspended sediment that increasers the turbidity in the reservoir. Turbidity present in the water alters the taste, colour and odour of the water and oxygen from the surface cannot be mixed to the bottom layer and oxygen is not released by photosynthesis in absence of light penetration (high turbidity levels) resulting in anoxic condition. Total Nitrogen (TN) in the catchment soil that contributes to the bottom of the reservoir is found to be high (201-217 kg/acre). Agriculture runoff in the month of (May, 2022) owing to precipitation results in high sediment concentration, that contributes to high nitrogen levels in the reservoir.
 Nutrients in suspended Sediments that have entered the reservoir altered the nutrient cycle in the reservoir ecosystem. High nutrient concentration in the silt characteristics i,e total nitrogen (159-168 kg/acre) and phosphorous (10.1-13.4 kg/acre) is due to stratification caused do level to low in hypolimnion layer and anoxic condition during summer resulting in growth of Phytoplankton the eutrophication. The suggested nutrient management strategies for the reservoirs catchment are optimizing nutrient application to the crop land, microbial water treatment before supplying it for drinking purpose, soil conservation structures in the reservoir catchment to restrict sediment entry to the reservoir and sewage treatment plant for the rural settlement.