Assessment of hydrographic parameters and trophic status of selected freshwater ecosystems of southwest India

\nNatural freshwater ecosystems, especially ponds, are highly vulnerable to increasing anthropogenic activities and natural alterations owing to their small size and volume. Variations in species diversity, continuous occurrence of harmful algal blooms and changes in aquatic ecosystems are some consequences of the resulting hydrological variations. The trophic state index is one of the easiest and most widely used methods for understanding the trophic status of such disturbed aquatic ecosystems. The present study analysed the variations in different hydrographic parameters with an emphasis on major nutrient status to understand the water quality of two freshwater ponds (S1 and S2) using Carlson's trophic state index (TSI). Assessing the water quality for two years, algal biomass, as indicated by chlorophyll a was maximum during pre-monsoon seasons (S1: 82.08 mg m−3 and S2: 204.97 mg m−3). Dissolved nutrients like nitrate, phosphate and silicate varied from 0.35 mg L−1 to 6 mg L−1, 0.119 mg L−1 to 0.67 mg L−1 and 2.44 mg L−1 to 14.39 mg L−1, respectively, during the study. The TSI result indicated the eutrophic to the hypereutrophic condition in the study area (TSI 71.9 to 82.4). The TSI values reached a maximum at S1 during monsoon 2019, while at S2, the peak value was observed during pre-monsoon 2021. The continuous occurrence of harmful cyanobacterial blooms dominated by Microcystis sp. observed from both freshwater ponds indicated the polluted and deteriorating condition of the ponds.\n