Assessing hydrogeochemistry, water quality index (WQI), and seasonal pattern of plankton community in different small and medium reservoirs of Karnataka, India

Changes in aquatic ecosystem due to anthropogenic or natural process are growing concern which requires regular monitoring for water quality to formulate guidelines for their proper management. The present study aimed to understand the limno-biotic status of nine different small (Kanva, Votehole, Anjanapura, and Gayathri) and medium (Jambadahalla, Tunga, Varahi, Shanthisagar, and Boranakanive) reservoirs of Karnataka state of India using physicochemical and the plankton diversity during the three different seasons (pre-monsoon, monsoon, and post-monsoon). The water quality parameters like transparency in terms of secchi disc depth (m), water temperature (°C), pH, EC (μS/cm), dissolved oxygen (mg/l), TDS (mg/l), total alkalinity (mg/l), NO 3 − -N (mg/l), PO 4 3− -P (mg/l), and SiO 2 (mg/l) besides planktonic diversity were measured using standard procedure. The variables were subjected to Pearson’s correlation analysis to determine the relationship among them during three seasons. Further principal component analysis (PCA) was done to explain the variance. The results revealed that all the reservoir water was alkaline in nature with marked seasonal differences and was fairly rich in dissolved oxygen except Gayathri. Electrical conductivity values of all the reservoirs were below the permissible limit (2000 μS/cm) with a noticeable concentration of PO 4 3− -P in all the reservoirs. High silicate content coupled with dominance of Mycocystis sp. in most of the reservoirs is an indication of eutrophic condition. Principal component analysis revealed the evidence of anthropogenic factors leading to deterioration of the water quality index of all the reservoirs from “poor” to “unsuitable category” except Tunga reservoir (Good quality). Since all these reservoirs support fisheries and are amenable to enhanced fisheries through fish seed stocking, there is an urgent need to monitor the water quality of these multipurpose reservoirs for conservation of aquatic biodiversity and maintain ecosystem health.