Assessment of Temporal Variation of Water Quality Parameters and the Trophic State Index in a Subtropical Water Reservoir of Bangladesh

Abstract

This study was conducted to determine the suitability of water quality for fisheries management in Kaptai Lake from February 2019 to January 2020. Results showed that the temperature, transparency, TDS, pH, DO, EC, alkalinity and hardness were 20.9 to 31.8°C, 17 to 303 cm, 40 to 105 mg/L, 6.82 to 7.96, 6.1 to 7.65 mg/L, 75.33 to 172.33 µS/cm, 37 to 83 mg/L and 35 to 190 mg/L, respectively. However, nutrients as NH3, NO3-, NO2-, PO43- and SO42- were 0.01 to 0.05, 0.03 to 2.21, 36 to 96, 0.01 to 0.04 and 0.3 to 1.9 mg/L, respectively. Chlorophyll a and trophic state index (TSI) were 0.70 to 2.12 µg/L and 27.43 to 37.79, respectively. Study revealed that SO42-, DO and TDS were higher than the standard of ECR. On the other hand, NH3, NO3-, NO2-, PO43-, temperature, transparency, pH, EC, total hardness, total alkalinity, Chlorophyll a and TSI were within the standard levels. Concentrations of NO3-, NO2-, PO43-, Chlorophyll a and TSI (CHL) showed no significant variation with seasons. Conversely, TDS, transparency, EC, alkalinity, hardness, and SO42- were lower in monsoon compared to pre-monsoon and post-monsoon seasons. Besides, temperature, NH3, DO and TSI (SD) were higher in monsoon season. Results concluded that the Kaptai Lake is in mesotrophic condition with TSI (CHL) less than 40, and prominently there was a positive relationship between Chlorophyll a and Trophic State Index (TSI). In this regard, major nutrients and Chlorophyll a concentration in the Kaptai Lake may have an impact on the aquatic environment.