Estimation of Water Quality in the Major Nursery Grounds of Hilsa: Insights from Plankton and Nutrient Regimes

The biological and physicochemical attributes of a river ecosystem usually reveal the status of the consequential species richness index of the biodiversity and subsistent aquatic life. Towards appraisal of water quality, physicochemical parameters (i.e., temperature, pH, DO, transparency alkalinity and hardness), water nutrients (nitrate, phosphate) and concentration of Chlorophyll a were determined. Samples were collected from six hilsa sanctuaries. The pH value was found slightly alkaline (7.6±0.6) and transparency was ranged (44.4±10.6 cm) followed by alkalinity (112.4 ±26.4 mg/L), hardness (304.5±69.5 mg/L), CO2 (10.3±1.2 mg/L), water temperature (25.6±0.8 ºC), nitrate (0.005±0.01 mg/L), phosphate (0.002±0.0004 mg/L) and DO (7.7±1.1 mg/L). Chlorophyll a was estimated (8.21 ± 2.3 µg/L), which represents the biomass of phytoplankton. The largest quantity of plankton (both in number and taxa) was found in the Meghna River basin as a natural food at station 1 (St-1) and Station 4 (St-4) compared to the other stations. Twelve groups (families) of phytoplankton comprising 26 genera and zooplankton having 14 genera were identified at all sampling stations. The density of plankton was found to be maximum (46×102 cells L-1) at Station 5 (St-5) and while minimum (24×102 cells L-1) at Station 6 (St-6) during the investigation. This evaluation of the physical, chemical, and biological profile of the environment in the country's sanctuary zones provides obvious evidence that is crucial for understanding the Hilsa Fisheries Management Action Plan and for the sustainable management of Hilsa Fishery.