Seasonal variation of aquatic flora and faunal diversity and physicochemical characteristics of Bhairab River water, Jashore, Bangladesh

Rivers play a vital role in sustaining biodiversity, livelihoods, and ecological balance across regions. This study examined the aquatic and terrestrial flora and fauna, along with physicochemical water quality parameters of the Bhairab River in the Jashore area during the wet (July–September 2023) and dry (January–March 2024) seasons. Cypriniformes were the most dominant fauna, comprising 45% and 28% of species in the wet and dry seasons, respectively, while Alismatales were the most prevalent flora, accounting for 42% and 57% across the same periods. Mean values of temperature, pH, turbidity, alkalinity, dissolved oxygen (DO), and biochemical oxygen demand (BOD) showed seasonal variations, with the highest values recorded as 31.8 °C (July), 7.68 (February), 785 NTU (July), 145 mg/L (March), 6.5 mg/L (July), and 1.95 mg/L (January), and the lowest values as 22.5 °C (January), 7.16 (July), 486 NTU (January), 115 mg/L (August), 4.5 mg/L (March), and 1.39 mg/L (July). The study identified industrial discharge, human encroachment, agricultural pesticide use, urbanization, and domestic activities as major contributors to the degradation of water quality, leading to a decline in fish availability and aquatic biodiversity. The findings highlight the urgent need for sustainable river management strategies to protect aquatic biodiversity and improve water quality in the Bhairab River.