An Integrated Approach to Assess Water Quality of the Karnaphuli Estuary through Nutrient Dynamics during the Dry Season

Abstract

The Karnaphuli River, one of the largest and most active rivers of Bangladesh, has historically served as a hub for numerous human activities such as port operations, shipping, and other operations. Numerous industrial plants, welding businesses, fertilizer firms, and multiple oil industries are all located along the riverbank. Thus, the water quality of this river is deteriorating as a result of pollutants being directly released into water bodies. Here, the contamination status of surface water (SW) collected from 10 stations within the Karnaphuli estuary (KE) in the dry season of 2023 was investigated. A comprehensive assessment was conducted using widely applied nutrient-related water quality indices, including the Nitrogen-Phosphorus Index (NPI), Trophic State Index (TRIX), and Carlson Trophic State Index (CTSI), derived from measured physicochemical parameters such as temperature, salinity, pH, turbidity, electrical conductivity (EC), density, dissolved oxygen (DO), and total dissolved solids (TDS), along with concentration of nutrients (phosphate, nitrate, nitrite, ammonia, and silicate) and chlorophyll-a. The results indicate that the quality of SW was generally qualified according to NPI, while TRIX and CTSI suggest predominantly oligotrophic to mesotrophic conditions, with localized variations across stations. Pearson correlation analysis revealed significant relationships among salinity-driven parameters and nutrient-biological interactions. Exploratory multivariate analyses (principal component analysis and hierarchical cluster analysis), supported by spatial distribution patterns, suggest possible influences of estuarine mixing processes and nearby anthropogenic activities on water quality variability, although direct source attribution requires further investigation.

The Dhaka University Journal of Earth and Environmental Sciences, Vol. 15(1), 2026, P 1-13