Water chemistry and water quality of a tidal river system in relation with riverbank land use pattern and regional climate in the southwest Bengal Delta of Bangladesh

Water chemistry of BRRS (Bhairab-Rupsha River System) is defining the water quality of BRRS, which is seasonally changed from premonsoon (March–May) to postmonsoon (June–August). The study identified the relation in changes of water chemistry and water pollution with riverbank land use patterns and regional climate through four analytical frameworks including—Hydrochemical framework; GIS and RS framework; Statistical framework; Climatic framework. Integration of these four frameworks defines the changes of water chemistry as in water quality and explores the relation in-between water chemistry, water quality, riverbank land use pattern, and regional climate. The concentration of ions is higher in premonsoon with low precipitation rate and high daily temperature. The spatial distribution of water chemistry of BRRS explored in upper reach (upstream), middle reach, and lower reach (downstream) according to the riverbank land use patterns. Highest EC is measured in upper reach and in middle reach with high Na⁺ at postmonsoon and in lower reach with high Cl⁻ at premonsoon. TDS is highest in upper reach with high Mg²⁺ at postmonsoon and in lower reach with high K⁺, Ca²⁺, Mg²⁺, and Cl⁻ in premonsoon. Water chemistry of BRRS is controlling by continental weathering in postmonsoon, and by high salt concentration in premonsoon. The combination of Piper plot and mixing diagrams explored precipitation-runoff dominates in postmonsoon and lacks ample discharge in the premonsoon press the tidal front downwards and consequently dominated by increasing salt concentration. The degree of pollution estimates % of pollution in BRRS which increases in premonsoon and decreases in postmonsoon. SAR, Na%, TDS, and EC explored that BRRS water is suitable for daily purposes and irrigation only in postmonsoon.