Anthropogenic and climatic drivers of hydroenvironmental change in urban freshwater wetlands of Doon Valley Uttarakhand

Urban wetlands are increasingly threatened by urbanization, climate change, and unplanned development. In the Doon Valley, these pressures have led to contamination and reduced nutrient-filtering capacity. This study reveals seasonal hydrochemical dynamics using stable isotopes (δ2H, δ18O(‰ VSMOW), deuterium-excess), physicochemical parameters, major ions, and trace elements. The water pollution index (WPI) and principal component analysis (PCA) were applied as statistical methods to assess water quality and identify potential sources. The results show that evaporation is the primary hydrological process. This is evident from the seasonal evaporation patterns, where summer samples indicate more substantial evaporation effects than winter samples. The overall trend lines differ from natural rainfall patterns, and the lower summer values further confirm more intense evaporation during this season. Carbonate weathering is the primary driver of major ion chemistry, with a dominance of Ca2+-HCO3− (Ca2+ + Mg2+/HCO3− ≈ 0.5), forming a consistent Ca2+-Mg2+-HCO3− hydrochemical facies. Although trace elements (Fe > Sr > Cr > Zn) were generally below regulatory limits, iron exceeded the maximum allowable level, reaching 750 µg/L. Principal Component Analysis (PCA) analysis highlighted two significant processes: evaporative concentration in winter and anthropogenic-biological influences in summer. Spatially, the Nakronda (NK) wetland demonstrated the highest pollution level, with a summer WPI of 0.50, mainly due to urbanization, while other areas recorded minimal pollution (WPI ≤ 0.3). This study emphasizes the vulnerabilities of these wetlands to evaporative stress and human-caused degradation, highlighting the need for targeted management strategies to enhance urban wetland resilience.