Evaluating the influences of seasonal water hydrochemistry variations and biochar-assisted heavy metal removal in Delhi’s urban wetlands: Implications for management strategies

Wetlands globally, crucial to both society and the environment, are losing their ecological and hydrological functions due to growing human populations and activities. This decline is particularly severe in metropolitan wetlands, where land use changes and development pressures are more intense. This study focuses on evaluating the water quality parameters of Delhi’s five urban wetlands including Hauz Khas Lake (HZL), Sanjay Lake (SL), Bhalswa Lake (BL), Vasant Kunj Lake (VKL), and Sanjay Van Lake (SVL) during winter (14—17^th January 2023) and summer (13—15^th May 2023) seasons. A total of 200 samples (20 samples from each lake) from HZL, SL, BL, VKL, and SVL were collected and analysed for 24 physicochemical parameters in both the seasons. Multivariate analysis was performed using a correlation matrix and principal component analysis (PCA)–biplot. Hydrochemical analysis was performed using Piper trilinear and Gibbs diagrams. Water suitability for irrigation was accessed using the chlorinity index, sodium adsorption ratio (SAR), Wilcox diagram, and Kelly index/ratio. Suitability for industrial purposes was evaluated using the Langelier saturation index (LSI) and Ryznar stability index (RSI). Drinking water suitability was assessed through the water quality index (WQI). The average (n = 3) water quality parameter values were compared to BIS and WHO drinking water standards. The average pH for HZL, SL, BL, VKL and SVL was alkaline (ranging from 7.2 to 9.9) in both the seasons. In winter, 4 parameters exceeded BIS permissible limits in HZL, 9 in SL, 12 in BL, 7 in VKL, and 6 in SVL. A similar trend was observed in summer, indicating that SVL and HZL are less polluted than SL, BL, and VKL. The chlorinity index, SAR, Kelly ratio, and Wilcox diagram indicated BL water’s unsuitability for irrigation in both seasons. RSI values above 8 for HZL, SL, BL, VKL, and SVL suggest corrosive nature of the water samples collected in both seasons. The main factors affecting the WQI were heavy metals (primarily Cd²⁺, Cr_T, Ni²⁺, Pb²⁺) and fluoride contamination. Finally, Himalayan pine needle biochar was prepared and used for ${Pb}^{2+}$ remediation from wetland water samples collected in both seasons. The findings of this study provide valuable insights into the water quality characteristics of the five wetlands during two seasons, aiding in water management and decision-making processes for sustainable utilization and conservation of water resources.