The Vellayani Lake, a vital freshwater source in Thiruvananthapuram city, Kerala, faces critical water-quality issues due to anthropogenic activities. This study investigates the lake’s hydrochemical properties and water quality using 14 samples collected from representative hotspots, following APHA (2012) standard procedures. The ionic order is Cl− > HCO3− > SO42 − > Na+ > Ca2+ > NH3 > K+ > PO43 − > Mg2 + > NO3− > NO2−, with pH ranging from 6.93 to 8.53. Electrical conductivity (EC) ranges from 763 to 1959 μS/cm, with higher values in some samples. Dissolved oxygen (DO) levels range from 2.1 to 8.31 mg/L, indicating zones of biological degradation. Elevated levels of pollutants such as NO2−, NH3, and PO43− exceed permissible limits in some samples. The Water Quality Index (WQI) classifies 14% of samples as excellent, 40% as good, and 46% as poor for drinking purposes. Although SAR and RSC indicate suitability, 71% of samples have KR > 1, suggesting a potential sodium hazard for irrigation use. Multivariate statistical analyses (PCA and HCA) reveal that both geogenic processes and anthropogenic inputs control water chemistry. The findings indicate deteriorating lake water quality, calling for the implementation of pollution control measures towards the UN-SDGs: Clean Water and Sanitation (SDG6) and Sustainable Cities (SDG11).
Kaliraj et al. (Tue,) studied this question.