Exploring spatiotemporal water quality change of eutrophicated urban lake

Abstract

The long-term health and ecological stability of urban water bodies are intrinsically linked to their water quality. This study assesses the current ecological state of the hyper-eutrophic, warm polymictic Hauz Khas Lake in Delhi, India, which has been rejuvenated with Sewage Treatment Plant (STP) effluent and suffered from eutrophication since then. The primary objective was to evaluate the lake's health by analyzing major physical, chemical, and biological parameters and to quantify changes over an eight-year period. Water quality was assessed using the Water Quality Index (WQI) and Trophic State Index (TSI), with further statistical analysis conducted via Principal Component Analysis (PCA). Our findings reveal that the lake is under significant stress from elevated nutrient inputs (NO₃-N: 1.9–3.13 mg/L, PO₄³⁻: 4–8 mg/L), resulting in a hyper-eutrophic state of 191.66 ± 10.68 (2022–23). The WQI ranged from 44.28 to 64.28, indicating medium to poor water quality with a slight degradation compared to 2015 data. PCA results show a significant intensification of interactions among water quality parameters over the last eight years, with the variance explained by the first two principal components increasing by 37.5 % and 28.57 %, respectively. This study concludes that while the STP-based rejuvenation strategy has maintained the lake's physical existence, it has led to severe hyper-eutrophication, highlighting the urgent need for advanced nutrient management strategies for urban lake conservation