Spatiotemporal Assessment of Water Quality in the Yamuna River (Delhi-NCR Stretch) Using Water Quality Index and Multivariate Statistical Analysis: A Seasonal Perspective

<title>Abstract</title> The Yamuna River is an important freshwater source in northern India that has been highly degraded owing to intense urbanization, industrialization, and unlimited effluent release from domestic and industrial effluents. The water samples were collected on a seasonal basis (pre-monsoon, post-monsoon, and winter) at eight strategically located monitoring stations between Soniavihar and Majra Sekhpur, which is approximately 22 km from the most polluted portion of the river. The results showed significantly low water quality at all sampling points, and the WQI was more than 100 at all eight stations, which means that the water was not suitable for consumption and use in agriculture without proper treatment. Seasonal analysis revealed considerable changes in the water quality parameters. The maximum pollution loads were observed during the pre-monsoon season, which had high values of BOD (~ 52 mg/L), COD (~ 225 mg/L), TDS, and EC, with critically low DO values (as low as 1.4 mg/L). In the post-monsoon season, there were higher levels of turbidity and nitrates caused by agricultural runoff than in the winter samples, which had comparatively better conditions, with higher levels of DO and lower levels of biological activity. Spatial analysis revealed that Najafgarh, Shahdara, and Okhla were crucial pollution hotspots that were heavily fed on by domestic sewage and industrial effluents. This study highlights the pressing importance of strict pollution control measures, the development of a wastewater treatment system, and cooperation between governmental agencies and local agencies to rehabilitate and preserve the ecological conditions of the Yamuna River.