Spatio-temporal trends in the flow and water quality: response of river Yamuna to urbanization.

Urban rivers are major victims of pollution and the river Yamuna is a notable example. Effective human intervention requires an understanding of the water quality response of rivers to urbanization. To this end, the time-series data from the Central Water Commission (CWC) and the Central Pollution Control Board (CPCB) was analyzed. The dataset included 44 parameters for twelve stations on Yamuna mainstream from 1978 to 2015. Statistical tests for analysis of trends revealed decreasing monsoon flows over the past decades. Furthermore, increasing non-monsoon flows from Delhi to Agra was indicative of a significant contribution from wastewater discharge to the river. Groundwater parameters such as electrical conductivity, hardness, and sodium content were found to increase in the river over the years. This suggests the use of groundwater that gets converted into domestic wastewater flowing in surface drains discharging into the river resulting in the deterioration of water quality of river Yamuna. Dissolved oxygen (DO) and ammonical nitrogen values from Delhi to Agra stretch do not support indigenous aquatic life. A positive correlation between total and fecal coliform in this river stretch indicates the dominance of domestic sewage. The expected significant correlation between DO and biochemical oxygen demand (BOD) was not observed throughout the river stretch. High values of DO reported by CPCB indicate the presence of photosynthetic activity in the river; hence diurnal DO measurement is suggested for validation. For the rejuvenation of river Yamuna, the focus of treatment should be shifted to coliform, DO, chemical oxygen demand, and nutrients. The present study analyzed the response of the riverine ecosystem to altered flow regimes and changes in river water quality, and the findings can serve as a basis for decision-makers engaged in river restoration and conservation efforts.