Taking the pulse of mother Ganga – The evolution of water pollution along the Ganges River

Water quality along the Ganga is critically impacted by multiple stressors, including agricultural, industrial and domestic pollution inputs, a lack and failure of water and sanitation infrastructure, increasing water demands in areas of intense population growth and migration, as well as the severe implications of land use and climate change. We report the findings of a collaborative effort to monitor the evolution of emerging and legacy pollutants along the 2500 km length of the Ganga and its major tributaries that was carried out over a six-week period in 2019 by three teams of more than 30 international researchers from 10 institutions. Surface water and sediment were sampled from more than 80 locations along the river and analysed for organic contaminants, nutrients, metals, pathogen indicators, microbial activity and diversity as well as microplastics, integrating in-situ fluorescence and UV absorbance optical sensor technologies with laboratory sample preparation and analyses. Water and sediment samples were analysed to identify the co-existence of pollution hotspots, quantify their spatial footprint and identify potential source areas, dilution, connectivity and thus, derive understanding of the interactions between proximal and distal of sources of solute and particulate pollutants.

Our results reveal the co-existence of distinct pollution hotspots that coincided for different contaminant groups but not others (e.g., microplastics). Interestingly, the downstream footprint of specific pollution hotspots from contamination sources along the main stem of the Ganga varied between contaminants bearing significant implications for the spatial reach and legacy of pollution hotspots. Furthermore, the comparison of the downstream evolution of multi-pollution profiles between surface water and sediment samples support interpretations of the role of in-stream fate and transport processes in comparison to patterns of pollution source zone activations across the channel. In reporting the development of this multi-dimensional pollution dataset, we aim to stimulate a discussion of the value of large river network surveys to better understand the relative contributions, footprints and impacts of complex pollution sources for integrated approaches in water resources and pollution management.