The overall chemistry of River Ganga is much cleaner than its tarnished image, at least in terms of toxic heavy metals, says a new study.

While most studies point towards a deterioration of water quality of the Ganga and its environmental threat, they are mostly based on easy to measure water quality parameters such as on biochemical oxygen demand (BOD and COD), dissolved oxygen (DO), pH, fecal coliform, and conductivity.

A team of scientists at the Indian Institute of Technology Kanpur has found out that the dissolved inorganic constituents like trace and toxic heavy metals of the Ganga River can be compared to the global average river composition, and local contamination hotspots are not persistent downstream.

The researchers came to a conclusion after carrying out 3,645 river water analyses of dissolved trace elements measured at 38 targeted locations in the Ganga Basin collected during the pre-monsoon, monsoon, and post-monsoon seasons of 2014, 2015, and 2016.

This work was supported by the Indo-U.S. Science and Technology Forum (IUSSTF) a bilateral organization under the Department of Science and Technology (DST) and U.S. Department of States along with Ministry of Earth Sciences (MoES), Government of India, and has been recently published by American Geophysical Union in the journal ‘Geochemistry, Geophysics, Geosystems’.

The detailed river chemistry database from the source to the sink of the River Ganga would not only help quantify the variability of dissolved trace elements across space and time but would also help probe water quality issues with a magnifying glass.

The study also shows that the reported contamination ‘hotspots’ exist, but they are much ‘localized’ and not persistent downstream. In fact, the dissolved trace metal composition of the river water was found to be one of the highest in sites close to the glacier (above 3000 meters), contrary to the expected in and around large cities and industrial zones, due to high physical and chemical weathering in the glacier-front.

“All existing studies are only restricted in and around effluent discharge sites, large cities, and bathing Ghats to capture contamination hotspots. They do not represent the overall water chemistry and are exaggerated estimates that are significantly biased toward geographically focused areas,” said Indra Sen, an Assistant Professor in the Department of Earth Sciences, IIT Kanpur.

The scientists are documenting the present-day background dissolved trace element concentrations of the River Ganga to assess future water quality changes in the basin. Soumita Boral, a Ph.D. student at IIT Kanpur and the lead author of the study, said, “concurrent sampling of river water along with other sources such as ice meltwater, snowmelt, groundwater, and rainfall allowed us to quantify the natural processes that control the distribution of trace elements in river water, and in turn, allowed us to quantify the present-day background levels.

India Co-Chair of IUSSTF, Prof. Ashutosh Sharma remarked that robust and reliable measurements all along the river and over time are of vital importance to map and understand the sources, sinks and distribution of pollutants to devise effective strategies for combating them. This study is a good step in that direction.

Publication link: https://doi.org/10.1029/2020GC009203