Tracing the sources of pollutants in Ganga river water using conventional and non-conventional isotope analysis in nitrates

Tracing the sources of pollutants in Ganga river water using conventional and non-conventional isotope analysis in nitrates

 

Abhayanand S. Maurya¹, Amzad H. Laskar², Nityanand S. Maurya³, Mao-Chang Liang⁴,

 

¹Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India

²Geosciences Division, Physical Research Laboratory, Ahmedabad 380009, Gujarat, India

³Department of Civil Engineering, National Institute of Technology Patna, India

⁴Institute of Earth Sciences, Academia Sinica, Taiwan

 

Ganga is the largest river in India providing fresh water to ~40 % of India’s population which is more than any other river in the world. It is also one of the most polluted rivers in the world. Pollution, mainly from human and industrial wastes in the Ganga poses significant threats to human health and environment. This is an attempt to identify and quantify the contribution of different sources in the river water pollution using stable isotopes in nitrate (NO₃^-). We measured non-conventional triple oxygen isotopes (∆¹⁷O_NO3=δ¹⁷O_NO3-λδ¹⁸O_NO3) along with the conventional isotopes (δ¹⁵N and δ¹⁸O) in NO₃^- and concentrations of major ions and metals (both heavy and trace ones) in Ganga river water to understand the sources and contribution from different pollution sectors. We also measured stable water isotopes (δD and δ¹⁸O) to understand the secondary processes such as in stream evaporation and inflow over the course of the river.  Water samples were collected from multiple locations starting from the clean water in the upstream region to all the way to the estuaries before the onset of monsoon, to best capture anthropogenic signals. ∆¹⁷O in NO₃^- is used to partition the atmospheric depositions from other sources such as human and industrial wastes and δ¹⁵N and δ¹⁸O values are used to partition the contribution of pollutants from different land sources such as municipal wastes and agricultural fertilizers. ∆¹⁷O in NO₃^- is also used to understand reaction processes which affect the isotopic composition such as nitrification, denitrification, volatilization, assimilation and mineralization as those processes mostly follow mass dependent fractionation without affecting ∆¹⁷O but influence the conventional isotopic compositions. We will present the results along with some recommendations for reducing the pollution level of the Ganga water.