Understanding the impact of agricultural activity in groundwater by water isotopes and dual isotope of dissolved nitrate

In general, availability of groundwater have shaped human settlement and land-use patterns by providing water for the people living in an area. However, anthropogenic activities including the agricultural practice impacted the quality and quantity of groundwater significantly. Therefore, it is crucial to monitor and quantify the human impact, and to find pathways towards more sustainable use of groundwater. The Hindon basin in the north-west part of Indo-Gangetic plain in India which once witnessed the Indus valley civilisation, now negatively affected by human influences. The river basin covers an area of ca. 7000 km² and is inhabited by more than 10 million people. The catchment of the Hindon river hosts sugar mills, paper mills, textile industry and intensified agricultural activities. The land-use pattern data shows that 66% of land is utilised for agriculture including orchards, 15% is used for settlements, 0.5% for industrial purposes, and less than 2% of the basin area has forest cover which is of poor quality. The main crops in the area is sugarcane, and urea is used extensively in the agricultural field. The run-off of nutrients and agrichemicals from the fields deteriorating the water quality, making the Hindon one of the most polluted stretches in the Indo-Gangetic plain.

To quantify the impact of agricultural activities in groundwater, water isotopes (δ²H and δ¹⁸O) and dual isotopes of dissolved nitrate (δ¹⁵N and δ¹⁸O) been measured in groundwater. The water isotope data suggest that impact in groundwater is so severe that the canal water, sourced from the glacier melt of the Himalaya, which pass of though the basin is recharging into the groundwater. The dual isotopes of nitrate suggest that the dissolved nitrate which is much above the WHO prescribed limit is mostly sourced from the fertilizer urea. Our result suggests that for sustainability, a multi-crop agricultural practice with less demanding water crop with reduction of use of urea is the need of the hour.