Excessive N inputs elevate nitrate concentrations of shallow and deep well groundwater

Excessive use of nitrogenous fertilizers causes nitrate contamination of surface and groundwater. We measured nitrate concentrations of 112 samples collected from shallow and deep groundwater wells at seven sites along the seasonally-flooded Indus river during the four sampling campaigns during 2016-2017.

Nitrate concentrations of shallow wells were 15-54 and 20-45 mg L-1 during the start and middle of dry season, respectively. However, at the end of the dry season, nitrate concentrations in 70% of both shallow and deep wells samples were above the permissible limits of 50 mg L-1 . δ18O data suggested lower recharge in deep well than shallow wells.