Wet deposition fluxes of atmospheric inorganic reactive nitrogen at an urban and rural site in the Indo-Gangetic Plain

Abstract

Excess nitrogen deposition is a matter of concern for sensitive ecosystems. However, understanding the sources and transport of Nr species has been a challenge due to limited observations of atmospheric deposition of the key Nr species across India. In this study, wet deposition of atmospheric inorganic Nr species was investigated during the year 2013 at two regionally representative sites: Delhi (an urban site) and Jaunpur (a rural site). These sites are located in the Indo-Gangetic Plain (IGP) region, which is one of the most populated and fertile regions of India. The average NH4+ concentrations in rain water were found to be 25.4 μeql−1 and 98.5 μeql−1 at the rural and urban sites, respectively, whereas average NO3− concentrations were 12.4 μeql−1 and 28.7 μeql−1 at the rural and urban sites (respectively). The annual average wet deposition fluxes of NH4+ and NO3− at Delhi were calculated as 10.45 and 3.05 kgN ha−1 yr−1 respectively, whereas at Jaunpur the fluxes were 3.19 and 1.56 kgN ha−1 yr−1 respectively. In order to assess the Nr deposition, our estimates showed 486% increase in NO3− (from 0.52 to 3.05 kgN ha−1 yr−1) while 283% NH4+ (2.72–10.44 kgN ha−1 yr−1) between 1994 and 2013 at Delhi, clearly indicating the effect of urbanization and Land Use Land Cover (LULC) change. Reduced versus oxidized N deposition contribution was also estimated. This study provides key quantitative information to support regional nitrogen budget estimates in south Asia.