Evidence for organic N deposition and its anthropogenic sources in China

Organic nitrogen (N) is an important component of the atmospheric deposition of reactive N, but its sources are essentially unknown. Assessing whether this dissolved organic N (DON) is of natural, anthropogenic or mixed origin is critically important in attempting to determine the scale of human perturbation of the global N cycle. Here we report evidence for atmospheric organic N deposition and its anthropogenic sources in China. Precipitation samples were collected and analyzed from 15 rural, suburban and urban sites during 2005 and 2006. The average deposition of DON was 8.6 kg ha−1 yr−1 with a volume-weighted concentration of 111 μmol L−1, which was much higher than in other regions of the world. The contribution of DON to total dissolved N (TDN) was approximately 30% on average, agreeing well with other reported data in the literature. Parallel collections of wet-only and bulk deposition showed wet deposition to be 68% on average, indicating a significant dry deposition component. Combining data from the Chinese sites with those from elsewhere in the world, significant (p<0.0001) correlations between DON and NH4–N, NO3–N and TDN suggest that atmospheric organic N originates from similar sources to dissolved inorganic N (DIN) (NH4–N and NO3–N), which are largely attributed to anthropogenic emissions from both agricultural and industrial sources.