The nitrogen overload problem is becoming one of dominantly environmental issues both at regional and global scales. Regional nitrogen biogeochemical cycling and modeling have been researched for more than 10 years in the Institute of Geographic Sciences and Natural Resources Research (IGSNRR), Chinese Academy of Sciences.

For a better understanding of the N cycling processes under changing human pressures, a research group led by Professor YAN Weijin recently constructed a more rigorous approach to a quantitative description of the annual N inputs and exports of DIN from the Changjiang River basin for the period of 1970-2003, based on the Global NEWS-DIN model.

Researchers estimated the inputs of nitrogen (N) and exports of dissolved inorganic nitrogen (DIN) from the Changjiang River to the estuary for the period 1970-2003, by using the global NEWS-DIN model. Mean DIN yields ranged from 260 kg N km-2yr-1 in 1970 to 895 kg N km-2yr-1 in 2003, with an increasing trend in the basin.

The study demonstrated a varied contribution of different N inputs to river DIN yields during the period 1970-2003. Chemical fertilizer contributed 25.4% of the river DIN yields; while manure N contributed 24.7% in the period 1970-2003. The contribution of atmospheric N deposition to DIN yields steadily increases, with an average of 20.6% in the whole period.

Finally, researchers also assess possible future trajectories of DIN export based on the Global NEWS implementation of the Millennium Ecosystem Assessment scenarios. The result indicates that anthropogenically enhanced N inputs dominate and will continue to dominate river DIN yields under changing human pressures in the basin. Therefore, nitrogen pollution is and will continue to be a great challenge to China.