Characteristics of nitrogen flow and its environmental effects in the Yellow River Basin, China.

In large river basins, the nitrogen (N) cycle is largely regulated by complicated interactions between human and natural elements. Nevertheless, the origins, fate and driving forces of reactive nitrogen (Nr) flows in the basins are still not clear. An estimation model of N flux was established for evaluating the Nr flow and its environmental effects in the Yellow River Basin of Henan Province (HYRB) by means of material flow analysis. Total N input and output of HYRB were calculated at 4090.9 and 3948.8 Gg N yr, causing 142.0 Gg yr of N stored in the basin. Industry, cropland and residential activities, respectively occupied for 42.2%, 23.2% and 12.3% of the whole input, as well as 43.6%, 25.1% and 12.3% of the whole output, which were central to HYRB's N cycle. Anthropogenic activities regulated above 95.0% of total inputs, and 49.5% of N outputs was emitted into the air and 4.5% into hydrosphere. High N input, energy intensive, imperfect sewage disposal facilities and low N utilization efficiency were the main reasons of contaminate. How to effectively regulate the input of high-strength N pollutant associated with insufficient N cycling and Nr elimination is the main issue in the Yellow River Basin. In present research also put forward corresponding control measures according to the evaluation of N flow and Nr release of HYRB. The research can supply science foundation for coordinating the human-environment relationship in large basins, and also has important reference significance for the formulation of Nr emission reduction strategies.