Excess nutrients from fertilizer application, pollution discharge, and water regulations outflow through rivers from lands to oceans, seriously impacting coastal water quality and ecosystems. Understanding the effects of human activities on riverine nitrogen movement is very important for water environmental management and nitrogen cycle research.

Prof. XIE Zhenghui and Dr. LIU Shuang from the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, and their co-authors described how they synchronously incorporated the schemes of river water temperature change, riverine dissolved inorganic nitrogen (DIN) transport and human activities including nitrogen discharge and water regulation into the land surface model CLM4.5 under the framework of CESM1.2.0.

Then the model was applied to explore the effects of anthropogenic nitrogen discharge on DIN transport in global rivers.

"We found that DIN in the USA has increased primarily due to the use of nitrogen fertilizers. In contrast, European rivers were affected mainly by point source pollution. However, both aspects are equally important for aquatic environments in China," said XIE.

Worsening water quality in the lower reach of the Pearl River. (Image from Google Earth)  

The total anthropogenic impact on the DIN exported to the Pacific Ocean has increased from 10% to 30%, more significantly than any other ocean, over the past 20 years.

In general, the results indicated that incorporating schemes related to nitrogen transport and human activities into land surface models could be an effective way to monitor global river water quality and diagnose the performance of the land surface modeling.

The study entitled "Effects of anthropogenic nitrogen discharge on dissolved inorganic nitrogen transport in global rivers" was published in Global Change Biology.