Climate change and human activities, including heat emission, nitrogen (N) emission, and water management are altering the hydrothermal condition and N transport in the soil and river systems, thereby affecting the global nitrogen cycle and water environment. "We need to assess the impacts of these human activities on global river temperature and riverine N transport," said Prof. XIE Zhenghui with the Institute of Atmospheric Physics at the Chinese Academy of Sciences, "because quantitative assessment can not only improve our understanding of the material and energy cycle that occur in response to anthropogenic disturbances, but also contribute to protection of river ecosystems."

 
Xie and his collaborators from the Chinese Academy of Sciences incorporated the schemes of riverine dissolved inorganic nitrogen (DIN) transport, river water temperature, and human activity into a land surface model, and thus developed a land surface model CAS-LSM. They applied the model to explore the impacts of climate change and anthropogenic disturbances on global river temperature and DIN transport.

"We found that the water temperature of rivers in tropical zones increased at about 0.5^oC per decade due to climate change from 1981 to 2010, and the heat emission of the once-through cooling system of thermal power plants further warmed the temperature. In Asia, power plants increased local river temperatures by about 60%." Said Dr. LIU Shuang, the lead author of the study published in Global and Planetary Change.

Climate change determined the interannual variability of DIN exports from land to oceans, and water management controlled the retention of DIN by affecting the water cycle and river thermal processes.

 
"From the perspective of anthropogenic N emission, we found the riverine DIN in the USA was affected primarily by N fertilizer use, the changes in DIN fluxes in European rivers was dominated by point source pollution, and rivers in China were seriously affected by both fertilization and point source emission." said Dr. WANG Yan, the lead author of the team's another study published in Journal of Advances in Modeling Earth Systems.  

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 coupling and calculation process of the CAS-LSM that includes the surface water and groundwater withdrawal and use, anthropogenic N emission, river water temperature changes, and DIN transport; partial model validation results; impacts of climate change and anthropogenic disturbances on global river water temperature and DIN exports. BGC stands for biogeochemistry, BGP stands for biogeophysics, and RT stands for river temperature.

This series of studies have been published in Global Change Biology, Global and Planetary Change, Journal of Advances in Modeling Earth Systems and other journals. One of the papers is highlights by Nature Climate Change.

References:
1) Shuang Liu, Zhenghui Xie, Bin Liu, Yan Wang,Junqiang Gao, Yujin Zeng, Jinbo Xie, Zhipeng Xie, Binghao Jia, Peihua Qin, Ruichao Li, Longhuan Wang, Si Chen. Global river water warming due to climate change and anthropogenic heat emission. Global and Planetary Change, 2020, 193: 103289. (https://doi.org/10.1016/j.gloplacha.2020.103289).
2) Yan Wang, Zhenghui Xie, Shuang Liu, Longhuan Wang, Ruichao Li, Si Chen, Binghao Jia, Peihua Qin, Jinbo Xie. Effects of anthropogenic disturbances and climate change on riverine dissolved inorganic nitrogen transport. Journal of Advances in Modeling Earth Systems, 2020, 12, e2020MS002234. (https://doi.org/10.1029/2020MS002234)
3) Shuang Liu, Zhenghui Xie, Yujin Zeng, Bin Liu, Ruichao Li, Yan Wang, Longhuan Wang, Peihua Qin, Binghao Jia, Jinbo Xie,. Effects of anthropogenic nitrogen discharge on dissolved inorganic nitrogen transport in global rivers. Global Change Biology, 2019,00: 1–21. (https://doi.org/10.1111/gcb.14570 )
4) Langenbrunner, B. Power plants warm rivers. Nature Climate Change, 2020, 10, 888. (https://doi.org/10.1038/s41558-020-00928-0)

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