Unravelling changes in global freshwater nitrogen cycling in the Anthropocene


Inland waters play an important role in global nitrogen (N) cycling and transport substantial N from land to sea. However, it remains unclear whether, when and why freshwater biogeochemical N cycling has changed in response to human activities, climate change, and other environmental conditions. In this study, we quantified the long-term changes in the global freshwater N cycling, i.e., inputs to global inland waters, in-stream retention and transformations, and export to oceans of different N forms, using the spatially explicit, integrated assessment model IMAGE-DGNM including the mechanistic in-stream biogeochemistry module (DISC). This model keeps track of N supply from the land, describes N transformations and transport along the river continuum through different waterbodies, and couples oxygen conditions with N dynamics. We validate the model against long-time-series observations of different variables from a series of rivers worldwide. Then we analyse the model results of the temporal changes in the global freshwater N transformation process flows for different N forms during 1900-2010, and unravel the mechanisms of the changes in the contributions of different N forms during N transport along the aquatic continuum and during different periods. On this basis, we also discuss the mechanism of in-stream retention processes in global inland waters.

Junjie Wang
Utrecht University
Salle Darcy, https://us02web.zoom.us/j/81298191014
Vendredi, 31 mars, 2023 - 12:00