Wednesday, 8:30 AM in BR D (RICC)
(subject to change)
The flux of nitrogen from large watersheds is determined in part by the input of nitrogen into the landscape by human activities, and much of the variation in nitrogen fluxes across watersheds can be explained by differences in net anthropogenic nitrogen inputs (NANI). Climate also plays a role in determining watershed nitrogen fluxes. While the nitrogen flux in some large watersheds exceeds 40% of NANI, in others the flux is 10% or less. Both freshwater discharge and temperature are related to the fraction of NANI that is exported from watersheds, with export higher when temperatures are lower and when discharge is greater. We believe these climatic controls act primarily by influencing the rate of denitrification in the landscape. Higher rates of denitrification at warmer temperatures would be expected, but higher rates of denitrification when discharge is less and the watershed is more dry may seem paradoxical. We suggest that lower discharge is associated with longer water residence time in riparian wetlands and low-order streams, and that this leads to more denitrification at the landscape scale. We will explore how climate change may alter nitrogen fluxes in particular regions through the combined influences on temperature and discharge.
