Uncertainty-based terrestrial critical loads of nutrient nitrogen in northern Saskatchewan, Canada

Atmospheric deposition of nitrogen (N) to boreal and taiga forests of Saskatchewan, Canada, is currently low, but there is concern over terrestrial eutrophication due to potential increases in deposition associated with industrial activities. Critical loads of nutrient N (CLnutN) were determined for five upland forest ecoregions according to the Simple Mass Balance (SMB) model using an uncertainty-based approach. Median ecoregion CLnutN ranged from 88 to 123 molc ha–1 yr–1 (1.2–1.8 kg N ha–1 yr–1), with higher CLnutN in the south. Median CLnutN for a small number of sites in the southernmost ecoregion were exceeded under both fire and harvest disturbance regimes, according to current N deposition. During the 21st century, median CLnutN were predicted to increase by more than 20% in response to climate driven increases in runoff and temperature. Current atmospheric deposition levels in the region are uncertain, and there is an ongoing need to monitor deposition and exceedance risk.