Characterizing atmospheric rivers and the effects of extreme precipitation on nitrate in agricultural settings

This study characterized the isotopic composition of extreme precipitation and surface waters and explored the relation between extreme precipitation and nitrate in southwest British Columbia. Atmospheric river (AR)-derived precipitation was isotopically depleted compared to non-ARs, but not distinct enough to be manifested in surface waters. The d-excess values of precipitation and surface waters varied seasonally and suggest that winter precipitation from high elevation contributes to summer surface waters. In the North Alouette Watershed (NA), surface water nitrate concentrations are low (~1.0 mg/L) and vary minimally after extreme precipitation events. In the Abbotsford Sumas Aquifer (ASA), nitrate in groundwater is elevated (~3.6 mg/L), but no relationship with extreme precipitation events was observed. At both locations, the sampling frequency was likely too low. However, numerical modelling of nitrate transport during extreme events suggests rapid mobilization in the ASA, while in the NA, nitrate remains stored in the vadose zone.