Smoke-Affected Rain Fertilizes Terrestrial and Aquatic Ecosystems.

Wildland fire smoke and ash are pervasive and a significant source of particulate matter to the atmosphere. In addition to effects on air quality, wildland smoke and ash deposit to ecosystems via dry (particulate) and wet (precipitation) deposition. Here we combine remotely sensed smoke polygon data with rainfall and weekly wet deposition data from > 250 U.S. National Atmospheric Deposition Program (NADP) sites to quantify wildland smoke influence on wet ion deposition during 2014, 2020, and 2022. Combined records of daily smoke and rain indicate that sites experienced 21 smoke-rain days (when smoke and rainfall co-occur), on average, in 2022 compared to 4 days in 2014 and 6 days in 2020. The number of smoke-rain days and their spatial distribution were driven more by variation in smoke than rain occurrence. Across 16 climate regions, the Upper Midwest was a persistent hotspot for smoke-rain days in all 3 years. Mixed effects models estimating site-level impacts of smoke-rain on a weekly basis showed that smoke-rain days had significant positive effects on wet deposition of all nine ions evaluated. Orthophosphate (PO