Implications of base cation deposition from increased climate-driven wildfires in the United States

Climate-driven increases in wildfires are altering atmospheric deposition patterns across the United States, with implications for ecosystem acidification and critical load (CL) exceedances. Using the 2002-2021 North American Chemical Reanalysis (NACR), we quantify multi-decadal trends in fire-derived base cation (Ca ²⁺ , Mg ²⁺ , K⁺, Na⁺) deposition and evaluate their capacity to buffer concurrent increases in reactive nitrogen (Nr) and sulfur (S) deposition from fires. We find substantial fire-derived enhancements in base cation deposition, often exceeding 100% near major wildfire regions, yet these increases are spatially inconsistent with Nr and S deposition maxima. Our results suggest that regions exhibiting the greatest relative increases in base cation deposition do not regularly coincide with those experiencing the largest Nr increases, thus limiting the potential for widespread acid buffering. After 2017, base cation contributions from fires rise sharply (~ 30 to 80%), reflecting intensifying fire activity, but combined Nr + S deposition remains overwhelmingly dominant, with increases 100 times larger than base cations due to fires. Overall, our results show that although fire-derived base cations provide localized buffering, they do not offset the broader rise in acidifying Nr and S deposition driven by climate-driven wildfires, reinforcing concerns about increasing CL exceedances in vulnerable western U.S. ecosystems.