Wildfires in the western United States are mobilizing PM2.5-associated nutrients and may be contributing to downwind cyanobacteria blooms
Wildfire activity is increasing and can be linked to climate change effects, including rising global temperatures and more frequent drought conditions. Wildfire emissions impact human health and sensitive ecosystems, particularly in the western United States where large fire frequency has increased. Herein, we linked 15 years (2006-2020) of particulate matter (PM2.5) chemical speciation data with smoke plume analysis to identify PM2.5-associated nutrients elevated in air samples on smoke-impacted days. Except for ammonium, all macro- and micro-nutrients analyzed (phosphorus, calcium, potassium, sodium, silicon, copper, aluminum, iron, manganese, magnesium, zinc, nitrate) were elevated on smoke days, with some nutrients episodically elevated >10,000% during select fire events. Air mass trajectory analysis and satellite cyanobacteria measurements of four case study fires suggest smoke composition influences cyanobacteria activity in lakes up to 230 kilometers downwind from fires. Cyanobacteria indices in downwind lakes markedly increased two to seven days following high airborne phosphorus concentrations from wildfire smoke. Since cyanobacteria blooms can be associated with the production of cyanotoxins and decreases in dissolved oxygen, this finding has important implications for drinking water reservoirs common in the western United States, and for lake ecology, particularly in alpine lakes with otherwise limited nutrient inputs.