Nutrients in smoke: do they contribute to cyanobacteria blooms in downwind waterbodies?
On this page:
Wildfire activity is increasing in many ecosystems globally due in part to climate change. Burned areas increase nutrient pulses to local waterbodies through lack of vegetation uptake and increased erosion. Indeed, higher concentrations of nutrients are routinely observed in streams for several years or more downgradient from burned areas. Less recognized, however, is the potential for nutrient additions to waterbodies via wildfire smoke. In a previous study, we used 15 years of air quality data to characterize nutrients associated with fine particulate matter (PM2.5) on wildfire-smoke impacted days in the western US. Smoke plume locations were identified using the US National Oceanic and Atmospheric Administration’s Hazard Mapping System, and air quality monitoring data were gathered from the US Environmental Protection Agency’s (EPA) Air Quality System. Most PM2.5-associated nutrients, including phosphorus, were significantly elevated on smoke-impacted days. Moreover, in a few cases in California, we observed a relationship between high phosphorus smoke plumes and downwind cyanobacteria blooms, as detected via the US EPA’s Cyanobacteria Assessment Network (CyAN). Here, we greatly expanded upon this work to test an effect of smoke on lakes across the contiguous US using CyAN’s network of almost 2,000 lakes in 2018. In all, we found that a subset of lakes showed an increase in cyanobacteria abundance in the two-weeks following intersection with wildfire smoke. Most of these lakes are located in the West and upper Midwest regions, subject to smoke from both US and Canadian fires; whereas, we generally did not observe the occurrence in lakes in the eastern US. Our results suggest smoke density plays a role in determining whether a bloom occurs, as does antecedent water temperatures. We are currently exploring the potential role of nutrient-status (e.g., oligotrophic lakes), land cover, and location in the landscape (e.g., elevation) as possible further explanatory variables. Overall, our findings contribute to growing evidence that wildfire smoke can affect downwind aquatic ecosystems.