Cyanobacteria blooms increase in downwind lakes after intersection with wildfire smoke

Area burned and wildfire emissions have increased in the United States (U.S.) and globally in recent years, impacting human health and ecosystems, including waterbodies. Almost all studies of water quality and fire have focused on the effects in burned watersheds, showing an increase in sediments, nutrients, and metals in local waterbodies for instance. By contrast, the effects on landscapes downwind of the fire epicenter and across watershed boundaries have received little attention to date. In this study, we linked wildfire smoke plumes with remotely sensed cyanobacteria data from over 2,000 lakes across the contiguous U.S. from the year 2018. We then explored changes in magnitude of lake chlorophyll a from cyanobacteria biomass following intersection with wildfire smoke. Chlorophyll a values for each lake were fitted to seasonal curves, and the residuals were tested in smoke vs. no-smoke periods. Values during and within two weeks after smoke periods were significantly elevated (1.5 µg/L) compared to values from non-smoke periods (-0.3 µg/L). Moreover, chlorophyll responses significantly increased with higher smoke density. We also tested results based on lake elevation and bloom magnitude at the onset of smoke exposure (baseline bloom magnitude). We observed significantly higher relative chlorophyll responses to smoke in higher vs. lower elevation lakes and for lakes with lower baseline bloom magnitude (i.e., more oligotrophic lakes) vs. higher baseline bloom magnitudes (i.e., more eutrophic lakes). We hypothesize that these increases in chlorophyll from cyanobacteria are caused by nutrients deposited in smoke and ash on lakes with already warm water temperatures. Since cyanobacteria blooms can be associated with the production of cyanotoxins and wildfire activity is increasing, this finding has implications for drinking water reservoirs across the U.S., and for lake ecology, particularly alpine lakes with otherwise limited nutrient inputs.

Impact/Purpose

This is an abstract for a planned presentation to the International Association for Landscape Ecology.  It details our findings on how PM2.5-associated nutrients may be impacting water quality in downwind lakes.  Using remote sensing, we detected cyanobacteria blooms in lakes downwind of fires, predominantly in the western U.S. and midwestern U.S.  These blooms occurred within two weeks following intersection with the smoke.  We also report on our findings that bloom magnitude increased with increasing smoke density.  Relative bloom magnitude also increased in higher elevation lakes and more oligotrophic lakes.  When published, this work will be of interest to water quality managers in the agency because of the deleterious effects that algal blooms can have on aquatic life, recreation, and drinking water.

Citation

Olson, Nicole E., Meredith M. Brehob, Robert D. Sabo, I. Pavlovic, Kathleen I. Shank, Sam Penry, Amalia M. Handler, Michael J. Pennino, R. Byron Rice, Katie L. Boaggio, AND Stephen D. LeDuc. Cyanobacteria blooms increase in downwind lakes after intersection with wildfire smoke. International Association for Landscape Ecology Annual Meeting, Raleigh, NC, April 13 - 17, 2025.