Harmful algal blooms in high-elevation Western United States lakes

Nutrient pollution and climate change can lead to eutrophication and harmful algal blooms (HABs) in lakes. While most research on eutrophication has been conducted in human-dominated watersheds, HABs have recently been reported in relatively undisturbed lakes in the Intermountain Western United States. In Wyoming, the number of HAB advisories has steadily increased from 3 water bodies in 2017 to >40 water bodies in 2023. Many blooms occur in remote lakes with forested watersheds, suggesting that controls on bloom formation may be different than in other regions where most studies have occurred. The increase in HAB advisories also contradicts recent remote-sensing based research suggesting that eutrophication is not widespread in the region. We investigated these trends and contradictions in water bodies in Wyoming through analysis of monthly monitoring data collected by our research group and by the State of Wyoming, and through high-frequency monitoring data generated from buoys equipped water quality sensors. Overall, data suggest that nutrient limitation may differ from other regions, with very low N:P ratios in some lakes that are susceptible to blooms. Productivity and algal biomass were variable across the surface of lakes, suggesting that spatial heterogeneity in primary production within individual lakes could explain the discrepancy between increasing HAB advisories and the lack of eutrophication trends from remote sensing data. Continued long-term lake monitoring in this region could elucidate key connections between climate change, lake water quality, and HABs.

Primary Presenter: Sarah Collins, University of Wyoming (sarahmcollins@gmail.com)

Authors:

Sean Bertalot, University of Wyoming  (sbertalo@uwyo.edu)

William Fetzer, University of Wyoming  (wfetzer@uwyo.edu)

Kevin Gauthier, University of Wyoming  (kgauthi2@uwyo.edu)

Annika Walters, USGS Cooperative Research Unit & University of Wyoming  (annika.walters@uwyo.edu)