No evidence of widespread algal bloom intensification in hundreds of lakes

Abstract

Algal blooms, the rapid proliferation of algal biomass often to nuisance or harmful levels, diminish aquatic ecosystem services. Freshwater blooms can cause substantial economic damage by interrupting water supply, limiting recreation, and reducing property values. The interaction between eutrophication and climate change has been hypothesized to drive widespread intensification of blooms in inland waters, although there is little empirical evidence that this trend is pervasive. Here, we show that bloom intensification in inland waterbodies – defined as trends in chlorophyll‐a of increasing bloom magnitude, severity, or duration – has not been widespread for hundreds of lakes in the US. Only 10.8% of the 323 waterbodies analyzed had significant bloom intensification. Conversely, 16.4% of the waterbodies had significant decreasing trends during the same period. While it is encouraging that bloom intensification is not currently widespread, continued efforts toward aquatic ecosystem protection and restoration are imperative for maintaining ecosystem services into the future.

Heterogenous controls on lake color and trends across the high-elevation U.S. Rocky Mountain region

“…A relatively small proportion of lakes (13%) exhibited characteristics indicative of decreasing water quality, either shifting from states of blue to greener or intensifying green/brown. Similarly, recent studies of chlorophyll-a trends in U.S. lakes have shown algal intensification to be occurring in a relatively small proportion of lakes with long-term field data (Wilkinson et al 2021). Lakes that did exhibit trends toward greener waters were diverse in their size, shape, watershed area, land cover, and climatic changes.…”

“…In addition, snowpack and summer weather conditions are strong controls on water chemistry and algal biomass for mountain lakes (Preston et al 2016, Sadro et al 2018, Oleksy et al 2020b, and these drivers are also changing. While there has been recent research examining regional to continental scale changes in lake nutrients (Stoddard et al 2016, Oliver et al 2017, water clarity (Topp et al 2021), lake color (Kuhn and Butman 2021), and algal blooms (Wilkinson et al 2021) there have been no regional studies, to our knowledge, on high-elevation lake shifts likely due to a lack of in situ water quality monitoring data (Read et al 2017).…”

Heterogenous controls on lake color and trends across the high-elevation U.S. Rocky Mountain region

“…For lakes in the Rocky Mountain region that changed over the past 36 years, most trended bluer (70%), suggesting an overall improvement in summer water quality. While there is a growing concern of widespread declines in water quality, our results build on recent studies that show regional improvements in water quality and a more nuanced understanding of changes in lakes occurring across large spatial scales (Topp et al, 2021;Wilkinson et al, 2021).…”

“…This may partially explain why rates of nitrogen deposition did not appear to have an effect of water color trends, even though excess nitrogen is implicated as a driver of ecological change in high-elevation lakes across the region (Burpee et al, 2022;Moser et al, 2019;. Second, we limited our analysis to median summer color, but it is possible that there are dynamics that have helped create the perception of lake greening, such as episodic algal blooms, which are increasing in some systems (Ho et al, 2019;Vadeboncoeur et al, 2021;Wilkinson et al, 2021). This could create issues where algal blooms really are present but are short and intense and thus not captured by Landsat's 8 or 16 day return sampling interval.…”

“…In addition, snowpack and summer weather conditions are strong controls on water chemistry and algal biomass for mountain lakes Preston et al, 2016;Sadro et al, 2018). While there has been recent research examining regional to continental scale changes in lake nutrients (Oliver et al, 2017;Stoddard et al, 2016), water clarity (Topp et al, 2021), lake color (Kuhn and Butman, 2021), and algal blooms (Wilkinson et al, 2021) there have been no regional studies, to our knowledge, on highelevation lake shifts likely due to a lack of in situ water quality monitoring data (Read et al, 2017).…”