Exploring temperature and precipitation impacts on harmful algal blooms across continental U.S. lakes

Abstract

Climate change is expected to impact the severity of harmful algal blooms in lakes and reservoirs through a number of mechanisms related to the influence of warming temperatures and changes to precipitation patterns. Evidence on the prevalence of individual mechanisms is lacking, however, with knowledge of many mechanisms restricted to studies of individual or small subsets of lakes. Here, we leverage over twelve hundred summertime lake observations from across the continental U.S. to explore evidence for the hypothesized risks from climate change attributable to specific mechanisms. Using a statistical model selection approach, we examine associations between temperature and precipitation variables and indicators of total phytoplankton abundance, species dominance, and toxicity. We find evidence in support of the hypotheses that summer temperatures drive total abundance, that the length of the summer drives cyanobacterial abundance, and that increased temperatures may reduce the observed toxicity of blooms in some cases. We find that nutrient concentrations are also likely to be impacted by lake warming, as increased temperatures are robustly associated with increased total phosphorus concentrations. Evidence for the impact of precipitation is mixed, however, as there is evidence to support that increased nutrient runoff from precipitation could support blooms but also that nutrient concentrations could be reduced through greater flushing due to precipitation. While statistical associations are not definitive evidence of formal mechanistic links, the geographic scale of the results is useful for identifying hypothesized mechanisms that are widespread across the continental U.S., and therefore for informing understanding of the influence of climate change. Ho and MichalakClimatic impacts on harmful algal blooms

Improvement in municipal wastewater treatment alters lake nitrogen to phosphorus ratios in populated regions

“…We conducted a GLM analysis (53) to quantify the relative associations of each explanatory variable with variations in TN and TP concentrations and TN/ TP mass ratios in lakes (SI Appendix, Supplementary Text S2). Explanatory variables included the five anthropogenic discharge variables (discharges from five different sources) and two climate variables (precipitation and temperature in watersheds) (36). Based on the Bayesian information criterion (36,54), the best models revealing the quantitative relationship between lake nutrients and anthropogenic discharges were established (results in SI Appendix, Table S4).…”

“…Explanatory variables included the five anthropogenic discharge variables (discharges from five different sources) and two climate variables (precipitation and temperature in watersheds) (36). Based on the Bayesian information criterion (36,54), the best models revealing the quantitative relationship between lake nutrients and anthropogenic discharges were established (results in SI Appendix, Table S4). These models were further applied in the simple scenario analysis.…”

Mapping Freshwater Chlorophyll-a Concentrations at a Regional Scale Integrating Multi-Sensor Satellite Observations with Google Earth Engine

“…The occurrence of harmful algal blooms (HABs) has increased in U.S. freshwater ecosystems in recent years [1][2][3][4]. Many cyanobacteria species can produce toxins that affect the nerve system, liver, and skin and cause harmful impacts on humans and animals using them for drinking water or recreation [5][6][7].…”

The Effectiveness of Global Constructed Shallow Waterbody Design Guidelines to Limit Harmful Algal Blooms

“…Therefore, specific design criteria that prevent HABs may also lead to degradation of other functions or purposes of the wetlands (Bledsoe et al, 2020). For example, short residence times can reduce the possibility of HABs (Ho & Michalak, 2020;Reichwaldt & Ghadouani, 2012), but longer residence times are required to remove nutrients and achieve overall nutrient reduction targets in the catchment. In these cases, the design tradeoffs may be approached with a risk-based framework where the design criteria selected are focused on the downstream risks.…”