Anthropogenic land use is associated with N-fixing cyanobacterial dominance in lakes across the continental United States

Cyanobacteria cause many water quality problems in lakes worldwide. Although many studies have examined factors that influence the structure of cyanobacterial communities, few have explicitly compared the effects of within-lake conditions (e.g., nutrient concentrations) and watershed parameters (e.g., land use) on a diverse array of cyanobacterial taxa. Here, we analyzed data from the 2007 U.S. Environmental Protection Agency's National Lakes Assessment to quantify how lakeshore anthropogenic land use, nutrient concentrations and ratios, and surface water temperatures predict cyanobacterial biovolume and dominance in 236 naturally-formed lakes spanning the continental U.S. We observed that anthropogenic lakeshore land use was the best predictor for cyanobacterial dominance, whereas in-lake nitrogen (N) and phosphorus (P) concentrations were the best predictors for cyanobacterial biovolume. Our analyses suggest that anthropogenic land use may influence cyanobacterial dominance via means other than increased nutrient concentrations. The sum of agricultural and human-developed lakeshore land use was the best predictor of N-fixing cyanobacterial dominance, but there was no significant relationship between anthropogenic land use and non-N-fixing cyanobacterial dominance. In addition, we observed a total N:P ratio threshold for cyanobacterial dominance in the phytoplankton community (150:1) that was much higher than previously reported ratios. Consequently, management strategies to control cyanobacteria need to account for eco-physiological variation among different cyanobacterial taxa, and should consider nutrients and the other effects of land use to control overall lake cyanobacterial biovolume and cyanobacterial dominance, as the two cyanobacterial metrics may be sensitive to different drivers.