Both biotic and abiotic predictors explain significant variation in cyanobacteria biomass across lakes from temperate to subarctic zones

Abstract

The development of cyanobacteria blooms is of increasing concern in many lakes worldwide, and as a result, modeling their predictors is vital for understanding where and why they occur. In this study, we developed and analyzed a 640‐lake data set that spans Canada and 12 ecozones to identify the drivers of cyanobacteria biomass and of several key toxin‐ and bloom‐forming genera (Microcystis, Aphanizomenon, and Dolichospermum). The database consisted of an exhaustive list of potential predictors (n = 55), including water chemistry, land‐use, and zooplankton variables. We applied a series of empirical modeling approaches to identify significant predictors and thresholds (generalized linear and additive models, mixed effect regression trees), all while accounting for ecozone variability. Across all modeling approaches, and ecozones total phosphorus was identified as the most important predictor of total cyanobacterial and focal genera biomass. In addition, cyanobacteria across Canada showed significant associations with increasing dissolved organic and inorganic carbon, and several ions. Despite the widely held notion that cyanobacteria are often toxic and/or a poor food source for zooplankton, we found a positive relationship between cyanobacteria and zooplankton, particularly with daphnid and copepod biomass. Localized top‐down forces and evolutionary adaptations resulting from long‐term exposure in eutrophic lakes are among the possible explanations for this observed positive association. By considering a suite of complementary modeling approaches, we found that nonlinear models provided greater predictive power and the random ecozone effect was minor due to the overarching importance of local abiotic and biotic factors.

Watershed, lake, and food web factors influence diazotrophic cyanobacteria in mountain lakes

“…P appeared to have a greater influence on diazotrophic cyanobacteria biomass than N in our study, concurring with other studies (Rigosi et al 2014;Wan et al 2019;MacKeigan et al 2023). In addition, epilimnetic P had an asymptotic nonlinear relationship with diazotrophic cyanobacteria, which may be due in part to accessible sediment P. We recognize not all total P is bioavailable.…”

“…A combination of abiotic and biotic factors can interact to cause harmful blooms of cyanobacteria in freshwater ecosystems (Paerl and Otten 2013;Ger et al 2016). Increasing loading of limiting nutrients, notably nitrogen and phosphorus, is a major factor driving increases in cyanobacterial biomass and harmful blooms in Northern Hemisphere lakes (Reynolds 2006;Rigosi et al 2014;Taranu et al 2015;MacKeigan et al 2023). While cyanobacteria often bloom in eutrophic conditions, there is increasing evidence of blooms in nutrient-poor waterbodies (Sterner et al 2020;Reinl et al 2021).…”

“…In addition, climate warming may favor cyanobacteria, which often have optimal growth temperatures higher than other phytoplankton (Reynolds 2006). Food web shifts, including nonnative fish introductions, may also contribute to harmful blooms, but the connection to cyanobacterial dominance and blooms is less certain (Paerl and Otten 2013;Ger et al 2016;MacKeigan et al 2023). The specific nature of how abiotic and biotic factors interact to control cyanobacterial blooms requires further study, especially in regions with minimal anthropogenic development where blooms occur and external nutrient loading is low (Paerl and Otten 2013;Taranu et al 2015;Sterner et al 2020;Reinl et al 2021).…”

“…Therefore, finding commonalities among lakes across a gradient of elevation requires careful consideration of environmental differences. Key determinants of bloom-forming cyanobacteria, such as nutrients, climate, and grazers, have not been well studied in mountain lakes, which could provide novel insights into the complex issue of harmful algal blooms across different lake types (MacKeigan et al 2023).…”

Anoxia begets anoxia: A positive feedback to the deoxygenation of temperate lakes

“…We found a strong positive association between surface water TP concentrations and surface water chl a , both within and across lakes, likely reflecting the fact that interannual variability in phosphorus concentrations can play an important role in regulating phytoplankton growth in lakes (Figures 4 and 5). Our study follows many decades of data that illustrate the positive effect of TP on phytoplankton biomass (MacKeigan et al., 2023; Schindler, 1974; Smith, 1982). In this study, we were unable to identify an effect of epilimnetic TN concentrations on chl a , suggesting that in these lakes, TP may play a more important role in regulating phytoplankton growth.…”