Cyanobacteria Dominance in Lakes and Evaluation of Its Predictors: a Study of Southern Appalachians Ecoregion, USA

Owing to their ecological and economic implications, the abundance of cyanobacteria has been an important subject in aquatic ecology. There has been a debate about which nutrients are a better predictor of cyanobacteria abundance, total nitrogen (TN), total phosphorus (TP) or nitrogen to phosphorus ratio (N:P). A classic study by Downing and coworkers in 2001 concluded that total N and total P are better predictors than TN:TP ratio. We picked lakes from a different region of the US, the Southern Appalachians (SAP), to test the same hypotheses using the National Lakes Assessment (NLA, 2007) database. This dataset consists of 116 selected sampling sites throughout the ecoregion. In this study, total cyanobacteria abundance was related to three predictors (N, P and N:P) using linear regression, non-parametric statistics and boosted regression trees (BRTs). Total N and total P were more strongly correlated to cyanobacteria abundance than N:P. Partial dependence plots from BRT analysis confirmed results of correlations showing higher relative influence values of TN and TP on cyanobacteria abundance. An important observation from both analyses was that cyanobacteria abundance increased rapidly with increasing TP above 5 μg TP/L. This is a similar response relationship between abundance of cyanobacteria and TP as reported by Downing et al. (2001). These TP thresholds for cyanobacteria dominance are important for TP management targets to control blooms in lakes.