Interannual variability in the seasonal plankton succession of a shallow, warm-water lake

Common seasonal plankton succession patterns in temperate lakes are well understood, and were described in the popular PEG-model. Seasonal plankton succession in warm-water lakes, however, is not as well known. Recent theory suggests that some lake systems are characteristic of having alternate system-states, where one of the system-states is characterized by dominance of cyanobacteria, and transition between system-states can be abrupt and undeterminable. Lake Somerville, a shallow, well-mixed, warm-water reservoir located in eastern TX, U.S.A., experiences occasional periods of cyanobacteria dominance. To increase our understanding of seasonal plankton dynamics in warm-water systems, we analyzed 14-years of plankton data spanning a 22-year period. During this period, succession dynamics characteristic of those described by the PEG-model were observed, as well as succession dynamics expected during periods of cyanobacteria dominance, i.e., greater accumulated phytoplankton biovolume, low secondary productivity, and low light penetration. In addition to the PEG-model and cyanobacteria type system-states, other states of the system that were intermediate between these were observed. Therefore, we conclude the lake does not behave according to the alternate system-states model. The change from year to year in early-year cyanobacteria dominance was abrupt and non-monotonic during this period. In addition, the early year performance of cyanobacteria appeared to influence the plankton succession trajectory for the remainder of the season. While the magnitude of lake-flushing early in the year accounted for ～37% of variability in cyanobacteria prevalence, many of the traditional factors impacting cyanobacteria dominance appeared insignificant.