Spatial and seasonal dynamics of phytoplankton groups and its relationship with environmental variables in Lake Okeechobee, USA

The concept of phytoplankton functional groups was used to assess phytoplankton community structure in an attempt to better understand their spatial and seasonal variation in Lake Okeechobee, USA. Samples were collected for analyses during summer and winter. 23 phytoplankton functional groups were identified among 102 species, of which 9 groups (H1, M, C, MP, Y, S1, J, X1 and X2) were categorized as dominant. Y represented by Cryptomonas ovate and H1, represented by Anabaena circinalis and Anabaena variabilis, were dominant in some sites in summer corresponding to higher temperatures. In winter, the biomass of the functional groups was dominated by chlorophyta group X2 corresponding to lower temperatures, and relatively high nutrients. Redundancy analysis (RDA) with Monte Carlo test revealed that water temperature (WT), TP, and TN were the most dominant environmental variables which influenced phytoplankton functional group distribution in Lake Okeechobee. Functional group H1 was associated with TN, pH, TP and WT. Similarly, functional group Y was significantly positively correlated with TN, TP and WT but negatively correlated with TN/TP ratios. This study reveals the importance of physical–chemical variables across a spatial and seasonal gradient, in structuring phytoplankton functional groups, and consequently in the assessment of environmental status of the lake.