Phytoplankton functional dynamics in a shallow polymictic tropical lake: the influence of emergent macrophytes

This study aimed at investigating the phytoplankton dynamics by employing taxonomic and functional models to test the hypothesis that emergent macrophytes could influence phytoplankton dynamics by increasing the stability of water column and harboring zooplankton. It was also hypothesized that functional models are better than taxonomic approaches to depict phytoplankton community structure in a polymictic tropical lake (Ziway, Ethiopia) with substantial macrophyte cover. Twelve sampling sites, extending from the macrophyte vegetation (Typha latifolia and Phragmites australis) covered littoral part to an open water side of the lake, were monitored monthly (January to August, 2016) for physical, chemical and biological parameters. A total of 93 taxa, distributed among six major taxonomic groups, 14 Reynolds functional groups and six morphology-based functional groups, were identified. The phytoplankton groups, which prefer stable water column and tolerate grazing dominated towards the macrophyte zones, while the phytoplankton capable of surviving strong mixing succeeded towards the completely mixing open water side of the lake. The results of the present study also suggest that the functional classification schemes are robust ways of detecting phytoplankton dynamics along the macrophyte-open water gradient in shallow tropical lakes.