Diel dynamic of phytoplankton functional groups in a tropical water supply, Extremoz Lake, northeastern Brazil/Dinâmica Nictemeral dos grupos funcionais fitoplanctônicos de um manancial tropical, Lagoa de Extremoz, nordeste do Brasil

This study analyzed the diel and vertical dynamics of phytoplankton functional groups in a natural tropical lake (Extremoz Lake, northeast Brazil) to investigate and understand the driver factors of the community during a severe drought period. Sampling of the abiotic variables and phytoplankton was performed at intervals of 6 hours over 24 hours in vertical profiles, in dry and rainy seasons (according to the historical average). The phytoplankton species were grouped according to the functional groups' approach sensu Reynolds et al. (2002). October 12 was considered as a dry period (18.4 mm), while March 13, due to the historical average, as a rainy season, due to the low rainfall during the study period (15.7 mm), it was called severe drought. The lake showed thermal and chemical destratification in both periods. Phytoplankton biomass was higher in the dry season and their vertical distribution was stratified in both periods. In both samplings there were less algal biomass during the night.