Presença de macrófitas submersas altera a dinâmica do fitoplâncton em reservatórios do semiárido?

Abstract

The aim of this study was to identify the effects of aquatic vegetation on the dyn amics of phytoplankton community. The hypothesis: Presence of submersed aquatic results in changes in nutrient concentrations, which in turn alters the dynamics of the phytoplankton community in semiarid reservoirs. To better understand these processes, we sought to answer the following questions: What environmental variables can better explain the change in the dynamics of these producers? There is competition between phytoplankton community and the submersed aquatic? Cyanobacteria release or inhibit the production of toxins in the presence of submersed aquatic? Monthly collections were made in Argemiro reservoirs Figueiredo (7º36'51,48 ''S, and 35º33'1,66''W) - this with the absence of aquatic plants, and Pessoa (7º29'20 "S and 36º17'3 "W) - with the presence of submersed aquatic, both located in the Brazilian semiarid region. The hydrological conditions of the reservoirs had to be quite different during the sample period (62 psf = 27; p <0.05). The systems studied had hot water above 22 ° C and pH increase over months. The phytoplankton community in both reservoirs was represented by 97 taxa grouped in five taxonomic groups: cyanobacteria (31%), Bacillariophyceae (29%), Chlorophyceae (20%), Euglenophyceae (11%), Zygnemaphyceae (9%). Of these taxa, 56 were common to both environments, 39 were unique environment with weeds, and 2 without aquatic environment. The largest biovolume phytoplankton values were observed for the tank with the absence of aquatic plants. It was observed that the underwater plants can act in determining the limnologic conditions of the ecosystem, because the growth of these enables the reduction of turbidity, since dense banks macrophytes limited resuspension of the pellet and limit the abundance of phytoplankton further processes competition for nutrients between these communities may restrict the development of phytoplankton. The relationship cyanobacteria / macrophytes took place in such a way that the lower algal biovolume, higher plant biomass and toxin concentration thus macrophyt es inhibits the growth of phytoplankton, but stimulates the process of toxin release.