Hydroclimatological effects and landscape patterns on the aquatic macrophyte and phytoplankton community in the arms of the Itaipu Reservoir – Brazil
Eutrophication is a consequence of the increase in the supply of nutrients, mainly phosphorus and nitrogen in aquatic ecosystems, favoring the excessive growth of aquatic macrophytes and phytoplankton and resulting in the loss of water quality. Thus, this study sought to understand the spatio-temporal dynamics of the macrophyte community and the phytoplankton of three arms of the Itaipu Reservoir. For that, it was decided to use the Trophic State Index and the following water quality parameters: total phosphorus, kjeldahl nitrogen, chlorophyll-a, pH, electrical conductivity, turbidity, transparency, water temperature, aquatic macrophytes and algal bloom. . In addition to variables related to water quality, hydroclimatological variables such as average elevation and natural flow and precipitation data, air temperature and wind speed were used. The following variables of use and land cover were used: livestock production, urban area, agricultural area, forest area and livestock production area. For that, multilevel models were used in the spatial and temporal dimension in order to verify the effect of different anthropic activities on the dynamics of aquatic macrophyte and phytoplankton communities in the three arms of the Itaipu reservoir. The partial results show that the hydrodynamics has a strong influence on the dynamics of macrophytes and algal bloom and that the riparian forest plays a fundamental role in maintaining water quality since areas where there is an increase in natural vegetation, it was possible to identify a drop in chlorophyll-a concentrations. The results of the models also show that temporary crops in the region and in urban areas contribute to the increase of nutrient input in the studied arms. The study concluded so far that the average level of the reservoir together with the variations in phosphorus concentrations as well as in the volume of precipitation are favoring eutrophication in the arms.