Many riverine ecosystems show environmental gradients of physical characteristics along its course, which results in the presence of aquatic plants' species. These are important components of the biodiversity that also play several ecological roles in the aquatic ecosystems. Understanding the functioning of these environmental gradients provides bases for the development of managing and conservation projects. The aim of this work is to evaluate the influence of an environmental gradient on a river stretch at the Itanhaem river basin and in the presence of six species of aquatic macrophytes: Egeria densa, Cabomba furcata, 1Potamogeton sp, Utricularia foliosa, Pistia stratiotes and Salvinia molesta. For that, the characterization of this gradient and the determination of the spots where these species occur are going to be done. Two samplings are going to be executed (summer and winter) for the collection of the watercourse physical's data (slope, height and plant covering at the border, canopy opening, width, depth, light attenuation coefficient, current velocity, land use and substratum), and the water's limnological data (temperature, pH, saltiness, turbidity, electric conducting, nitrogen, total kjeldal nitrogen, N-nitrite, N-nitrate, N-ammoniacal, total phosphor, P-ortophosphate, alkalinity and suspended sediment) and for the identification and location of the macrophytes species along the stretch. The physical and limnological data collected are going to be interpolated by the kriging method with the Arcgis 9.3 software, so that a environmental gradient map will be generated. The data generated by the interpolation are going to be plotted in graphics and the maximum and minimum values calculated. Linear models and generalized additives (GLM and GAM) are going to be used to relate the presence of the species with the environmental gradient.
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