Caracterização morfológica das lagoas de Osório, norte da planície costeira do Rio Grande do Sul, Brasil

Abstract

The understanding of water dynamics and ecological relations in limnological studies necessarily includes the morphology of the water body. The scientific knowledge of morphometric parameters is fundamental not only for measurements and quantification, but also for the understanding of internal processes that influence nutrient dynamics and the biological communities distribution. The coastal plain of Rio Grande do Sul was formed by erosion and deposition processes during marine transgression and regression process, associated with fluvial and wind erosion during the Quaternary. During the Pleistocene and Holocene, four depositional systems, called barrier-lagoon, were settled comprising a great diversity of humid ecosystems, among them the lakes along the coast of the Atlantic Ocean, mostly containing fresh water. Due to their genesis, the lakes are shallow with relative depth less than 2% and maximum depth of 11 meters in the middle coast of Rio Grande do Sul. The study aimed to morphologically characterize the lakes of Osório, Rio Grande do Sul, Brazil. Due to the regional characteristics of toponymy and segmentation some lakes could be evaluated as one or more water bodies, resulting in the characterization of 20 water bodies from the 16 official names attributed to the lakes. Bathymetric surveys were conducted between the years 2013 and 2015, based on echo sounder coupled with GPS and application of remote sensing and GIS. As results were produced an article submitted to the Brazilian Journal of Water Resources and a chapter in book titled “Atlas Socioambiental do Município de Osório”. In the article titled "Morphological characterization of thirteen lakes in Osório, northern coastal plain of Rio Grande do Sul, Brazil" were morphologically characterized 13 lakes in Osório, Rio Grande do Sul, Brazil. Cluster analysis distinguished four morphological groups, confirmed by Discriminant Analysis. Principal component analysis identified the first component positively charged with parameters of size and negatively charged with relative depth, while the second component was positively charged with maximum and average depths and negatively charged with perimeter development and volume development. Therefore, size parameters were more important for the lakes classification than depth parameters. The coastal lakes shallowness (maximum depth = 4.6 m, largest average depth = 2.2 m) is a fundamental element for water resources management, since their low volume and small size make them more susceptible to eutrophication processes. In the chapter titled "Morfologia", the lakes are presented with bathymetric map, aerial photo, morphometric parameters and a description of the main characteristics for each lake. The chapter is presented in a didactic and accessible language in order to reach a wide public. Morphological data are essential ecological understanding of lakes, especially if associated with analyzes of transparency, turbidity, vertical distribution of nutrients and oxygen and application of trophic indexes, as well as being a subsidy for the water resources management.