EFFECTS OF WATERSHED LAND OCCUPATION AND LAND USE ON THE TROPHIC STATE OF TWO SHALLOW LAKES ......

The main effect of increased external phosphorus inputs is cultural eutrophication, which is currently regarded as one of the most serious hazards to water bodies. Anthropogenic activities such as watershed use and land occupation might hasten this process. The goal of this study was to determine the impacts of land use and land cover on the trophic status of two shallow lakes (Lakes Paó and Santa Lcia in Paraná, Brazil). At three monitoring stations in the lakes, water and sediment samples were collected over six months. Land-use and land-cover mapping were carried out using visual interpretation of high-resolution satellite photos. Throughout the study period, Lake Paó remained eutrophic with a low euphotic zone (ZEU1), while Lake Santa Lucia remained oligotrophic with clear waters (ZEU1). Lake Paó's extensive eutrophication was linked to substantial sewage inputs from nonpoint sources, since the urban/built-up area accounted for 37.63 percent of its riparian zone (the lakeshore), compared to only 2.43 percent in Lake Santa Lucia. Our findings demonstrated the need of keeping phosphorus levels low and riparian vegetation to a minimum in order to reduce the risk of eutrophication and hence preserve water quality.

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