Seasonal and Spatial Variability of Nutrients in Tropical Streams Due to Anthropogenic Activities A case study in a Brazilian rain forest reserve

Rapport, 2001

The Parque Estadual Turístico do Alto Ribeira (PETAR) is an Atlantic rain forest reserve in South-eastern Brazil. A few small villages are located inside the watersheds of the three main rivers that cross the park, Betari, Iporanga and Pilões. Untreated domestic sewage from households is often discharged directly into the watercourses. Subsistence agriculture is practiced by most of those families, which adds nutrients to the stream due to increased soil erosion. Additionally, larger farms located near the headwater of PETAR rivers use fertilizers to improve soil condition. The main goal of this study is to investigate seasonal and spatial variability in nutrient concentration in PETAR watercourses due to inputs from human settlements and agricultural areas within or near the park. Twenty-one sites located in fifteen streams were surveyed during field campaigns carried on in June and November 1998. Nitrogen and phosphorus concentration, as well as other physical and chemical water parameters (temperature, pH, dissolved oxygen, conductivity, hardness and alkalinity), were measured. Most of the seasonal and spatial chemical variability of the surveyed streams can be explained by natural factors such as bedrock characteristics, topography and climate conditions. However, anthropogenic factors may also affect the quality of PETAR streams. At the headwaters of Iporanga and Pilões Rivers an increase in nutrient concentration was observed. That can be a consequence of domestic sewage discharge, fertilizers application in agriculture or even use of explosives containing nitrogen in mining activities. Indication of early stages of eutrophication (observed increase in plant biomass and measured increase in nutrients availability and chemical demand of oxygen) was found in Monjolos Stream downstream outlets of domestic sewage from the village of Bairro da Serra.