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