9630278 Deegan This project will examine how the conversion of moist tropical forest to cattle pasture in the Amazon Basin alters the patterns and rates of element cycles in soils and how these changes are linked to changes in the chemistry and ecology of small streams. The Amazon is a region with one of the world's highest rates of conversion of natural ecosystems to human dominated use. Cattle pasture is the dominant use of deforested lands. Conversion of native forest to pasture causes large changes in the patterns and rates of nutrient cycling and the potential for nutrient losses from soils. Small streams function as key hydrologic and biochemical links between upland soils and downstream aquatic ecosystems. This project will examine soils and streams in small drainage basins in Rondonia, rapidly developing state in the southwest Brazilian Amazon. Four pairs of drainage basins will be compared. One basin in each pair will drain intact forest, the other will drain land that has been cleared and planted to cattle pasture. The availability of nitrogen, phosphorus and major ions will be examined in drainage basin soils. Measurements of streamwater concentrations and forms of nitrogen, phosphorus, major cations and anions, trace elements and suspended sediments in the paired catchments will link changes in soil chemistry with stream biogeochemistry. To determine how long the influence of one land use is maintained as streams pass through one land use to another, the rates at which nutrients are taken up will be determined by measuring solute concentrations upstream and downstream of land use boundaries and by experimental injections of nitrate and phosphate and a non-reactive tracer in forest and pasture streams to determine how biogeochemical inputs from soils in the drainage basin affect stream organic matter production. This work will provide important new information that will help to predict the effect of agricultural development and deforestation. Examination of stream pro ductivity will provide new information on how land use change affects biological functions that maintain water quality and support fisheries that are important to human well-being. On a longer time frame, this project will provide a foundation for future modeling efforts to link land use changes in small watersheds with biogeochemical changes in the larger rivers of the Amazon using models of water routing and within stream biogeochemical processing. This proposal was submitted to the Environmental Geochemistry and Biogeochemistry solicitation, and the project is being jointly supported by the Divisions of Earth Sciences (Geosciences), Environmental Biology (Biological Sciences), Mathematical Sciences (Mathematical and Physical Sciences) and International Programs -Brazil (Social, Behavioral & Economic Sciences).
