Towards a Model of the Biogeochemistry of Continental-Scale River Basins: An Amazon Case Study

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Richey Research is proposed her to consider the dynamics ogf large-scale drainage basins, using the Amazon Rivet system as a test case. The central question to be addressed in this proposal is, How does a large river system obtain and subsequently modify its biogeochemical composition? The question and hypothesis will be divided into parts: (1) How is the biogeochemical stay of the river system influenced by the land surfaces? (2) How are the land effects modified during transit through the river system? The summaty working hypothesis is that, "The quantity and composition of dissolved and particulate bioactive materials in a parcel of water at any downstreasm node in the river system is predictable as the product of a common set of processes which occur differentially according to upstream conditions of relative typography, soil organic content and texture, water and residence time, and floodplain extent." To test this hypothesis the research objectives are to: (1) Implement and carry out a field sampling program that will efficiently provide samples from throughout the basin, including from the mainstem, from transects along major tributaries, and into headwater regions of Peru and Bolivia. Ultrafiltration techniques will be used to process water across a spectrum of particle and molecular sizes. (2) Develop a quantitative model based on routing water and particulate and dissolved substances through the rivernetwork. This effort will couple the hydrology and chemistry models we have previously developed with our new information. (3) Conduct experiments to determine terrestial effects on organic matter composition. Using a modeling approach, upper bounds of fine organic material thwt exist in the fine particle fraction will be determined as will the chemical selectivity. Simulated absorption experiments will be the third test for active partioning within the drainage basin. (4) Controls on particulate export will be investigated using measurments and modeling of sediment mobil ization and routing. Isotopic tracers will be used to determine the location of material origin. (5)