ND-03 Abstract

Key Connections in Amazonian Stream Corridors

Maria Victoria Ramos Ballester, CENA/USP (SA-PI)
Linda A. Deegan, Marine Biological Laboratory (US-PI)
Alex V. Krusche, CENA-USP (SA-PI)
Reynaldo Luiz Victoria, CENA/USP (SA-PI)

Deforestation in the Amazon has the potential to alter the biogeochemistry of carbon and major nutrients over large regions and to alter the movements of these materials among adjoining ecosystems. Small streams dominate the total length of stream channels in the landscape. They receive material from adjacent uplands and contribute material to larger rivers. Because of their position, small streams and their associated riparian zones thus play a key role in the landscape as links and regulators of material fluxes between terrestrial ecosystems and larger rivers of the Amazon Basin.

Our goal is to develop an understanding of how C and nutrients are transformed as water moves from uplands through small streams to larger rivers in forested and deforested landscapes of the Amazon. We will do this by: 1) focusing on carbon and nutrient transformations in riparian zones and small stream channels--key points in the landscape where these transformations are potentially of major importance but very poorly known in tropical landscapes; 2) comparing these transformations in drainage basins with forest and pasture land use and in streams of different sizes, and; 3) coupling our process level work with information on land use and riparian zone structure derived from remote sensing and models of stream channel processing to predict transfers of organic matter and nutrients to larger rivers in stream networks. The work will be focused in central Rond˘nia.

In riparian zones, we will determine the spatial variability of water entering and leaving the riparian zones of forest and pasture streams of different sizes using surveys of ground water characteristics. We will use 15N, nutrient and conservative tracer additions to identify key processes and rates of transformation in the groundwater of forest and pasture riparian zones.

In stream channels, we will use 15N tracer additions in forest and pasture streams to determine key processes and rates of transformation, and production and consumption of dissolved organic carbon and dissolved inorganic carbon. We will use the isotopes of 13C in dissolved organic carbon and dissolved inorganic carbon and different particulate and dissolved constituents to trace the sources of C to streams. We will extend this work to a regional basis with surveys of nutrients and organic matter in 2-5th order streams in forest and pasture land use on different soil types within the region.

At the regional scale, satellite images will be used to classify areas to land use type, riparian zone type and extent and length of stream channels of different stream orders in forest and pasture. A multi-compartment stream biogeochemistry model will be used to predict the transformations of C and N and their downstream transport in streams of different sizes and land uses. We will integrate watershed land use area and stream channel length in different land use types to estimate regional impacts of land use change on biogeochemical cycles in small streams and transport from small streams to larger rivers.

This project will bring together studies of land and water biogeochemistry and link them together with an understanding of changes in processes that occur in key points in the landscape. It will provide new information on how these processes change when forest is replaced by pasture and it will put this information in a framework to predict the effects of forest-to-pasture conversion on stream water quality and C and nutrient transport to larger rivers.