The objective of this chapter is to summarize current understanding of the hydrological function and nutrient dynamics of Amazonian forest derived from work in microcatchments and how these processes are affected by land use and land cover changes, mainly the conversion of forest to pasture. Our conclusions are based on field observations in catchments located in different regions of Amazonia. This chapter is divided into sections that provide (1) a general overview of small catchment research in LBA and then address (2) runoff and water budgets, (3) the influences of soil, vegetation, and riparian zones on stream chemistry and element budgets, and (4) the potential influence of catchment scale on the hydrological and biogeochemical processes that control water and element budgets. The first section provides a background on the principle sites where microcatchments have been studied as part of LBA and the questions that have driven research at these sites. The second section reviews intensive studies of runoff, streamflow, and catchment water balance and how these processes are altered by clearing of tropical forest for pasture. The third section synthesizes what is known about the processes that control the concentrations and export of materials that reach streams via different hydrological flow paths in Amazonian forest and how these processes and flow paths are altered by deforestation and land use change. The fourth section summarizes what we know about how hydrological and biogeochemical processes change with scale and how this understanding can be used to both predict catchment response to land use change and manage Amazonian landscapes to maintain valuable hydrological and biogeochemical functions. © 2009 by the American Geophysical Union. All rights reserved.
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