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The origin of stream flows in small Amazon forest and pasture watersheds: an end-member mixing analysis approach

Joaquín E. Chaves, Marine Biological Laboratory, Woods Hole MA, USA, jchaves@mbl.edu (Presenting)
Christopher Neill, Marine Biological Laboratory, Woods Hole MA, USA, cneill@mbl.edu
Helmut Elsenbeer, Institute of Geoecology, University of Potsdam, Germany, helsenb@uni-potsdam.de
Alex V. Krusche, Laboratório de Ecologia Isotópica, CENA, USP, Piracicaba, SP, alex@cena.usp.br
Sonja Germer, Institute of Geoecology, University of Potsdam, Germany, sgermer@rz.uni-potsdam.de
Sérgio Candido de Gouveia Neto, Laboratório de Ecologia Isotópica, CENA, USP, Piracicaba, SP, sneto@cena.usp.br

Soil compaction and reduced soil infiltration in cattle pastures on deforested lands enhance quick lateral flows and increase the stream channel responses to precipitation. We quantified how deforestation for pasture changes the amount and timing of sources of water that moves from watersheds to streams using an end member mixing analysis. We evaluated contributing sources to storm flow during an entire rainy season in forest and pasture watersheds drained by 0-order, intermittent streams. Water yield was 17 % of precipitation in the pasture and 1 % of precipitation in the forest. During the early rainy season, canopy throughfall contributed 77% to total forest stream flow, groundwater contributed 20% and shallow soil water contributed 3%. As moisture increased towards the late rainy season and the forest catchment became more responsive to precipitation, throughfall remained the single most important source of stream flow (51%), however shallow soil water (24%) and groundwater (25%) became more important sources. In the pasture, sources to stream flow varied less between early and late rainy, with an overall contribution of 60% overland flow, 45% groundwater, and 5 % soil water. These results suggest that:1) there is great potential for the alteration of the hydrological budgets of larger watersheds as the proportion of deforested land in the Amazon increases, and 2) the potential to deliver water with higher solute concentrations increases as more rainfall is diverted into fast flowpaths , which increases solute delivery by erosion and bypasses active sites of solute removal.

Science Theme:  ND (Nutrient Dynamics)

Session:  2A: Hydrological and Meteorological Processes

Presentation Type:  Oral

Abstract ID: 98

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