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Runoff sources and land cover change in the Amazon: an end-member mixing analysis from small watersheds |
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| Authors: | Christopher Neill Joaquin E. Chaves Trent Biggs Linda A. Deegan Helmut Elsenbeer Ricardo O. Figueiredo Sonja Germer Mark S. Johnson Johannes Lehmann Daniel Markewitz Marisa C. Piccolo |
| Affiliation: | 1. The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA 9. Science Systems and Applications Inc., NASA Calibration and Validation Office, 1450 South Rolling Rd., Halethorpe, MD, 21227, USA 2. Department of Geography, San Diego State University, San Diego, CA, 92182-4493, USA 3. Institute of Geoecology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Golm, Germany 4. Embrapa Meio Ambiente, Rodovia SP 340 - KM 127, 5-Caixa Postal 69, Jaguari??na, SP, Brazil 10. Berlin-Brandenburg Academy of Sciences and Humanities, J?gerstr. 22/23, 10117, Berlin, Germany 5. Department of Earth and Ocean Sciences, Institute for Resources, Environment and Sustainability, University of British Columbia, 6339 Stores Road, Vancouver, BC, V6T 1Z4, Canada 6. Department of Crop and Soil Sciences, Cornell University, 918 Bradfield Hall, Ithaca, NY, 14853, USA 7. D. B. Warnell School of Forest Resources, University of Georgia, Athens, GA, 30602, USA 8. Laborat??rio Ciclagem de Nutrients, Centro de Energia Nuclear na Agricultura, Universidade de S?o Paulo, Avendia Centen??rio, 303, CEP 13416-000, Piracicaba, SP, Brazil |
| Abstract: | The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change runoff sources to streams by shifting runoff to more surficial flow pathways. We applied end-member mixing analysis (EMMA) to 10 small watersheds throughout the Amazon in which solute composition of streamwater and groundwater, overland flow, soil solution, throughfall and rainwater were measured, largely as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia. We found a range in the extent to which streamwater samples fell within the mixing space determined by potential flowpath end-members, suggesting that some water sources to streams were not sampled. The contribution of overland flow as a source of stream flow was greater in pasture watersheds than in forest watersheds of comparable size. Increases in overland flow contribution to pasture streams ranged in some cases from 0% in forest to 27?C28% in pasture and were broadly consistent with results from hydrometric sampling of Amazon forest and pasture watersheds that indicate 17- to 18-fold increase in the overland flow contribution to stream flow in pastures. In forest, overland flow was an important contribution to stream flow (45?C57%) in ephemeral streams where flows were dominated by stormflow. Overland flow contribution to stream flow decreased in importance with increasing watershed area, from 21 to 57% in forest and 60?C89% in pasture watersheds of less than 10?ha to 0% in forest and 27?C28% in pastures in watersheds greater than 100?ha. Soil solution contributions to stream flow were similar across watershed area and groundwater inputs generally increased in proportion to decreases in overland flow. Application of EMMA across multiple watersheds indicated patterns across gradients of stream size and land cover that were consistent with patterns determined by detailed hydrometric sampling. |
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