Solute and sediment export from Amazon forest and soybean headwater streams Riskin, Shelby H. Neill, Christopher Jankowski, KathiJo Krusche, Alex V. McHorney, Richard Elsenbeer, Helmut Macedo, Marcia N. Nunes, Darlisson Porder, Stephen 2017-01-10T15:55:14Z 2017-01-10T15:55:14Z 2017-01-04
dc.description Author Posting. © Ecological Society of America, 2016. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 27 (2017): 193–207, doi:10.1002/eap.1428. en_US
dc.description.abstract Intensive cropland agriculture commonly increases streamwater solute concentrations and export from small watersheds. In recent decades, the lowland tropics have become the world's largest and most important region of cropland expansion. Although the effects of intensive cropland agriculture on streamwater chemistry and watershed export have been widely studied in temperate regions, their effects in tropical regions are poorly understood. We sampled seven headwater streams draining watersheds in forest (n = 3) or soybeans (n = 4) to examine the effects of soybean cropping on stream solute concentrations and watershed export in a region of rapid soybean expansion in the Brazilian state of Mato Grosso. We measured stream flows and concentrations of NO3−, PO43−, SO42−, Cl−, NH4+, Ca2+, Mg2+, Na+, K+, Al3+, Fe3+, and dissolved organic carbon (DOC) biweekly to monthly to determine solute export. We also measured stormflows and stormflow solute concentrations in a subset of watersheds (two forest, two soybean) during two/three storms, and solutes and δ18O in groundwater, rainwater, and throughfall to characterize watershed flowpaths. Concentrations of all solutes except K+ varied seasonally in streamwater, but only Fe3+ concentrations differed between land uses. The highest streamwater and rainwater solute concentrations occurred during the peak season of wildfires in Mato Grosso, suggesting that regional changes in atmospheric composition and deposition influence seasonal stream solute concentrations. Despite no concentration differences between forest and soybean land uses, annual export of NH4+, PO43−, Ca2+, Fe3+, Na+, SO42−, DOC, and TSS were significantly higher from soybean than forest watersheds (5.6-fold mean increase). This increase largely reflected a 4.3-fold increase in water export from soybean watersheds. Despite this increase, total solute export per unit watershed area (i.e., yield) remained low for all watersheds (<1 kg NO3− N·ha−1·yr−1, <2.1 kg NH4+-N·ha−1·yr−1, <0.2 kg PO43−-P·ha−1·yr−1, <1.5 kg Ca2+·ha−1·yr−1). Responses of both streamflows and solute concentrations to crop agriculture appear to be controlled by high soil hydraulic conductivity, groundwater-dominated hydrologic flowpaths on deep soils, and the absence of nitrogen fertilization. To date, these factors have buffered streams from the large increases in solute concentrations that often accompany intensive croplands in other locations. en_US
dc.description.sponsorship NSF Grant Numbers: DEB-0640661, DEB-0949370; Fundação de Amparo á Pesquisa do Estado de São Paulo Grant Number: FAPESP 03/13172-2; Watson Graduate Student Fellowship; Center for Latin American and Caribbean Studies at Brown University en_US
dc.identifier.citation Ecological Applications 27 (2017): 193–207 en_US
dc.identifier.doi 10.1002/eap.1428
dc.language.iso en_US en_US
dc.publisher John Wiley & Sons en_US
dc.subject Agroecosystems en_US
dc.subject Biogeochemistry en_US
dc.subject Brazil en_US
dc.subject Hydrology en_US
dc.subject Land-use change en_US
dc.subject Streams en_US
dc.subject Watershed en_US
dc.title Solute and sediment export from Amazon forest and soybean headwater streams en_US
dc.type Article en_US
dspace.entity.type Publication
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