A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...
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THE FOREST/PASTURE CONVERSION EFFECTS ONSMALL CATCHMENT HYDROLOGICAL PROCESSES INTHE EASTERN AMAZONIASchuler, A.E. 1 , J.M. Moraes 1 , R. de O. Figueiredo 2 , D. Markewitz 3 ,T. Dunne 4 , E. Davidson 5 , R.L.Victoria 1 .1 CENA/USP, Piracicaba, SP-Brazil; 2 IPAM, Belém,PA –Brazil; 3 The University of Georgia, A<strong>the</strong>ns, GA-USA; 4 The University ofCalifornia, Santa Barbara, CA-USA; 5 Woods Hole Research Center,Woods Hole, MT-USACorresponding Author: Centro de Energia Nuclear na Agricultura/ USP, Piracicaba, SP –Brazil 13416-903E-mails: schuler@cena.usp.br, jmmoraes@cena.usp.br,rofig@amazon.com.br, dmarke@smokey.forestry.uga.edu,tdunne@bren.ucsb.edu, edavidson@whrc.org, reyna@cena.usp.brThe aim of evalu<strong>at</strong>ing <strong>the</strong> forest/pasture conversion effects on nutrients transfers in <strong>the</strong>humid tropical forest <strong>Amazon</strong>ia has lead to a research project linking hydrological fluxes andecosystem mass balance studies. In order to model <strong>the</strong> w<strong>at</strong>er flow mechanisms and <strong>the</strong>irrel<strong>at</strong>ionship <strong>with</strong> nutrient cycling processes in tropical forests, two monitoring sets wereinstalled on a couple of swales <strong>with</strong> forest and pasture each one, loc<strong>at</strong>ed on a 10,000 hac<strong>at</strong>chment draining towards Igarape 54 in <strong>the</strong> Eastern <strong>Amazon</strong>ia.The hydrological monitoring includes <strong>the</strong> following measurements: streamflow;overland flow; subsurface flow; w<strong>at</strong>er table depth; rainfall and throughfall under canopyforest; a physical survey in both swales, measuring <strong>the</strong> hydraulic conductivity of s<strong>at</strong>ur<strong>at</strong>ed soil(Ks<strong>at</strong>), bulk density, w<strong>at</strong>er retention curve and soil granulometry, besides a topographicsurvey. The soil hydraulic conductivity showed high values in a shallow depth under forest(230.3 mmh -1 ), while in <strong>the</strong> pasture, <strong>the</strong> median value reached 3.7 mmh -1 . Rainfall d<strong>at</strong>a show30% of rainfall intensity exceeds <strong>the</strong> pasture Ks<strong>at</strong> value near <strong>the</strong> surface, gener<strong>at</strong>ing Hortonianoverland flow. In both land cover an impeding layer rel<strong>at</strong>ed to a dense plinthite horizon wasfound <strong>at</strong> around 0.80-0.90 m. This leads to a perched w<strong>at</strong>er table development <strong>at</strong> a shallowdepth. In pastures, <strong>the</strong> near surface compacted soil is possibly rel<strong>at</strong>ed to <strong>the</strong> “root-zonecollapse”, due to burnings, c<strong>at</strong>tle trampling and rain drop impact causing splash erosion andsurface sealing. Such changes in soil surface hydraulic properties might move <strong>the</strong> deliverymechanism from deep and l<strong>at</strong>eral subsurface flow to infiltr<strong>at</strong>ion-excess overland flow,increasing hillslope runoff considerably. How much this alters <strong>the</strong> nutrient leaching p<strong>at</strong>ternshas been inquired in <strong>the</strong> proceeding hydrological modeling studies.
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