Hydrological Processes in Small Forest and Pasture Catchments of the Eastern Amazonia
Marysol
A. E.
Schuler, IPAM, Belem, PA-Brazil, marysol@ipam.org.br
(Presenting)
Jorge
Marcos de
Moraes, CENA/ USP, Piracicaba, SP-Brazil, jmmoraes@cena.usp.br
Thommas
Dunne, UCSB, Santa Barbara, CA - USA, tdunne@bren.ucsb.edu
Ricardo
de O.
Figueiredo, EMBRAPA/CPATU, Belem, PA-Brazil, ricardo@cpatu.embrapa.br
Daniel
Markewitz, UGA, Athens, GA - USA, dmarke@smokey.forestry.uga.edu
Eric
A.
Davidson, WHRC, Woods Hole, MA-USA, edavidson@whrc.org
Reynaldo
L.
Victória, CENA/ USP, Piracicaba,SP-Brazil, reyna@cena.usp.br
In order to evaluate the effects of land use change on hydrological processes, we monitored two small catchments (<1.0 ha) drained by ephemeral channels, from 1999 to 2002 at Paragominas, Pará, in the Eastern Amazonia. One catchment was in pasture on soils classified as Plintossolo (Ultisol), and the other was forested on soils classified as Latossolo Amarelo (Oxisol). Both soils had a hydraulic impeding layer of plinthite at 1-m depth, where saturated hydraulic conductivities (Ksat) were 0.1 to 1.0 mm h-1. Median near surface Ksat values were 230 mm h-1 in forest and 3.7 mm h-1 in pasture. Annual precipitation was 1640±190 mm, which was partitioned as throughfall (84±4%), forest canopy interception (16±4%), overland flow (4±2% in forest and 14±6% in pasture) and subsurface flow (1% on both sites). Ephemeral channels discharged 3±1% of annual precipitation in forest and 14±6% in pasture.
Soil moisture and Penman-Monteith evapotranspiration (ET) estimates were calculated using a simple bucket model, coupled with a surface conductance (gc) model to restrict ET. Soil tension was measured and volumetric water content (VWC) calculated from tensiometer data. Coupled bucket model estimates were compared to VWC observations to evaluate model fitness and sensitivity.
From measured and modeled storages and fluxes for the two catchments we were able to quantify the effects of forest-to-pasture conversion on the water balance and the runoff components. Soil properties and fluxes results indicate that forest-to-pasture conversion caused: (1) decreased evapotranspiration; (2) increased overland flow and channel discharge; (3) increased water storage in soils; (4) modified relative distribution of the water balance components.
Submetido por Marysol A. E. Schuler em 18-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)