HR: 09:15h
AN: H51J-06 INVITED    [Abstracts]
TI: Overland Flow Generation Under Contrasting Land use in Amazonia (Rondônia, Brazil)
AU: * Germer, S
EM: sonjagermer@uni-potsdam.de
AF: University of Potsdam, Inst. of Geoecology, Karl-Liebknecht-Str. 24-25, Potsdam, 14476, Germany
AU: Neill, C
EM: cneill@mbl.edu
AF: Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, United States
AU: Krusche, A V
EM: alex@cena.usp.br
AF: Laboratório de Ecologia Isotópica, CENA –USP, POBox 96, Piracicaba, SP 13.400-970, Brazil
AU: Elsenbeer, H
EM: helsenb@rz.uni-potsdam.de
AF: University of Potsdam, Inst. of Geoecology, Karl-Liebknecht-Str. 24-25, Potsdam, 14476, Germany
AB: Human transformation of the Earth's land surface has large and important consequences for the functioning of hydrological processes in watersheds. Changes in land cover and land use can modify the relative contribution of overland flow, subsurface flow and groundwater flow to stream discharge. The conversion of tropical primary forest to pasture is known to reduce soil hydrologic conductivity (Ksat) significantly. To study the influence of reduced Ksat on overland flow generation and to get insight into the interaction of Ksat, the development of perched water tables and the occurrence of overland flow, we compared the hydrology of two small catchments under primary open tropical forest and pasture in the southwestern Brazilian Amazon basin. Of 176 rainfall events that occurred from August 2004 to July 2005, 70 events generated stream flow in the pasture, but only 37 events generated stream flow in the forest catchment. Overland flow was 18% of incident rainfall in the pasture but only 1% in the forest. On event basis, the overland flow response ranged between 0 and 54% of incident rainfall in the pasture and 0 and 14% of incident rainfall in the forest. Piezometer with automatic water level loggers were installed in 12.5, 20 and 50 cm soil depth at ten sites per catchment. Perched water tables were observed in 12.5 and 20 cm soil depth in both catchments, but more frequently in the pasture. Piezometer hydrographs depended on rainfall characteristics and on their position relative to the stream channel and indicate slow subsurface flow. We conclude from our study that reduced Ksat due to land use change from primary forest to pasture results in 1) a significant increase of overland flow and 2) a more frequent shift between aerobic and anaerobic conditions from the soil surface to a depth of 20 cm. We expect both phenomena to influence catchment biogeochemistry, as illustrated by a closer look at nitrate.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0469 Nitrogen cycling
DE: 1632 Land cover change
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1838 Infiltration
SC: Hydrology [H]
MN: 2007 Fall Meeting