HR: 0800h
AN: H51B-1126    [Abstracts]
TI: Influence of Wildfire-Created Hydrophobicity on Watershed Flow Paths and Surface Water Quality in City Creek, San Bernardino Mountains, CA
AU: * Morrissey, S K
EM: skmbruin@excite.com
AF: Department of Geological Sciences, California State University Los Angeles 5151 State University Drive, Los Angeles, CA 90032 United States
AU: Kong, H
EM: kongh@seas.ucla.edu
AF: Department of Civil and Environmental Engineering, University of California Los Angeles, Los Angeles, CA 90095 United States
AU: Rademacher, L K
EM: lradema@calstatela.edu
AF: Department of Geological Sciences, California State University Los Angeles 5151 State University Drive, Los Angeles, CA 90032 United States
AU: Hogue, T S
EM: thogue@seas.ucla.edu
AF: Department of Civil and Environmental Engineering, University of California Los Angeles, Los Angeles, CA 90095 United States
AU: Santilena, R
EM: rsantil2@calstatela.edu
AF: Department of Geological Sciences, California State University Los Angeles 5151 State University Drive, Los Angeles, CA 90032 United States
AB: Wildfires alter surface water quality by changing the physical hydrology and biogeochemical interactions in a watershed. Lignin and other waxy organic compounds vaporize during intense fires. Recondensation of these waxy compounds form coatings on soil particles, which can create a hydrophobic layer. The presence of a hydrophobic layer changes flow paths to the stream channel by increasing overland flow and decreasing flow to subsurface reservoirs. Stream water chemistry is altered by the change in flow paths, as overland flow has shorter travel and mineral/vegetation interaction times than subsurface pathways. Nitrogen, sulfur, potassium and carbon are affected by burning the vegetation. The stream water temporarily receives increased fluxes of these solutes after storm events. Post-fire changes in vegetation also contribute to changes in water quality. The 21 square mile City Creek watershed, located in the San Bernardino Mountains, CA, was burned by the Old Fire in fall 2003. A recently developed air permeameter technique was used to estimate the hydrophobicity of the burned soils. The air permeability was determined by measuring the flow rate and change in pressure and by using the equation: Kair = [(flow rate)(air viscosity)(length of sample)]/[(change in pressure)(area of sample)]. Air permeability was correlated to soil hydraulic conductivity by a relationship developed in previous studies: Log (Ksat)= 1.27 x log(Kair) + 14.11. Vegetation in City Creek watershed consists of chaparral, woodland and conifer forests, with the greatest increases of hydrophobicity in the chaparral. Increased hydrophobicity in the City Creek watershed increased the contribution of overland flow to City Creek, as indicated by the decrease in delta-18O during storm events. This approximately 2 per mil decrease in delta-18O is indicative of the direct influence of precipitation and overland flow on the stream, rather than the continuous groundwater contribution during baseflow periods. Increased overland flow also causes increases in nitrogen, sulfur, potassium and carbon in the creek immediately after storm events during the first few months after the fire.
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1615 Biogeochemical processes (4805)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting