HR: 1340h
AN: B33D-1064    [Abstracts]
TI: Soil Moisture Controls on Ecosystem Scale Water and Carbon Fluxes in Semiarid Grassland and Shrubland
AU: * Kurc, S A
EM: kurc@colorado.edu
AF: University of Colorado, Geological Sciences 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AU: Small, E E
EM: eric.small@colorado.edu
AF: University of Colorado, Geological Sciences 2200 Colorado Ave., Boulder, CO 80309-0399 United States
AB: Soil moisture distribution emerges as a key link between hydrologic and ecologic processes in semiarid grassland and shrubland as it influences evapotranspiration, respiration, and assimilation. In support, we present three years of data (2002 - 2004) collected from a semiarid grassland and shrubland within the Sevilleta National Wildlife Refuge of central New Mexico; these two sites are separated by only a few kilometers. Instrumentation in this study includes an eddy covariance tower and typical micrometeorological devices at both locations. Additionally, the grassland site features 6 soil moisture profiles and the shrubland site features 4 soil moisture profiles, with the maximum depth of any profile at 52.5 cm. At both sites, most rain falls during the summer monsoon season, but large storms do occur at other times of the year, e.g. spring of 2004. Soil moisture pulses at 2.5 cm follow almost all rain events, whereas only 4 pulses in the 3 year record are observed at 52.5 cm in the grassland and 2 in the shrubland; these deeper pulses follow large precipitation events or a series of smaller events. The daily times series of evapotranspiration (ET) is similar between the grassland and shrubland, supporting the results of Kurc and Small 2004. This ET time series reflects changes in the soil moisture at 2.5 cm. In contrast, though the daily time series of net ecosystem exchange (NEE_CO2) at both sites peak simultaneously, the magnitudes of peaks in net negative ecosystem exchange (NEE_CO2-) and net positive ecosystem exchange (NEE_CO2+) are larger at the grassland than at the shrubland. Furthermore, pulses associated with NEE_CO2- peaks last much longer than ET pulses, on the order of 1 to 2 months, without any particular adherence to seasonality. These NEE_CO2- pulses reflect changes in deeper soil moisture, i.e. 52.5 cm at the grassland and 37.5 cm at the shrubland. Finally, evidence of moisture driven soil respiration is found throughout the NEE_CO2 time series, with spikes of NEE_CO2+ following most rain events; however, longer pulses of NEE_CO2+ also occur during relatively dry periods. Modeled respiration and assimilation are speculative but indicate that the relationship between assimilation and soil moisture is best at depths at least 30cm below the surface.
DE: 0476 Plant ecology (1851)
DE: 1800 HYDROLOGY
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology (0476)
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: Fall Meeting 2005