HR: 0800h
AN: H31B-1309    [Abstracts]
TI: A Seasonal Comparison of Nutrient Cycling Along two Reaches of the San Pedro River, AZ
AU: * Klasner, L M
EM: laura@hwr.arizona.edu
AF: University of Arizona Department of Hydrology & Water Resources/SAHRA, JW Harshbarger Building, Rm122 PO Box 210011 1133 E. James E. Rogers Way, Tucson, AZ 85721-0011 United States
AU: Brooks, P D
EM: brooks@hwr.arizona.edu
AF: University of Arizona Department of Hydrology & Water Resources/SAHRA, JW Harshbarger Building, Rm122 PO Box 210011 1133 E. James E. Rogers Way, Tucson, AZ 85721-0011 United States
AU: Meixner, T
EM: tmeixner@hwr.arizona.edu
AF: University of Arizona Department of Hydrology & Water Resources/SAHRA, JW Harshbarger Building, Rm122 PO Box 210011 1133 E. James E. Rogers Way, Tucson, AZ 85721-0011 United States
AB: The San Pedro River, one of the last free-flowing rivers in the Semi-arid southwest, is threatened both by decreases in water availability and increases in nutrient inputs from growing populations within the basin. To quantify the effects of hydrology and water availability biogeochemical cycling of C and N we conducted two intensive week-long sampling campaigns on the San Pedro River, one before (June) and one during (August) the 2005 monsoon season. During each campaign we measured discharge, nutrients, and major solute concentrations entering and exiting two experimental reaches. In addition we performed two longitudinal sampling events with discharge and chemistry measured to identify hotspots of biogeochemical transformation. Water samples were analyzed for major biogeochemical reactants including dissolved and particulate organic carbon (DOC and POC), dissolved and particulate organic nitrogen (DON and PON), ammonium, and nitrate; water isotopes (I'18O and I'2H) and major ions (Cl, SO4, Ca, Mg, Na) were used as biogeochemically conservative tracers of hydrologic flowpaths. Both total dissolved nitrogen (TDN) (mean = 0.92 ppm, SD = 0.12) and DOC (mean = 4.92 ppm, SD = 0.63) concentrations during the monsoon sampling period were significantly higher than during the pre-monsoon season (DOC mean = 2.09 ppm, SD = 0.52; TDN mean = 0.24 ppm, SD = 0.06). N concentrations during the premonsoon season exhibited a diurnal cycle with highest concentrations during night suggesting in situ biologically mediated transformations were the primary controls on concentrations. In contrast, N concentrations during the monsoon season appeared to be controlled primarily by advective transport. These results, combined with the high spatial resolution sampling, existing data on potential rates of N transformation, and a dynamic flow model are being used to parameterize the DAYCENT biogeochemical for the stream-riparian-hyporheic corridor. If successful, this effort will provide a mechanism for scaling hotspots and hot moments in these dynamic environments.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005