HR: 09:30h
AN: H51G-07    [Abstracts]
TI: Diel Variation of Oxygen and Inorganic Carbon in a High Productivity, High Alkalinity Stream: Biological and Geochemical Controls
AU: * Tobias, C R
EM: crtobias@usgs.gov
AF: U.S. Geological Survey, 431 National Center, Reston, VA 20192 United States
AU: Bohlke, J
EM: jkbohlke@usgs.gov
AF: U.S. Geological Survey, 431 National Center, Reston, VA 20192 United States
AB: Dissolved oxygen (O$_{2}$) and inorganic carbon (DIC) measurements are frequently used for assessing the metabolic balance and ecological function of aquatic systems. In many cases, oxygen and DIC dynamics are related to each other with fixed stoichiometry (C:O$_{2}$ approximating 1:1) based upon photosynthesis and/or respiration. This stoichiometry has proven reproducible (with some variation) in systems where the oxygen and carbon balances are dominated by biological processes. However, high alkalinity aquatic systems may have an added geochemical control on daily DIC dynamics causing deviation of C:O$_{2}$ stoichiometry from that fixed by biological processes alone. As part of a study examining stream metabolism in agricultural watersheds, we measured diel variation of dissolved O$_{2}$, \delta $^{18}$O$_{2}$, DIC, and \delta $^{13}$C-DIC in a low-order, high-alkalinity stream, mid-continent USA to determine biological and geochemical controls on O$_{2}$ and DIC dynamics and stoichiometry. High rates of primary production generated large diel fluctuations in O$_{2}$ concentration (up to 50 percent above O$_{2}$ saturation during the day and 20 percent undersaturation at night). \delta $^{18}$O$_{2}$ isotopes varied inversely with O$_{2}$ concentration and were enriched by up to 12 permil at night. \delta $^{13}$C-DIC exhibited a 3.5 permil diel variation. Changes in DIC concentration were inversely correlated to changes in O$_{2}$ concentration at a C:O$_{2}$ ratio of nearly 3:1 indicating the influence of both biological and geochemical controls on the DIC pool. Relative contributions of stream metabolism and abiotic carbonate reactions were examined with a numerical model that included primary production, respiration, and carbonate reactions to simulate diel variation in O$_{2}$ and DIC concentration and isotopes.
DE: 1800 HYDROLOGY
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting