HR: 1340h
AN: B23B-1265    [Abstracts]
TI: Carbonate Mineral Weathering Contributions to the HCO3- Flux from Headwater Mid-latitude Streams in the Face of Increasing Atmospheric CO2
AU: * Szramek, K
EM: szramekk@wlu.edu
AF: Dept.of Geology Washington and Lee University, 204 West Washington St., Lexington, VA 24450, United States
AU: Ogrinc, N
EM: nives.ogrinc@ijs.si
AF: Jozef Stefan Institute Dept. of Environmental Sciences, Jamova 39, Ljubljana, 1000, Slovenia
AU: Walter, L M
EM: lmwalter@umich.edu
AF: Dept. of Geological Sciences University of Michigan, 2534 C. C. Little Building 1100 North University Ave, Ann Arbor, MI 48104, United States
AB: As anthropogenic liberated CO₂ increases in the atmosphere, landscape level responses of the carbon cycle to perturbations associated with global warming are likely to be observed in carbonate bearing regions. Within physically open weathering environments, carbonate (calcite and dolomite) mineral solubility is proportional to pCO₂ and inversely proportional to temperature, with the solubility of dolomite progressively greater than calcite below 25°C. Changes in weathering zone CO₂ occur as CO₂ drawdown is increased due to CO₂ fertilization effects on plant growth, to warmer mean annual temperatures, or to land use changes. The rise in weathering zone CO₂ will significantly augment the open system solubility of carbonate minerals and increase the DIC content of surface waters (unconfined groundwaters and rivers). The thermodynamic relationships between calcite and dolomite indicate the further need to examine the role of dolomite on the global riverine DIC budget. On a continental scale, the global weathering budget indicates the importance of northern hemisphere landmasses to riverine fluxes of Ca²⁺, Mg²⁺ and DIC as HCO₃^-. The results of a hydrogeochemical study of carbonate mineral equilibria and weathering fluxes for headwater streams within the Danube, the James and the St. Lawrence River Basins is presented. Available long-term geochemical and discharge data along with detailed catchment geochemical views of surface water and soil weathering zones were determined to examine the historical and current contribution of carbonate weathering to the geochemical fluctuations of the these headwater regions and the ability of these watersheds to maintain current conditions in the facing of increasing CO₂. In order to gauge how these streams with variable climates, land use practices, lithologies, and weathering zone thicknesses compare to each other, river runoff and HCO₃^- concentrations are normalized to catchment area. The resulting carbonate weathering intensity on a global scale, shows the study regions exceeding the world average by factors of between 2 to 20. Within each stream, variability of HCO₃^- concentrations are minimal over a wide range of discharges indicating that carbonate weathering is not limited by solubility. A closer look at dolomite weathering contributions estimated from riverine Mg²⁺ fluxes exceeds the world average by factors between 2 to 15. Our results indicate that both calcite and dolomite mineral weathering within temperate zone watersheds will be able to carry an increased flux of HCO₃^- to the ocean as global atmospheric CO₂ increases. In addition this work reinforces the significant contribution of dolomite weathering to the global HCO₃^- flux.
DE: 0330 Geochemical cycles (1030)
DE: 0428 Carbon cycling (4806)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1806 Chemistry of fresh water
DE: 1886 Weathering (0790, 1625)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting