Carbonate mineral weathering in mid-latitude watersheds: Importance of calcite and dolomite dissolution on dissolved inorganic carbon acquisition and transport.

摘要

The advent of global warming due to anthropogenic forcing has increased awareness of the global carbon cycle. The removal of CO2 from the atmosphere occurs via silicate and carbonate mineral weathering and this CO 2 is "trapped" when carbonate is re-precipitated in the ocean. Only silicate weathering creates a net sink for CO2, while carbonate weathering provides a short-term drawdown on the scale of decades to thousands of years. Silicate mineral dissolution rates however are on the order of thousands to millions of times slower than carbonate mineral weathering. On a human time scale (hundreds of years), the weathering of carbonate minerals may play an important role in the regulation of anthropogenic CO2.; Increased atmospheric CO2 will influence dissolved inorganic carbon (DIC) within global rivers, via the enhancement of mineral weathering. Carbonate mineral solubility in physically open weathering environments is proportional to soil Pco2; so carbonate-weathering intensities should be affected by land use and soil thickness.; To understand the ramifications of increased DIC in rivers, it is imperative to understand watershed scale processes that control and regulate the dissolved inorganic carbon cycle within watersheds. This dissertation investigates the fundamental controls on the acquisition, cycling, and transport of DIC from forested temperate carbonate bearing watersheds in Michigan and Slovenia. These investigations have culminated in an extensive database on ground and river waters that is used to further the understanding of carbonate weathering and DIC fluxes from watersheds.; Watersheds with thicker soils are able to reach greater HCO3 - concentrations, than watersheds with thinner soils. Higher mean annual precipitation in Slovenia allows the Slovenian watersheds to have significantly higher HCO3- and Mg2+ weathering intensities than the Michigan watersheds. In some cases carbonate back precipitation is occurring within the watershed due to high calcite saturation states in the stream waters.; Comparing the volume of carbonate removed from the watershed to the flux of dissolved inorganic carbon from the watershed indicates that back precipitation is negligible in the overall DIC flux from the watershed. Both calcite and dolomite weathering contribute to the DIC flux. In Slovenia, dolomite weathering is contributing approximately half the HCO3- flux from the watershed.