Dissolved organic carbon and methane in a regional confined aquifer,southern Ontario,Canada: Carbon isotope evidence for associated subsurface sources |
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| Institution: | 1. British Geological Survey, Keyworth NG12 5GG, UK;2. British Geological Survey, Wallingford OX10 8BB, UK;3. University of Bristol, School of Earth Sciences, Bristol BS8 1TH, UK;4. University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham B15 2TT, UK;5. Environment Agency, Wallingford, Oxon OX10 8BD, UK;6. British Geological Survey, Edinburgh EH14 4AP, UK;1. University of Liège, ArGEnCo, Hydrogeology and Environmental Geology, Aquapôle, Liège, Belgium;2. Chemical Oceanography Unit, University of Liège, Liège, Belgium;3. Department of Geosciences, Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain;4. Department of Catchment Hydrology, Helmholtz Centre for Environmental Research - UFZ, Halle (Saale), Germany;1. Lithosphere Fluid Research Lab (LRG), Department of Petrology and Geochemistry, Institute of Geography and Earth Sciences, Eötvös Loránd University (ELTE), Pázmány Péter sétány 1/C, Budapest 1117, Hungary;2. Mining and Geological Survey of Hungary (MBFSZ), Colombus utca 17-23, Budapest 1145, Hungary;3. Institute for Geological and Geochemical Research (IGGR), Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Budaörsi út 45, Budapest 1112, Hungary;4. Isotope Climatology and Environmental Research Centre (ICER), Institute for Nuclear Research, Bem tér 18/c., Debrecen 4026, Hungary;5. Geographical Institute (GI), Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Budaörsi út 45, Budapest, 1112, Hungary;6. Isotope Geosciences Unit, Scottish Universities Environmental Research Centre (SUERC), East Kilbride G75 0QF, Scotland, UK |
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| Abstract: | Information regarding the origin, composition and transport of natural dissolved organic carbon (DOC) in groundwater is necessary to understand the transport of metals and organic pollutants, as well as for the use of14C in DOC as an isotopic groundwater dating method. Previous research in several groundwater systems has suggested soil organic C is the predominant source of high molecular weight DOC to the subsurface. Through the use of stable isotopes,14C and geochemical analyses, this study shows that significant concentrations of DOC and CH4 in a regional confined aquifer can be generated in situ from subsurface sedimentary organic sources. The DOC and CH4 produced is a combined result of degradation of buried peats and bacterial action, resulting in high DOC concentrations and strongly methanogenic conditions in the aquifer. The DOC and CH4 comprise, on average, nearly 50% of the total dissolved C pool in the central part of the aquifer. Methanogenic conditions complicate isotopic groundwater dating by the conventional dissolved inorganic carbon (DIC) method. Estimates of isotopic groundwater residence time using DOC14C data are proposed by the application of14C isotope and mass balance corrections. |
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