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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2018-627
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2018-627
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Feb 2019

Research article | 12 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Isotopic and chromatographic fingerprinting of the sources of dissolved organic carbon in a shallow coastal aquifer

Karina T. Meredith1,2, Andy Baker2,4, Martin S. Andersen2,3, Denis M. O'Carroll2,3, Helen Rutlidge2,3, Liza K. McDonough2,4, Phetdala Oudone2,4, Eliza Bryan5, and Nur Syahiza Zainuddin6 Karina T. Meredith et al.
  • 1Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, 2234, Australia
  • 2Connected Waters Initiative Research Centre, UNSW Sydney, Australia
  • 3School of Civil and Environmental Engineering, UNSW Sydney, Australia
  • 4School of Biological, Earth and Environmental Sciences, UNSW Sydney
  • 5Golder Associates, Sydney, NSW, Australia, 124 Pacific Highway, St. Leonards, New South Wales 2065, Australia
  • 6Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia

Abstract. The terrestrial sub-surface is the largest source of freshwater globally. The organic carbon contained within it and processes controlling its concentration remain largely unknown. The global median concentration of dissolved organic carbon in groundwater is low compared to surface waters suggesting significant processing in the subsurface. Yet the processes that remove this dissolved organic carbon (DOC) in groundwater are not fully understood. The purpose of this study was to investigate the different sources and processes influencing DOC in a shallow anoxic coastal aquifer. Uniquely, this study combines liquid chromatography organic carbon detection with inorganic (δ13CDIC) and organic (δ13CDOC) carbon isotope geochemical analyses, to fingerprint the various DOC sources that influence the concentration, carbon isotopic composition and character with distance from surface water sources, depth below surface and groundwater residence time (using 3H) in groundwater. It was found that the average groundwater DOC concentration was five times higher (5 mg L−1) than the global median concentration and it doubled with depth, but the chromatographic character did not change significantly. The anoxic saturated conditions of the aquifer have limited the rate of organic matter processing leading to enhanced preservation and storage of the sources such as peats and palaeosols. All groundwater samples are more aromatic for their molecular weight in comparison to lakes and rivers and surface marine samples. The destabilisation or changes in hydrology, whether by anthropogenic or natural processes could lead to the flux of up to ten times more unreacted organic carbon from this coastal aquifer than compared to deeper inland aquifers.

Karina T. Meredith et al.
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Karina T. Meredith et al.
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Short summary
Dissolved organic carbon within groundwater and processes controlling it, remain largely unknown. Groundwater is lower compared to surface waters. The average groundwater concentration at this coastal site was five times higher than the global median, doubling with depth, but with no change in chromatographic character. The lack of oxygen limited the rate of organic matter processing leading to enhanced preservation. Changes in coastal hydrology could lead to the flux of unreacted organic carbon.
Dissolved organic carbon within groundwater and processes controlling it, remain largely...
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