Understanding the carbon cycle in a Late Quaternary-age limestone aquifer system using radiocarbon of dissolved inorganic and organic carbon

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dc.contributor.authorBryan, Een_AU
dc.contributor.authorMeredith, KTen_AU
dc.contributor.authorBaker, AAen_AU
dc.contributor.authorAndersen, MSen_AU
dc.contributor.authorPost, VEAen_AU
dc.date.accessioned2023-01-13T02:24:21Zen_AU
dc.date.available2023-01-13T02:24:21Zen_AU
dc.date.issued2017-04-26en_AU
dc.date.statistics2022-11-10en_AU
dc.description.abstractEstimating groundwater residence time is critical for our understanding of hydrogeological systems, for groundwater resource assessments and for the sustainable management of groundwater resources. Due to its capacity to date groundwater up to 30 thousand years old, as well as the ubiquitous nature of dissolved carbon (as organic and inorganic forms) in groundwater, 14C is the most widely used radiogenic dating technique in regional aquifers. However, the geochemistry of carbon in groundwater systems includes interaction with the atmosphere, biosphere and geosphere, which results in multiple sources and sinks of carbon that vary in time and space. Identifying these sources of carbon and processes relating to its release or removal is important for understanding the evolution of the groundwater and essential for residence time calculations. This study investigates both the inorganic and organic facets of the carbon cycle in groundwaters throughout a freshwater lens and mixing zone of a carbonate island aquifer and identifies the sources of carbon that contribute to the groundwater system. Groundwater samples were collected from shallow (5-20 m) groundwater wells on a small carbonate Island in Western Australia in September 2014 and analysed for major and minor ions, stable water isotopes (SWIs: δ18O, δ2H), 3H, 14C and 13C carbon isotope values of both DIC and DOC, and 3H. The composition of groundwater DOC was investigated by Liquid Chromatography-Organic Carbon Detection (LC-OCD) analysis. The presence of 3H (0.12 to 1.35 TU) in most samples indicates that groundwaters on the Island are modern, however the measured 14CDIC values (8.4 to 97.2 pmc) suggest that most samples are significantly older due to carbonate dissolution and recrystallisation reactions that are identified and quantified in this work. 14CDOC values (46.6 to 105.6 pMC) were higher than 14CDIC values and were well correlated with 3H values, however deeper groundwaters had lower 14CDOC values than expected. LC-OCD chromatography of these groundwaters were found to contain higher concentrations of humic substances, that are most likely attributed to the presence of paleosol horizons at depth in the limestone, which are a common feature in aeolianite deposits along the Western coast of Australia and are related to Quaternary sea level change. The paleosols likely contribute old organic matter to the deeper groundwaters, which may explain the lower 14CDOC values. This study has shown that a combined approach that utilises both DIC and DOC tracers, as well as 3H, is required to identify the sources and evolution of carbon in a groundwater system, as well as the processes that effect the application of 14C dating to groundwaters within a carbonate aquifer. © 2017 Author(s). CC Attribution 3.0 License.en_AU
dc.identifier.citationBryan, E., Meredith, K. T., Baker, A., Andersen, M. S., & Post, V. E. (2017). Understanding the carbon cycle in a Late Quaternary-age limestone aquifer system using radiocarbon of dissolved inorganic and organic carbon. Poster presented at the European Geosciences Union General Assembly 2017, Vienna, Austria, 23–28 April 2017. (pp. 5826). Retrieved from: https://meetingorganizer.copernicus.org/EGU2017/EGU2017-5826-1.pdfen_AU
dc.identifier.conferenceenddate28 April 2017en_AU
dc.identifier.conferencenameEuropean Geosciences Union General Assembly 2017en_AU
dc.identifier.conferenceplaceVienna, Austriaen_AU
dc.identifier.conferencestartdate23 April 2017en_AU
dc.identifier.otherEGU2017-5826en_AU
dc.identifier.pagination5826en_AU
dc.identifier.urihttps://meetingorganizer.copernicus.org/EGU2017/EGU2017-5826-1.pdfen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/14344en_AU
dc.language.isoenen_AU
dc.publisherEuropean Geosciences Unionen_AU
dc.subjectQuaternary perioden_AU
dc.subjectCarbon 14en_AU
dc.subjectAquifersen_AU
dc.subjectLimestoneen_AU
dc.subjectCarbonen_AU
dc.subjectCarbon cycleen_AU
dc.titleUnderstanding the carbon cycle in a Late Quaternary-age limestone aquifer system using radiocarbon of dissolved inorganic and organic carbonen_AU
dc.typeConference Posteren_AU
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