Marine water from mid-holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance

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dc.contributor.authorLee, Sen_AU
dc.contributor.authorCurrell, MJen_AU
dc.contributor.authorCendón, DIen_AU
dc.date.accessioned2017-05-01T00:01:42Zen_AU
dc.date.available2017-05-01T00:01:42Zen_AU
dc.date.issued2016-02-15en_AU
dc.date.statistics2017-05-01en_AU
dc.description.abstractA multi-layered coastal aquifer in southeast Australia was assessed using environmental isotopes, to identify the origins of salinity and its links to palaeo-environmental setting. Spatial distribution of groundwater salinity (electrical conductivity values ranging from 0.395 to 56.1 mS/cm) was examined along the coastline along with geological, isotopic and chemical data. This allowed assessment of different salinity sources and emplacement mechanisms. Molar chloride/bromide ratios range from 619 to 1070 (621 to 705 in samples with EC > 15 mS/cm), indicating salts are predominantly marine. Two distinct vertical salinity profiles were observed, one with increasing salinity with depth and another with saline shallow water overlying fresh groundwater. The saline shallow groundwater (EC = 45.4 to 55.7 mS/cm) has somewhat marine-like stable isotope ratios (δ18O = − 2.4 to − 1.9 ‰) and radiocarbon activities indicative of middle Holocene emplacement (47.4 to 60.4 pMC). This overlies fresher groundwater with late Pleistocene radiocarbon ages and meteoric stable isotopes (δ18O = − 5.5 to − 4.6‰). The configuration suggests surface inundation of the upper sediments by marine water during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today's level. Profiles of chloride, stable isotopes, and radiocarbon indicate mixing between this pre-modern marine water and fresh meteoric groundwater to varying degrees around the coastline. Mixing calculations using chloride and stable isotopes show that in addition to fresh-marine water mixing, some salinity is derived from transpiration by halophytic vegetation (e.g. mangroves). The δ13C ratios in saline water (− 17.6 to − 18.4‰) also have vegetation/organic matter signatures, consistent with emplacement by surface inundation and extensive interaction between vegetation and recharging groundwater. Saline shallow groundwater is preserved only in areas where low permeability sediments have slowed subsequent downwards propagation. The configuration is unlikely to be stable long-term due to fluid density; this may be exacerbated by pumping the underlying aquifer. © 2015, Elsevier B.V.en_AU
dc.identifier.citationLee, S., Currell, M., & Cendón, D. I. (2016). Marine water from mid-Holocene sea level highstand trapped in a coastal aquifer: evidence from groundwater isotopes, and environmental significance. Science of The Total Environment, 544, 995-1007. doi:10.1016/j.scitotenv.2015.12.014en_AU
dc.identifier.govdoc7466en_AU
dc.identifier.issn0048-9697en_AU
dc.identifier.journaltitleScience of The Total Environmenten_AU
dc.identifier.pagination995-1007en_AU
dc.identifier.urihttps://doi.org/10.1016/j.scitotenv.2015.12.014en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/8657en_AU
dc.identifier.volume544en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectAquatic ecosystemsen_AU
dc.subjectQuaternary perioden_AU
dc.subjectShoresen_AU
dc.subjectAquifersen_AU
dc.subjectSalinityen_AU
dc.subjectIsotopesen_AU
dc.titleMarine water from mid-holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significanceen_AU
dc.typeJournal Articleen_AU
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