☆ 4.5 Article

Submarine groundwater discharge and associated fluxes of alkalinity and dissolved carbon into Moreton Bay (Australia) estimated via radium isotopes

MARINE CHEMISTRY (2015)

期刊

MARINE CHEMISTRY

卷 174, 期 -, 页码 1-12

出版社

ELSEVIER SCIENCE BV

DOI: 10.1016/j.marchem.2015.03.019

关键词

Permeable sediments; Mangrove; Subterranean estuary; Carbon cycle

类别

Chemistry, Multidisciplinary Oceanography

资金

CSIRO Coastal Carbon Cluster
Australian Research Council [DP120101645, LE120100156, DE140101733, DE150100581]

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摘要

Submarine groundwater discharge,(SGD) can release solutes into the coastal ocean. This study used radium isotopes (Ra-224, (223) Ra, and Ra-226) to investigate SGD and its influence on alkalinity (TAlk), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) inputs to Moreton Bay, Queensland, Australia. The average residence time of the bay was estimated to be about 40 days using radium isotope ratios, which is comparable to a previous physical model that revealed average residence times of 50 days. Radium isotopes identified several SGD hotspots around the bay. Using a Ra-226 mass balance, a very minimum SGD flux of 1.1 x 10(7) m(3) d(-1) (or 0.7 cm/day) was calculated relying on extreme assumptions including the use of maximum 226Ra concentration for the groundwater endmember attained from 45 spatially distributed samples. Using more reasonable assumptions (i.e., the average Ra-226 concentration in the groundwaters as the end member), a total SGD rate of 6.7 x 10(7) +/- 22 x 107 m(3)/day (or 4.4 +/- 1.5 cm/day) was estimated, which was similar to 18 times greater than the average annual discharge of all the major river inputs into the bay (i.e., the sum of Brisbane, Caboolture, Pine, and Logan Rivers). The average groundwater concentrations of TAlk, DIC and DOC were 1.5, 1.7 and 6.7 times greater than Moreton Bay surface waters, respectively. Fluxes of SGD-derived TAlk, DIC and DOC were estimated to be 161, 156, and 36 mmol/m(2)/day, respectively. When upscaled to the Bay area, these SGD fluxes became 20 to 38 times higher than the estimated annual input of all the major rivers. SGD is regionally important from a hydrological and carbon cycle perspective even if extreme assumptions are made to minimize SGD estimates. However, it remains unclear whether the SGD traced by radium isotopes in Moreton Bay is composed of fresh or saline groundwater. (C) 2015 Elsevier B.V. All rights reserved.

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Geochemical dynamics and depositional history from mangrove sediments within the Pearl River estuary

Yiying Sun, Haixian Xiong, Man-Ting Lee, Chris Brodie, Yongqiang Zong

Summary: This study investigated the geochemical dynamics of sediment organic matter in mangrove wetlands and found significant exchanges of mangrove OM with marine and mixed forest OM. Despite these exchanges, distinct values of delta C-13, TOC and C/N were observed in modern surface sediments of different vegetational zones, confirming their usefulness as coastal environmental proxies. The proxies, combined with chronologies based on radiocarbon, 210 Pb and 137 Cs analyses, were successfully used to reconstruct the depositional history of the mangrove wetland, providing new insights into environmental responses to natural and anthropogenic drivers.

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