Other
Scientific paper
Dec 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996gecoa..60.4645r&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 60, Issue 23, pp.4645-4652
Other
10
Scientific paper
The fluxes of 226 Ra (half-life = 1600 years) and 228 Ra (half-life = 5.7 years) from the North Inlet salt marsh to the sea are much larger than can be supported by decay of their Th parents in the surface marsh sediments. These fluxes are sustained almost entirely by groundwater flow through the marsh. An average groundwater flow of approximately 10 cm 3 cm -2 day -1 is indicated if the groundwater activities we have measured are representative. The fluxes of 223 Ra (half-life = 11.4 day) and 224 Ra (half-life = 3.6 day) are factors of 22, and ten more than those expected from the flux of 226 Ra. Groundwater also sustains most of the flux of the short-lived isotopes. The measured Ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment. We present a model to explain the anomalous distribution pattern of these isotopes. Despite their large throughput, the inventories of desorbable 226 Ra and 228 Ra in the top 15 cm sediment layer are very low. Nevertheless, the activities of 226 Ra and 228 Ra in the porewaters are large, indicating a low distribution coefficient (~10) for radium and a short retention time (~10 days) in the surface sediment layer. We surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins. This source must be recognized while considering mass balance of any tracer, be it radium, nutrients, other metals, or 18 O.
Moore Willard S.
Rama
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