Using the radium quartet for evaluating groundwater input and water exchange in salt marshes

Journal Article · Sun Dec 01 04:00:00 EST 1996 · Geochimica et Cosmochimica Acta

OSTI ID:543103

Moore, R; Moore, W S ^[1]

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1. Univ. of South Carolina, Columbia, SC (United States)

The fluxes of {sup 226}Ra (half-life = 1600 years) and {sup 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{sup 3} cm{sup -2} day{sup -1} is indicated if the groundwater activities we have measured are representative. The fluxes of {sup 223}Ra (half-life = 11.4 day) and {sup 224}Ra (half-life = 3.6 day) are factors of 22, and ten more than those expected from the flux of {sup 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 {sup 226}Ra and {sup 228}Ra in the top 15 cm sediment layer are very low. Nevertheless, the activities of {sup 226}Ra and {sup 228}Ra in the porewaters are large, indicating a low distribution coefficient ({approximately}10) for radium and a short retention time ({approximately}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 {delta}{sup 18}O. 11 refs., 2 figs., 4 tabs.

• OSTI ID: 543103
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 23 Vol. 60; ISSN 0016-7037; ISSN GCACAK
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
HYDROLOGY
MARSHES
RADIUM 226
RADIUM 228
SALINITY
SEAWATER
SOUTH CAROLINA
TRACER TECHNIQUES