New perspectives on radium behavior within a subterranean estuary

Meagan Eagle Gonneea*, Paul J. Morris, Henrieta Dulaiova, Matthew A. Charette

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

114 Citations (Scopus)

Abstract

Over the past decade, radium isotopes have been frequently applied as tracers of submarine groundwater discharge (SGD). The unique radium signature of SGD is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers, yet little is known about what controls Ra cycling in this system. The focus of this study was to examine controls on sediment and groundwater radium activities within permeable aquifer sands (Waquoit Bay, MA, USA) through a combination of field and laboratory studies. In the field, a series of sediment cores and corresponding groundwater profiles were collected for analysis of the four radium isotopes, as well as dissolved and sediment associated manganese, iron, and barium. We found that in addition to greater desorption at increasing salinity, radium was also closely tied to manganese and iron redox cycling within these sediments. A series of laboratory adsorption/desorption experiments helped elucidate the importance of 1) contact time between sediment and water, 2) salinity of water in contact with sediment, 3) redox conditions of water in contact with sediment, and 4) the chemical characteristics of sediment on radium adsorption/desorption. We found that these reactions are rapid (on the order of hours), desorption increases with increasing salinity and decreasing pH, and the presence of Fe and Mn (hydr)oxides on the sediment inhibit the release of radium. These sediments have a large capacity to sorb radium from fresh water. Combined with these experimental results, we present evidence from time series groundwater sampling that within this subterranean estuary there are cyclic periods of Ra accumulation and release controlled by changing salinity and redox conditions. (c) 2007 Elsevier B.V. All rights reserved.

Original languageEnglish
Pages (from-to)250-267
Number of pages18
JournalMarine Chemistry
Volume109
Issue number3-4
DOIs
Publication statusPublished - 16 Apr 2008

Keywords

  • WAQUOIT BAY
  • desorption
  • subterranean estuary
  • radium
  • submarine groundwater discharge
  • redox reactions
  • TH-SERIES NUCLIDES
  • adsorption
  • ZONE
  • RIVER
  • SUBMARINE GROUNDWATER DISCHARGE
  • TRANSPORT
  • COASTAL WATERS
  • barium
  • U-SERIES
  • PERMEABLE SEDIMENTS
  • sediments
  • distribution coefficient
  • ion exchange
  • SANDY UNCONFINED AQUIFER

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