Publication Date:
2022-05-26
Description:
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 109 (2008): 250-267, doi:10.1016/j.marchem.2007.12.002.
Description:
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.
Description:
This work is a result of research
sponsored by NSF (OCE- 0425061 to M.A.C.), the WHOI-NOC Student Exchange
program (to P.J.M), and the WHOI Postdoctoral Scholar program (to H.D.).
Keywords:
Radium
;
Sediments
;
Desorption
;
Adsorption
;
Barium
;
Submarine groundwater
;
Subterranean estuary
;
Redox reactions
;
Ion exchange
;
Distribution coefficient
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
Permalink
