Salt marsh submarine groundwater discharge as traced by radium isotopes

Abstract Submarine groundwater discharge (SGD) generally occurs through permeable sediments where the hydraulic head of an aquifer is above sea level, and often includes a recirculated seawater component. In order to determine SGD to the Great Sippewissett Marsh, West Falmouth, MA, we measured the activities of four radium isotopes (226Ra, 228Ra, 223Ra, 224Ra) at the marsh inlet in July 1999 and 2001 and compared our data with Ra activities measured at the same location in 1983 and 1985. A radium-based approach for estimating SGD to the marsh yielded a summer average of 3900 m3 day−1. This flux was in good agreement with independent estimates from the literature, which ranged from 600 to 23,000 m3 day−1. Radium activities of the long-lived isotopes (226Ra, 228Ra) were on average more than two times higher in 1999 than during the three other time periods. These results suggest that drought conditions leading to enhanced seawater–sediment interactions may be an important mechanism in delivering certain dissolved substances to coastal waters.

[1]  E. Carpenter,et al.  Nutrient and particulate fluxes in a salt marsh ecosystem: Tidal exchanges and inputs by precipitation and groundwater 1 , 1978 .

[2]  M. Charette,et al.  Oxidative precipitation of groundwater‐derived ferrous iron in the subterranean estuary of a coastal bay , 2002 .

[3]  W. Moore.  The subterranean estuary: a reaction zone of ground water and sea water , 1999 .

[4]  Rama,et al.  Using the radium quartet for evaluating groundwater input and water exchange in salt marshes , 1996 .

[5]  H. Hemond,et al.  Subsurface flow in salt marsh peat: A model and field study1 , 1982 .

[6]  M. Charette,et al.  Utility of radium isotopes for evaluating the input and transport of groundwater‐derived nitrogen to a Cape Cod estuary , 2001 .

[7]  Brian L. Howes,et al.  Transport of groundwater-borne nutrients from watersheds and their effects on coastal waters , 1990 .

[8]  W. Moore,et al.  Evaluation of salt marsh hydrology using radium as a tracer , 1993 .

[9]  W. Moore.  Ages of continental shelf waters determined from 223Ra and 224Ra , 2000 .

[10]  Thomas C. Cambareri,et al.  Watershed Delineation and Ground Water Discharge to a Coastal Embayment , 1998 .

[11]  W. Moore.  High fluxes of radium and barium from the mouth of the Ganges-Brahmaputra River during low river discharge suggest a large groundwater source , 1997 .

[12]  D. Childers,et al.  Subtidal advective water flux as a potentially important nutrient input to southeastern U.S.A. Saltmarsh estuaries , 1989 .

[13]  W. Moore,et al.  Measurement of 223Ra and 224Ra in coastal waters using a delayed coincidence counter , 1996 .

[14]  W. Burnett,et al.  Measurement and significance of the direct discharge of groundwater into the coastal zone , 2001 .

[15]  S. B. Moran,et al.  Seasonal changes in groundwater input to a well‐mixed estuary estimated using radium isotopes and implications for coastal nutrient budgets , 2002 .

[16]  W. Moore.  Large groundwater inputs to coastal waters revealed by 226Ra enrichments , 1996, Nature.

[17]  J. Sarmiento,et al.  Techniques for precise mapping of 226Ra and 228Ra in the ocean , 1985 .

[18]  W. Moore,et al.  Using Ra isotopes to examine transport processes controlling benthic fluxes into a shallow estuarine lagoon , 2000 .

[19]  D. Lee.  Groundwater‐solute influx , 1980 .

[20]  W. Moore,et al.  Marsh nutrient export supplied by groundwater discharge: Evidence from radium measurements , 2000 .

[21]  J. Teal,et al.  On the measurement of tidal exchanges and groundwater flow in salt marshes1 , 1980 .

[22]  W. Moore,et al.  Extraction of radium from natural waters using manganese‐impregnated acrylic fibers , 1973 .