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Home | Tampa Bay Study | Data | Ra/Rn Isotopes

This page is archived and is no longer being maintained. Content was last updated in 2015. For current research, visit http://coastal.er.usgs.gov/.
Tampa Bay Study | Data | Task 2: Water & Sediment Quality - Biogeochemical Cycles | Ra/Rn Isotopes

Open enlargement of Tampa Bay  Study: data collection site mapOpen enlargement of Tampa Bay  Study: data collection site map

View enlargement of: Tampa Bay collection sites, Alafia River inset
Groundwater can be an important source of water and associated contaminants to many coastal waters, particularly in Florida where groundwater is so near the earth’s surface. The influence of submarine groundwater discharge (SGD) on the estuarine processes of Tampa Bay is a primary focus of US Geological Survey scientists, who study the presence and quantities of chemical constituents and naturally occurring radionuclides within the water column, nearby groundwater and rivers in order to calculate the likely sources and quantities of SGD to Tampa Bay and its tributaries.

Since groundwater can be a potential source of contaminants to the bay, and vice versa, knowledge of how groundwater/surface water interact gained from this study improved our ability to model hydrologic processes.

In this study, investigations into the distribution of a suite of naturally occurring Uranium/Thorium-series isotopes (e.g., 222Rn, and 223Ra, 224Ra ,228Ra, 226Ra) were collected during spring and summer of 2003/2004 (wet and dry years) to evaluate the source and origin of high nutrient levels within the bay. Activities were measured at the surface, in the water column, and at select groundwater sites within the Tampa Bay estuarine system. By developing a Ra mass balance, a bay-wide estimate of submarine groundwater discharge was used to calculate SGD-derived nutrient fluxes into the bay. Such SGD-derived nutrient flux estimates were then compared to local riverine nutrient loading estimates.

Results demonstrated that four naturally occurring isotopes were useful in deriving SGD to Tampa Bay. SGD rates were estimated at 1.6 to 10.3 cubic meters per meter per day, when extrapolated over the Tampa Bay shoreline. See more results regarding SGD and nutrient loads by selecting the tables below.

Ra and Rn isotopes as natural tracers of submarine groundwater discharge in Tampa Bay, Florida:

Contour plots of Ra-226 and Ra-228 during June and August 2003.

Contour plots of 226Ra and 228Ra (dpm 100L) during June and August 2003.

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Contour plots of dissolved organic nitrogen (DON), silicate (SiCO4), total dissolved nitrogen (TDN), and phosphate (PO4) concentrations.

Contour plots of dissolved organic nitrogen (DON), silicate (SiCO4), total dissolved nitrogen (TDN), and phosphate (PO4) concentrations.

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A 2-D profile of streaming resistivity values on the lower Alafia River showing the location of the fresh water / salt water interface.

A 2-D profile of streaming resistivity values on the lower Alafia River showing the location of the fresh water / salt water interface.

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Results from stationary, time-series Rn-222 measurements in the Lower Alafia River.

Results from stationary, time-series 222Rn measurements in the Lower Alafia River.

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Submarine Groundwater Discharge (SGD) and Nutrient Load Tables
Table A. Estimated range in nutrient loads to Tampa Bay from submarine groundwater discharge (SGD) as well as from river discharge.
Table A. Estimated range in nutrient loads to Tampa Bay from submarine groundwater discharge (SGD) as well as from river discharge. View enlargement
Table B. Summary results of submarine groundwater discharge rate estimates to Tampa Bay
Table B. Summary results of submarine groundwater discharge rate estimates to Tampa Bay.
View enlargement


Data Sets:


Groundwater Ra activities and associated nutrient concentrations in three shallow, bay-side wells in Tampa Bay, Florida (metadata)

Concentrations of dissolved phosphate, silicate, nitrite + nitrate, dissolved organix nitrogen, and total dissolved nitrogen for selected sites in Tampa Bay, Florida (metadata)

Concentrations of salinity, Ra-isotopes, and SPM in Tampa Bay, Florida (metadata)

Salinity and concentrations of uranium, vanadium, and barium across an Alafia River salinity gradient (metadata)

Groundwater nutrient concentrations (metadata)


These data sets are in ArcGIS Shapefile format. To view these files, you must have ESRI ArcGIS Software or other GIS software. A freely available lightweight version of ESRI's software is ArcGIS Explorer.



Related Products:

The Impact of Groundwater and Contaminants on Tampa Bay (USGS Open-File Report 2005-1015, January 2005)

Center for Coastal & Watershed Studies > Submarine Groundwater Discharge

The Tampa Bay studies in biogeochemical cycles are presented in a special volume of Marine Chemistry - an international journal for studies of all chemical aspects of the marine environment.


Select Journal Publications:


Peter W. Swarzenski, Mark Baskaran, Carl S. Henderson and Kim Yates. 2007. Tampa Bay as a model estuary for examining the impact of human activities on biogeochemical processes: An introduction. Marine Chemistry 104(1-2) : 1-3.

M. Baskarana, , and P.W. Swarzenski. 2007. Seasonal variations on the residence times and partitioning of short-lived radionuclides (234Th, 7Be, 210Pb) and depositional fluxes of 7Be and 210Pb in Tampa Bay, Florida. Marine Chemistry 104 (1-2) : 27-42.

* Peter W. Swarzenski, Chris Reich, Kevin D. Kroeger and Mark Baskaran. 2007. Ra and Rn isotopes as natural tracers of submarine groundwater discharge in Tampa Bay, Florida. Marine Chemistry 104 (1-2) : 69-84.

Peter W. Swarzenski, and Mark Baskaran. 2007. Uranium distribution in the coastal waters and pore waters of Tampa Bay, Florida. Marine Chemistry 104 (1-2) : 43-57.

Kevin D. Kroeger, Peter W. Swarzenski, Wm. Jason Greenwood and Christopher Reich. 2007. Submarine groundwater discharge to Tampa Bay: Nutrient fluxes and biogeochemistry of the coastal aquifer. Marine Chemistry 104 ; 85-87.

* Data on this page are presented within this journal article.



U.S. Department of the Interior, U.S. Geological Survey, Gulf of Mexico Integrated Science
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