Introduction

Despite the recreational and 

economic value of coastal bays and 

estuaries, these ecosystems are often 

among our most ʻtroubledʼ natural 

environments. Urbanization, agriculture, mining, and shipping are 

just a few activities that can have a 

profound and lasting impact on the 

coastal zone. In order to maintain a 

healthy coastal ecosystem, it is crucial 

to develop reasonable management 

practices around expert scientific 

information. We still have much to 

learn about the quantity and quality 

of groundwater being discharged into 

Tampa Bay, Florida. We also need 

to improve our knowledge of a wide 

range of contaminants entering the 

bay and must be able to determine 

where they accumulate in seafloor 

sediments. Such buried contaminants 

can potentially be harmful to biota if 

they are released to the water column. 

U. S. Geological Survey (USGS) scientists and research partners from the 

University of South Florida (USF), 

the University of Florida (UF), and 

the Florida Marine Research Institute (FMRI) are mapping sources of 

groundwater, measuring groundwater 

flow into Tampa Bay, and assessing the impact of contaminants and 

sediments on bay water quality and 

ecosystem health. 

Approach

Groundwater and surface water 

exchange

Surface water runoff into the bay 

can be easily quantified as stream discharge. In the Tampa Bay watershed, 

however, much of this runoff may contain an additional component called 

baseflow – or groundwater flow. The 

abundant and reversible exchange of 

groundwater and surface water complicates water budget estimates and 

may also play an important role in the 

delivery of certain contaminants to 

the bay. For example, the exchange of 

water across the sea floor may change 

the chemical behavior of some contaminants, potentially making them 

more toxic. To determine the origin 

of water entering the bay, scientists 

are conducting a suite of surveys and 

analyses, such as streaming resistivity mapping. A series of sensors that 

send an electrical pulse to the seafloor 

is towed behind a boat. The information conveyed when the electrical 

pulse bounces back to the sensors 

can be used to determine if the water 

below the sea floor is fresh or salty. 

Measurements of groundwater and 

Resistivity (ohm-m)

Open-File Report 2005-1015

January 2005

U. S. Department of the Interior

U. S. Geological Survey

Tampa Bay Study area showing the locations of groundwater and surface water 

measurements ( ), sediment samples 

 and suspended particulate matter 

study areas ( ).

3-D Fence Diagram of Tampa Bay showing saltwater saturation.

Gulf of Mexico Integrated Science - Tampa Bay Study

The Impact of Groundwater and Contaminants on Tampa Bay
For more information, please contact:

http://gulfsci.usgs.gov

Paul Carlson, FWC/Florida Marine Research Institute

Darryl L. Felder, University of Louisiana at Lafayette

Mario Fernandez, USGS/Water Resources Discipline

Paul L. Klerks, University of Louisiana at Lafayette

Sarah Kruse, University of South Florida

John Martin, University of Florida

Peter W. Swarzenski, Task Leader, 

U.S. Geological Survey, Geologic Discipline

600 Fourth Street South, St. Petersburg, FL 33701

Email: pswarzen@usgs.gov 

Kimberly Yates, Project Chief 

U.S. Geological Survey, Geologic Discipline

Email: kyates@usgs.gov

Contributing Scientists:

surface water also are being taken to 

help assess water circulation in Tampa 

Bay. This information will be used to 

help develop water circulation, water 

quality, sediment transport, and habitat distribution models.

Sediments

USGS scientists are identifying 

where contaminated sediment is 

located in Tampa Bay, what types of 

contaminants (i.e., pesticides, herbicides, and oil and gas byproducts) 

may be present, and how such contaminants may impact the ecological health of the bay. When bottom 

sediments are stirred up, they can be 

carried to other parts of the bay where 

they may affect the health and distribution of plants and animals. The 

physical characteristics of sediments, 

such as their size and type, are also 

being measured to help predict how 

often sediments are resuspended into 

the water column, and to where they 

might be transported.

Bioturbation

Ghost shrimp are abundant in 

Tampa Bay and can dig deep (~1 m) 

into the sediment to create extensive 

burrow networks. Research partners 

from the University of Louisiana at 

Lafayette are studying how this process can modify water and sediment 

characteristics. For example, if the 

ghost shrimp burrow into groundwater, they can increase the exchange 

rate between groundwater and surface 

water, thereby affecting the chemistry 

of the surface water. As they eject 

sediment from their burrows, they can 

increase the amount of sediment or 

contaminants entering the bay.

Role of suspended particulate matter 

Suspended particles in the water 

column of Tampa Bay may consist 

of resuspended, riverine, or biologically produced particles (i.e., algal 

blooms). These particles may act as 

scavengers for reactive contaminants 

and may also slow down seagrass 

restoration efforts by attenuating 

light necessary for photosynthesis. 

Scientists are identifying the nature 

of the suspended particulate matter 

within the bay and are examining 

the relation between light penetration into the water column and the 

concentration and composition of 

suspended particles. 

Links to other project research

Groundwater influx and the availability of contaminants are consistently one of the top management 

priorities in defining present ecosystem health of Tampa Bay. Research 

along these themes is closely tied into 

complementary studies that address 

1) the geological evolution of the bay 

that can provide an historic context 

from which one can build predictive 

capabilities and 2) work on the fringing wetlands that can provide insight 

into the mechanisms of a very effective water/contaminant filter during 

runoff, and also into the diversity 

of specialized habitats or ecotones. 

Multi-faceted maps are being created 

that can uniquely identify the geologic control on coastal hydrologic 

processes.

Map depicting the resistivity surveys for 2001 to 2004. Resistivity mapping assists 

scientists in determining differences in water salinity.