OFR 00-492: Quantifying Submarine Groundwater Discharge to Indian River Lagoon, Florida

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Introduction

U.S. Department of the Interior
U.S. Geological Survey
Open-File Report 00-492

Hydrodynamics

Authors: Peter Swarzenski, Jonathan Martin, Jaye Cable, Rita Bowker

Quantifying Submarine Groundwater Discharge to Indian River Lagoon, Florida

Introduction:

Figure 1. Sampling for submarine groundwater discharge in Indian River Lagoon.

Figure 1. Sampling for submarine ground discharge in Indian River Lagoon.

The discharge of submarine ground water has recently been shown to be an important process in many environmentally fragile coastal ecosystems. However, groundwater discharge into coastal bottom water is still an often-overlooked component of many hydrologic and oceanic models.

The exchange of interstitial water across the sediment/water interface may introduce anthropogenic pollutants, may be an important part of coastal nutrient cycles, and may cause excess nutrient loading, thereby potentially degrading the coastal water quality. Here we report on Year-1 results from a co-operative (USGS-UF-LSU) project that is investigating the role of submarine groundwater discharge into Indian River Lagoon, Florida..

Figure 2. Parameters of submarine ground water discharge. May occur where ever an aquifer is hydraulically connected to the sea through permeable bottom sediments: Decreases with distance from shore (Ghyben-Herzberg Principle); Directly affected by ground water withdrawals; Potential point source for contaminants.

Figure 2. Parameters of submarine ground water discharge.
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The Indian River Lagoon system (Fig. 1) extends over 250 km along the east-central coast of Florida and consists of three inter-connected lagoonal basins: Mosquito, Banana River, and Indian River lagoons. Exchange of lagoon water with the Atlantic Ocean is limited to four tidal inlets (Sebastian, Ft. Pierce, St. Lucie and Jupiter) that occur in the southern reaches of Indian River lagoon.

The following processes control the salinity of lagoon water: precipitation, the exchange of water through these inlets, wind, tidal forcing, evaporation, surface runoff and potential submarine groundwater discharge. In this system, the intensity and duration of wind have the most pronounced affect on lagoon water levels.

The overall objective of this project was to determine the rate and potential ecological significance of submarine groundwater discharge to Indian River Lagoon (Fig. 2).

Figure 3. Site location map for upper Indian River Lagoon, Florida.
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The study area during the first year of the project included the northern most 10 km of the Indian River Lagoon (~48 km2). Of the 28 sampling stations, 22 were arranged in shore-perpendicular transects; the remaining six stations were distributed within the lagoon center (Fig. 3).

At each station, lagoon and interstitial water samples were collected, and groundwater seepage rates were measured using conventional seepage meters. Interstitial water samples were obtained from four stations using custom-built multi-samplers. Six groundwater samples were collected from wells surrounding the lagoon.

Two additional samples were collected from tributaries to the lagoon including Turnbull Creek and Haulover Canal. Sampling of the seepage stations, groundwater wells, and tributaries occurred in May 1999, to coincide with the end of the normal dry season, and in August 1999, during the normal rainy season. A third trip in December 1999 was used only to sample interstitial water.