© 1997 Walt Dineen Society

Walt Dineen Society Annual Conference '97

Session VII: Marine Ecology Abstract #: 97702

Michael Byrne and John Meeder
U.S. Geological Survey, Miami, FL 33156


Salinity and specific nutrient concentrations exhibit an offshore profile in the upper Biscayne Bay aquifer suggestive of groundwater discharge into the nearshore bay. By 400 M the upper groundwater salinity is usually near normal marine and the benthic communities are dominated by Thallasia testudinum from that point further offshore. Initial flow measurements indicate groundwater discharge of nutrient rich waters in the inshore areas which are dominated by Halodule wrightii and Penicillus -Batophora communities and filamentous algae.

The objectives of this study are: 1) to quantify the groundwater nutrient load to nearshore Biscayne Bay, 2) identify the source of nutrients and 3) document their effects on the benthic communities. This report focuses on the groundwater aspects of this National Park and SFWMD funded research.

Fifteen pairs of wells were drilled along five transects perpendicular to The Biscayne Bay shore line from a distance of 50 to 800 M off shore. Transects are located south of Dinner Key and north of Mowry Canal. The wells at each station consist of an upper well above a semi-impermeable layer (1-3 M) and a lower well (5-7 M). Wells and surface water were sampled in June, September, 1996 and January 1997. Samples were anayzed for salinity (in the field) and the following nutrients; NO2, NO3, NH4 , TP, chlorophyll, TOC, TN, SRP, and APA. Upper aquifer concentration to TP and ammonia (10 to 20 times surface water concentrations) levels are high.

Biscayne Bay National Park is conducting a study to return sheet flow to the bay. This research will establish the impact groundwater has prior to the return of sheet flow.


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