Summary Introduction Methods Geologic Setting Results Rock Analysis Water Chemistry Ground Water Contamination QC/QA Conclusions Future Studies Acknowledgments References Appendices

This study has documented elevated nutrients in offshore ground waters, and bacterial data indicate groundwater movement away from shore. However, direct measurement and/or a driving mechanism for seaward groundwater flow has not been determined. Based on our data we believe there are several avenues of research that could determine both the direction of flow and the origin of elevated offshore groundwater nutrients.

1. Stable isotopes of nitrogen may be used to identify the source of nitrogen in NH₄ or NO₂ and NO₃. This technique has the potential for differentiating between N derived from fertilizers and animals as well as identifying N from natural organics or ancient ground waters.
2. Direct measurements of flow rate and direction can be accomplished by installing a cluster of wells in several offshore locations and then injecting a fluorescent dye or bacterial tracer into a central well. Continuous monitoring of closely spaced surrounding wells should indicate the net direction and flow rate of ground water. Similar studies could be done on land by installing monitoring wells around existing onshore disposal wells into which tracers have been added.
3. To determine rates of tidally induced groundwater flux, seepage meters similar to those used by Simmons (1986) would be installed in areas where algae are known to be experiencing abnormal growth. In this study seepage meters would be cemented directly to rock surfaces. Flow into these collectors could be measured with simple manometers like those described by Simmons (1986). This study would allow not only collection of escaping ground water for nutrient analysis, but would more directly determine the relation between algal growth and escaping ground water.
4. Wells on the Florida Bay side of the Keys should also be monitored for nutrients and salinity. Preliminary observations of wells installed since initiation of this study indicate strong tidal pumping even where there is little if any surface tidal fluctuation. Hydrologic connection between tidal pumping on the seaward side of Key Largo and the bay side of the island has been further confirmed with pressure transducer studies (Halley et al., in prep.). The relation between the Florida reef tract ground waters, the Keys and ground water beneath Florida Bay and the southern Everglades begs investigation.