Case History of a Typical Dredge-Fill Project in the Northern Florida Keys: Effects on Water Clarity, Sedimentation Rates and Biota

Griffin, George

INTRODUCTION: In the late 1960's and especially the early 1970's, the rate of development in the Florida Keys increased rapidly and undesirable side effects began to be reported. Significant problems included the shortage of potable water, lack of adequate sewage and solid waste disposal facilities, and excess traffic on the two-lane overseas highway; however, the problem mentioned most often in newspaper and magazine accounts was a supposed relationship between excess siltation produced by dredging and the decline in health of the coral reefs that lie several miles offshore. It appeared from these popular accounts that the only living coral reefs in the continental United States were in imminent danger of extinction and that Florida's most valuable park resource, the underwater John Pennekamp Coral Reef State Park, was being rapidly destroyed. Although the news stories concerning the decline of the reefs have been shown in our research to be more fictional than factual, they did serve the useful purpose of kindling scientific interest into the problems posed by development in the Keys and led directly to a decision by Dr. Eugene Wallen, then Director of the Harbor Branch Foundation Laboratory, to establish a field laboratory on Key Largo. To encourage this effort, the Florida Division of Recreation and Parks loaned the use of a small building in the Pennekamp Park, the University of Florida granted the writer a long leave of absence to serve as Project Director and Chief scientist of the facility. Dr. Joseph Simon of the University of South Florida loaned some necessary field equipment, and the Trustees of the Internal Improvement Trust Fund allowed Mr. Bill Stimmel to work with us in the field. With this valuable assistance, and especially the active encouragement of Dr. Wallen and Mr. J. Seward Johnson, the writer was able to establish the laboratory and mount the research program in a very short period of time, and by October 1972, the project was actively collecting data. As originally conceived, a team of sedimentologists and biologists was to provide quantitative data on the type, quantity, distribution and effects of the effluent generated by typical dredge-fill projects in the upper Keys, especially within the offshore area of the Pennekamp State Park. This aim was expanded at an early stage to include a baseline study of natural water clarity throughout the upper Keys marine area, and other basic sedimentological, physical, and biological parameters. The limits of the expanded study area are shown on Figure 1, on which the boundaries of the Pennekamp State Park, the most important reefs, and our repeated water sampling traverses are indicated. These additional studies, to be reported in the scientific literature, were needed to provide a framework in which to evaluate the effects of dredging and other developmental activities and as a baseline against which to compare future environmental studies in the same area. As it actually developed, during the active field term of the study (October 1972 to December 1973), a state imposed moratorium on new dredge permits resulted in decreased dredge activity, and only one major dredge-fill development actually occurred on the reef-side of the Park area--that of Joseph R. Harrison, Jr., in the Basin Hills area of upper Key Largo. However, that project was typical of dredge-fill practices in the Keys and was in most respects well suited as a model of the effects of dredging. The only non-ideal aspect was that dredging began before we had adequate time to establish the pre-dredging baseline conditions at the site. However, this defect was beyond our control, and contemporaneous studies in nearby control areas were substituted....