DEFINING NATURAL FRESHWATER FLOW FOR CRITICAL ECOSYSTEMS: A CASE STUDY FROM SOUTH FLORIDA

The 20th century brought substantial changes to the south Florida ecosystem – urbanization, agriculture, tourism, and the construction of a massive water control system including canals, levees, flood gates and other structures. Currently underway, the Comprehensive Everglades Restoration Plan (CERP) is attempting to restore the natural quantity, quality and timing of freshwater flow through the terrestrial Everglades ecosystem (including Everglades National Park and Big Cypress National Preserve) into the estuaries and marine ecosystems (which include Biscayne National Park, Florida Bay and the Ten Thousand Islands area of Everglades NP, and the Florida Keys National Marine Sanctuary). In order to restore the natural flow of freshwater, land management agencies must first understand what components of the changes seen over the last century have been due to natural changes and what components can be attributed to anthropogenic changes. Natural factors such as climate change and sea level rise are outside the scope of the CERP, yet they will have a profound impact on the future of south Florida and must be considered in the planning process.

Faunal and floral assemblage data from radiometrically dated sediment cores taken throughout the region have provided information on the historical movement of freshwater through the system and the natural variations that existed prior to the significant alteration of the environment through engineering. Our results show that the south Florida ecosystem was responding to natural changes in climate and sea level prior to 1900. During the 20th century the rates of change increased in the estuaries and terrestrial ecosystem and those changes are consistent with reduced freshwater flow. The documentation of pre-engineering baseline conditions allows us to estimate the contribution of engineering to 20th century change. The pre-1900 natural trends and patterns can be projected into the future to define restoration targets that take natural changes into consideration. In order to be attainable and sustainable, the target salinity values for the estuaries and marine ecosystems must replicate the dynamics of both anthropogenic and natural forcing.