Sustainability of Subtropical Coastal Zones in Southeastern Florida: Challenges for Urbanized Coastal Environments Threatened by Development, Pollution, Water Supply, and Storm Hazards

The subtropical Atlantic coastal zone of southeastern Florida supports nearly 7 million inhabitants on a coastal plain conurbation that stretches from West Palm Beach to Miami. About a quarter of the present population originally settled on higher topography along the shore-parallel Atlantic Coastal Ridge. From about the middle 1900s, however, urbanization intensified along the shore and spread westward into freshwater marshlands. Population densities approaching 2500 persons per km-2along some coastal sectors and dredge and fill operations to create urban land in western marshes degraded coastal environments bringing in question sustainability. Efforts to maintain environmental integrity initially focused on shore protection first via "hard" engineering works, which later ont included massive beach renourishment projects along developed coasts subject to critical erosion. Marine algal blooms, led to eutrophication, degraded coastal water quality, and deterioration of coral reefs indicate environmental problems at least as serious as beach erosion. Recognition of a potential eco-catastrophe, collapse of entire marine and coastal wetland ecosystems in southern Florida, led turn to the Everglades Restoration Project, the largest single environmental recovery effort in the world. Cleanup of terrestrial systems is essential to sustainability of marine ecosystems now jeopardized by nutrient loading. Serious degradation of the Florida Reef Tract, a coral-algal barrier reef system, is beyond question as extensive sectors of coral reef die from increased loading of nearshore waters by elevated nitrogen (N) and phosphorus (P) nutrient levels delivered to the coast by submarine groundwater discharge (SGD). The source of N-P input into the Biscayne Aquifer, which has one of the highest carbonate aquifer transmissivities in the world, is sugar cane farming in the Everglades Agricultural Area on the inner portion of the coastal plain. Groundwater discharges for Palm Beach County are, for example, estimated from a groundwater MODFLOW model at$1,659 \times 10^6$ $m^3 yr^{-1}$. Total N in ground-water below the coastal plain adjacent to remnant Everglades averages about 1.25 mg 1-1. SGD nutrient fluxes to the coast are 5727 and 414 metric tons per year for P and N, respectively. Surface water contributions for P and N are respectively 197 and 2,471 metric tons per year. Nutrient delivery to beach and nearshore environments is a serious problem that threatens coastal water