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South Florida has experienced accelerated urban growth in the 20th century. Urbanization began along the Atlantic Coastal Ridge because the land is relatively high, most suited to development, and close to the marine transport that was essential to the original coastal settlements. Extension of the railroad to Miami at the turn of the century sparked a phenomenal growth. It should be noted that although there is also a coastal ridge on the west coast, the Everglades presented a formidable barrier between these two coastal areas.

The largest urban system (the Miami-Fort Lauderdale-West Palm Beach complex) is primarily along the narrow coastal ridge and extends from Palm Beach County to south Dade County. Through the years the flood-control and water-management practices have made some land west of the ridge available for development (fig. 19).

The modern urban systems have only been made possible by highly concentrated forms of energy. For example, industry, electrical power, and automotive engines all contribute to a very large energy consumption or metabolism in cities, about a hundred times higher than most other ecosystems (Lugo and others, 1971). Such a highly concentrated power density in urban areas may lead to serious ecological problems, however, and the resultant effect is greater dependence on fossil-fuel sources:

Many of the problems of cities may come from the high power flows and local, high densities of power concentration. The intensity of these power flows tends to be destructive of the lower-powered ecological systems in contact with these higher powered areas. Just as a natural ecosystem is diminished when some of the inputs required for its main energy reactions are limited, so the cities can be limited by restrictions on the amount and concentration of the critical inputs. The water crisis in south Florida comes about because development of power plants and other fuel usages increases urban development generally, so that water becomes the limiting factor. In effect, water, as a critical limiting requirement to overall energy flows, becomes the energy releasing source. Energies of other types can be used to develop special water sources, but if such special sources are developed, the system's energy costs are then higher than in some other cities with which there is industrial competition. The system without an abundant life support from nature is not economically competitive. The possibility exists that south Florida is already near that optimum at which the input of the power sources and the inputs of the natural environment such as air, water, waste sink capacity, recycling capacities, and recreation capacities, are at their maximum balanced combination. (Lugo and others, 1971.)

FIGURE 19. The urbanized Atlantic Coastal Ridge. [larger image]

Urbanization has reached its present level of development because of low-cost energy sources. Continued growth or even maintenance of the present system depends on such sources. If energy costs increase, as present trends indicate, the quality of urban life can be expected to deteriorate.

Air pollution is one indicator of a deterioration in environmental quality. Air in south Florida becomes polluted when certain meteorologic conditions, particularly temperature inversions, occur simultaneously with high amounts of gasoline-engine exhaust and smoke from Everglades fires, dump fires, and burning sugarcane near Lake Okeechobee. These inversions occur when the air temperature increases with height above the ground. This condition creates a stable layer of air that tends to trap pollutants (Gerrish, 1973). Incidents of air pollution tend to increase in frequency in south Florida in the dry season when fires become common. In addition to the specific incidents of air pollution, the general air quality has deteriorated over the last 10 years, as indicated by the increase in haze. The deterioration is due primarily to the increase in vehicular traffic and expanding industry.

Recent studies have shown that unstable conditions from low-level inversions occur frequently, not only inland but at the coast practically every night (Gerrish, 1973). Low-level inversions form punctually at night. They are quite strong and persist for about 14 hours. Inversions are generally stronger with east winds, a fact that suggests that the temperature of the upper air is increased by the heat plume from densely urban parts of Miami and that urbanization creates poor dispersion conditions downwind from the heat islands (Gerrish, 1973).