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Despite the obvious benefit of a year-round growing season, most of south Florida was originally not suited to farming because of annual flooding. Agricultural activity increased in the 1920's as more and more peat soil in the northern Everglades was drained. Drainage also opened land for farming between the Everglades and the Atlantic Coastal Ridge (fig. 4) and in parts of the Western Flatlands. Increasing availability of farm machinery, fertilizers, and pesticides allowed for intensive farming and farming of marginal lands. On rock land, for example, machinery was used to break up the original rock surface and produce a coarse soil suitable for farming (Nicholas, 1973).
Today, farming is concentrated primarily in the northern Everglades, the Western Flatlands, and the rocky glades west of the Atlantic Coastal Ridge (figs. 2 and 4). Sugarcane (fig. 25), vegetables, and citrus are the most important crops. Vegetables from the region provide a large part of the Nation's winter supply. More than $750 million is earned annually from production of sugarcane, vegetables, sod, and rice, and has provided more than 20,000 full-time equivalent jobs (Snyder and Davidson, 1994).
Much of the farming in south Florida depends on the rich muck land for the production of sugarcane, snap beans, celery, cabbage, sweet corn, as well as other crops. However, oxidation is progressively removing this important rich organic soil. As water levels are regulated for agricultural development, muck is alternately covered by water and exposed to the air. During low-water periods of drying, the muck oxidizes and the probability of fire increases. Subsidence rates in the EAA have averaged about 1 in/yr. An elevated water table reduces oxidation, and in recent years, management to maintain elevated water levels in the soil has probably reduced the average rate of soil subsidence (Barry Glaz, Department of Agriculture, written commun., 1994). Forced abandonment of farms is predicted in the intensively farmed muck land because of soil subsidence. Other farms will be abandoned or sold to urban and residential development as land taxes and land values increase (Alexander and Crook, 1973).
Pesticides are widely used in south Florida to control insects, fungi, weeds, and other undesirable organisms. These compounds vary in their toxicity, persistency, and transport. Some of the more persistent pesticides, such as DDT, chlordane, dieldrin, and aldrin, have been banned for use in the State, but their residues still occur in the environment. Although pesticides are usually applied to specific areas and directed at specific organisms, these compounds often become widely distributed and pose potential hazards to nontarget biota.
The major pesticides used for agricultural crops in south Florida and their estimated application rate are listed in table 1. Herbicides having the highest application rates, including atrazine, bromocil, simazine, 2-4-D, and diuron, are among the most frequently detected pesticides in Florida's surface waters (Shahane, 1994). Insecticides currently applied in south Florida, such as ethion and endosulfan, are sometimes detected in Florida's surface waters. By far the greatest frequency of insecticide detection is from chlorinated hydrocarbon insecticides that are no longer used in the State, such as DDD, DDE, DDT, dieldrin, and heptachlor. These insecticides also are the most frequently detected pesticides in bottom sediments (Shahane, 1994).
Fertilizers are widely used in south Florida to maintain high levels of agricultural productivity. Fertilizers sold in the study unit from July 1, 1990, through June 30, 1991, contained about 140,000 tons of inorganic nitrogen and 56,000 tons of phosphate (U.S. Environmental Protection Agency, written commun., 1991). The rates of fertilizer application for this period, which were based on county sales, are shown in figure 26. The average rates of fertilizer application for the study unit were 7 tons/mi2 for nitrogen and 3 tons/mi2 for phosphate. The highest rates of application (19 tons/mi2 for nitrogen and 8 tons/mi2 for phosphate) were in Palm Beach County.
Cattle ranching and dairy farming are important agricultural activities in south Florida (fig. 27). The total number of cattle in the study unit in 1994 was almost 1 million (U.S. Department of Agriculture, written commun., 1994). Cattle ranching and farming is most intensive near and to the north of Lake Okeechobee, where densities can exceed 200 head of cattle per square mile (fig. 28). High densities of cattle are a potential source of nutrients that can degrade the surface and ground waters of the region.
U.S. Department of the Interior, U.S. Geological Survey
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