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South Florida's hydrologic systems

Water quality

Water quality of the east coast urban and agricultural area

History of the Study
Regional System
Hydrologic Systems
- Importance of Water
- Aquifers
- Water Balance
- Hydrologic Changes
- Quantity Problems
- Resource Limits
- Quality
  -  Effects on man
  -  Big Cypress Swamp
  -  Lake Okeechobee
  -  Everglades
  >  Urban & ag. area
  -  Ground-water
Final Word
PDF version
The east coast area, where degradation of water quality has been most noticeable in recent years, includes the urban-industrial and the eastern agricultural areas. Most degradation has been in urban canals, especially during periods of low flow when many urban canals are covered with algae and scum and are choked with aquatic weeds. These conditions have been brought about through the discharge of improperly treated nutrient-laden sewage into canals. Average concentrations of nitrate and phosphorus in the water of urban canals were 6 to 15 times greater than that of the Big Cypress Swamp. Water in one urban canal contained 125 times the average phosphorus content of Big Cypress Swamp water (Klein and others, 1973). Recent directives from the Environmental Protection Agency and ordinances passed by local governments are designed to reduce discharges of waste water to inland canals. Enforcement is difficult, however, because adequate facilities are not yet available for ocean or outfalls other than inland canals.

Rapidly expanding urbanization has increased the average dissolved-solids concentrations of canal waters to about 400 mg/l, or about 50 percent higher than that of the waters of the Big Cypress Swamp. The increase is mainly the result of storm runoff into canals from parking lots, streets, and construction sites. Included in the materials carried in the runoff may be debris, oil and grease, pesticides, and toxic metals (Klein and others, 1973).

Data indicate that concentrations of toxic metals are clearly most prevalent in urban-industrial areas. Lead and arsenic have been found in water and sediment in concentrations above recommended limits. These and other toxic metals extensively used in manufacturing are included in waste products discharged into waterways, from which they may enter the ground-water system and the public water supply (Klein and others, 1973).

An ample supply of dissolved oxygen is most important for water of good quality, especially in urban areas where much of the oxygen is used in the decomposition of sewage. In polluted canals with a luxuriant growth of plants, the dissolved-oxygen content is high during daylight. During the night, however, the dissolved-oxygen content may approach zero as the oxygen is depleted to oxidize sewage. Thus many urban canals lack popular sport fish such as bass and are inhabited, instead, by gar and mullet, which are able to tolerate low levels of dissolved oxygen (Klein and others, 1973).

In recent years, PCB's have been detected in increasing concentrations in water, sediments, and fish in south Florida (Klein and others, 1973). These compounds have about the same toxic effects on wildlife as pesticides, but in addition, it is believed that PCB's have distinct toxic effects on humans, namely on the skin and the liver. Common uses of PCB's include ballasts for fluorescent light fixtures, insulation of electrical wiring, adhesives, formulation for epoxy paints, and carbonless reproducing paper.

Although traces of PCB's have been found in the Everglades and the Big Cypress Swamp areas (Carter and others, 1973), they are most prevalent in the industrial areas. A fish sample from a canal at Miami International Airport contained PCB's in a concentration of 1,000 µg/ kg (Freiberger and McPherson, 1972). Attention should be given to the fact that PCB's can enter the ground-water system in urban areas and eventually find their way into the drinking-water supply.

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Last updated: 04 September, 2013 @ 02:04 PM (KP)