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Miller, R.L., McPherson, B.F., and Haag, K.H., 1999,
Water quality in the southern Everglades and Big Cypress Swamp in the vicinity of the
Tamiami Trail, 1996-97: U.S. Geological Survey Water-Resources Investigations Report
99-4062, 16 p.
The quality of water flowing southward in the Everglades and Big Cypress Swamp was
characterized by three synoptic surveys along an 80-mile section of the Tamiami
Trail and along a 24-mile transect down the Shark River Slough, by monthly sampling
of a background reference site in the central Big Cypress Swamp, and by sampling of
fish tissue for contaminants at several sites near the Trail. The quality of water
along the Trail is spatially variable due to natural and human influences.
Concentrations of dissolved solids and common ions such as chloride and sulfate were
lowest in the central and eastern Big Cypress Swamp and were higher to the west due to
the effects of seawater, especially during the dry season, and to the east due to canal
drainage from the northern Everglades. Concentrations of total phosphorus tended to
decrease from west to east along the 80-mile section of the Trail, and were usually
about 0.01 milligram per liter or less in the Everglades. Short-term loads (based on
average discharge for 4 days) of total phosphorus and total Kjeldahl nitrogen (ammonia
plus organic nitrogen) across four gaged sections of the Tamiami Trail were highest in
the Everglades near the S-12 structures primarily due to the relatively greater
discharges in that section. Concentrations of dissolved solids and total phosphorus
at the central Big Cypress Swamp site increased significantly during the dry season
as waters ponded. Effects of nearby, upstream agricultural activities were evident
at a site in the western Big Cypress Swamp where relatively high concentrations of
total phosphorus, total mercury, and dissolved organic carbon and high periphyton
biomass accumulation rates were measured and where several pesticides were detected.
The most frequently detected pesticides along the Trail were atrazine (14 detections),
tebuthiuron (11 detections), and metolachlor (5 detections), and most concentrations
were less than 0.1 microgram per liter. DDT compounds were the only pesticides detected
in fish from five sites. Total DDT ranged from 5 to 6 micrograms per kilogram in
largemouth bass and from 11 to 17 micrograms per kilogram in Florida gar.
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