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Florida Everglades

South Florida Ecosystem Assessment: Everglades Water Management, Soil Loss, Eutrophication and Habitat - EPA 904-R-00-003, September 2000

Executive Summary

The United States Environmental Protection Agency South Florida Ecosystem Assessment Project is an innovative, long-term research, monitoring and assessment effort. Its goal is to provide timely scientific information that is critical for management decisions on the Everglades ecosystem and its restoration. The purpose of this report is to document 1993 to 1996 baseline conditions in the Everglades and Big Cypress prior to ecosystem restoration efforts. The project is unique to South Florida in two aspects: (1) its probability-based sampling approach permits quantitative statements about ecosystem health; and (2) its extensive spatial coverage and sampling intensity are unprecedented.

This project:

  • contributes to the Comprehensive Everglades Restoration Plan by quantifying pre-restoration conditions in three physiographic regions: Everglades ridge and slough; marl prairie/rocky glades; and Big Cypress Swamp.
  • provides information on four groups of Everglades restoration success indicators: water column, soils and sediments, vegetation, and fishes.
  • provides a baseline against which future conditions can be compared and the effectiveness of restoration efforts can be gauged.
  • assesses the effects and potential risks of multiple environmental stresses on the Everglades ecosystem such as water management, soil loss, water quality degradation, habitat loss, and mercury contamination.
  • provides unbiased estimates of ecosystem health with known confidence limits, while allowing one to differentiate between seasonality and inter-annual variability versus the effects of restoration efforts.
  • provides data with multiple applications: updating and calibrating surface water management models; updating models that predict periphyton or vegetation changes in response to phosphorus enrichment or phosphorus control; developing empirical models in order to better understand interrelationships among mercury, sulfur, phosphorus, and carbon; developing water quality standards to protect fish and wildlife.

Samples were collected from the freshwater portion of the Everglades and Big Cypress. From 1993 to 1996 surface water, soil or sediment, periphyton, and mosquitofish were sampled from about 200 canal locations and over 500 marsh locations. These samples represent the ecological condition in over 750 miles of canals and over 3,000 square miles of freshwater marsh. A second phase of sampling, conducted in 1999 at about 250 marsh locations, is summarized in companion reports.

Key findings:

  • Pronounced water quality gradients: Water discharged from Everglades Agricultural Area canals is loading the public Everglades with excess phosphorus, carbon, and sulfur. Concentrations progressively decrease downstream.
  • Canals are a conduit for pollutant transport: The canal system is an effective conduit for the transport of degraded water into and through the Everglades marsh system. Water management affects water quality. Downstream water quality would be improved if delivery canals were eliminated or if they were operated to maximize surface water sheetflow and the diluting influence of rainfall and cleaner marsh water.
  • Varying water quality: Surface water conductivity, phosphorus, carbon, nitrogen, and sulfur vary greatly throughout Big Cypress and the Everglades and are dependent upon location, time of year, and water management practices.
  • Phosphorus enrichment: As of 1995 to 1996, about 44% of the Everglades canal system and 4% of the marsh area had total phosphorus concentrations exceeding the 50 part per billion Phase I control target. As phosphorus control programs continue to advance, this probability-based sampling can be repeated to determine whether the Everglades' condition is improving.
  • Soil loss in the public Everglades: From 1946 to 1996, about one-half of the peat soil was lost from about 200,000 acres of the public Everglades. Water management must be improved to maintain the remaining marsh soils if the plant communities and wildlife habitat of these wetlands are to be preserved.
  • Marsh habitat a mosaic: Wet prairie and sawgrass marsh were the two dominant plant communities in the Everglades, representing 44% and 47% of the sites sampled. Water quantity and water quality must be managed to maintain these important habitats. Cattail was present at 10% of these sites, and was associated with elevated soil phosphorus or proximity to canals.
  • Periphyton conspicuous: Well-defined periphyton mats, a defining characteristic of the Everglades marsh complex, were found at 67% of the sample sites.
  • Ecological condition varies by location and time: The condition of the Everglades varied greatly with location. Rainfall-driven portions of the system that are distant from the influence of canal water, such as the interior of Arthur R. Marshall Loxahatchee National Wildlife Refuge and the southwest portion of Water Conservation Area 3A, were found to have good water quality and low soil phosphorus. The interior of Loxahatchee National Wildlife Refuge tended to have the most pristine water quality and the lowest phosphorus concentrations in peat soils. In contrast, northern Water Conservation Area 3A had poorer water quality, soil loss due to water management, elevated soil phosphorus, and cattail encroachment. Water Conservation Area 2A had evidence of phosphorus enrichment and cattail encroachment, along with high water sulfate and conductivity. Big Cypress had good water quality and no obvious indications of phosphorus enrichment. Water quantity conditions at a given location vary with season and year.
  • Environmental threats interrelated: Ecological stressors such as water management, soil loss, water quality degradation, cattail expansion, and mercury contamination are often interrelated. Management actions must be holistic.

This project provides a critical benchmark for assessing ecosystem health and the effectiveness of Everglades restoration activities into the twenty-first century. As Everglades protection efforts proceed, this probability-based sampling can be repeated to document the effectiveness of these actions.

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