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EVERGLADES ECOSYSTEM ASSESSMENT
Water Management and Quality,
Eutrophication,
Mercury Contamination,
Soils and Habitat
Monitoring for Adaptive Management
A R-EMAP Status Report
EPA 904-R-07-001, August 2007
US-EPA, Region 4
EXECUTIVE SUMMARY
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The United States Environmental Protection Agency’s Everglades Ecosystem Assessment Program is a long-term research, monitoring and assessment effort. Its goal is to provide critical, timely, scientific information needed for management decisions on the Everglades ecosystem and its restoration. Since 1993, three phases of marsh sampling and one phase of canal sampling have been conducted throughout the Everglades at over 1000 different locations. The Program is unique to South Florida in that it combines several key aspects of scientific study: a probability-based sampling design, which permits quantitative statements across space about the condition of the ecosystem; a multi-media aspect; and extensive spatial coverage.
This Program:
- contributes to documenting the effectiveness of phosphorus and mercury control efforts;
- contributes to the joint federal-state Comprehensive Everglades Restoration Plan (CERP) by quantifying 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: surface water, soil and sediment, vegetation, and fish;
- 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 stressors on the Everglades ecosystem, such as water management, soil loss, water quality degradation, habitat loss, and mercury contamination; and
- 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.
This report summarizes the results for the Program’s 2005 Phase III biogeochemical sampling. This survey documented ecological condition for the 2,063-square-mile freshwater portion of the Everglades Protection Area. As with any assessment of the environment at large, the long-term goal of the Everglades R-EMAP Program is to first describe, then diagnose, and finally to predict the status of ecosystem conditions. The focus of this report is the description of the study area as a whole. Future publications will include examination of various parts of the system individually. Diagnosis and prediction will be the focus of future Program publications.
Key findings:
- Mercury contamination -- very slight changes in water: Statistical analyses of Program data indicate that there was a small decrease in the concentration of methylmercury in surface water in the wet season in 2005 as compared to the wet season in 1995. Conversely, there was a very slight increase in the concentration of total mercury in surface water in the wet season in 2005 as compared to 1995. This parameter had a median of 2.0 parts per trillion for the duration of the Program, well below the Everglades’ water quality criterion of 12 parts per trillion. Unfortunately, attainment of the present criterion for surface water has not prevented bioaccumulation to unacceptable levels in prey fish.
- Mercury contamination -- declining in mosquitofish, but still elevated: The overall mercury concentration in mosquitofish, a key prey fish for Everglades gamefish and wading birds, dropped markedly from 1995-1996 to 1999 and from 1999 to 2005. This phenomenon was observed during the wet season and the dry season. However, during the 2005 wet season approximately 65% of the marsh exceeded 77 parts per billion, a concentration USEPA has recommended in trophic level 3 fish as being protective of top predators such as birds and mammals. The highest concentrations continue to be observed in Water Conservation Area (WCA) 3 and Everglades National Park (the Park), as was the case in 1995-1996. Over the entire study area fish mercury was highly correlated with mercury in forms of periphyton, but not with mercury in surface water.
- Mercury contamination -- bioaccumulation varies greatly over space: The bioaccumulation of mercury from the water column to mosquitofish varies spatially by a factor of approximately 10 throughout the Everglades. The highest concentrations of methylmercury and total mercury in surface water generally occur in WCA 2 and parts of the Arthur R. Marshall Loxahatchee National Wildlife Refuge (the Refuge) - areas that do not have high mercury in mosquitofish. An inhibitory mechanism may explain the lack of bioaccumulation in these waters. Significant, negative correlation coefficients were found between bioaccumulation and forms of carbon and sulfur. The Program’s sulfur, carbon, phosphorus and mercury data can be used to identify conditions associated with hot spots of mercury in biota, and to corroborate process studies designed to identify factors that enhance or inhibit mercury methylation and bioaccumulation. In addition, Program food web assessments will be available for most wet season sample sites, to shed additional light on bioaccumulation.
- Pronounced water quality gradients: There are clear spatial gradients in surface water phosphorus, sulfate, organic carbon, nitrogen, chloride and conductivity in the Everglades marsh. These gradients are due to the relative contribution of rainwater, stormwater and groundwater. The highest concentrations typically occur during the wet season in WCA 2, due to its proximity to the Everglades Agricultural Area and stormwater discharges. Concentrations progressively decrease downstream. Location, time of year, and water management practices are important factors that affect water quality.
- Canals are a conduit for pollutant transport: The canal system, constructed to provide flood control and water supply, is also 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 canals were eliminated or if they were operated to maximize surface water sheetflow and the diluting influence of rainfall and cleaner marsh water. Regardless, pollutants should be controlled at the source prior to discharge into the Everglades.
- Phosphorus enrichment: There was a slight decline in surface water phosphorus observed during the 2005 wet season sampling event as compared to 1995. During the November 2005 sampling event approximately 27% of the Everglades marsh had a surface water phosphorus concentration greater than 10 parts per billion. However, during 2005 soil phosphorus exceeded 500 milligrams per kilogram (mg/kg), Florida’s definition of "impacted", in 24% of the Everglades, and it exceeded 400 mg/kg, CERP’s restoration goal, in 49% of the Everglades. These proportions are higher than the 16% and 34%, respectively, observed in 1995-1996.
- Sulfate enrichment: About 57% of the Everglades marsh had a surface water sulfate concentration exceeding 1.0 parts per million (ppm), CERP’s restoration goal. This contrasts with 66% observed in 1995. During November 2005 surface water sulfate was about 90 ppm in WCA2, well above marsh background of < 1.0 ppm. Interior portions of the Everglades distant from stormwater discharges from the Everglades Agricultural Area had concentrations < 1.0 ppm, although elevated concentrations were still found as far south as Shark Slough within the Park. The surface water sulfate concentration in the Everglades overall during the wet season showed a slight decrease from 1995- 1996 to 2005.
- Soil loss in the public Everglades: The Program previously found that from 1946 to 1996, about one-half of the peat soil was lost from approximately 200,000 acres of the public Everglades that had been subjected to drier conditions. No overall change in soil depth was observed from 1996 to 2005. About 25% of the Everglades overall has 1.0 feet or less of soil, as does 53% of the Park. 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. The northern portion of WCA 3 must be rehydrated if further soil loss is to be prevented.
- Marsh habitat is a mosaic: Sawgrass marsh and wet prairie were the two dominant plant communities in the Everglades, representing 58% and 32% of the sites sampled in 2005. Water quantity and water quality must be managed properly to maintain these important habitats. Cattail was present, but not necessarily dominant, at 19% of the sites sampled in 2005, and was generally associated with elevated soil phosphorus or proximity to canals.
- Periphyton is conspicuous: Well-formed calcareous periphyton mats, a defining characteristic of the Everglades marsh complex where naturally hard water exists, were found at 63% 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 the Refuge and the southwest portion of WCA 3, were found to have good water quality and low soil phosphorus. The interior of the Refuge tended to have good water quality and the lowest phosphorus concentrations observed in peat soils. In contrast, northern WCA 3 had poorer water quality, thinner soil due to water management practices, elevated soil phosphorus, and extensive cattail encroachment. Water Conservation Area 2 had phosphorus enrichment and cattail encroachment, along with high sulfate, organic carbon, nitrogen, chloride and conductivity in surface water. Water depth at any given location varies with season and year.
- Environmental threats are interrelated: Ecological stressors such as water management, soil loss, water quality degradation, cattail expansion, and mercury contamination are often interrelated. Efforts to manage water quantity and pollutants such as phosphorus, mercury and sulfur should be integrated.
The Everglades R-EMAP Program has provided monitoring and assessment data for measuring ecosystem health and the effectiveness of Everglades restoration activities from the 1990s into the twenty-first century. As CERP restoration efforts and Everglades phosphorus and mercury control efforts proceed, this probability-based sampling can be repeated to document the condition of the Everglades and the effectiveness of these actions.
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This document is available here for downloading and viewing. |
If you need additional information or assistance with this document,
contact Peter Kalla at (706) 355-8778 or (706) 355-8500
or via email at Kalla.Peter@epa.gov
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EVERGLADES ECOSYSTEM ASSESSMENT Water Management and Quality, Eutrophication, Mercury Contamination, Soils and Habitat EPA 904-R-07-001, August 2007 |
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104 pages |
14.4 MegaBytes |
Full Report | |
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690 KiloBytes |
Biogeochemical Data | ||
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4 pages |
20 KiloBytes |
Sampling Design and Station Coordinates | |