Water: Monitoring & Assessment
Wetland Bioassessments in the Florida Everglades
Florida Department of Environmental Protection
2600 Blair Stone Road, MS 6511
Tallahassee, Florida 32399-2400
Office: (850) 921-9821
Purpose(s) of Project
This project was initiated to monitor biological assemblages across a nutrient gradient in the Florida Everglades in support of regulatory efforts to define a numeric water quality criterion for phosphorus. The goal is protection of natural populations of aquatic flora and fauna in the Everglades Protection Area.
The historic Florida Everglades consisted of approximately four million acres of shallow saw grass marsh, with wet prairies and aquatic sloughs interspersed with tree islands. Today, only 50 percent of the original Everglades ecosystem remains, primarily as a result of drainage and conversion of large portions of the northern and eastern Everglades for agricultural or urban land use. The remaining portions of the historic Everglades are located in the Water Conservation Areas (WCAs) and Everglades National Park (ENP).
The Everglades ecosystem evolved under extremely low phosphorus concentrations and is considered an oligotrophic ecosystem. A large body of evidence indicates that phosphorus is the primary limiting nutrient throughout the remaining Everglades. The introduction of excess phosphorus to the Everglades has resulted in ecological changes over large areas of the marsh. The Everglades Forever Act (EFA; Section 373.4592, Florida Statutes), passed by the Florida Legislature in 1994, stated that waters flowing into the part of the remnant Everglades known as the Everglades Protection Area (defined as Water Conservation Areas 1, 2A, 2B, 3A, 3B and ENP) contain excessive levels of phosphorus and that a reduction in levels of phosphorus will benefit the ecology of the Everglades Protection Area. The EFA requires the Florida Department of Environmental Protection (FDEP) and the South Florida Water Management District (SFWMD) to complete research necessary to establish a numeric phosphorus criterion for the Everglades Protection Area.
The SFWMD Everglades System Research Division (ESRD) initiated a succession of studies for the purpose of phosphorus criterion development. The studies began in 1993 and continue to the present, and are a part of the research and monitoring being conducted in the Everglades. Biological monitoring for the ESRD studies was initiated in early 1994 in WCA 2A. Data from this and other studies are being used by FDEP in the development of a numeric phosphorus criterion for the Everglades Protection Area.
SFWMD ESRD initially selected 13 sites along two transects located downstream of canals discharging into WCA 2A and extending down the phosphorus gradient into least affected areas of the marsh. Sampling sites ranged from the canal inflows (discharge structures on the northeastern margin of WCA 2A) to a site nearly 15 km downstream from the canal inflows. Three of the 13 main sites specifically were chosen to represent the least affected area of WCA 2A with respect to anthropogenic disturbance (sites U1-U3). A series of 15 additional "intermediate" sites was added to the study later to obtain better spatial coverage of the lower portion of the transects. The sites have been monitored for water, sediment, and biological quality.
Periphyton, macroinvertebrate, and macrophyte communities in WCA 2A change substantially from reference conditions at approximately seven to eight km downstream of canal discharges into WCA 2A.
Data analysis has shown that biological populations at the two stations (E5 and F5) nearest to the three initial reference sites (U1-U3) are very similar in terms of biological community structure. This suggests that these areas, despite slight phosphorus enrichment, still support reference condition biota. The somewhat higher phosphorus regime at the next stations (E4 and F4 and beyond) is associated with greater biological changes. Experimental field dosing studies (mesocosms) conducted by SFWMD ESRD show that the addition of phosphorus causes changes in periphyton assemblages consistent with those observed in the transect study.
The WCA 2A transect periphyton data for each site and date have been analyzed using the entire taxonomic assemblage encountered and using lists of pollution-sensitive and pollution-tolerant species based on available literature and experimental phosphorus addition studies (the mesocosms) in WCA 2A. Macroinvertebrate data have been analyzed using the Florida Index and the macroinvertebrate component of the Lake Condition Index (LCI), measures of the numbers of pollution-sensitive taxa in a sample that are routinely used by FDEP in bioassessments of streams and lakes. The use of these methods with the WCA 2A transect data has demonstrated a clear signal of biological disturbance along the nutrient gradient in WCA 2A. FDEP is using this information as well as information from other studies conducted in the Florida Everglades to develop a numeric phosphorus criterion for the Everglades Protection Area.
The information provided here is based solely on the transect study by SFWMD ESRD in WCA 2A. Research and monitoring of Florida Everglades water, sediment, and biological quality is being conducted by several research groups in WCA 2A, WCA 1 (Arthur R. Marshall Loxahatchee National Wildlife Refuge), Everglades National Park (ENP), and WCA 3A, including studies by SFWMD ESRD similar to the WCA 2A transect study.