The Everglades of south Florida has been altered extensively to accommodate human settlement. This has contributed to 85-95 percent declines of wading bird populations; 68 plant and animal species becoming threatened or endangered; extensive infestation with invasive, exotic plants; and widespread mercury contamination.
In response to these trends, the federal Water Resources Development Act of 1992 authorized a comprehensive review of the Central and South Florida Project to examine the potential for restoration of the Greater Everglades Ecosystem. The result of the review was the Comprehensive Everglades Restoration Plan (CERP, or “Restoration Plan”)—the largest ecosystem restoration effort ever pursued. The National Research Council Committee on the Restoration of the Greater Everglades Ecosystem (CROGEE) was established in 1999 in response to a request from the U.S. Department of the Interior on behalf of the South Florida Ecosystem Restoration Task Force (SFERTF) to provide advice on scientific aspects of the design and implementation of the Restoration Plan. This report evaluates conclusions and recommendations developed by the Science Coordination Team (SCT) 1 of the SFERTF with respect to the environmental significance, creation, maintenance, degradation, research needs, and performance measures for flow in the ridge and slough landscape.
The CROGEE’s mandate (see Box ES-1) includes providing the Task Force with scientific overview and technical assessment of the restoration activities and plans, while also providing focused advice on technical topics of importance to the restoration efforts. One such topic that the committee has addressed is the methods by which hydrologic performance measures are identified for the Restoration Plan and the way that these measures will be used to assess the restoration process.
One of the commonly stated goals of the Restoration Plan is to “get the water right.” This has largely meant restoring the timing and duration of water levels and the water quality in various portions of the Everglades. Water flow has been considered mainly in the context of discharge to estuaries, but not elsewhere. There are several legitimate reasons why flow (in terms of direction, speed, and rate) has not been emphasized in the Restoration Plan. The most important of these is a relative lack of field information on both pre- and post- disturbance flow, except at flow structures and in canals. Further, modeling of surface water flow has not been very helpful for local flow estimates. This is due to both model
The SCT serves as the senior science advisory group to the SFERTF and the SFERTF Working Group. The SCT is responsible for recommending research plans and priorities; and facilitating the integration, synthesis, and application of the best scientific information (including the Social Sciences) available for the South Florida Ecosystem Restoration effort. For more information, see <http://www.sfrestore.org/sct/sctcharter.html>.
BOX ES-1 Committee on Restoration of the Greater Everglades Ecosystem Statement of Task
The CROGEE provides scientific guidance to multiple agencies charged with restoration and preservation of the Central and South Florida aquatic ecosystem, i.e., the Greater Everglades. The NRC activity provides a scientific overview and technical assessment of the many complicated, interrelated activities and plans that are occurring at the federal, state, and nongovernmental levels. In addition to strategic assessments and guidance, the NRC provides more focused advice on technical topics of importance to the restoration efforts when appropriate.
Topics such as the following (to be determined to the mutual agreement of the restoration program management and the NRC) are expected to form the bases for the committee’s investigations:
constraints such as a coarse grid size, and natural factors such as low gradients, complex microtopography, and dense vegetation.
There are, however, compelling reasons to believe that flow affects important physical, chemical, and biological processes in the Everglades. Flow in wetlands generally enhances mixing, and it transports biologically important materials including nutrients, organic matter, gases, seeds, and spores. More important, there are major landforms in the Everglades—notably parallel ridges and sloughs, and tree islands—that are ecologically important and aligned with present and past flow directions. This alignment suggests that their genesis and maintenance have been importantly shaped by flow. For this reason, better understanding of the role of flow in shaping Everglades landscapes is critical to the restoration effort.
To focus on this issue, the SCT sponsored a flow workshop at the Greater Everglades Ecosystem Restoration conference in December 2000. It then prepared a white paper on the role of flow in the Everglades ridge and slough landscape, had it peer-reviewed, and released it in final form in January 2003. Between the peer review and the final release, the CROGEE held a Workshop on Flows and Levels in the Ridge and Slough Region of the Everglades in Miami, Florida on October 15, 2002 to gather additional background and information and to discuss the science informing the White Paper’s conclusions and recommendations.
CONCLUSIONS AND RECOMMENDATIONS
The current understanding of flow effects, and the origin and maintenance of the ridge and slough landscape, is well summarized in a recently published Science Coordination Team White Paper (SCT, 2003). The ecological importance of the topographic structure in this landscape is well documented, as is the degradation of that structure in many areas, particularly in association with major linear structures (levees, canals, etc.) that inhibit flow. The development and use of performance measures that quantify changes through time in the geometry of ridges, sloughs, and tree islands, as proposed in the White Paper, are well justified. Performance measures that incorporate remote sensing are attractive because they are relatively inexpensive yet provide integrated information about the ecosystem condition. However, since considerable flattening of the landscape may occur before degradation is detectable by remote sensing, a network of transects to monitor microtopographic changes is also a high priority.
Several plausible explanations of the mechanisms for the formation and maintenance of the ridge and slough landscape have been proposed, and some involve flow, but none have been investigated in depth. Evidence of the importance of flow is circumstantial rather than based on support for a particular mechanism. Nonetheless, despite the scant quantitative data, the circumstantial evidence is strong that direction, speed, and rate of flow have important effects on the parallel ridges, sloughs, and tree islands in the central Everglades. Ignoring flow introduces an important source of uncertainty in the implementation of the Restoration Plan.
Alternative mechanisms can to some extent be evaluated from readily accomplished work such as analysis of underlying bedrock topography, detailed surface topographic mapping, and measuring accumulation of organic sediment. Nonetheless, more extensive, focused research will also be necessary. Most of the essential elements of such a research program are described in the White Paper. Immediate attention should be given to the development of alternative conceptual models of the formation and maintenance of the ridge and slough landscape, and the most compelling models should be used to develop research hypotheses and questions that can be used to guide the design of a research program. Paired comparisons between relatively intact landscapes and degraded ones may be particularly informative.
As noted in the White Paper, the conditions responsible for the development of the ridge and slough landscape may be different from those responsible for its maintenance. Research on maintenance of the landscape has a more direct impact on restoration, and should have higher priority than research on the original conditions governing its formation (see Box 2-1). The White Paper’s recommendation to conduct a comprehensive multidisciplinary study of the paleoenvironmental history of the ridge and slough landscape is well justified in this regard.
Because it is not clear whether the ridge and slough landscape is maintained by average or extreme conditions, it is important that monitoring be designed to provide integrated measurements of flow and sediment transport for the full range of flow conditions, especially including extreme events. This will be challenging and expensive, and measurement sites should be co-located with sites where other related research on the ridge and slough landscape is occurring. In this context, the connectivity of sloughs at different water elevations might prove useful in understanding directions and magnitudes of flow under different conditions. This measure will depend heavily on detailed and highly precise topographic information across the landscape.
Given the potential role of flow in landscape maintenance, restoration efforts should attempt to incorporate flows approximating historical discharges, velocities (speed and
direction), timing, and distribution in their design. However, development of numeric performance measures for speed of flow would not be appropriate until there is a better scientific understanding of the processes that underlie maintenance of ridges and sloughs, including water flows, water levels, extreme events, fire, and their interactions. At present, neither a minimum nor a maximum flow speed to preserve the landscape can be established.