Conclusions and Recommendations
The current understanding of the effects of flow on wetland ecosystems and the origin and maintenance of the ridge and slough landscape is well summarized in the 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 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 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 detail. 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, velocity, and rate of flow (i.e., discharge) 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 be evaluated to some extent 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 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 in 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 flows, levels, extreme events, and fire, and their interactions. At present neither a minimum nor a maximum flow to preserve the landscape can be established.