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Web Extra Wednesday, July 2

Water flow shapes the Everglades landscape

Anyone who has ever tiptoed past the hissing alligators or watched the patient anhingas spread their wings to dry probably left the Everglades with an understanding that flowing water is the basis for this unique ecosystem. Visitors to the national park and surrounding areas are also likely to see the stresses that development has placed on the region and the ambitious plan underway to restore and preserve the environment. A recent National Research Council (NRC) study finds that defining the relationship between water flow and landscape features will be critical to these restoration efforts.

Described by Marjory Stoneman Douglas in 1947 as a "River of Grass," the unique landscape and ecosystem are the result of the slow movement of fresh water from where it spills out of Lake Okeechobee southward across a gentle slope to Florida Bay. Development in southern Florida over the last century has obstructed, consumed and otherwise injured this broad, shallow river. In 1992, the federal and state governments began collaborating with farmers, residents, environmentalists, businesses and many different types of scientists to develop the largest ecosystem restoration project in the world, the Comprehensive Everglades Restoration Plan (CERP), authorized by Congress in 2000.

The Everglades ecosystem is a habitat to many species of plants and animals, including wading birds like those seen here. Photo courtsey of the South Florida Water Management District.

In seeking to restore what is arguably a river, CERP's most commonly stated goal is to "get the water right." But surprisingly, the flow of water — the central process responsible for the existence of the Everglades — has not been the subject of restoration research activities until recently. Hydrologic research has focused largely on restoring the natural location, duration and timing of water levels. But last August, the Science Coordination Team (SCT) of the working group charged with the restoration decided to prioritize and draw attention to the overlooked physical and ecological dimensions of the movement of water. The science advisory team released a draft white paper exploring the influence of water flow on the Everglades landscape. And last month, NRC released a report evaluating the SCT findings. The committee found that water flow in the Everglades appears to play a major role in ecosystem structure.

These results have dire implications for one of the major habitat types in the Everglades, the ridge and slough landscape. Prior to disturbance by water management activities, sawgrass ridges alternated with open sloughs to form a linear pattern aligned parallel to the direction of flow. According to both the white paper and the report, alteration of flow patterns by canals, levees and other barriers is degrading this pattern — transforming the ridge and slough topography and vegetation into uniform sawgrass stands. This transformation continues to have destructive effects on life in the Everglades; areas dominated by dense sawgrass support fewer and less diverse animals. These effects extend throughout the food web, but have the most dramatic impact on the highly visible wading birds.

Both reports stop short of demonstrating clear evidence for the mechanisms linking flow to the landscape. The white paper proposes a number of processes for the formation and maintenance of the ridge and slough pattern, almost all of which depend on the presence of flow — for example, sediment transport, erosional formation and extreme hydrological events. Though no one has investigated these mechanisms in depth, the authors of the NRC report conclude that, "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." The authors suggest the testing of several hypotheses in future research to pinpoint the actual process.

The Taylor slough in the South Florida Everglades. Photo courtesy of the South Florida Water Management District.

The NRC report also endorses the areas prioritized in the white paper for further study, especially a multidisciplinary paleoenvironmental history. Similarly, it backs the performance measures proposed by SCT for monitoring and assessing restoration progress, largely based on remote sensing techniques. Noting that "considerable flattening of the landscape may occur before degradation is detectable by remote sensing", the NRC authors suggest that monitoring efforts utilize a network of transects, and include measurements of flow and sediment transport for the entire range of flow conditions.

Future research resulting from these reports should yield significant returns for the restoration effort. Understanding how water moves through sloughs will provide insight into mixing and the transport of nutrients, organic matter, gases, seeds and spores. Also important is understanding how the flow conditions that created the ridge and slough landscape might differ from those that currently maintain the system. Although both of these problems are relevant, the NRC report assigns a higher priority to maintenance research, underlying the ultimate goal of restoration. Understanding the flow conditions required to maintain the landscape features is vital to establishing long-term sustainability in Everglades.

Brett Beaulieu
AGI/AIPG Geoscience Policy Intern

Links:

The Role of Flow in the Everglades Ridge and Slough Landscape, South Florida Ecosystem Restoration Working Group Science Coordination Team report
Does Water Flow Influence Everglades Landscape Patterns?, National Research Council report


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