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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
