Labile landscape: Ecosystem effects of geomorphologic change under natural and managed hydrology in the Florida Everglades

Background/Question/Methods

The term “wetlands” inherently suggests an ecohydrological research approach. In the Everglades, the need for such an approach is particularly strong, for natural as well as anthropogenic reasons. Efforts to restore the Everglades require a thorough understanding of the linkages between the hydrology and the biota. These linkages appear to be more numerous and more often bi-directional than in most other wetlands. The Everglades complexity appears to arise from its very large size, its peat substrate, its slope and its patterning, and from the marked affects of more than a century of human water management.

The focus of our research is the understanding of current and pre-drainage (pre-1880) Everglades hydrology, soils, and vegetation. Our approach combines determination of historical ecology based on first-hand, but non-traditional sources such as expedition logs, military records and land surveys from the 1800s; photogrammetric analyses of the earliest available (but post-drainage) aerial photography; and hydrologic and vegetation analyses of the current system.

Results/Conclusions

The peatland patterning present throughout the largest Everglades landscape ("Ridge and Slough;" 600,000 ha) was strongly directional and was formed by 30-60 cm differences in peat elevation. This patterning of peat means that not only are Everglades flora and fauna sensitive to water depths, but so is the very structure of the landscape. Using quantitative measures, we have mapped losses of pattern in the horizontal and vertical dimensions.

The very slight Everglades slope (ca. 5 x 10^-5) produces a lentic marsh appearance, however, careful measurements reveal non-zero velocities. Pre-drainage observers consistently confirmed this, emphasizing that the water was "not stagnant" and that the visible flows were oriented parallel to the landscape directionality. The consistency of pattern directionality with pre-drainage topography and flow orientation leaves little doubt that a link between flow and landscape pattern once existed. The slope of the pre-drainage water surface was parallel to the sloped ground surface; that is, water depths were nearly constant along the length of the 90+ km downstream landscape axis. The shallow slope and the hydraulic resistance of the vegetation and peat microtopography maintained this riverine configuration.

In contrast, the currently impounded portions of the remaining Everglades ("Water Conservation Areas") reduce or eliminate water flow and create wedge-shaped water depths, deepest downstream, with associated disruption of peatland patterning and vegetation. We will describe ecohydrologic linkages of the current and historical system, and discuss future efforts for preserving and restoring the Everglades Ridge and Slough patterning.