SUSCEPTIBILITY OF THE RIDGE AND SLOUGH LANDSCAPE TO HYDROLOGIC CHANGE

The ridge and slough landscape is a widespread habitat in the Everglades and consists of a system of dense sawgrass ridges separated by relatively open waterlily sloughs. Using pollen and chronological (lead-210 and carbon-14) analyses of sediment cores, we tested the hypothesis that 20th century habitat compartmentalization and water-management practices altered the structure of the ridge and slough landscape.

We collected and analyzed pollen from a suite of surface samples in different subenvironments within the landscape to determine if they could be distinguished using pollen assemblages. These subenvironments include: dense sawgrass (Cladium) with scattered buttonbush (Cephalanthus) in the ridges; shorter, less dense sawgrass with abundant buttonbush and occasional Crinum and Sagittaria in the ridge/slough transition zone; and waterlily (Nymphaea), Utricularia, Panicum, and Eleocharis in the sloughs. Using a Mann-Whitney test and cluster analyses, we determined that ridge assemblages differ significantly from those in the slough, primarily in abundance of Cladium pollen.

Transects of cores collected across the ridge and slough gradient at sites in Water Conservation Area (WCA) 3A and 3B show that the ridge and slough landscape has remained distinct for the last 2,000 years. During the 20th century, pollen assemblages indicate anthropogenic induced changes such as the effect of water impoundment in WCA 3A on ridge assemblages. The ridge/slough transition zone appears to be the most susceptible to climatic and anthropogenic induced changes, and shows a series of ridge expansions and contractions over the last 1,000 years. In all cores, the slough appears to be the more stable landscape feature.

These data demonstrate how rapidly the ridge and slough landscape can respond to specific hydrologic changes and can be a useful tool in predicting responses to future hydrologic changes