Home Introduction Climate Variability Impacts on Ecosys. Degradation & Restoration in Chesapeake Bay Baseline Variability: Chesapeake Bay Chesapeake Bay WQ & Climate Variability FL Everglades: Hydro. Changes & Degradation >Everglades Climate Variability & Relevance Role of Time in Restoration Planning Acknowledgements References Figures

One of the tenets of Everglades restoration planning is to "get the water right" (Sklar et al., 2005) based on the assumption that restoration of historic water flow and quality will result in restoration of predrainage vegetation and landscape structure. Pollen-based reconstruction of Everglades hydrologic variability over the last 2,000 years indicates that fluctuations between severe droughts and wet conditions characterize the system. During severe droughts, deep-water slough vegetation was replaced by drought-tolerant species and moderate hydroperiod marshes (such as during the MWP; Fig. 6). In some cases, the system was resilient enough to recover to predrainage states within a few decades, but in others, droughts triggered long-term development of different communities, such as tree islands and sawgrass ridges (Bernhardt et al., 2004; Chmura et al., 2006; Willard et al., 2006).

Everglades pollen assemblages from the last 2,000 years generally indicate that predrainage hydroperiods were longer and water depths were greater than in the modern wetland. This translated into greater delivery of freshwater and lower salinities in the estuaries before the onset of water management, which is confirmed by molluskan and benthic foraminiferal assemblages from Florida Bay (Brewster-Wingard and Ishman, 1999) and molluskan assemblages from the fresh-salt water ecotone near Biscayne Bay (Gaiser et al., 2006). Comparison of proxy-based estimates of predrainage salinity and hydroperiod with ecosystem-model based predictions indicates that the models consistently predict higher salinity and shorter hydroperiod than the paleoecological data (Pitts, 2006). Thus, proxy evidence increasingly is used to validate and modify existing models, such as the Natural Systems Model, that play a large role in establishing hydrologic targets for the entire ecosystem (Sklar et al., 2005; Marshall et al., 2006).

Paleoecological evidence also has been critical for understanding the feedbacks between land-cover change and regional climate. To determine whether reported 20^th century increases in temperatures and decreases in precipitation could have resulted, at least in part, from the extensive hydrologic changes, a series of climate modeling experiments were undertaken. Pollen data and historic records were used to reconstruct pre-1900 land cover characteristics (hydroperiod, water depth, substrate) for the entire Florida peninsula. Using the Regional Atmospheric Modeling System (RAMS), a coupled mesoscale atmospheric - ecosystem dynamics model, the predrainage dataset was compared with the equivalent dataset from 1993 (Fig. 5) (Marshall et al., 2004). Results of the experiments indicate that land-cover changes alone were sufficient to decrease summer precipitation by 10-12%, with an accompanying increase in diurnal temperature variability (Marshall et al., 2004). These results imply that successful restoration of the pre-drainage hydrology and vegetation will further alter diurnal temperature variability and annual precipitation totals, affecting wetland hydrology and estuarine salinity. Acknowledgement of the potential interactions between land-cover change and climate is an integral part of adaptive management strategies aimed at optimizing chances for a sustainable restoration strategy.

Figure 6. Pollen evidence for vegetation change in Florida Everglades. Percent abundance of Cladium (sawgrass), Amaranthaceae (water hemp), and Myrica (wax myrtle) pollen, site 3A15, Water Conservation Area 3A, Florida, USA. Double-headed arrows indicate timing of initial 20th century water diversion. The peak abundance of Amaranthaceae between ~800 and 1200 AD indicates lower water levels and shorter hydroperiods during a sustained interval of drought. The shifts between long and moderate hydroperiod wetlands highlight the resilience of slough vegetation to natural fluctuations in climate. Modern analogs and estimated hydroperiod are based on comparison with surface sample database (modified from Willard et al., 2001). [larger image]