Chapter 6: Hydrologic Needs - Effects of Hydrology on the Everglades Protection Area (EPA)

SUMMARY This chapter discusses the multidisciplinary approaches currently in place to manage the hydrologic patterns of the Everglades Protection Area (EPA). The primary focus of this chapter is on the hydrologic trends and ecological assessments in the EPA in relation to the 2001 drought. Much attention has been given to the lowest-recorded Lake Okeechobee water levels in Florida history. Low lake levels led to water supply restrictions for urban and agricultural regions. Plans were developed to alter (i.e., lower) the Water Conservation Area (WCA) regulation schedules for the next dry season to reduce the Lower East Coast’s (LEC’s) dependency on Lake Okeechobee for water supply. However, the trends in the EPA were not as dramatic as in Lake Okeechobee, partly because the previous year had above average water levels due to Hurricane Irene and partly because this year’s rainfall pattern in the Everglades was not significantly lower than the 32-year historic average. Despite a general reduction in rainfall in the WCAs of 23 percent and an average reduction of structure inflows to the WCAs of 45 percent, compared to the 32-year historic average, average weekly water levels in the WCAs were 0.4 to 0.7 feet higher than average. This apparent disconnect between water levels and rainfall appears to be due to water conservation and active management to hold water in the WCAs, but may also be due to the lag time between low rainfall and its expression as low water levels in specific regions of the Everglades. Therefore, the full impact of the 2001 drought may not be felt until the 2002 dry season. These hydrologic trends can be expressed as rapid alterations to the biogeochemical processes in the Everglades or as slow alterations to the biomass and community structure. Tree islands are one of those slow components of ecological and cultural significance. In our continuing efforts to understand tree-island function and structure in relation to hydrology, this chapter presents new information on their creation and link to groundwater hydrology. A theory behind the development of tree islands is that nutrients released from a small island head (as a function of hydroperiod) will leach downstream (as a function of surface and groundwater flows) to form a nutrient-rich substrate for island head and tail expansion. Preliminary data collected over one growing season show that, in general, porewater nutrients are highest on the head of tree islands. The exchange of nutrients between the porewater and surface water has yet to be established. However, preliminary data show that nitrogen and phosphorus concentrations in the porewater were over 100- and 20-fold higher, respectively, than the overlying surface water, indicating an upward flux.