fact sheet >
U.S. Department of the Interior
The broad expanse of wetlands that composes the Everglades formed about 5,000 years ago as a vast, flat region that tilts slightly to the south and drains into the shallow Florida Bay and Gulf of Mexico. Early Native Americans settled south Florida between 10,000 and 12,000 years ago and began cultivating maize (corn) as early as 2,400 years ago. Strik-ing changes in this wetland-estuarine ecosystem have been attributed largely to increasing urban and agricultural activity during the past century. One set of environmental changes affecting the ecosystem may have resulted from construction of a complex canal and levee system to control flooding and provide a steady supply of fresh water to a growing population and to agriculture. This system has drained over half of the Everglades wetland and has altered the flow of fresh water into Florida Bay to an unknown extent.
Changes in the biota, nutrient supply, and fire frequency are interpreted by study of different components in the cores. For example, the past distribution of plants in the region can be determined through analysis of pollen and larger plant remains in the cores. Analysis of small invertebrates, such as mollusks, ostracodes, and foraminifers, and algae, such as diatoms and dinoflagellate cysts, provides details on changes in salinity, nutrient levels, and substrate conditions. Studies of the sedimentology of the cores provide information on broad-scale changes of substrate in the region. Biogeochemical analyses provide information on changes in chemical and nutrient input through time, as well as insights into broad-scale vegetation changes. Analysis of charcoal content of cores tracks changes in fire frequency and associated vegetation and nutrient patterns. Integration of all these types of data enables scientists to understand the processes that formed the ecosystems and to interpret cause-and-effect relationships between biotic changes and alteration of physical and chemical characteristics of the environment.
This research requires careful dating of samples by several techniques. Dating using radioactive isotopes, such as cesium-137 (137Cs) and lead-210 (210Pb), provides good chronological control, particularly for the last 150 years. 137Cs, produced by atmospheric testing of nuclear weapons, is useful in determining whether the material was deposited since the late 1950's. A longer time scale, for the last 150 years, is provided by 210Pb, which is constantly supplied to the atmosphere through the decay of uranium in naturally occurring materials. A cross-check on radiometric dates is provided by the record of the pollen in the sediments, because several exotic (non-native) plants have been introduced in south Florida in the last 200 years. Because the timing of the introduction of these species is known through historical records, the first appearance of their pollen in the sediments provides a time marker.
USGS scientists and collaborators are quantifying both biotic and chemical changes that occurred during the last 150 years in the south Florida ecosystem. These data are being used to verify the validity of the study methods for reconstruction of changes documented by the historical record. Additionally, ongoing work on deeper parts of cores is yielding new information on earlier events that have not been well-documented. Invertebrates preserved in a core from one of the Florida Keys indicate an increase in salinity around 1930 as well as a change from a sandy substrate to one populated by higher abundances of seagrasses. The pollen record also indicates minor changes in the Everglades vegetation at about the same time. Ongoing analyses of cores from elsewhere in the bay will help to determine whether these patterns are consistent and whether these changes are correlated with known environmental changes in the region. In parts of the Water Conservation Areas, water is being impounded, and cattail vegetation gradually is increasing in abundance and displacing the original sawgrass community. Analysis of pollen and geochemistry from a core from this area indicates that major changes occurred shortly after 1960. The pollen record reflects increased abundance of pollen of cattails and the saltwort family; both groups tend to become more abundant with increased disturbance. Peat accumulation rates also have increased, along with the concentrations of various nutrients and metals. Increases in phosphorus, sulfur, copper, and zinc probably result from increased agricultural activities and application of fertilizer. Increases in mercury and other metals also are noteworthy, and possible causes for the increases currently are under investigation.
Integration of these data types enables USGS scientists to
reconstruct the historic south Florida ecosystem and to
under-stand past changes in the system. Such information is
particularly useful for modeling the ecosystem in efforts to
determine the "best" restoration plan. It also provides a
foundation for develop-ment of indicators for measuring the
success of the restoration efforts. By providing impartial data
on sites throughout the Everglades and Florida Bay ecosystem to
modelers, resource managers, and other interested parties in south
Florida, the U.S. Geological Survey is playing a key role in
restoring the natural ecosystem functions of the region.
Click here for a printable version of this fact sheet (note: document will open in a new browser window)
For more information contact:
Debra A. Willard or Lynn Brewster-Wingard
SOFIA Project: Ecosystem History of Biscayne Bay and the Southeast Coast
U.S. Department of the Interior, U.S. Geological Survey
This page is: http://sflwww.er.usgs.gov/publications/fs/171-95/index.html
Comments and suggestions? Contact: Heather Henkel - Webmaster
Last updated: 04 September, 2013 @ 02:03 PM(TJE)