The Problem

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A large portion of south Florida, including all of Everglades National Park, is currently undergoing restoration. The goal of restoration is to return the Park and surrounding areas to their natural state, by restoring the natural flow of water through the ecosystem. A number of human-induced factors altered the ecosystem during the 20th century, including . . . construction of bridges, canals, and other water control structures; development of the Everglades Agricultural Area; growing population of southern Florida. In order to restore the ecosystem to its natural state, however, we must first understand what it was like prior to significant human activity in the area. We also must understand the natural range of variation that occurs in an unaltered system.

Our Goals

To determine what Florida Bay was like in the 1800's, specifically: How salty was the water? What type and how much underwater vegetation grew there? How abundant and diverse were the animals? To determine the natural range of variation of the system; i.e. how much and how fast the system changed in the 1800's. To compare the changes seen in the 1800's to the changes seen in the 1900's, and to see if those changes can be matched to human activities, to natural events, or to a combination of factors.

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Our Method.....Or.....How do you look backwards through time?

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Sediment cores, like the ones being collected at left, preserve a record of the plants and animals that lived at that site over time. The plant and animal remains in the core, and the core sediments tell us about the biological, chemical and physical properties that existed in the past. Cores taken from Florida Bay are generally 1-2 meters long, and preserve a 100-200 year history of the Florida Bay estuary. By studying the modern environment we learn how the animals live today. We gather data on how salty the water is, what temperature, how deep, and what is the bottom like. Then when we find the same shells in the core, we can figure out how salty the water was in the past, what was the bottom like, etc. This is a basic principle of all paleoecologic studies: the present is the key to the past.

USGS researchers remove piston (the device that creates a vacuum which draws soft sediments up into core tube) from core tube, before transporting cores. Cores can be collected with relatively simple tools in the soft muddy sediments of Florida Bay. After collection, these cores are x-rayed, photographed, and then sampled in 2-cm slices. The sediment slices are then washed through sieves to remove the plant and animal remains preserved in the cores.

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What have we learned?

Changes in salinity and water quality indicators in Florida Bay
Taylor Creek, Northern Transition Zone	East-central Florida Bay
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By studying the molluscs in modern Florida Bay, we have learned that Brachidontes can tolerate wide extremes in salinity (euryhaline), and that it is also tolerant of diminished water quality (low oxygen). Anomalocardia is typical of the northern transition zone of Florida Bay, where the fresh terrestrial water mixes with the salty estuarine water. The changes in the abundance of these two species over the last 100-200 years in the cores indicates changes in salinity, and the rate of fluctuation of salinity. A steady decline in the influx of a group of very low salinity molluscs is seen at Talyor Creek core throughout the 20th century.

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Why is underwater vegetation so important? [larger image] The photograph (above) shows a bed of Turtle Grass (Thalassia). These grass beds are a very important part of the ecosystem because they provide feeding grounds, nurseries, and habitats for many types of marine life (upper right photos). Many animals we like to eat such as shrimp, lobster, and fish live in grass beds. These beds also are important foraging sites for many species of migratory birds.

Some animals that live on the seagrasses, such as molluscs and ostracodes, have hard shells that are preserved in the sediments. By studying the abundance of these animals in the sediment cores, we can get an idea of how dense the grass beds were in the past. (See left figure.)

By studying cores collected from Florida Bay, we have learned that salinity and underwater plant and animal life have changed over the last 200 years, but the most substantial amount of change has occurred in the last 50 years. These cores are providing essential data on the timing and nature of changes in the south Florida Ecosystem to the people responsible for restoration, which allows them to set cost-effective goals. If we attempt to “fix” natural changes, then our efforts wil be wasted. However, if restoration efforts focus on human-induced changes to the environment, then the restoration will be sustainable and cost-effective.

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Related information:

SOFIA Project: Ecosystem History: Florida Bay and the Southwest Coast