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hydrogeology of a dynamic system in the florida keys: a tracer experiment >
concerns and local ecosystem impacts
Concerns And Local Ecosystem
Impacts
| Concerns about the health of local ecosystems,
such as the coral reefs (8km offshore from the Florida Keys) and Florida
Bay (an area of shallow water that lies to the north of the Florida Keys
and south of the Florida Everglades), have increased over the past decade.
Processes responsible for changes in the water clarity of Florida Bay,
and the increase in algal cover and disease of corals throughout the Florida
Keys reef tract, have provoked a lot of attention to determine what may
be the causes. A water quality protection program, spearheaded by the
U.S. Environmental Protection Agency, was instigated by the creation of
the Florida Keys National Marine Sanctuary. Issues that were of interested
to the USEPA, among a long list of other concerns, were the sources of
nutrients to near-shore marine waters. The source of nutrients that we
were concerned with were from the shallow Class V waste-water injection
wells. There are approximately 1,500 permitted Class V injection wells
throughout the Florida Keys, as well as, some 30,000 septic tanks and 5,000
cesspools. This project evolved from the request by the USEPA. First
we did a study that looked at ground water in three different areas of
the Keys that went from onshore to offshore. Then our attention was focused
on looking at 1) how the ground water flows near the Keys and 2) what effects
the local groundwater flow system might have on the input of nutrients
to the overlying water column. (Click on any of the images below for
a full-sized version.) |
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| Water clarity in Florida Bay has deteriorated
in the past decade. Above is a photo of clear water in Florida Bay.
At times the water can become a pea-green color due to algal blooms or
milky- white because of storm-induced stirred-up mud. |
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This photo shows algal mats
floating in brown murky water in Florida Bay. These algal mats form on
the bottom of the Bay in the sediments and occasionally float to the surface. |
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| Healthy elkhorn corals (A.
palmata) in 1992 at Carysfort Reef, just off northern Key Largo. |
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Black band disease (shown above) is caused
by a cyanobacteria which destroys the corals delicate living tissue. The
disease starts at a point and spreads rapidly outward. It leaves behind
dead coral which could become overgrown with algae. |
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Photographs of a typical water treatment
facility in the Florida Keys. These small treatment plants are typically
called "package plants". It is a three stage treatment facility: 1) aeration,
2) clarifier, and 3) chlorination. In the far left photograph the aeration
tank is to the left, the clarifier tank is to the right, and the chlorination
tank is to the right in the foreground (not in photo).
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Picture (above) and diagram (left) of
a typical Class V injection well. A typical Class V injection well is
drilled to 90 ft (27 m) and cased with PVC to 60 ft (18 m). These systems
are very efficient. However, the injected fluids (fresh water) enter marine
ground water which then, combined with the extremely high permeability
of the Key Largo Limestone, buoy quite rapidly to the shallow subsurface. |
Installation of several septic
tanks at a local motel in Key Largo. |
Next: Geology of the Florida Keys
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