elevation gradient found along the transect but also help to maintain the
salinity
gradient and salt water intrusion in the estuary.The water cycle of the system
is
mostly pressure driven but with a few recirculating pumps to maintain flow.
The
dynamics of the water flow is as follows: salt water is pumped from the marine
tank
to the water tower. A portion of the water is then pressure fed into a reservoir
for the
algal turf scrubbing system which is the nutrient control mechanism for the
mesocosm (Adey et al. 1993, Jensen 1994). Algal scrubbers are mats of algae
grown on screens, which receive pulses of water in the form of waves. As
the water
passes over the algal mat, the algae strip nutrients from the water and incorporate
them into their biomass. Once a week the algal scrubbers are harvested by
scraping
the excess algae from the screens. The biomass can either be removed from
the
system if nutrients are too high or returned to the system if nutrients are
too low.
This action regulates nutrient concentrations and allows control over water
quality
of the system.
From the algal scrubbers water is returned to the marine tank. Water from
the tower
also flows into the wave generator of the marine and into the fringing red
mangrove
tank. The three part tide motor and the flexible tide return arm regulate
the semi-
diurnal tidal cycle by controlling the rate of return of water to the marine
tank (tank
1) from the estuary (tank 2).
Freshwater flow is provided by a reverse osmosis machine which transforms
saltwater into water molecules and brine. The freshwater is fed into the
headwaters
of the estuary while the brine is returned to the marine tank. Thus, use
of the reverse
osmosis machine simulates both large-scale evaporation from the marine end
of the
system by concentrating the brine as well as precipitation input of freshwater
to the
headwaters of the estuary. Additional precipitation is simulated with an
overhead
sprinkler system or manually with a hose.
METHODS
Preliminary data from the Marine Systems Lab's routine monitoring program
are
reported to demonstrate correspondence between the mesocosm and the Florida
Everglades. Air and water temperature are recorded daily in the mesocosm
with
maximin thermometers. Salinity is measured daily throughout the system in
the
morning and afternoon with a refractometer. These data have been recorded,
with
minor interruptions, since construction on the system was completed in 1988.
In
1993 a more detailed microclimate and hydrology monitoring program was initiated
that includes measurements of evaporation, water inputs (simulated precipitation),
water level fluctuation, relative humidity, wind speed and solar radiation.


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