14
The most recent geological formation in the Everglades is the Lake Flirt Marl,
composed of soft gray marl or calcareous mud, which is almost universally present
under the deeper muck of the upper Everglades (Hoffmeister 1974). The Lake Flirt
Marl is unique because of its impermeability, which prevents the percolation of
ground waters in the organic soils of the region. The top 15 m of rock strata in the
northern half of the Everglades is relatively impermeable and restricts that northern
section to natural water control through confining layers (McVoy et al. 2011).
However, in the lower half of the Everglades, the strata becomes looser and highly
water-bearing as the rim is approached, thereby, allowing canals to cut through the
permeable strata and drain adjacent lands (McVoy et al. 2011).
The Everglades are presently bounded on the eastern side by a coastal fringe of
sand dunes, on the western side by the Ocaloacoochee Slough and the Big Cypress
Swamp, and extend to the southern and southwestern coast of Florida, where the
salt-water marshes and mangrove swamps form the southern border (Gleason 1984;
Myers and Ewel 1990). Currently, the glades constitute the third, or downstream,
unit of the watershed that forms the interior of the Florida Peninsula below the
twenty-eighth parallel (Light and Dineen 1994). The first, or tributary, unit of this
drainage basin, the Kissimmee River, drains about two-thirds of the area. The second, or middle, unit of this watershed is Lake Okeechobee, a shallow body of fresh
water whose surface elevation is now regulated between 4 and 6 m. The combined
area of all three units once equaled 25,000 km
2
(Light and Dineen 1994). Under
natural conditions, prior to the advent of artificial drainage, the outflow of the waters
from the Kissimmee River and Lake Okeechobee naturally passed onto, and
through, the Everglades (Davis 1943; McVoy et al. 2011).
Inside the Kissimmee-Everglades watershed basin is a wide and flat plain,
flanked by natural drainage ways that have imperceptibly divided the area into a
sawgrass plain bordered by a series of ridges and sloughs. The vegetative accumulation, or soil, varies from an average thickness of eight feet at Okeechobee’s shores
to the thinnest of deposits at the sides of the Everglades (Allison 1943; Cohen and
Spackman 1984). The line of demarcation between the glades and adjoining areas is
extremely irregular, which extends as a stretch of grassland that may be under 0.6 m
of water at the end of the rainy season, but in most years is dry enough for the cultivation of a winter vegetable crop (Sklar et al. 2001). The actual boundary between
the Everglades and the adjoining prairie is usually marked where the sedges of the
glades are met by true grasses, cypress, salt marsh, or mangroves (Myers and Ewel
1990; Rutchey et al. 2008) (Fig. 1.6).
1.2.2 Nutrients
Even though water quality data prior to the 1940s is limited, the Everglades are
believed to have been an oligotrophic environment, characteristic of extremely low
levels of nutrients, such as phosphorus (P) (Davis and Ogden 1994). These low
surface-water concentrations are naturally self-regulating and are a major reason
C.W. Finkl and C. Makowski
The most recent geological formation in the Everglades is the Lake Flirt Marl,
composed of soft gray marl or calcareous mud, which is almost universally present
under the deeper muck of the upper Everglades (Hoffmeister 1974). The Lake Flirt
Marl is unique because of its impermeability, which prevents the percolation of
ground waters in the organic soils of the region. The top 15 m of rock strata in the
northern half of the Everglades is relatively impermeable and restricts that northern
section to natural water control through confining layers (McVoy et al. 2011).
However, in the lower half of the Everglades, the strata becomes looser and highly
water-bearing as the rim is approached, thereby, allowing canals to cut through the
permeable strata and drain adjacent lands (McVoy et al. 2011).
The Everglades are presently bounded on the eastern side by a coastal fringe of
sand dunes, on the western side by the Ocaloacoochee Slough and the Big Cypress
Swamp, and extend to the southern and southwestern coast of Florida, where the
salt-water marshes and mangrove swamps form the southern border (Gleason 1984;
Myers and Ewel 1990). Currently, the glades constitute the third, or downstream,
unit of the watershed that forms the interior of the Florida Peninsula below the
twenty-eighth parallel (Light and Dineen 1994). The first, or tributary, unit of this
drainage basin, the Kissimmee River, drains about two-thirds of the area. The second, or middle, unit of this watershed is Lake Okeechobee, a shallow body of fresh
water whose surface elevation is now regulated between 4 and 6 m. The combined
area of all three units once equaled 25,000 km
2
(Light and Dineen 1994). Under
natural conditions, prior to the advent of artificial drainage, the outflow of the waters
from the Kissimmee River and Lake Okeechobee naturally passed onto, and
through, the Everglades (Davis 1943; McVoy et al. 2011).
Inside the Kissimmee-Everglades watershed basin is a wide and flat plain,
flanked by natural drainage ways that have imperceptibly divided the area into a
sawgrass plain bordered by a series of ridges and sloughs. The vegetative accumulation, or soil, varies from an average thickness of eight feet at Okeechobee’s shores
to the thinnest of deposits at the sides of the Everglades (Allison 1943; Cohen and
Spackman 1984). The line of demarcation between the glades and adjoining areas is
extremely irregular, which extends as a stretch of grassland that may be under 0.6 m
of water at the end of the rainy season, but in most years is dry enough for the cultivation of a winter vegetable crop (Sklar et al. 2001). The actual boundary between
the Everglades and the adjoining prairie is usually marked where the sedges of the
glades are met by true grasses, cypress, salt marsh, or mangroves (Myers and Ewel
1990; Rutchey et al. 2008) (Fig. 1.6).
1.2.2 Nutrients
Even though water quality data prior to the 1940s is limited, the Everglades are
believed to have been an oligotrophic environment, characteristic of extremely low
levels of nutrients, such as phosphorus (P) (Davis and Ogden 1994). These low
surface-water concentrations are naturally self-regulating and are a major reason
C.W. Finkl and C. Makowski