SPECIAL PUBLICATION NO. 27


 The soils of the Everglades Agricultural Area are classified by soil sci-
entists on the basis of the percentage of inorganic matter they contain
and their thickness. The Torry Series soils occur within two to five miles
of Lake Okeechobee. They contain black organic layers more than 51
inches thick and are characterized by a range of 35 percent to 70 percent
mineral matter (mostly the clay minerals sepiolite and montmorillonite)
(Snyder, et al., 1978) and are not considered peats according to ASTM
standards. The Terra Ceia, Pahokee, Lauderhill and Dania soils are dark
organic soils which are differentiated from one another based on their
thickness above bedrock. The Terra Ceia soils are the thickest, with the
Pahokee, Lauderhill and Dania becoming successively thinner. As the
process of subsidence occurs, Terra Ceia soils will become Pahokee soils
since Pahokee soils differ from Terra Ceia soils only in their thickness
(Snyder, et al., 1978).

 Subsidence

 Subsidence refers to the loss of thickness which is incurred by organic
soils when they are drained. A group of physical processes are responsi-
ble for subsidence, including 1) shrinkage due to dessication, 2) consoli-
dation by loss of the buoyant force of groundwater and loading, or both,
3) compaction by tillage, 4) wind erosion, 5) burning and 6) biochemical
oxidation (Stephens, 1974). The processes of drying, consolidation and
compaction do not result in actual loss of soil (Shih, 1980). Stephens and
Johnson (1951) documented an increase of oven dried weight for Ever-
glades peat from about 9 pounds to about 16 pounds per cubic foot after
cultivation. This increase in density corresponds to a decrease although
there is little actual loss of soil.
 The processes of wind erosion, burning and oxidation do, however,
result in the actual loss of organic soils (Shih, 1980). Wind erosion is
thought to have minor effects in the Everglades Agricultural Area.
Numerous charcoal-rich lenses which represent ancient fires have been
found at depth in cores through the organic soils of the Everglades and
coastal swamps (Cohen, 1974). Attempts to correlate charcoal layers
from core to core were futile suggesting that fires were not widespread
geographically. The fires were confined mainly to sawgrass-dominated
peats. Modern observation indicated that fires are very common in saw-
grass communities and it is suggested that sawgrass may be especially
well-adapted to survival of fires (Cohen, 1974).
 The most serious cause of long term subsidence in the Everglades is
biochemical oxidation. Biochemical oxidation has been responsible for
55 to 75 percent of the total soil loss in the upper Everglades Agricultural
Area (Stephens, 1974). Although original plans for drainage in the Ever-
glades recognized that subsidence would occur, the causes were appar-
ently misunderstood (Stephens and Johnson, 1951). Shrinkage of origi-
nal peat due to drainage was taken into account, but the slow continual
loss of peat due to biochemical oxidation was not considered.