Wenger 72944 Especificações descarregar pdf (Página 69)

Section 2 Existing Conditions/Affected Environment

EAA Storage Reservoirs Revised Draft PIR and EIS February 2006

2-5

2.3.3 Soils

The EAA is primarily underlain by peat and muck although much of the peat

has been altered to muck by oxidation processes. The soils are predominantly

organic and contain some fine sands. The EAA is part of what was once the

largest region of organic soil in the world with a thickness up to 17 feet. The

organic soil is composed of brown to black peat and muck and currently has a

maximum thickness of approximately eight feet. The peat was formed primarily

from the detritus of native sawgrass. This region of organic soil was formed in a

limestone basin, which accumulated layers of peat from sawgrass and mud

brought in by fresh water flows from Lake Okeechobee. The peat in the

Everglades area ranges in age from approximately 3,600 to 5,250 years

(McDowell, et. al., 1969). Wetlands within the EAA contain calcitic mud (marl)

soils. This calcitic mud is exposed to short periods of standing water and is often

associated with thick algal mats and periphyton.

According to the U.S. Department of Agriculture (USDA) and Natural Resources

Conservation Service (NRCS) Soil Survey, 88% of the EAA is comprised of Terra

Ceia Muck, Pahokee Muck, Lauderhill Muck and Torry Muck. The remaining

12% contains 44 different types of soils. Eighty-four percent of Compartment A

is comprised of Pahokee Muck and Lauderhill Muck. The remaining 16% is

comprised of 19 different types of soils.

The agricultural productivity of the soil is affected by subsidence. Peat soils are

subjected to subsidence and surface elevation loss when drained. Oxidation is

caused by compaction and is the conversion of organic carbon in the soil to

carbon dioxide gas and water. It is an irreversible process. Until natural

drainage was disrupted, the EAA experienced an annual hydrocycle of 9 to 12

months of flood and 0 to 3 months of slight drainage. The historical sawgrass

peat accretion rate is estimated at 0.03 inches per year. Currently, instead of

accretion, there has been subsidence at a long-term average rate between 1 and

1.2 inches per year. In the 1900s, soil loss was attributed to aggressive water

management Seven hundred thousand acres of the EAA were drained to

facilitate agricultural production. Currently, this area is Florida’s most

important agricultural region with approximately 77% of the EAA devoted to

agriculture production.

Studies from 1946 and 1996 suggest that in some areas of the Everglades,

one-half of the soil has been lost. The EAA lost up to 28% of its soils. WCA-3,

which had 3 to 5 feet of peat in 1946, showed only 1 to 3 feet of peat present in

1996, and some areas had less than one foot. Uncultivated areas have

experienced up to three feet of subsidence, which occurs when drainage

desaturates the peat soil (Shih, et. al., 1997). The resulting surface soil becomes

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Wenger 72944 Especificações Página 69