• Most U.S. wetlands are in Alaska
• Wetland area in the lower 48 states has decreased by a little over half since the 1600's
• Recently wetlands have been lost to agricultural and residential development
• Hydraulic engineering projects have considerably altered the interaction between surface and subsurface water systems in southern Florida
• Wetlands south of Lake Okeechobee have been replaced by sugar cane fields
• Development in southern Florida has resulted in less groundwater recharge, salt-water intrusion alongeast coast, polluted run-off from sugarcane fields, and reduced habitats for fish, birds, and mammals

Distribution of wetlands
etlands cover approximately 103 million acres in the lower 48 states and an additional 170 million acres in Alaska. In the lower 48, Florida (11 million acres), Minnesota (9 million acres), and Texas (7.6 million acres) have the greatest areas of wetlands. Wetlands areas have declined by approximately 55% since the 1600's in the U.S. outside of Alaska. California (91%), Ohio (90%), and Iowa (89%) have experienced the greatest proportional losses of wetland area.

The principal reasons for wetland losses in recent years (1985-1995) were the agricultural draining of wetlands (79% of losses) and draining and infilling of wetlands as a result of urbanization and development (21% of recent losses). The rate of wetland losses has declined from nearly 500,000acres/yr (1950's) to 117,000 acres/yr (1985-1995).

Example: Florida Everglades
The Kissimmee River, Lake Okeechobee, and the Everglades are the key components of the largest drainage basin in southern Florida. The Kissimmee river feeds Lake Okeechobee which supplies water that flows south through the Everglades, one of the world's largest freshwater wetlands.  Marjory Stoneman Douglas termed the slow, unchannelled flow of water through the sawgrass prairie of the Everglades a "river of grass". The bulk of the input of water into the Everglades is from precipitation (89%) with the rest due to run-off. Most of the outflow occurs by evapotranspiration (66%).

View of Florida peninsula from the space shuttle. Original image courtesy of NASA's Earth from Space program. Water flows down a gentle slope (3-6 cm/km) from Lake Okeechobee toward the Everglades.

Beginning in the early 1900's, development of southern Florida resulted in the construction of thousands of miles of canals that diverted water away from wetland environments. Development proceeded with four goals (the 4 D's): dike it, dam it,divert it, drain it. The result of this hydraulic engineering was greater flood control and expanded agriculture. Although these were beneficial for land-owners, development often had negative consequences for the local ecosystems. The original Everglades wetland system was largely a consequence of a combination of hydrological conditions defined by the hydroperiod (duration of surface water) and hydropattern (depth of water). Water management practices associated with the expansion of farming and urban development altered flows in the Everglades and changed both the hydroperiod and hydropattern.

Kissimmee River channelization project (1961). Note original channel's meanders on either side of straightened channel. Image courtesy of South Florida Water Management District.

Some consequence of these changes were:

• channelization (straightening) of  Kissimmee River destroyed wetlands and fish and wildlife habitat
• loss of transitional wetland habitat that provided feeding and nesting habitat for wading birds
• polluted run-off from agricultural operations (e.g. sugar-cane fields)
• decreasing soil formation and exposure of peat results in fire hazard in dry periods (Spring) or during drought conditions
• salt-water intrusion along the east coast
• less groundwater recharge and reduced flow of water to Florida Bay along the southern coast.

Changes in selected land use patterns in southern Florida from 1900 to 1973. Note the loss of wetland vegetation (sawgrass), growth of agriculture (sugar cane) and expansion of coastal cities.

The creation of artificial wetlands is necessary as urban growth has destroyed natural wetland environments and population growth has placed greater demands on groundwater sources. Water demand in Broward County, Florida, increased by 40 million gallons per day from 1980 to 1990, as population increased by 200,000. The South Florida Water Management District has purchased thousands of acres of land to be used to enhance groundwater recharge in an effort to halt the decline of groundwater levels.