Hydrology and Physiography of Groundwater and Wetland Habitats - Freshwater Ecology: Concepts and Environmental Applications - page 59

TABLE 4.3 Conversion and Losses of Various Wetland Types Including Agricultural and Urban
Uses from the Mid-1970s to the Mid-1980s in the United States a

Conversion

Wetland Amount in Amount in Total loss Urban to other

type mid-1970s mid-1980s (gain) Agricultural land use Deep water Other wetland types

Swamps 223000 209000 14000 4000 240 200 4360 5200

Marshes 98000 99000 1000 1500 150 0 350 3000

Shrubs 63000 62000 1000 1000 0 0 1700 1700

Ponds 22000 25000 3000 900 0 0 1800 300

Total 406000 396000 11000 5600 390 200 4600 200

a Deep water represents conversion to lakes or reservoirs and conversions are placed in the “other” category if
they are not to agriculture, urban, or deep water. Values are given in thousands of square kilometers. Positive
values indicate a net gain (data from Dahl et al. , 1991).

glades have been lost since pre-European times (Mitsch and Gosselink,
1993). This degree of loss is typical for all types of wetlands in the United
States. Twenty-two states have lost more than half of their wetlands in the
past 200 years (Fig. 4.11). The amount of loss and interconversion among
wetland types has been great (2.5% lost over a period of 10 years) and
driven primarily by agriculture. The creation of small ponds from wet-
lands is an important aspect of human activities (Table 4.3). Peatlands are
under pressure throughout the world as a source of peat moss for gar-
dening. In Southeast Asia, existing wetlands have been modified or new

60

56 54

50

74

56

85

90

73

52 85 87

50

91

87 81

59

67

72

50

59

52

FIGURE 4.11 States that have lost 50% or more of their wetlands since 1780, labeled with
percentage lost (data from Dahl et al., 1991).