272
Europe. It refers to a peat-forming wetland which
receives nutrients from sources other than precipitation, generally through groundwater movement. However, the ‘marshes’ (the ‘reed swamps’
in Europe) have mineral soils rather than peat
soils. It is believed that the American terminology had developed without much regard to
whether the system is peat forming. Most of the
North American marshes are peat forming
regardless of their geological origins. Most of the
marshes are generally classifi ed as palustrine,
riverine or lacustrine, persistent or nonpersistent
and emergent wetlands, mainly based on the classifi cation developed by the US Fish and Wildlife
Service (Cowardine et al. 1979 ).
There have been large number of works on the
inland FW wetlands. Some of these are Good
et al. ( 1978 ), Gore ( 1983a , b ), Denny ( 1985a , b ),
G.D. Adams ( 1988 ), Gopal and Masing ( 1990 ),
Weller ( 1994 ), Mitsch and Gosselink ( 2000 ),
Kar ( 2007 ) and so on.
18.6.1 Geographical Extent
and Geological Origin
There are ambiguities regarding the accuracy of
the estimates of the number of FW marshes in the
world. Some of the possible reasons could be as
follows: (a) They are often ephemeral or convert
to other types of wetlands, such as unvegetated
fl ats or forested wetlands over a relatively short
period of time; (b) they may be confused with or
miscounted with peatlands, particularly fens; and
(c) it is very diffi cult to make their classifi cation
and inventory in view of wide variety of dominant vegetation covers and water depths (from
saturated soils to 1 m of water depth) of the FW
marshes. Robin et al. ( 1975 ) and Matthews and
Fung ( 1987 ) had, respectively, estimated that
there are 89–101 million ha of ‘non-forested
swamps’ (which are also not peatlands in the
world). According to them, most of these wetlands could be FW marshes by a process of elimination. This range, thus, probably, represents a
reasonable measure of the extent of inland
marshes in the world. It also suggests that inland
marshes, probably, represent <20 % of the total
amount of wetlands in the world. Concomitantly,
Aselmann and Crutzen ( 1989 , 1990) estimated
that there are 27 million ha of marshes in the
world. However, this estimate appears to be quite
low because the USA and Canada alone have an
estimated 42 million ha. Nevertheless, there
appear to be 8–10 million ha of inland marshes in
the lower 48 states, another 17 million ha of
inland marshes in Alaska and another 16 million
ha of inland marshes in Canada.
Region
Area
(million ha)
Reference
World
89.4
Robin et al. ( 1975 )
100.8
Matthews and
Fung ( 1987 )
United States
(lower 48 states)
7.7
Hofstetter ( 1983 )
9.9
Hall et al. ( 1994 )
United States
(including Alaska)
26.9
Hall et al. ( 1994 )
Canada
15.9
Zoltai ( 1988 )
There are several groups of FW marshes.
Some of these are briefl y discussed below.
18.6.2 Prairie Potholes
and Nebraska Sandhills
The Prairie Pothole Region of North America is
one of the dominant areas of FW marshes in the
world. They had originated in millions of depression formed by glacial action. They are plenty in
moraines of undulating glacial regions, especially in a 780,000 km
2 region of west of the
Great Lakes in Minnesota, Iowa and the Dakotas
in the USA and in Alberta, Manitoba, etc., in
Canada. It is believed that there was about
80,000 km
2 of these potholes in the region before
the advent of the Europeans (Leitch 1989 ). Thus,
the Prairie Pothole Region was about 10 %
wetland during the presettlement times.
The Nebraska sandhill region is situated
south of the Prairie Pothole Region. It is a large
(52,000 km
2
) stabilised dune fi eld which comprises
one-fourth of the state of Nebraska. The region is
now dominated by cattle ranches and irrigated
crops (Novacek 1989 ).
18 Classifi cation of Wetlands
Europe. It refers to a peat-forming wetland which
receives nutrients from sources other than precipitation, generally through groundwater movement. However, the ‘marshes’ (the ‘reed swamps’
in Europe) have mineral soils rather than peat
soils. It is believed that the American terminology had developed without much regard to
whether the system is peat forming. Most of the
North American marshes are peat forming
regardless of their geological origins. Most of the
marshes are generally classifi ed as palustrine,
riverine or lacustrine, persistent or nonpersistent
and emergent wetlands, mainly based on the classifi cation developed by the US Fish and Wildlife
Service (Cowardine et al. 1979 ).
There have been large number of works on the
inland FW wetlands. Some of these are Good
et al. ( 1978 ), Gore ( 1983a , b ), Denny ( 1985a , b ),
G.D. Adams ( 1988 ), Gopal and Masing ( 1990 ),
Weller ( 1994 ), Mitsch and Gosselink ( 2000 ),
Kar ( 2007 ) and so on.
18.6.1 Geographical Extent
and Geological Origin
There are ambiguities regarding the accuracy of
the estimates of the number of FW marshes in the
world. Some of the possible reasons could be as
follows: (a) They are often ephemeral or convert
to other types of wetlands, such as unvegetated
fl ats or forested wetlands over a relatively short
period of time; (b) they may be confused with or
miscounted with peatlands, particularly fens; and
(c) it is very diffi cult to make their classifi cation
and inventory in view of wide variety of dominant vegetation covers and water depths (from
saturated soils to 1 m of water depth) of the FW
marshes. Robin et al. ( 1975 ) and Matthews and
Fung ( 1987 ) had, respectively, estimated that
there are 89–101 million ha of ‘non-forested
swamps’ (which are also not peatlands in the
world). According to them, most of these wetlands could be FW marshes by a process of elimination. This range, thus, probably, represents a
reasonable measure of the extent of inland
marshes in the world. It also suggests that inland
marshes, probably, represent <20 % of the total
amount of wetlands in the world. Concomitantly,
Aselmann and Crutzen ( 1989 , 1990) estimated
that there are 27 million ha of marshes in the
world. However, this estimate appears to be quite
low because the USA and Canada alone have an
estimated 42 million ha. Nevertheless, there
appear to be 8–10 million ha of inland marshes in
the lower 48 states, another 17 million ha of
inland marshes in Alaska and another 16 million
ha of inland marshes in Canada.
Region
Area
(million ha)
Reference
World
89.4
Robin et al. ( 1975 )
100.8
Matthews and
Fung ( 1987 )
United States
(lower 48 states)
7.7
Hofstetter ( 1983 )
9.9
Hall et al. ( 1994 )
United States
(including Alaska)
26.9
Hall et al. ( 1994 )
Canada
15.9
Zoltai ( 1988 )
There are several groups of FW marshes.
Some of these are briefl y discussed below.
18.6.2 Prairie Potholes
and Nebraska Sandhills
The Prairie Pothole Region of North America is
one of the dominant areas of FW marshes in the
world. They had originated in millions of depression formed by glacial action. They are plenty in
moraines of undulating glacial regions, especially in a 780,000 km
2 region of west of the
Great Lakes in Minnesota, Iowa and the Dakotas
in the USA and in Alberta, Manitoba, etc., in
Canada. It is believed that there was about
80,000 km
2 of these potholes in the region before
the advent of the Europeans (Leitch 1989 ). Thus,
the Prairie Pothole Region was about 10 %
wetland during the presettlement times.
The Nebraska sandhill region is situated
south of the Prairie Pothole Region. It is a large
(52,000 km
2
) stabilised dune fi eld which comprises
one-fourth of the state of Nebraska. The region is
now dominated by cattle ranches and irrigated
crops (Novacek 1989 ).
18 Classifi cation of Wetlands