278
modifi ed by human activities mainly due to
urbanisation, grazing, etc. Moreover higher-order
streams have been affected by intervention like
damming, water withdrawals and depletion of
instream fl ow. More information in this regard
could be obtained from Williams and Wolman
(1984) and Rood and Mahoney (1990).
These different systems could be well discussed in terms of parameters like landforms and
process gradients, notably, continental gradient,
intra-riparian longitudinal continuum, lateral
trans-riparian gradient and so on (Baker 1989;
Gregory et al. 1991). Further, continental and
regional scales help in ascertaining climate pattern. Climate is also related to latitude, altitude
(elevation), etc. In addition, water levels may also
be controlled by evapotranspiration, which, in
turn, is governed by air temperature (Sharitz and
Gibbons 1982).
Notwithstanding the above, the riparian zone
changes along the course of a river system from
its headwaters to its mouth. The structure and
function of aquatic communities along a river
system were described by Vannote et al. (1980).
In this connection, the intra-riparian continuum
may refer to the same continuum in the riparian
corridor along a river’s course (Johnson and
Lowe 1985). Further, the characteristics of the
communities along the river are determined by
the geologic setting and by the geomorphic,
hydrologic and other physical processes, which
provide the physical environment within which a
riparian community develops. In this connection,
it may be mentioned here that most rivers have
three major geomorphic zones, namely , erosion,
storage and transport and sediment deposition
(Graf 1988; Harris 1988).
Notwithstanding the above, the physicochemical characteristics of the soil of riparian ecosystems are different from those of either upland
ecosystems or permanently fl ooded swamps.
However, the substrates may change rapidly and
dramatically in these dynamic systems.
Concomitant to above, soil oxygen is one of
the most signifi cant features of bottomland soils.
However, anaerobic conditions are developed
fast when the fl oodplain is fl ooded. This may,
sometimes, happen in a period as short as a few
days. Moreover, when the fl oodplain is dewatered,
aerobic conditions return fast. Under such conditions, most riparian plants are unable to function
normally under extended periods of anoxia.
Nevertheless, some plants have special adaptations which enable them to survive during the
extended periods of little soil aeration.
Many wetlands are rich in nutrients. In fact,
the bottomland hardwood (riparian) wetlands of
the SE USA (southeastern United States) generally have ample available nutrients because of a
number of different processes. Sometimes, there
is high concentrations and availability of nutrients, like phosphorus, mainly due to high clay
content of the soils and their continual replenishment during fl ooding. Further, the high organic
content may result in higher concentrations of
nitrogen than could be found in upland soils of
low organic content (Patrick 1981).
Further details in this regard could be found in
Baker (1989), Patten (1998) and so on.
The vegetation of high-order SE riparian ecosystems is dominated by diverse types of trees
which are adapted to wide variety of environmental conditions on the fl oodplain. However, in
many cases, the plant zonation may not be linear
topographically nor is it vegetationally discrete.
Summary
1. Wetlands have a worldwide similarity which
crosses the climate bar.
2. Various parameters are used for the classifi -
cation of wetlands. Aquatic plants are signifi cant components of a wetland ecosystem,
and they are often considered in the classifi -
cation of wetlands.
3. In coastal areas, different types of wetlands
are infl uenced by alternate fl oods and ebbs of
tides. The salinity of the water approaches
that of the ocean near the coastlines.
4. The total area of coastal or estuarine wetlands is 3.2 million ha in the USA (including
Alaska). Out of this, 1.9 million ha is salt
marsh and 0.5 million ha is mangrove.
5. The salt marshes are found throughout the
world along protected coastlines in the
middle and high latitudes. These are complex
ecosystems which are in dynamic balance
18 Classifi cation of Wetlands
modifi ed by human activities mainly due to
urbanisation, grazing, etc. Moreover higher-order
streams have been affected by intervention like
damming, water withdrawals and depletion of
instream fl ow. More information in this regard
could be obtained from Williams and Wolman
(1984) and Rood and Mahoney (1990).
These different systems could be well discussed in terms of parameters like landforms and
process gradients, notably, continental gradient,
intra-riparian longitudinal continuum, lateral
trans-riparian gradient and so on (Baker 1989;
Gregory et al. 1991). Further, continental and
regional scales help in ascertaining climate pattern. Climate is also related to latitude, altitude
(elevation), etc. In addition, water levels may also
be controlled by evapotranspiration, which, in
turn, is governed by air temperature (Sharitz and
Gibbons 1982).
Notwithstanding the above, the riparian zone
changes along the course of a river system from
its headwaters to its mouth. The structure and
function of aquatic communities along a river
system were described by Vannote et al. (1980).
In this connection, the intra-riparian continuum
may refer to the same continuum in the riparian
corridor along a river’s course (Johnson and
Lowe 1985). Further, the characteristics of the
communities along the river are determined by
the geologic setting and by the geomorphic,
hydrologic and other physical processes, which
provide the physical environment within which a
riparian community develops. In this connection,
it may be mentioned here that most rivers have
three major geomorphic zones, namely , erosion,
storage and transport and sediment deposition
(Graf 1988; Harris 1988).
Notwithstanding the above, the physicochemical characteristics of the soil of riparian ecosystems are different from those of either upland
ecosystems or permanently fl ooded swamps.
However, the substrates may change rapidly and
dramatically in these dynamic systems.
Concomitant to above, soil oxygen is one of
the most signifi cant features of bottomland soils.
However, anaerobic conditions are developed
fast when the fl oodplain is fl ooded. This may,
sometimes, happen in a period as short as a few
days. Moreover, when the fl oodplain is dewatered,
aerobic conditions return fast. Under such conditions, most riparian plants are unable to function
normally under extended periods of anoxia.
Nevertheless, some plants have special adaptations which enable them to survive during the
extended periods of little soil aeration.
Many wetlands are rich in nutrients. In fact,
the bottomland hardwood (riparian) wetlands of
the SE USA (southeastern United States) generally have ample available nutrients because of a
number of different processes. Sometimes, there
is high concentrations and availability of nutrients, like phosphorus, mainly due to high clay
content of the soils and their continual replenishment during fl ooding. Further, the high organic
content may result in higher concentrations of
nitrogen than could be found in upland soils of
low organic content (Patrick 1981).
Further details in this regard could be found in
Baker (1989), Patten (1998) and so on.
The vegetation of high-order SE riparian ecosystems is dominated by diverse types of trees
which are adapted to wide variety of environmental conditions on the fl oodplain. However, in
many cases, the plant zonation may not be linear
topographically nor is it vegetationally discrete.
Summary
1. Wetlands have a worldwide similarity which
crosses the climate bar.
2. Various parameters are used for the classifi -
cation of wetlands. Aquatic plants are signifi cant components of a wetland ecosystem,
and they are often considered in the classifi -
cation of wetlands.
3. In coastal areas, different types of wetlands
are infl uenced by alternate fl oods and ebbs of
tides. The salinity of the water approaches
that of the ocean near the coastlines.
4. The total area of coastal or estuarine wetlands is 3.2 million ha in the USA (including
Alaska). Out of this, 1.9 million ha is salt
marsh and 0.5 million ha is mangrove.
5. The salt marshes are found throughout the
world along protected coastlines in the
middle and high latitudes. These are complex
ecosystems which are in dynamic balance
18 Classifi cation of Wetlands