191
A terrestrial system is said to be dry.
It could be said that ‘wetlands’ are an ‘inbetween world’ (intermediate) between upland
terrestrial ecosystems and deep water aquatic
ecosystems. Accordingly, they have characteristics of both the systems. However, there are some
major differences between wetlands and drier
upland ecosystems. In the wetlands, more nutrients are tied up in organic deposits and are lost
from the ecosystem cycling as peat deposits or
organic exports. Further, wetlands are more frequently open to nutrient fl uxes than the upland
ecosystems. As such, they may not be much
dependent on the recycling of nutrients. However,
wetlands, which are not open to these fl uxes,
often have lower productivities and slower nutrient
cycling than comparable upland ecosystems.
Concomitant to above, wetlands are similar to
deep aquatic ecosystems, in that most of the
nutrients are primarily tied up in sediments and
peats. In most deep aquatic systems, the retention
of nutrients in organic sediments is probably longer than in wetlands. However, wetlands usually
involve larger biotic storages of nutrients than do
deep aquatic ecosystems, which are primarily
plankton-dominated.
Further, another important difference between
wetlands and lakes is that most wetland plants
obtain their nutrients from the sediments, whereas
phytoplankton depends on nutrients dissolved in
the water column. Wetland plants have often been
called ‘ nutrient pumps ’, which bring nutrients
from the anaerobic sediments to the above- ground
strata. On the other hand, phytoplankton in lakes
could be viewed as ‘ nutrient dumps ’, which take
nutrients out of the aerobic zone and, through settling and death, deposit the nutrients in the anaerobic sediments. Thus, the plants in these two
environments could be viewed as having decidedly different functions in nutrient cycling.
11.6 The Diffi culty of Defi ning
Wetlands
Some of the related diffi culties are discussed below:
(a) Water is present in a wetland for at least
some part of the year. But the depth and
duration of fl ooding vary considerably from
wetland to wetland and from year to year.
Some wetlands are continually fl ooded.
Others are fl ooded only briefl y at the surface
or even just below the surface. Similarly, the
boundaries of the wetlands cannot always be
determined by the presence of water at any
one time. It is because fl uctuating water levels may vary from season to season.
(b) Wetlands are often located at the margins
between deep water and terrestrial uplands.
They are also often infl uenced by both the systems. It has been suggested by some that this
ecotone position may serve as an evidence
that wetlands are mere extensions of either the
terrestrial or the aquatic ecosystem or both.
They have no separate identity. Nevertheless,
most wetland scientists, however, observe
emergent properties in wetlands which are not
found in either upland or deep water systems.
(c) The wetland biota (plants, animals and
microbes) range varies widely from those
which have adapted themselves to live in
either wet or dry conditions ( facultative ) to
those which are adapted to only a wet environment ( obligate ). Thus, it is diffi cult to use
them as wetland indicators.
(d) Wetlands vary widely in size from small
prairie potholes of a few hectares to large
expanses of wetlands several hundreds of
square kilometres in area. This range of scale
is not unique to wetlands. But the matter of
scale is important for their conservation.
(e) The location of wetlands may also vary
greatly from inland to coastal wetlands and
from rural to urban regions. However, many
ecosystem types, e.g. forests or lakes, have
similar ecosystem structure and function.
However, there are great differences amongst
different wetland types, such as coastal salt
marshes and inland pothole marshes.
(f) Wetland condition, i.e. the degree to which
the wetland is infl uenced by human beings,
varies greatly from region to region and from
wetland to wetland. In the villages, the
wetlands are likely to be associated with
farmlands. On the other hand, in the urban
areas, the wetlands are often subjected to the
11.6 The Diffi culty of Defi ning Wetlands
A terrestrial system is said to be dry.
It could be said that ‘wetlands’ are an ‘inbetween world’ (intermediate) between upland
terrestrial ecosystems and deep water aquatic
ecosystems. Accordingly, they have characteristics of both the systems. However, there are some
major differences between wetlands and drier
upland ecosystems. In the wetlands, more nutrients are tied up in organic deposits and are lost
from the ecosystem cycling as peat deposits or
organic exports. Further, wetlands are more frequently open to nutrient fl uxes than the upland
ecosystems. As such, they may not be much
dependent on the recycling of nutrients. However,
wetlands, which are not open to these fl uxes,
often have lower productivities and slower nutrient
cycling than comparable upland ecosystems.
Concomitant to above, wetlands are similar to
deep aquatic ecosystems, in that most of the
nutrients are primarily tied up in sediments and
peats. In most deep aquatic systems, the retention
of nutrients in organic sediments is probably longer than in wetlands. However, wetlands usually
involve larger biotic storages of nutrients than do
deep aquatic ecosystems, which are primarily
plankton-dominated.
Further, another important difference between
wetlands and lakes is that most wetland plants
obtain their nutrients from the sediments, whereas
phytoplankton depends on nutrients dissolved in
the water column. Wetland plants have often been
called ‘ nutrient pumps ’, which bring nutrients
from the anaerobic sediments to the above- ground
strata. On the other hand, phytoplankton in lakes
could be viewed as ‘ nutrient dumps ’, which take
nutrients out of the aerobic zone and, through settling and death, deposit the nutrients in the anaerobic sediments. Thus, the plants in these two
environments could be viewed as having decidedly different functions in nutrient cycling.
11.6 The Diffi culty of Defi ning
Wetlands
Some of the related diffi culties are discussed below:
(a) Water is present in a wetland for at least
some part of the year. But the depth and
duration of fl ooding vary considerably from
wetland to wetland and from year to year.
Some wetlands are continually fl ooded.
Others are fl ooded only briefl y at the surface
or even just below the surface. Similarly, the
boundaries of the wetlands cannot always be
determined by the presence of water at any
one time. It is because fl uctuating water levels may vary from season to season.
(b) Wetlands are often located at the margins
between deep water and terrestrial uplands.
They are also often infl uenced by both the systems. It has been suggested by some that this
ecotone position may serve as an evidence
that wetlands are mere extensions of either the
terrestrial or the aquatic ecosystem or both.
They have no separate identity. Nevertheless,
most wetland scientists, however, observe
emergent properties in wetlands which are not
found in either upland or deep water systems.
(c) The wetland biota (plants, animals and
microbes) range varies widely from those
which have adapted themselves to live in
either wet or dry conditions ( facultative ) to
those which are adapted to only a wet environment ( obligate ). Thus, it is diffi cult to use
them as wetland indicators.
(d) Wetlands vary widely in size from small
prairie potholes of a few hectares to large
expanses of wetlands several hundreds of
square kilometres in area. This range of scale
is not unique to wetlands. But the matter of
scale is important for their conservation.
(e) The location of wetlands may also vary
greatly from inland to coastal wetlands and
from rural to urban regions. However, many
ecosystem types, e.g. forests or lakes, have
similar ecosystem structure and function.
However, there are great differences amongst
different wetland types, such as coastal salt
marshes and inland pothole marshes.
(f) Wetland condition, i.e. the degree to which
the wetland is infl uenced by human beings,
varies greatly from region to region and from
wetland to wetland. In the villages, the
wetlands are likely to be associated with
farmlands. On the other hand, in the urban
areas, the wetlands are often subjected to the
11.6 The Diffi culty of Defi ning Wetlands