271
competitive advantage to the mangroves over
salt-intolerant species.
(c) Salinity varies from season to season.
18.5.5 Dissolved Oxygen (DO)
Reduced conditions exist in most mangrove soils
when they are fl ooded. However, the degree of
reduction depends on the duration of fl ooding
and the openness of the wetland to freshwater
and tidal fl ows (McKee et al. 1988 ).
18.5.6 Ecosystem Functions
Studies on dynamics of mangrove wetlands pertaining to certain functions like net primary productivity, litter production, organic export and
nutrient cycling have revealed the importance of
physical conditions of tides, salinity and nutrients
to these wetlands. A wide range of productivity
have been measured in mangrove wetlands due to
the wide variety of hydrodynamic and chemical
conditions which are prevalent. Further, the
decomposition process in mangroves have been
studied with litter bag measurements for a number of different plants and in a number of different mangrove types. When crabs and other
invertebrates are abundantly found in mangrove
wetlands, they may play a signifi cant role in the
decomposition of mangrove litter due to their leaf
litter consumption and shredding of leaves into
smaller particles (Twilley 1997). Crab’s biological control of decomposition had been summarised by Camilleri ( 1992 ), which is briefl y
given below:
(a) The shredded leaf particles are likely to be
exported from the mangrove ecosystem than
are the larger leaves.
(b) Particulate organic materials are made available to a large number of detritivores by the
shredded materials.
(c) There is more rapid decomposition and better recycling of nutrients because the shredded particles are more easily colonised by
microfauna and microorganisms.
In addition to the above, the mangrove
swamps are said to be important exporters of
organic material to the adjacent estuaries
through a process called ‘outwelling’ (Lee 1995).
Further, the role of mangrove wetlands as both a
habitat and a source of food for estuarine fi sheries is one of the most cited functions of these
ecosystems. Moreover, Golley et al. ( 1962 ) had
developed a synoptic energy budget of a Puerto
Rican mangrove wetland. In addition, a number
of qualitative and quantitative compartment
models have been developed on the functional
characteristics of mangroves in the USA (Chen
and Twilley 1998 ).
More informations on mangrove ecosystems
could be available in Lugo ( 1990a , b ), Lugo
and Snedaker ( 1974 ), Chapman ( 1976a , b ), W.E
Odum et al. ( 1982 ), Tomlinson ( 1986 ), Armentano
( 1990 ), Twilley ( 1998 ), Rützler and Feller ( 1996 ),
Alongi ( 1998 ) and so on.
18.6 Freshwater Marshes: Inland
Wetlands
Freshwater inland marshes are possibly the most
diverse of the marsh types in the globe. They
are non-tidal freshwater systems dominated by
grasses, sedges and other freshwater (FW) emergent hydrophytes. There are variations amongst
them in their geological origins and in their driving hydrologic forces. Their size varies from the
small pothole marshes of <1.0 ha to the enormous
tropical wetlands and the immense sawgrass
monocultures of the Florida Everglades.
It is pertinent to note here that the terminology
for inland FW wetlands is often confusing and
contradictory. For example, in Europe, the term
‘reed swamp’ is often used to describe one type
of FW marsh dominated by Phragmites spp. On
the other hand, in the USA, the word ‘swamp’
usually refers to a forested wetland. It may be
noted here that the extremes of FW marshes are
clearly different; but at the boundaries between
two wetland types (e.g. marsh and bog), the
distinction is not always clear. Further, the term
‘fen’ is used to indicate one kind of marsh in
18.6 Freshwater Marshes: Inland Wetlands
competitive advantage to the mangroves over
salt-intolerant species.
(c) Salinity varies from season to season.
18.5.5 Dissolved Oxygen (DO)
Reduced conditions exist in most mangrove soils
when they are fl ooded. However, the degree of
reduction depends on the duration of fl ooding
and the openness of the wetland to freshwater
and tidal fl ows (McKee et al. 1988 ).
18.5.6 Ecosystem Functions
Studies on dynamics of mangrove wetlands pertaining to certain functions like net primary productivity, litter production, organic export and
nutrient cycling have revealed the importance of
physical conditions of tides, salinity and nutrients
to these wetlands. A wide range of productivity
have been measured in mangrove wetlands due to
the wide variety of hydrodynamic and chemical
conditions which are prevalent. Further, the
decomposition process in mangroves have been
studied with litter bag measurements for a number of different plants and in a number of different mangrove types. When crabs and other
invertebrates are abundantly found in mangrove
wetlands, they may play a signifi cant role in the
decomposition of mangrove litter due to their leaf
litter consumption and shredding of leaves into
smaller particles (Twilley 1997). Crab’s biological control of decomposition had been summarised by Camilleri ( 1992 ), which is briefl y
given below:
(a) The shredded leaf particles are likely to be
exported from the mangrove ecosystem than
are the larger leaves.
(b) Particulate organic materials are made available to a large number of detritivores by the
shredded materials.
(c) There is more rapid decomposition and better recycling of nutrients because the shredded particles are more easily colonised by
microfauna and microorganisms.
In addition to the above, the mangrove
swamps are said to be important exporters of
organic material to the adjacent estuaries
through a process called ‘outwelling’ (Lee 1995).
Further, the role of mangrove wetlands as both a
habitat and a source of food for estuarine fi sheries is one of the most cited functions of these
ecosystems. Moreover, Golley et al. ( 1962 ) had
developed a synoptic energy budget of a Puerto
Rican mangrove wetland. In addition, a number
of qualitative and quantitative compartment
models have been developed on the functional
characteristics of mangroves in the USA (Chen
and Twilley 1998 ).
More informations on mangrove ecosystems
could be available in Lugo ( 1990a , b ), Lugo
and Snedaker ( 1974 ), Chapman ( 1976a , b ), W.E
Odum et al. ( 1982 ), Tomlinson ( 1986 ), Armentano
( 1990 ), Twilley ( 1998 ), Rützler and Feller ( 1996 ),
Alongi ( 1998 ) and so on.
18.6 Freshwater Marshes: Inland
Wetlands
Freshwater inland marshes are possibly the most
diverse of the marsh types in the globe. They
are non-tidal freshwater systems dominated by
grasses, sedges and other freshwater (FW) emergent hydrophytes. There are variations amongst
them in their geological origins and in their driving hydrologic forces. Their size varies from the
small pothole marshes of <1.0 ha to the enormous
tropical wetlands and the immense sawgrass
monocultures of the Florida Everglades.
It is pertinent to note here that the terminology
for inland FW wetlands is often confusing and
contradictory. For example, in Europe, the term
‘reed swamp’ is often used to describe one type
of FW marsh dominated by Phragmites spp. On
the other hand, in the USA, the word ‘swamp’
usually refers to a forested wetland. It may be
noted here that the extremes of FW marshes are
clearly different; but at the boundaries between
two wetland types (e.g. marsh and bog), the
distinction is not always clear. Further, the term
‘fen’ is used to indicate one kind of marsh in
18.6 Freshwater Marshes: Inland Wetlands