269
18.4.3 Biogeochemistry
The sediments of FW coastal marshes are generally fairly organic. The sediments are generally
anaerobic except for a thin surface layer. The
condition is refl ected in the absence of nitrate.
Ammonium is reduced to low levels in the summer by plant uptake, although it is present during
winter. Further, almost all the sediment nitrogen
is bound in organic form. However, phosphorus
is more variable. The water of the marsh varies in
chemical composition according to season and
source of water.
18.4.4 Ecosystem Function
A number of production estimates have been
made for FW coastal marshes. Productivity is
generally high (generally, 1,000–3,000g/m
2
/year).
The large variations reported from different studies stems, in part, from a lack of standardisation of
measurement techniques. But the actual differences could be attributed to certain factors, like
type of plant and its growth habit, tidal energy and
other factors, e.g. soil nutrients (Reader 1978 ),
grazing, parasites, toxins and other factors which
may limit production (de la Cruz 1978 ). Further,
the elevation gradient across an FW coastal marsh
and the resulting differences in vegetation and
fl ooding patterns may account for different broad
zones of primary production.
18.4.5 Nutrient Budgets
Nutrient cycling and nutrient budgets in coastal
FW wetlands appear to be generally similar to
those of salt marshes. They are fairly open systems which have the capacity to act as long-term
sinks, sources or transformers of nutrients.
18.4.6 Ecosystem Models
Quantitative models of carbon and energy fl ow
through the detrital food web in FW coastal
wetlands are practically non-existent. However,
there may be conceptual models showing the
principal nutrient and energy fl ows of different
types of tidal FW marshes.
Further information on the tidal FW marshes
could be found in Good et al. ( 1978 ), Simpson
et al. ( 1983 ), WE Odum et al. ( 1984 ), Bowden
( 1984 , 1987 ), and so on.
18.5 Mangrove Swamps
(Wetlands)
The coastal salt marsh of temperate middle and
high latitudes gives way to its analogue, the mangrove swamp, in the tropical and subtropical
regions of the world. It is believed that the tidal
salt marshes are replaced by the mangrove
swamps in subtropical and tropical regions of
the world. It is important to note here that the
word ‘mangrove’ refers both to the wetland
itself and to the salt-tolerant trees which dominate these wetlands. Mangrove swamps are dominant coastal ecosystems, which cover an area of
c 240,000 km
2 throughout the world. The mangroves occupy c 287,000–500,000 ha in the USA.
This area is a small fraction of the c 14 million ha
of the mangroves found worldwide (Finlayson
and Moser 1991 ). In the USA, the mangrove wetlands are limited primarily to the southern tip of
Florida. However, small mangrove stands are
scattered as far north as Louisiana and Texas.
The mangrove swamp is an association of
halophytic trees, shrubs and other plants growing
in brackish to saline tidal waters of tropical and
subtropical coastlines. This coastal, forested wetland is infamous for its impenetrable maze of
woody vegetation, its unconsolidated peat
(which, perhaps, has no bottom) and its many
adaptations to the double stresses of fl ooding
and salinity. On the basis of their topography
and hydrodynamics, mangrove wetlands have
been classifi ed into the following types: (a) fringe
mangroves, (b) riverine mangroves, (c) basin
mangroves and (d) dwarf or scrub mangroves. The
mangroves have developed a number of adaptations to suit to the saline wetland environment,
18.5 Mangrove Swamps (Wetlands)
18.4.3 Biogeochemistry
The sediments of FW coastal marshes are generally fairly organic. The sediments are generally
anaerobic except for a thin surface layer. The
condition is refl ected in the absence of nitrate.
Ammonium is reduced to low levels in the summer by plant uptake, although it is present during
winter. Further, almost all the sediment nitrogen
is bound in organic form. However, phosphorus
is more variable. The water of the marsh varies in
chemical composition according to season and
source of water.
18.4.4 Ecosystem Function
A number of production estimates have been
made for FW coastal marshes. Productivity is
generally high (generally, 1,000–3,000g/m
2
/year).
The large variations reported from different studies stems, in part, from a lack of standardisation of
measurement techniques. But the actual differences could be attributed to certain factors, like
type of plant and its growth habit, tidal energy and
other factors, e.g. soil nutrients (Reader 1978 ),
grazing, parasites, toxins and other factors which
may limit production (de la Cruz 1978 ). Further,
the elevation gradient across an FW coastal marsh
and the resulting differences in vegetation and
fl ooding patterns may account for different broad
zones of primary production.
18.4.5 Nutrient Budgets
Nutrient cycling and nutrient budgets in coastal
FW wetlands appear to be generally similar to
those of salt marshes. They are fairly open systems which have the capacity to act as long-term
sinks, sources or transformers of nutrients.
18.4.6 Ecosystem Models
Quantitative models of carbon and energy fl ow
through the detrital food web in FW coastal
wetlands are practically non-existent. However,
there may be conceptual models showing the
principal nutrient and energy fl ows of different
types of tidal FW marshes.
Further information on the tidal FW marshes
could be found in Good et al. ( 1978 ), Simpson
et al. ( 1983 ), WE Odum et al. ( 1984 ), Bowden
( 1984 , 1987 ), and so on.
18.5 Mangrove Swamps
(Wetlands)
The coastal salt marsh of temperate middle and
high latitudes gives way to its analogue, the mangrove swamp, in the tropical and subtropical
regions of the world. It is believed that the tidal
salt marshes are replaced by the mangrove
swamps in subtropical and tropical regions of
the world. It is important to note here that the
word ‘mangrove’ refers both to the wetland
itself and to the salt-tolerant trees which dominate these wetlands. Mangrove swamps are dominant coastal ecosystems, which cover an area of
c 240,000 km
2 throughout the world. The mangroves occupy c 287,000–500,000 ha in the USA.
This area is a small fraction of the c 14 million ha
of the mangroves found worldwide (Finlayson
and Moser 1991 ). In the USA, the mangrove wetlands are limited primarily to the southern tip of
Florida. However, small mangrove stands are
scattered as far north as Louisiana and Texas.
The mangrove swamp is an association of
halophytic trees, shrubs and other plants growing
in brackish to saline tidal waters of tropical and
subtropical coastlines. This coastal, forested wetland is infamous for its impenetrable maze of
woody vegetation, its unconsolidated peat
(which, perhaps, has no bottom) and its many
adaptations to the double stresses of fl ooding
and salinity. On the basis of their topography
and hydrodynamics, mangrove wetlands have
been classifi ed into the following types: (a) fringe
mangroves, (b) riverine mangroves, (c) basin
mangroves and (d) dwarf or scrub mangroves. The
mangroves have developed a number of adaptations to suit to the saline wetland environment,
18.5 Mangrove Swamps (Wetlands)