267
18.3.1 Geographical Extent
Salt marshes are found in the middle and high
latitudes along intertidal shores throughout the
world. They may be narrow fringes on steep
shorelines or expanses of several kilometres
wide. They may occur near river mouths, in bays,
on protected coastal plains and around protected
lagoons.
18.3.2 Geomorphology
The physical features of tides, sediments, freshwater inputs and shoreline structures determine
the development and extent of salt marsh wetlands within their geographical range. Salt
marshes could be broadly classifi ed into (a) those
that were formed from reworked marine sediments on marine-dominated coasts and (b) those
that were formed in deltaic areas where the main
source of mineral sediment is riverine.
18.3.3 Marsh Stability
The long-term stability of a salt marsh is determined by the relative rates of two processes,
namely , (a) sediment accretion on the marsh
which causes it to expand outwards and grow
upwards in the intertidal zone and (b) coastal
submergence caused by rising sea level and
marsh surface subsidence. To some extent, these
two processes are self-regulating.
18.3.4 Hydrology
Tidal energy represents a subsidy to the salt
marsh which infl uences a wide range of physiographic, chemical and biological processes,
including sediment deposition, mineral and
organic infl ux and effl ux. These physical factors,
in turn, infl uence the species which occur on the
marsh and their productivity.
18.3.5 Panes
A distinctive feature of salt marshes is the
occurrence of panes (pans). The term ‘pan’ is
used to describe bare, exposed or water-fi lled
depressions in the marsh (Wiegert and Freeman
1990 ).
18.3.6 Chemistry
The development and zonation of vegetation in
the salt marsh are infl uenced by several chemical
factors. Three of the most important are the soil,
water and salinity, which are linked with tidal
fl ooding frequency; the availability of nutrients,
particularly macronutrients, e.g. nitrogen; and the
degree of anaerobiosis, which controls the pathway of decomposition and nutrient availability.
18.3.7 Ecosystem Structure
The salt marsh ecosystem has diverse biological
components which include plants, animals and
microbes in the marsh. It also includes plankton,
invertebrates and fi sh in the tidal creeks, panes
and estuaries.
18.3.8 Ecosystem Function
Some of the important functions of salt marsh
ecosystem are as follows:
(a) Annual gross and net primary productivity of
macrophytes are high in much of the salt
marsh.
(b) Direct grazing of vascular plant tissue is a
minor energy fl ow in the salt marsh.
(c) Fungi and bacteria are primary consumers
which break down and transform indigestible
plant cellulose into protein-rich microbial
biomass for consumers. This detrital pathway is a major fl ow of energy utilisation in
the salt marsh.
18.3 Tidal Salt Marshes
18.3.1 Geographical Extent
Salt marshes are found in the middle and high
latitudes along intertidal shores throughout the
world. They may be narrow fringes on steep
shorelines or expanses of several kilometres
wide. They may occur near river mouths, in bays,
on protected coastal plains and around protected
lagoons.
18.3.2 Geomorphology
The physical features of tides, sediments, freshwater inputs and shoreline structures determine
the development and extent of salt marsh wetlands within their geographical range. Salt
marshes could be broadly classifi ed into (a) those
that were formed from reworked marine sediments on marine-dominated coasts and (b) those
that were formed in deltaic areas where the main
source of mineral sediment is riverine.
18.3.3 Marsh Stability
The long-term stability of a salt marsh is determined by the relative rates of two processes,
namely , (a) sediment accretion on the marsh
which causes it to expand outwards and grow
upwards in the intertidal zone and (b) coastal
submergence caused by rising sea level and
marsh surface subsidence. To some extent, these
two processes are self-regulating.
18.3.4 Hydrology
Tidal energy represents a subsidy to the salt
marsh which infl uences a wide range of physiographic, chemical and biological processes,
including sediment deposition, mineral and
organic infl ux and effl ux. These physical factors,
in turn, infl uence the species which occur on the
marsh and their productivity.
18.3.5 Panes
A distinctive feature of salt marshes is the
occurrence of panes (pans). The term ‘pan’ is
used to describe bare, exposed or water-fi lled
depressions in the marsh (Wiegert and Freeman
1990 ).
18.3.6 Chemistry
The development and zonation of vegetation in
the salt marsh are infl uenced by several chemical
factors. Three of the most important are the soil,
water and salinity, which are linked with tidal
fl ooding frequency; the availability of nutrients,
particularly macronutrients, e.g. nitrogen; and the
degree of anaerobiosis, which controls the pathway of decomposition and nutrient availability.
18.3.7 Ecosystem Structure
The salt marsh ecosystem has diverse biological
components which include plants, animals and
microbes in the marsh. It also includes plankton,
invertebrates and fi sh in the tidal creeks, panes
and estuaries.
18.3.8 Ecosystem Function
Some of the important functions of salt marsh
ecosystem are as follows:
(a) Annual gross and net primary productivity of
macrophytes are high in much of the salt
marsh.
(b) Direct grazing of vascular plant tissue is a
minor energy fl ow in the salt marsh.
(c) Fungi and bacteria are primary consumers
which break down and transform indigestible
plant cellulose into protein-rich microbial
biomass for consumers. This detrital pathway is a major fl ow of energy utilisation in
the salt marsh.
18.3 Tidal Salt Marshes