207
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_13, © Springer India 2013
Wetland biogeochemical cycles feature a blending
of chemical transformations and chemical transport processes which are, perhaps, not shared by
many other ecosystems. Wetland soils are called
‘hydric soils’. They are formed when oxygen is
cut off due to the presence of water. This results
in reduced conditions. They could be either
‘organic soils’ of ‘mineral soils’. The hydric
mineral soils could be identified through redox
concentrations, redox depletions and reduced
matrices. Further, transformations of N, S, Fe,
Mn and C occur as a result of these anaerobic
conditions. Some transformations cause toxic
situations, as with the production of H 2 S. Others
such as denitrification and methanogenesis cause
a loss of chemicals to the atmosphere. It is important to note here that many of the transformations
are mediated by anaerobic microbes. Concomitant
to above, chemicals are hydrologically transported to wetlands through precipitation, surface
flow, groundwater, etc. It may also be noted here
that wetlands dominated by precipitation are generally nutrient poor. And the concentration of
chemicals flowing into wetlands from the other
three sources is highly variable. Further, wetlands could be sources, sinks or transformers of
chemicals. However, not all wetlands are nutrient
sinks, nor are the patterns consistent from season
to season or from year to year. Further, wetlands
are often chemically coupled to adjacent ecosystems by the export of organic materials. However,
the direct effect on the adjacent ecosystems is
sometimes quite difficult to quantify. Concomitant
to above, wetlands are quite similar to terrestrial
and other aquatic ecosystems, in that they
could be high-nutrient or low-nutrient systems.
However, there are a number of differences, particularly with regard to sediment storage of nutrients and also in the functioning of the vegetation
in the cycle of different nutrients.
The transport and transformation of chemicals
in ecosystems is known as ‘biogeochemical
cycle’. It involves a great number of interrelated
physical, chemical and biological processes. The
biogeochemical processes are markedly influenced by the unique and diverse hydrologic
conditions in wetlands. These processes lead to
changes in the chemical forms of materials within
wetlands. Also, these processes, in turn, play
important roles to determine overall productivity
of wetlands.
The biogeochemistry of wetlands could be
divided into following aspects: namely, (a) intrasystem cycling through various transformation
processes and (b) the exchange of chemicals
between a wetland and its surroundings. It is
important to note here that the permanent or
intermittent flooding of these ecosystems causes
certain processes to be more dominant in the
wetlands than in either upland or deep aquatic
ecosystems, whereas it is said that few transformation processes are unique to wetlands; e.g.
anaerobic conditions prevail in wetlands. It may
be noted here that the soils in wetlands are usually
characterised by waterlogged conditions during a
part or whole of the year. This results in reduced
13
Wetland Biogeochemistry
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_13, © Springer India 2013
Wetland biogeochemical cycles feature a blending
of chemical transformations and chemical transport processes which are, perhaps, not shared by
many other ecosystems. Wetland soils are called
‘hydric soils’. They are formed when oxygen is
cut off due to the presence of water. This results
in reduced conditions. They could be either
‘organic soils’ of ‘mineral soils’. The hydric
mineral soils could be identified through redox
concentrations, redox depletions and reduced
matrices. Further, transformations of N, S, Fe,
Mn and C occur as a result of these anaerobic
conditions. Some transformations cause toxic
situations, as with the production of H 2 S. Others
such as denitrification and methanogenesis cause
a loss of chemicals to the atmosphere. It is important to note here that many of the transformations
are mediated by anaerobic microbes. Concomitant
to above, chemicals are hydrologically transported to wetlands through precipitation, surface
flow, groundwater, etc. It may also be noted here
that wetlands dominated by precipitation are generally nutrient poor. And the concentration of
chemicals flowing into wetlands from the other
three sources is highly variable. Further, wetlands could be sources, sinks or transformers of
chemicals. However, not all wetlands are nutrient
sinks, nor are the patterns consistent from season
to season or from year to year. Further, wetlands
are often chemically coupled to adjacent ecosystems by the export of organic materials. However,
the direct effect on the adjacent ecosystems is
sometimes quite difficult to quantify. Concomitant
to above, wetlands are quite similar to terrestrial
and other aquatic ecosystems, in that they
could be high-nutrient or low-nutrient systems.
However, there are a number of differences, particularly with regard to sediment storage of nutrients and also in the functioning of the vegetation
in the cycle of different nutrients.
The transport and transformation of chemicals
in ecosystems is known as ‘biogeochemical
cycle’. It involves a great number of interrelated
physical, chemical and biological processes. The
biogeochemical processes are markedly influenced by the unique and diverse hydrologic
conditions in wetlands. These processes lead to
changes in the chemical forms of materials within
wetlands. Also, these processes, in turn, play
important roles to determine overall productivity
of wetlands.
The biogeochemistry of wetlands could be
divided into following aspects: namely, (a) intrasystem cycling through various transformation
processes and (b) the exchange of chemicals
between a wetland and its surroundings. It is
important to note here that the permanent or
intermittent flooding of these ecosystems causes
certain processes to be more dominant in the
wetlands than in either upland or deep aquatic
ecosystems, whereas it is said that few transformation processes are unique to wetlands; e.g.
anaerobic conditions prevail in wetlands. It may
be noted here that the soils in wetlands are usually
characterised by waterlogged conditions during a
part or whole of the year. This results in reduced
13
Wetland Biogeochemistry