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13.8 Chemical Mass Balances
of Wetlands
A quantitative description of the inputs, outputs
and internal cycling of materials in an ecosystem
is called an ‘ecosystem mass balance’. If the
material being measured is element(s) like P, N or
C (which are essential for life), then the mass balance is called ‘nutrient budget’. It may be noted
here that mass balance has been developed in
wetlands to describe the ecosystem function(s). It
was developed also to determine the importance
of wetlands as sources, sinks and transformers of
chemicals. Detailed literature on the subject of
the influence of wetlands on water quality, the net
result of these mass balances and similar aspects
may be found in Johnston et al. (1990), Johnston
(1991) and so on.
Intra-system cycling involves exchanges
among various pools or standing stocks of chemicals within a wetland. This cycling includes pathways, such as litter production, re-mineralisation
and various chemical transformations. Further,
the ‘translocation’ of nutrients from the roots
through the stems and leaves of vegetation is
another important intra-system process which
results in the physical movement of chemicals
within a wetland.
There are much variations in the chemical
balances which have been developed for various wetlands. A few generalisations are given
below:
(a) Wetlands serve as sources, sinks and transformers of chemicals, depending on the wetland type, the hydrologic conditions and the
length of time the wetland has been subjected
to chemical loadings.
(b) Seasonal patterns of nutrient uptake and
release are characteristic of many wetlands.
(c) Wetlands are often coupled with adjacent
ecosystems through chemical exchanges
which significantly affect both the systems.
(d) Nutrient cycling in wetlands differs from both
terrestrial and other aquatic ecosystems.
(e) Anthropogenic changes have led to considerable changes in chemical cycling in many
wetlands.
13.9 Wetland pH
Wetland soils and overlying waters occur over a
wide range of pH. Organic soils in wetlands are
often acidic. This is particularly found in peatlands where there is little groundwater inflow.
Conversely, mineral soils often have more neutral
or alkaline conditions. There are specific connections between redox potential and pH. It is
because the specific redox potential at which
chemicals are stable in either reduced or oxidised
states is pH dependent.
13.10 Anthropogenic Effects
In many wetlands, human influence has caused
significant changes in the chemical cycling. These
changes have been occurring as a result of clearing
of land and subsequent erosion; hydrological modifications, such as stream channelisation and dams;
and pollution. It may be noted here that increased
erosion in uplands leads to increased deposition of
sediments in the lowland wetlands, such as forested
swamps. This, in turn, may cause increased
Biochemical Oxygen Demand (BOD) and may
alter the hydrological regime of the wetlands in a
relatively short period of time. Concomitantly,
stream channelisation and dams may lead to
changes in the flooding frequency in many wetlands. This may alter the inputs of nutrients. It may
be noted here that dams generally serve as ‘nutrient
traps’. They retain materials which would otherwise nourish downstream wetlands. Further, in
some cases, stream channelisation has led to stream
downcutting which ultimately drains wetlands.
Notwithstanding the above, there have been
some works on the role of wetlands in global climate change (Immirzi et al. 1992; Mitsch and Wu
1995; and so on).
13.11 Inference
It could be said that ‘wetlands’ are an ‘in-between
world’ (intermediate) between upland terrestrial
ecosystems and deep water aquatic ecosystems.
13.11 Inference
13.8 Chemical Mass Balances
of Wetlands
A quantitative description of the inputs, outputs
and internal cycling of materials in an ecosystem
is called an ‘ecosystem mass balance’. If the
material being measured is element(s) like P, N or
C (which are essential for life), then the mass balance is called ‘nutrient budget’. It may be noted
here that mass balance has been developed in
wetlands to describe the ecosystem function(s). It
was developed also to determine the importance
of wetlands as sources, sinks and transformers of
chemicals. Detailed literature on the subject of
the influence of wetlands on water quality, the net
result of these mass balances and similar aspects
may be found in Johnston et al. (1990), Johnston
(1991) and so on.
Intra-system cycling involves exchanges
among various pools or standing stocks of chemicals within a wetland. This cycling includes pathways, such as litter production, re-mineralisation
and various chemical transformations. Further,
the ‘translocation’ of nutrients from the roots
through the stems and leaves of vegetation is
another important intra-system process which
results in the physical movement of chemicals
within a wetland.
There are much variations in the chemical
balances which have been developed for various wetlands. A few generalisations are given
below:
(a) Wetlands serve as sources, sinks and transformers of chemicals, depending on the wetland type, the hydrologic conditions and the
length of time the wetland has been subjected
to chemical loadings.
(b) Seasonal patterns of nutrient uptake and
release are characteristic of many wetlands.
(c) Wetlands are often coupled with adjacent
ecosystems through chemical exchanges
which significantly affect both the systems.
(d) Nutrient cycling in wetlands differs from both
terrestrial and other aquatic ecosystems.
(e) Anthropogenic changes have led to considerable changes in chemical cycling in many
wetlands.
13.9 Wetland pH
Wetland soils and overlying waters occur over a
wide range of pH. Organic soils in wetlands are
often acidic. This is particularly found in peatlands where there is little groundwater inflow.
Conversely, mineral soils often have more neutral
or alkaline conditions. There are specific connections between redox potential and pH. It is
because the specific redox potential at which
chemicals are stable in either reduced or oxidised
states is pH dependent.
13.10 Anthropogenic Effects
In many wetlands, human influence has caused
significant changes in the chemical cycling. These
changes have been occurring as a result of clearing
of land and subsequent erosion; hydrological modifications, such as stream channelisation and dams;
and pollution. It may be noted here that increased
erosion in uplands leads to increased deposition of
sediments in the lowland wetlands, such as forested
swamps. This, in turn, may cause increased
Biochemical Oxygen Demand (BOD) and may
alter the hydrological regime of the wetlands in a
relatively short period of time. Concomitantly,
stream channelisation and dams may lead to
changes in the flooding frequency in many wetlands. This may alter the inputs of nutrients. It may
be noted here that dams generally serve as ‘nutrient
traps’. They retain materials which would otherwise nourish downstream wetlands. Further, in
some cases, stream channelisation has led to stream
downcutting which ultimately drains wetlands.
Notwithstanding the above, there have been
some works on the role of wetlands in global climate change (Immirzi et al. 1992; Mitsch and Wu
1995; and so on).
13.11 Inference
It could be said that ‘wetlands’ are an ‘in-between
world’ (intermediate) between upland terrestrial
ecosystems and deep water aquatic ecosystems.
13.11 Inference