Geoscience Reference
In-Depth Information
Their chemical status depends to a large extent
on the presence of oxygen in wetland water and
soil. Nitrogen is a major nutrient that is often
a limiting factor for plant growth in wetland
habitats. Human activities have greatly increased
nitrogen input, and excess nitrogen leads to
hypoxic conditions in coastal marine environ-
ments. Phosphorus is another limiting nutrient
in many wetlands. Although phosphorus is con-
sidered to be essential for life, some bacteria
have the ability to substitute arsenic for nearly
all phosphorus in their bodies. Potassium, sulfur,
iron and manganese are generally more abun-
dant and, thus, are not limiting factors in most
wetland environments.
Carbon is the chemical basis for life, forms
greenhouse gases, and is a primary component
of fossil fuels. Wetlands, particularly peatlands,
are major carbon reservoirs as well as sources
for carbon dioxide and methane. Carbon is
taken into wetlands primarily via plant photo-
synthesis in the aerobic zone and lost mainly by
organic decay and decomposition in both the
aerobic and anaerobic zones. The accumulation
or release of carbon depends on the balance
between productivity and decay, and the rate of
decay is generally of greater importance than
productivity for long-term accumulation of peat.
In a general way, peatlands exert a damping
inl uence on climate change. During warm inter-
vals peatlands expand, accumulate carbon, draw
down greenhouse gases, and minimize global
warming; the opposite takes place during cool
periods. It is possible that this mechanism may
have initiated glacial cycles during the Pleis-
tocene and led to late Holocene cooling.
Burning fossil fuels, forest clearance, and
other human activities are causing atmospheric
carbon to increase by about 3 Gt (
2 ppm) per
year. Beyond the enormous, but as yet uncer-
tain, climatic implications for greenhouse
warming, many other consequences for wet-
lands result from mining and burning fossil
fuels. Mining has direct negative impacts on
wetland habitats; burning fossil fuels generates
acid rain that alters downwind water and soil
chemistry and releases greenhouse gases that
may inl uence climate. Burning oil shale in
Estonia during the Soviet era released l y ash
that caused severe impacts for nearby bogs;
however, these bogs have demonstrated
remarkable self-recovery following large reduc-
tions in l y-ash pollution during the past two
decades.
Homo sapiens
are conducting an uncon-
trolled global experiment involving large-scale
use of fossil fuels, land conversions, and water
consumption in order to support and raise the
living standard for a rapidly growing human
population. The greatest impacts of this human
experiment on wetlands involve the carbon and
nitrogen cycles as well as biodiversity. In all
three, results have already exceeded so-called
boundary limits. The conservative nature of
wetland l ora and fauna gives them the capacity
to survive under adverse conditions. However,
any realistic hope of mitigating human impact
on the carbon and nitrogen cycles means a
combination of reducing the consumption of
fossil fuels and effectively lowering carbon and
nitrogen emissions from their use, particularly
in the United States and Canada.
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