warmer climate in the southern part of Ontario means that our wetlands
are host to species that do not occur in similar wetlands to the
north. These wetlands are part of the Carolinian Zone and frequently
have more in common with wetlands in the northern United States
than with the rest of Canada. What all wetlands have in common though,
is wet soil.
exist in areas where the soil is saturated (full of water) for most
of the year. The reasons that the soil is saturated vary. The wetland
may be on the edge of a lake or pond with vegetation growing out
of the water and in soils at the lake margins. The lake level determines
the location of the wetland by controlling where the zone of soil
saturation exists. Alternatively the wetland may be in a depression
so that water cannot easily escape and the soil remains saturated.
Wetlands also occur in locations of groundwater upwelling. The water
table is the upper boundary of groundwater. Where groundwater flows
upwards from a groundwater source, like a spring, soils become waterlogged.
This requires that the wetland not be on a steep slope so that the
water cannot run off easily.
Creek Swamp. Photo by Alan Ernst.
wetlands occur in areas where the water cannot escape. Water will
always flow to the lowest point in an area and these areas are where
lakes and wetlands form. It is a misconception that water is held
in wetlands because of the absorptive properties of vegetation and
soil. Gravity and topography determine where wet areas persist.
Wetlands do slow water down as it flows because they are large relatively
flat areas with vegetation that act as a barrier This is why wetlands
make good flood control areas even if they have limited storage
capacity for water, which is determined by the volume of the low-lying
Wetland soils are known for their wetness but they should also be
known for their high organic content. Most wetland soils have a
higher amount of organic material than terrestrial soils, even those
that are based on mineral soils like marshes. The wetlands that
are the best at storing organic material as soil are known as peatlands
due to their thick deposits of organic material ('peat').
Peatlands are often called 'carbon sinks'.
are things that take in something and hold onto it, whereas
'sources' release them.
is the element that makes up the majority of the solid tissue in
our bodies, and in those of almost all living things. Carbon dioxide
is also the main greenhouse gas that contributes to global climate
change. It is important that we do not destroy ecosystems like wetlands
that act as carbon storage units and 'carbon sinks'. Peatlands are
considered to be the biggest terrestrial carbon reservoirs on Earth
but they also release carbon dioxide and methane (another carbon
compound) through decomposition. If they are left undisturbed carbon
storage is greater than carbon release; however, if they are disturbed
they can become carbon sources. The Summit Bog at Copetown is an
example of a peatland that has become a source of carbon to the
atmosphere because of human disturbance through surrounding land
use change (e.g. conversion from wetland to farmland and urban areas).