The 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.

Wetlands 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.

Fletcher Creek Swamp. Photo by Alan Ernst.

All 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 area.

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'.

Carbon 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).