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The wonder of local wetlands

What is a Wetland?

A wetland, defined at its simplest, is just what its name describes: land that is wet. To be more specific, it is land that is saturated with enough water for a long enough period that the soils are waterlogged, and standing or slow-flowing water may also be present. As well, the resident flora and fauna are adapted to a wet habitat and lifestyle. 

Why are Wetlands Important?

Wetlands were traditionally regarded as areas of wasted land, as they were generally not suitable for industrialized agriculture or good areas on which to construct buildings and other infrastructure. They also tended to be regarded as eyesores, and soggy areas plentiful with annoying mosquitoes and other insects as well as smelly mud. However, wetlands are extremely important to the natural environment as well as to humans, and can also be visually stunning landscapes. Just some of the benefits and services provided by wetlands for humans and the environment include:

•  Minimizing the impact of flooding events due to their immense capacity to absorb and store water

•  Minimizing the effects of drought by slowly and continuously releasing water to the environment (i.e. through streams or groundwater)

•  Biological productivity, meaning they support an abundance of plant and animal life. This not only contributes to biodiversity, but can also provide essentials such as food, medicine, and building materials to humans.

•  Recreational opportunities through activities such as bird watching and fishing, as well as valuable educational opportunities. Many wetlands also have great importance to First Nations people in terms of resource and cultural value.

•  Improving water quality, wetland plants use and assimilate excess nutrients in the water, and microorganisms feed on and break down harmful pollutants. For this reason, wetlands are known as “nature’s kidneys,” and purposefully using natural or constructed “treatment” wetlands for waste management is becoming a more common practice.

•  Reducing erosion by trapping sediments in the roots of plants, which can reduce degradation to plant and wildlife habitat caused by excess sediment

•  Providing habitat to rare, migratory, and at-risk species. It is estimated that roughly a third of all threatened or endangered species in North America rely on wetlands as critical habitat. 

•  Carbon sequestering (especially in peatlands); meaning carbon is stored long-term instead of being released into the atmosphere and exacerbating climate change

Wetland Classification

The Canadian Wetland Classification System defines a hierarchical approach to classify wetlands. This system includes class, form, and type, from broadest to most specific. Wetlands are separated into different classes based on their environment and how they developed.  The Canadian Wetland Classification System defines and uses 5 wetland classes.1

1) Bog:

Bogs are a type of peatland, which means they accumulate partially decomposed organic material called peat. Bogs are interesting in that the only sources of water that feeds them are direct precipitation, such as rain, snow, and fog, and are therefore referred to as ombrotrophic. All other classes of wetlands are fed by other sources of water in addition to precipitation. These sources include (but are not limited to) streams and groundwater, which generally contain higher quantities of minerals than precipitation. Therefore, all the other classes of wetlands are referred to as minerotrophic. Bog waters are acidic and tend to be in the 4.0 to 4.8 range on the pH scale, and are low in dissolved minerals. This acidity comes in part from precipitation (which is mildly acidic), but more so from the acid that is created through the decomposition of peat. Bogs usually have a high water table generally at or near the ground’s surface level.   

The most typical species to find in a bog are mosses in the genus Sphagnum, commonly known as peat mosses. Other plants that prefer acidic soils, called ericaceous plants, can also be found in bogs, and trees (often black spruce) may or may not be present as well. Due to their acidic conditions, bogs are the least biologically productive of all wetland classes, but often have unique and sensitive species.

Bogs are typically formed of two layers. The thinner surface layer contains the roots of living plants, and since oxygen is present decomposition of dead plants can take place here. However, the deeper layer of a bog consists of waterlogged peat that is very low or completely lacking in oxygen. Without oxygen, full decomposition of organic matter cannot occur, which is why peat accumulates. Any peat that survives total decomposition in the surface layer will eventually make its way down to the deeper layer, where it will be stored. This lower layer can be very thick: on average it has a depth of 3-5 metres, but has been found to be as deep as 10 metres.

Given that they essentially act like huge sponges, bogs provide the essential ecological service of storing and slowly releasing water, which can help in areas prone to flooding. Since their acidic habitat provides a lot of challenges for life, the living things that have adapted to live there are some of the most unique that exist, such as the carnivorous sundew plant. 

2) Fen:

Fens are also a type of peatland, however they are minerotrophic instead of ombrotrophjc, meaning they receive water from sources other than just precipitation, and therefore they are richer in dissolved minerals and are less acidic than bogs. Fens commonly have ground and surface water flow, with a water table that experiences fluctuations. 

Because of the higher mineral content and lower acidity of the soil, fens are generally able to support a much more diverse community of plants than bogs can. The types of plants that grow in a fen are heavily dependent on the depth of the water table and the water chemistry.  In wetter fens, grass and grass-like plants (called graminoids) as well as mosses (bryophytes) tend to dominate, while in drier fens shrubs and trees may be more common. Interestingly, fens can eventually become bogs if the peat layer builds up enough so that the fen is separated from its groundwater supply, and becomes reliant on precipitation only. 

Fens are similar to bogs in that they can reduce the risk of flooding by trapping and storing water, and are also hosts to many unique animals and plants. As with bogs, the thick layer of peat that forms in fens contains a very large amount of stored carbon, keeping it out of the atmosphere. 

3) Marsh:

Marshes are wetlands with shallow water present that fluctuates over some period of time: daily, seasonally, or annually, due to inundation by slow-moving or standing water. Therefore, marshes can receive their water from a number of sources, including stream flow, precipitation, tides and runoff, and many can also be fed by groundwater. The fluctuation of marsh water levels can be dramatic, and is due to changes in the amount or frequency of input from one of its water sources, or a change in the marsh’s water output capacity. Marshes can be freshwater or marine. 

Marshes often have high nutrient levels, and the pH of a marsh is often around neutral. Being high in nutrients and having a neutral pH means that marshes overall have the highest levels of biological productivity of all wetland classes. This allows many different kinds of plants to grow in there habitats, and in turn can support many animal species. The characteristic smelliness of marsh habitat is due to the decomposition that occurs here as a result of its highly productive ecosystem, which produces gases such as methane. The plant communities that grow in marshes are comprised of many different types of aquatic plants, such as graminoids (grasses, sedges, and rushes), as well as water-tolerant shrubs, floating and submerged plants, mosses and algae. A marsh can be divided into zones based on the tolerance of plants to different water depths and the duration that the soil remains wet. Upland plants exist in the outermost (driest) zone of the marsh, and aquatic plants in the innermost (and wettest) zone.  

Marshes can be important in times of drought, due to their ability to release water slowly over a long period of time, maintaining the flow of water to streams or recharging groundwater sources. On the flip side of the coin, marshes can also help mitigate the effects of flooding by slowing down the flow and storing excess water. Marshes also provide the ecosystem service of filtering and cleaning water: as water moves through a marsh, pollutants can settle out on the bottom and are broken down by microbes or stored in sediments. Excess nutrients can be used by marsh plants, and resident microorganisms can use many pollutants for food, thereby breaking them down. 

4) Swamp:

“Swamp” is a term often used by people when describing any wetland, and often has a negative connotation associated with it. However, for a wetland to be grouped in the swamp class, it must follow specific developmental and environmental criteria just as with the other four classes of wetlands. Like other wetland classes, swamps are important features in the environment, and can often be very picturesque, meaning the negative perception of swamps is quite unfair! 

A swamp is a wetland that is dominated by woody plants (i.e. trees and shrubs). While other wetland classes may have trees present, to be classified as a swamp the percent cover of trees in a wetland should be greater than 30%. The soil in swamps is saturated with water during the growing season, and they may also have standing water present at certain times of the year. The soil in swamps can consist of mineral soils as well as peat, with highly decomposed peat being accumulated over time due to the presence of large amounts of woody vegetation.  

The different plant communities in swamps can be grouped into one of three very general categories: a thicket swamp (meaning it is dominated by shrubs), a coniferous swamp, or a deciduous swamp. Of course, many swamps may exhibit a mix of these three community types. Often, coniferous swamps will be found in areas of poorer nutrient content (though they can also be found in higher nutrient areas), while deciduous and thicket swamps tend to be in richer nutrient conditions. Shrub swamps often occur in wetter areas, while deciduous swamps occur in drier areas. 

Like marshes, swamps are important for minimizing the effects of flooding. Forested swamps near the banks of rivers can help by retaining some of the floodwaters, and may experience high productivity due to the nutrient content of the floodwaters as well. Swamps can also be a valuable source of timber, though responsible resource use is important to ensure the ecological function of the swamp can be sustained over time. 

5) Shallow Water:

Shallow water wetlands are a class recognized by the Canadian Wetland Classification System, though not by the province of Ontario.  They are defined as a type of transitional habitat between lakes and marshes. Shallow water wetlands generally have standing water year round at fairly stable levels, with some exceptions during periods of drought. To be classified as a shallow water wetland, the wetland should have a standing water level of less than 2 metres depth in the summer, and at least 75% of the total wetland area should be open water. This means they are too deep for emergent vegetation to grow within most of the wetland area, though there may be some floating or submerged plants. Shallow water wetlands are also commonly known as ponds or sloughs.

Like other classes of wetlands, shallow water wetlands can help with maintaining stream and groundwater flow, as well as minimizing the effects of flooding. They can also be nutrient-rich environments, conducive to a biologically productive habitat. 

Rouge Park Wetlands

It’s estimated that just 10.6% of the total land cover in Rouge Park consists of wetland, Most of this wetland area is classified as swamp (9.4%), with marsh coming in second (1.3%), and negligible amounts of fen, bog, and shallow water wetlands are also present. Rouge Park is home to natural and constructed wetlands, both of which are important features in the ecological landscape of the park. In terms of the entire Rouge watershed, a complete inventory of all wetlands has not been done, it’s estimated that currently mapped wetlands account for < 1% of all Rouge watershed land.2 

The Beare wetland is located at the top of Beare Road, not far from the Rouge Valley Conservation Centre, and is a great example of successful restoration and wetland construction. The story begins with the Beare landfill, now visible as the very large hill past the end of the road, which was in service from the mid-1960s to mid-1980s. Its garbage was frequently covered by a layer of soil so as to minimize unpleasant smells and animal scavenging. In addition, when the landfill was eventually decommissioned, a cap of soil a few metres thick was placed over the mound of refuse. All that soil, sand and gravel was taken from pits west of the landfill across the train tracks, a process that effectively destroyed the natural habitat of that location for the duration of the landfill’s operation. This area was referred to in the past as the Beare Road Borrow Pits.

Once the soil pits were no longer being used for landfill purposes, the area was very slow to regenerate on its own. All the topsoil had been taken away, leaving a hard subsoil that was unfit to support many different species of plants and animals. After the site languished for 17 years following the closure of the landfill, the Friends of the Rouge Watershed group decided to try and restore the habitat of the pits. Their first effort was to plant the area with native trees, however this was only minimally successful. It was then suggested by a local naturalist that restoring the area into a wetland complex may be a better fit. Various sizes of wetland ponds were excavated, some deep enough to hold several metres of water year round and others serving as vernal pools, new top soil was brought in, and many volunteers helped to plant the bare soil with native plants. Since its grand opening in 2006, the Beare wetland complex has become home not only to the native plants that were planted there, but also many native wetland animal species that have moved in to this ideal habitat, including some species at risk such as the threatened Blanding’s turtle.3 

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