Text Size
| |
| |
| |
Wetlands
Loss and Fragmentation of Wetlands along the Great Lakes–St. Lawrence Shoreline
Background
More and more, people see wetlands as dynamic, productive and diverse ecosystems. Many visitors to wetlands immediately appreciate their natural beauty, experience the sense of tranquility they offer and recognize their role in the local landscape. Others value wetlands for their important practical functions, such as erosion control and flood regulation. These special places are wildlife nurseries and nesting sites, feeding grounds and resting places, water filters and reservoirs. They help protect shoreline areas from storm damage and attract fish, birds, amphibians, reptiles and mammals. They are also great places for people to explore and reconnect with nature.
 |
Martin Jean, St. Lawrence Centre |
Wetlands are lands that are seasonally or permanently covered by shallow water, or land where the water table is close to or at the surface. The presence of water causes the formation of hydric soils and allows water-tolerant plant species to dominate. Shoreline wetlands include all wetland types that are in some way hydrologically connected to and influenced by the Great Lakes and the St. Lawrence River. Although swamp, marsh, fen and bog wetlands are common within the Great Lakes–St. Lawrence Basin, shoreline wetlands are typically marsh, swamp and, in some cases, fen communities. Even if most people make little distinction between wetland types, shoreline marshes, temperate swamps and northern bogs are each unique ecosystems that support different species of plants and animals.
Unfortunately, the functions and values of wetlands are still not widely recognized. As a result, approximately two-thirds of the Lower Great Lakes and St. Lawrence River wetlands have been lost over the past four centuries. The proportion reaches 80% and higher in southwestern Ontario and the Montreal area. Wetlands located along urban shoreline areas are especially at risk due to high development pressure and stresses such as water-level regulation.
In order to conserve and restore wetlands effectively, government and non-government agencies require extensive information regarding wetland location, type, size and function. Due to the need for fine-scale spatial information, current management strategies have come to rely heavily on digital tools such as remote sensing, modeling and geographic information systems (GIS) to assist and maximize conservation efforts.
This fact sheet examines trends in wetlands located along the Canadian shores of the Great Lakes, from Lake Superior down through the St. Lawrence River to where the water becomes brackish (Figure 1). Both wetland loss and fragmentation are analysed and discussed.
Figure 1Location map of study area Click inside the red boxes for more information |
|
Important Environmental Conditions
Hydrology (water quantity and quality), soils and sediments, and shoreline morphology are key environmental factors that influence shoreline wetland distribution and wetland communities. The Great Lakes–St. Lawrence River shoreline provides a wide variety of these factors in various combinations, resulting in diverse hydrogeomorphic environments along a shoreline that supports a variety of wetland community types. Each section of the basin has unique long- and short-term hydrologic patterns. Over the last 20 years, annual water levels have fluctuated as much as 1.5 m in Lake Huron and as little as 0.6 m in Lake Ontario or 0.3 m in Lake Saint-François, due to the regulation of these basins. The presence of large tides (a mean water level of 0.3 m at Trois-Rivières and 3.7 m at Quebec City) and salt water (beginning at Rivière-Ouelle) further diversify wetlands along the Great Lakes–St. Lawrence Basin. The areal extent and diversity of wetlands is dependent on long- and short-term water-level fluctuations. Alternating high and low water levels maintain a dynamic shoreline process that both removes vegetation and allows its re-establishment over a multi-year cycle. In terms of water quality, nutrient inputs from adjacent watersheds also greatly influence the condition of shoreline wetland communities. For example, surface-water runoff from upland agricultural fields is often nutrient-rich compared to groundwater or runoff from forested watersheds.
Soils and sediments, which are greatly influenced by bedrock type and surface deposits, are another important component influencing wetland characteristics. The bare Precambrian granite of the Canadian Shield forms much of Lake Superior’s shoreline and the north shore of the Upper and Lower estuaries. Softer sedimentary rock and till occur along much of lakes Erie and Ontario, and the fluvial and upper estuarine section of the St. Lawrence River shoreline. Shoreline erosion and the redeposition of these softer materials have created common shoreline protection features such as sand bars, sand spits and barrier beaches in the Lower Great Lakes.
Wetlands Classification
Wetland classification systems are developed to identify and categorize different wetland types. Traditional wetland classification systems rely largely on vegetative cover because the type of plant cover (or lack thereof) can be reliably interpreted from aerial photographs or remote sensing. This classification, although not specific to shoreline wetlands, also provides information on the associated plant and wildlife communities that typically occur within each wetland type.
 |
Swamps are wetlands dominated by trees and shrubs, with periodic standing water, limited drainage and often neutral or slightly acidic organic soils. | |
John Mitchel |
||
 |
Marshes are wetlands that are almost always flooded and are characterized by a mixture of emergent, floating and submerged aquatic vegetation such as reeds, sedges, pondweeds and water lilies. Marshes can be further divided into low marsh (always flooded) and high marsh or wet meadow (flooded during spring only). | |
Canadian Wildlife Service |
||
 |
Shallow waters are transitional zones between wetlands that are saturated or seasonally wet (bogs, fens, marshes and swamps) and permanent, deep-water bodies. They are characterized by the dominance of floating and submerged aquatic vegetation. | |
Canadian Wildlife Service |
||
 |
Bogs are peat-accumulating wetlands that trap precipitation as the major water source. They typically have acidic organic soils and often contain Sphagnum mosses and ericaceous shrubs. Although still abundant within the Upper Great Lakes watershed, bogs that were once common in the St. Lawrence Lowlands have almost disappeared today. | |
Canadian Wildlife Service |
||
 |
Fens are peat-accumulating wetlands with groundwater as the dominant water source. They support a variety of plant species, including orchids, sedges and grasses. They are typically located within the Upper Great Lakes and are naturally rare within other regions of the Great Lakes–St. Lawrence system. |
|
Environment Canada |
Vegetation- and soil-based classifications are often not enough to describe differences between wetland types. Hydrologic (water) and geomorphic (land) features can also be used to classify wetlands. This hydrogeomorphic context provides an understanding of the environmental variables that will influence plant and wildlife communities within the wetland, such as vegetation distribution and abundance. The classification scheme described below was recently developed for and applied to Great Lakes shoreline wetlands. Within this scheme there are three broad systems, each based on the main hydrologic influence on the wetland. Further division within these systems is also possible, even required in many situations.
 |
Lacustrine wetlands are predominantly influenced by lake forces in protected bays or on a stretch of open shoreline. | |
Environment Canada |
||
 |
Riverine wetlands are primarily controlled by river processes, although frequent or periodic back flooding of lakes into rivers connect these wetlands to lake processes. | |
Environment Canada |
||
|
Barrier-protected wetlands are those that, due to shoreline processes, have become physically separated from a lake or a river by a barrier beach or a series of beach ridges. Water levels in these wetlands, however, are still largely influenced by the lake or river through groundwater connections or periodic opening of the beach ridge. Both lacustrine and riverine processes may influence these wetlands. |
Date modified: 2008/05/01 – Important Notices
