Wetland Stresses

The importance of wetlands to both humans and ecosystems is increasingly being recognized; however, there are many direct and indirect stresses that continue to threaten habitats. Stresses can also be classified as natural or human-induced. Many wetlands are able to adapt to natural stresses, such as storms, ice damage and low water levels. Unfortunately, human-induced stresses often occur so quickly and drastically that wetlands are not able to fully recover. Working Around Wetlands is an informative brochure that provides basic information on how landowners can minimize stress to wetlands when working in close proximity to wetlands on their property.

Direct Stresses

Direct stresses are those that occur within a wetland, such as dredging, filling, draining, and invasive species. They are usually human-induced, highly visible and can result in rapid changes to wetlands.

Great Lakes coastal wetlands are often located at river mouths and in protected areas which are also favourable places for harbours. As a result, dredging has historically occurred in wetland areas to allow the safe entry of boats. Deepening the water and removal of sediments can result in the destruction of wetland habitat. In the same way, draining and filling of small wetlands for urban development and to increase agricultural area results in significant losses of wetland area and function each year.

Invasive species are those that reproduce so aggressively that they displace native plants in the area that they have become established. Common invasive wetland plants include Purple Loosestrife and Eurasian Water Milfoil. Aggressive fish and wildlife can also be a problem. Carp, a fish introduced from Europe, damages wetland ecosystems while feeding and spawning by uprooting submerged vegetation and increasing the cloudiness of the water which decreases light penetration required for plant growth.

Indirect Stresses

Indirect stresses are often less pronounced, causing changes to occur to wetland function and vegetation communities over a longer period of time. It is often difficult to pinpoint the exact source of these stresses.

Indirect stresses include runoff from upstream agricultural practices, sewage treatment plants and industrial sources which can cause loading of nutrients, sediments and toxic chemicals in downstream wetlands. Due to the collective contribution of sources, it is often difficult to remediate these problems. Fortunately, wetlands are able to assimilate some nutrients and toxic chemicals through plant uptake and the interaction of flowing water with microbial communities active in the wetland soils. These tiny organisms are able to transform and break down nutrients and some toxic chemicals.

Another indirect stress is lakewide water level regulation, which occurs on Lake Superior and, to a more significant extent, on Lake Ontario. Regulation is carried out to maintain water levels in the Great Lakes at a level appropriate to accommodate navigation, shipping, hydroelectric power and shoreline landowners. However, this means less natural variability in water levels, to which coastal wetlands have adapted over many years. Alternating high and low water levels often lead to more diverse plant communities: thus, consistent high or low water levels can cause less diverse systems by excluding those species that rely on periodic changes in water level.