Our Wetlands:The Kidneys of the Mississippi
By Alyson Symon
Mississippi Valley Conservation Authority
Often seen as unproductive land, wetlands are starting to gain broad recognition as an essential part of a healthy, balanced ecosystem. Wetlands play a critical role in regulating the movement of water within our watersheds and in doing so provide numerous benefits.
Why We Value Wetland
Wetlands have the ability to purify our water supply through natural filtration systems that absorb chemicals, nutrients, sediments and impurities from the water – in essence they are regarded as “nature’s kidneys”. They process nitrogen, produce oxygen and have high capacity to sequester and store carbon. Wetlands help to regulate water levels by absorbing water during wet periods and releasing it slowly during dry periods, reducing flooding and easing drought impacts. They also regulate the movement of water between the surface and the underlying aquifers by recharging and discharging groundwater. Wetlands along river and lakeshore areas help to reduce erosion by slowing flow, dissipating wave energy and buffering the shoreline. And on top of all of that, wetlands are among the most productive ecosystems in the world, providing specialized habitat to numerous species of plants and animals.
A Brief History of Wetlands in Ontario
Shown on the accompanying map, our local wetland features first originated with the retreat of the last glaciers some 13,000 years ago. In the western part of the Mississippi Watershed, where the landscape is dominated by the rugged topography of the Precambrian (Canadian) Shield, the retreating ice sheet left a scoured landscape of exposed bedrock outcroppings, steep slopes, thin soil cover, and poor drainage. The glaciers scoured deep pockets that became today’s lake beds and shallower pockets that created a mosaic of small wetlands. In the eastern part of the watershed we see much larger wetlands that formed on the flatter sedimentary deposits of the post-glacial Champlain Sea.
It is estimated that before European Settlement (c 1800) 25% of the Southern Ontario landscape was covered in wetland, with the highest percentages in southwestern and eastern Ontario. Settlement resulted in vast areas of wetland being drained or filled for agriculture, development and peat extraction. Ducks Unlimited Canada reports that Southern Ontario has lost 1.4 million ha or 72% of the pre-settlement (c. 1800) wetlands. Locally, wetland losses have been greatest in the more populated and good agricultural areas and least in the Precambrian (Canadian Shield) area where the rugged topography and shallow soil cover are generally not suited to farming. In Mississippi Valley it is estimated that 65% of the original wetlands in the eastern half of the watershed have been lost.
The Wetlands of Mississippi Lake
Even with the historic loss of wetland in much of southern Ontario, there remains a relatively high concentration of wetland area around Mississippi Lake. The Lake lies on the transition zone between the Canadian Shield on the west side, and the limestone plains of the Champlain Sea on the east side, occupying a stretch of the Mississippi River that would have originally been dominated by wetlands. The Lake was created in the 1820s when the surrounding low lying wetland areas were flooded from the construction, and subsequent elevating, of the Carleton Place dam. As a result, Mississippi Lake has characteristics that make it quite different from most of the other lakes in the watershed. Wetlands occupy about 35% of Mississippi Lake’s shoreline whereas other lakes in the watershed, located on the more rugged Canadian Shield, typically have less than 5%. In fact, the Mississippi Lake wetlands account for approximately 20% of the total wetland area across the entire Mississippi River watershed.
Four large wetlands on and immediately upstream of Mississippi Lake have been classified as Provincially Significant Wetland (PSW), meaning that, based on an evaluation system, they were classified as having features and functions that afford them special protection under the Ontario Planning Act. The McEwan Bay PSW, at the east end of the Lake, is part of the Mississippi Lake National Wildlife Area and is also protected as a migratory bird sanctuary. There is the Mississippi Lake PSW located on the western shore of the Lake and the two large PSWs immediately upstream of the lake, that are collectively known as the Haley Lake-Steward Lake Wetland Complex. These PSWs support a diverse range of habitat including shoreline areas of marsh and aquatic vegetation as well as large areas of silver maple swamp that are flooded only in the spring and depend on those seasonal fluctuations in water level.
One other large wetland surrounding McGibbon Creek on the east side of the Lake has been evaluated but did not rank as a PSW in the scoring. The other light green coloured areas on the map also represent the many small wetlands that were not evaluated or were not classified as Provincially Significant. When combined, these other smaller wetlands make up roughly 310 square kilometers in additional wetland area, on top of the 130 square kilometers in combined area of the larger Provincially Significant Wetlands. While small on their own, the non-PSW wetlands represent a significant amount of wetland area within the Mississippi watershed that is not formally protected.
A recent study to assess the climate change vulnerability of aquatic ecosystems in the Mississippi and Rideau Conservation Authority watersheds rated the vulnerability of the wetlands in terms of how they are expected to respond to predicted changes in climate. Wetland vulnerability was based on decreased quality, or loss due to drying, that may result from projected changes in air temperatures, precipitation and groundwater inflow. The study found that most wetlands in the Mississippi watershed are at risk of shrinking or drying.
Recognizing the long term value of these wetlands, Mississippi Valley Conservation Authority (MVCA) has initiated a program to improve the protection of wetlands through its regulations. This came out of changes to the Conservation Authorities Act in 1998 and the approval an amended Regulation in 2004 that allowed Conservation Authorities to start regulating development in and adjacent to wetlands. Starting in 2006 MVCA began to regulate only those wetlands that were designated as Provincially Significant Wetlands. MVCA is now seeking to expand its regulation to cover all wetlands that are greater than 0.5 hectares and that are hydro-logically connected to another surface water feature. MVCA has produced new draft mapping to identify regulation limits around these identified wetland areas.
The process for amending the MVCA regulation involves public consultation followed by approval by the MVCA Board of Directors. If you’d like to find out more about this, visit the MVCA website where you will find more information and will be able to view the draft mapping: http://mvc.on.ca/wetlands/
You may also be interested in reading some of the sources of information for this article:
Chu, C. 2014. Climate Change Vulnerability Assessment for Aquatic Ecosystems in the Mississippi and Rideau Conservation Authority Watersheds. The Mississippi-Rideau Region Climate Change Adaptation Project. Ont. Min. Nat. Resour., Clim. Change Res. Rep. CCRR-43
Ducks Unlimited Canada. 2010. Southern Ontario wetland conversion analysis: final report. Ducks Unlimited. Barrie, ON.
Keddy, P. 1999. Earth, Water, Fire. An ecological Profile of Lanark County. (First Edition). Motion Creative Printing, Carleton Place,. Ontario.
Mitsch, W. J. and J. G. Gosselink. Wetlands (2nd edn.), Van Nostrand Reinhold, New York, 1993.
Snell, E. 1987. Wetland distribution and conservation in southern Ontario. Working Paper No. 48. Inland Waters and Land Directorate, Environment Canada. Ottawa, ON.
If you would like to learn about wetland ecology we recommend a book titled “Wetland Ecology: Principles and Conservation”, written by Dr. Paul Keddy a local ecologist and author who worked as a professor of ecology for over 30 years and has studied wetlands, forests and other upland communities of the Ottawa Valley, the Maritimes, and the Gulf of Mexico.
Reference: Wetland Ecology: Principles and Conservation (2nd. Edition). Paul A. Keddy (2010). Cambridge University Press, Cambridge, UK. 497 pp.
We all have a part to play, but MVCA is the responsible agency: