The following article is from an archived newsletter. See our Shared Waters newsletter.

Tracking Coastal Wetland Response to Changing Great Lakes Water Levels

Mike Shantz

The IJC’s Great Lakes- St. Lawrence Adaptive Management (GLAM) Committee is interested in improving the understanding of how Great Lakes coastal wetlands change over time in response to fluctuating water levels.

By initiating efforts to validate and improve existing models used to simulate wetland vegetation response under a wide variety of water level scenarios, the GLAM Committee will be in a better position to evaluate the performance of plans for regulating outflows from Lake Superior and Lake Ontario.

Coastal wetlands along the Great Lakes shoreline provide many valuable ecological services to local and regional communities, such as shoreline stabilization and improving water quality, and are considered some of the most biologically diverse and productive habitat within the Great Lakes basin.

They occur at the transition between open water and drier upland areas and are home to a wide variety of plants that create habitat for numerous fish and wildlife species; some that are found nowhere else in the basin.

field sampling
Field sampling in a Lake Ontario coastal wetland using a GPS receiver (tall pole) and plot. Credit: Canadian Wildlife Service

Given the importance of coastal wetlands to the ecosystem, models of how wetland vegetation responds to changes in water levels over time are important in the evaluation of the environmental implications of outflow regulation. Since these model results were a factor in the decision to implement Plan 2014 for Lake Ontario and the St. Lawrence River, wetland monitoring efforts of the GLAM Committee have been particularly focused on the response of wetland vegetation to water level fluctuation along the Lake Ontario and upper St. Lawrence River shoreline.

Coastal wetlands are dynamic, meaning they change constantly over time in response to a variety of factors including natural long-term changes in Great Lakes water levels. Often such changes are difficult to observe because they typically occur slowly and may be delayed following an event.

As water levels fluctuate within a given season, year or multiple years, plants in the wetland will respond based on their water tolerance. From deeper water to the shore, as plants change from submerged to emergent or upland, their suitability as habitat for various fish and wildlife also changes.

If water levels remain low for a few years, the higher elevation areas of the wetland that had previously been wet will become drier and more suitable for upland plant species (such as non-native common buckthorn) that can’t tolerate very wet conditions.

At the same time, plant seeds like soft-stem bulrush buried in newly exposed sediment can germinate and grow, providing new shelter and nutrition for wildlife. During periods of high lake levels, areas of the wetland at higher elevation that are dry in most years will become wetter and upland vegetation species that were able to survive during dry conditions will die off. This allows plants to flourish that are more tolerant of moist conditions, such as Canada Blue-joint and tussock sedge.

Unique Monitoring Efforts

gps base station
An example of a GPS base station and portable receiver. Credit: Canadian Wildlife Service

With the support of the IJC’s International Watersheds Initiative, the GLAM Committee and its partners, including the Canadian Wildlife Service and the New York Natural Heritage Program, were able to complete wetland vegetation monitoring at a number of Lake Ontario sites in 2015 and 2017 and will be carrying out additional monitoring in 2018.

While many agencies monitor different aspects of Great Lakes coastal wetlands, the work being done in support of the IJC’s GLAM Committee is unique because the approach involves the collection of data for vegetation species and precise bottom elevation information.

The approach requires the use of modern global positioning equipment to determine location and elevation.

In 2015, sampling took place at eight wetland sites around Lake Ontario and the upper St. Lawrence River while 32 sites were sampled in 2017.


In 2017, record high water levels on Lake Ontario provided scientists with the chance to gather data at elevations that had not been flooded for decades. These real-world observations are essential to understanding how vegetation communities respond over time to different water level conditions at different shoreline elevations.

Data collected at multiple plots, within multiple sites and over many years under a wide range of water level conditions, including potential future low water conditions, directly support GLAM Committee efforts to test regulation plan performance by estimating vegetation response under various Lake Ontario outflow management scenarios and confirm whether expected improvements in wetland health will occur through the implementation of Plan 2014.

The GLAM Committee will continue monitoring 16 Canadian sites in September 2018 and expects to continue periodic wetland monitoring efforts in the future to ensure sites are visited under a wide range of water level conditions when the most dramatic changes in vegetation are expected to be observed.

Going forward, the GLAM Committee also is looking at supplementing the current field sampling approach with data from new technologies including imagery acquisition from drones and high-resolution satellite imagery. Combined, the information will indicate the elevation at which various plant communities are found as well as the extent of those plant communities within the wetland.

In addition to providing critical information for validating the water regulation plan models, these GLAM Committee studies are contributing valuable knowledge on wetland vegetation adaptation to guide local wetland protection and restoration efforts by communities and organizations in Ontario, Quebec and New York, as well as other regions in the Great Lakes where coastal wetlands occur.

differences wetland vegetation
Differences in wetland vegetation within sample plots at different elevations. Credit: Canadian Wildlife Service
Mike Shantz

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