Upon completion of the Lynde Shores Conservation Area Management Plan (March 1999), Cranberry Marsh was identified as a coastal wetland that was in very poor health. The Central Lake Ontario Conservation Authority investigated possible causes of the deterioration of the marsh and in September 1999 adopted the recommendations of the Cranberry Marsh Zone Management Strategy in order to bring the marsh back to a healthy state.

The main recommendation in the Management Zone Strategy was to restore the health of the marsh by first de-watering it and subsequently by regulating its water levels.

Draining the marsh should allow aquatic vegetation to rejuvenate and therefore provide enhanced wildlife and aquatic habitat. In a healthy marsh, the open water community typically does not exceed 50% of the total area. In 1998 Cranberry Marsh was composed of 75% open water with poor water quality and very little vegetation.

Purple Loosestrife Control

To implement the Strategy’s recommendation, the Conservation Authority contacted Ducks Unlimited Canada because of their expertise in wetland restoration and management. As an organization dedicated to the conservation of wetlands, Ducks Unlimited Canada agreed to enter into a partnership with the Conservation Authority to design and install a water control structure at Cranberry Marsh with the Conservation Authority responsible for monitoring the marsh and long-term maintenance of the structure.

After the structure was installed at the southwest corner of Cranberry Marsh in March 2001, the marsh was de-watered to expose the seedbank and allow it to germinate. Through the summer, various types of vegetation flourished in the marsh including aquatic (e.g. softstem bulrush, broadleaf arrowhead) and semi-aquatic (e.g. smartweed) species. In fall 2001, the control structure was closed so that the fall rains could flood the wetland to a shallow depth in order to insulate the new vegetation from the cold winter temperatures.

As the vegetation becomes well established over subsequent growing seasons, water levels will gradually increase to the point that diverse and interspersed vegetation communities can be maintained with minor, if any, water level adjustments over a period of several years. In the past, vegetation in Great Lakes coastal wetlands was maintained at a high level of diversity due to large fluctuations in water levels. Since Great Lakes water level regulation began in 1958, these fluctuations have likely been insufficient to produce cycles of de-watering/high water levels necessary to keep regenerating vegetation communities. With the control structure in place, CLOCA will be able to simulate these low and high water level cycles. The length of the cycle is site-specific, but generally ranges from seven to ten years, when another de-watering will be required.

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