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Posted on 2012 Nov 30

Mississippi RiverWatchers – Release November 30, 2012

Tree roots still submerged in water in late August 2011

Tree roots still submerged in water in late August 2011

On November 28 the Mississippi Valley Field Naturalists (MVFN) and The Mississippi RiverWatchers made a joint submission to the Standing Advisory Committee (SAC) of the Mississippi River Water Management Plan concerning the extensive damage to the soft maple trees in the Appleton Wetland.

This wetland, technically a soft maple swamp, floods during the spring, but normally has a period of low water level during the summer and fall. Soft maple trees are flood tolerant, and will remain healthy as long as the base of the trees and the top roots can dry out for a period during the growing season in summer and early fall. Continuous immersion for two years will result in dead trees.

MVFN have made a detailed study of the damage to the Appleton Wetlands starting in 2010 and additional information was supplied by RiverWatchers members.

Three different possible causes were examined: disease and insect damage, higher than normal river water flows over the past decade, and increased water levels caused by the modified flashboards at the weir just above the railway bridge in Almonte.

MVFN and RiverWatchers concluded that disease and insect damage were not the cause of the tree die-off. They also concluded that higher than normal river water flows were not the cause of the problem. Further comment by Mississippi Valley Conservation (MVC) and Ministry of Natural Resources (MNR) biologists confirmed these conclusions.

In 2004, coincident with the use of modified flashboards on the Almonte weir, higher than normal water levels were observed during the summer in the wetland. That has continued to the present time. In 2006, two years after the change, significant tree die-off was documented. As previously noted, this is what would be expected after two years of immersion. Photographs were shown of the tree die-off in the wetlands. They also show that water levels in summer and early fall are now much higher than in the past.

The conclusions were that the die-off of wetland trees is caused by higher water levels in the river during the summer and early fall months as a result of modified flashboards.

Comments to the meeting by MNR biologist Shaun Thompson confirmed that the likely cause of the die off was high water levels in the summer and not other causes.

After the presentations the Standing Advisory Committee formally requested that MNR reopen the Water Management Plan for Reach 18 of the Mississippi River to determine the cause of the Wetland die-off and to adjust the Water Management Plan where appropriate.

The RiverWatchers group will also be making a similar request to MNR.

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