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Saturday, May 8, 2021: Lessons from Neal Marsh

As we walked around Neal Marsh yesterday admiring the clear water and the beaver channels that resident beavers created to get from the adjacent Des Plaines River into the marsh, Dr. Hey explained to us that the water in the marsh isn't actually from the river but rather rises up from the ground.

You will notice in the image that there are lots of bodies of water clustered around the Des Plaines River. That's actually what rivers are supposed to look like. They aren't supposed to be straight, fast blue lines--and they weren't, before beavers were all but trapped out of existence. Beaver dams slow down the water, divert it to the sides to form other channels and bodies of water. Slowing down the water prevents soil erosion and also encourages biodiversity by allowing for more fish spawning. A man made riffle, with a convex shape, was installed at Neal Marsh to help slow down the water. Similarly, in other areas around the country, as part of river restoration projects that include relocating beavers, researchers are installing Beaver Dam Analogues, or man made beaver dams, to slow down waterways. The BDAs slow the water down enough to allow the beavers to build their own dams, which eventually restores the health of the rivers.

Dr. Hey also explained that mesh had been installed at the bottom of that stretch of the Des Plaines River to help control the nonnative carp that had moved into the river. When the mesh is in place, the carp can't dredge the bottom of the river for food, and it allows native species to gain a foothold and start making a comeback. Carp used to compose 90% of the fish biomass and now their numbers are much lower. Carp are not desirable because their dredging muddies the waters and contributes to erosion. Dr. Hey reports that the Chicago Botanic Gardens uses the same mesh to control carp in its waterways.

More tomorrow!


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