Thursday, October 15, 2015

The Hand of Man

The Good, the Bad and the Ugly
On a recent trip to Bull Shoals, Chris and Deb Barnhart took photographs which show rather dramatically how the hand of man has affected our Ozark waters.  The picture above demonstrates two of the effects that Europeans' arrival in the Western Hemisphere has had on the White River.  One is a dense collection of zebra mussels.

The threat of this invasive species is well known but somewhat distant in our daily lives.  They reproduce prolifically, coating rocks and gravel bottoms as well as water structures, blocking water intake pipes.  Their razor shells turn shorelines into no wade zones.  They out compete native mussel species and steal the food supply from fish at the bottom of the food chain.

Zebra bluff - click to enlarge
The threat comes home when it happens here.  Bull Shoals has a dense population of zebras, coating the bluffs exposed when the water level went down over 10 feet this year.  They prefer hard substrates such as rock and even the shells of native mussels, impairing their movement.  The varying density of mussels on the bluff may represent the variation of rate the lake levels decreased.

Once again, the question of are they good or bad is answered "it depends."  With all their faults, there have been some benefits.  Each mussel filters a liter of water daily, removing plankton, algae and cyanobacteria from the water, a benefit in polluted waters like Lake Erie.  This improves water clarity, allowing sunlight to penetrate deeper.  Their feces falls to the floor, increasing the biomass, available to bottom feeders.  In one lake the yellow perch catch has increased 5-fold.

While no one is proposing importing them to unspoiled lakes, there is some benefit and reason for hope in this.  Zebra mussels are not going to disappear, but nature has a way of compensating for change, restoring some sort of balance over the years.  Lake floor invertebrates and fish reap the benefits of their poop (hey, it has to go somewhere!)  Studies on Lake Champlain have shown that twice the number of invertebrates lived in areas with zebra mussels.

After the zebra mussel population peaks, it frequently drops off some and in one case they weren't found later.  While this is too much to hope for and results will vary by climate and lake, it isn't the end of lake as we know it.

Now to the center of the photograph at the top, this was an unknown posed to me by Chris, a challenge I totally failed.  If it puzzles you too, tune in to the next blog.  Hint: It started out underwater and was exposed by falling lake levels.

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