Wednesday, July 17, 2013

Is it Clear Sailing for Casey Lake?

By Bill Bartodziej, Ecologist, RWMWD

The natural shoreline buffer along Casey Lake Park.

With the apparent loss of the carp population over the winter, all eyes have been peeled on how the Casey Lake system will respond.  Will we see crystal clear water?  Will the aquatic plants take off? Will the stocked bluegill spawn?

In spring, the water clarity had substantially increased from years past.  But would this water quality response be evident in the heat of the summer?  As we write this, we can report that Casey is still clear.  In fact, it is quite easy to see the Casey Lake bottom down to a maximum depth of three feet.  Over the last decade, summer meant murky water for Casey.  This was, in part, due to an abundance of carp that stirred up the lake bottom sediments.  These rough fish are also linked to increasing phosphorus in lake systems.  In Casey, it is likely that carp were responsible for big algal blooms that turned the water green.  The changes that we are seeing out there this year are pretty dramatic.

A submersed rock on the Casey lake bottom, and duckweed floating above.

 We have water quality data to support our casual observations.  Watershed and lake managers use “Chlorophyll-a” to measure how much algae is in the water.  Our watershed uses a grading scale, A to F, to report cholorphyll a measurements.  A lot of chlorophyll-a, typically over 50 ug/l in our watershed, signals water quality problems.  Below is a graph for Casey Lake:


From 2009-2012, chlorophyll-a in Casey Lake was in the D to F range, large algal blooms made it extremely difficult to see more than a foot into the water.  So far this year, chlorophyll a values have jumped significantly into the A range.  This dramatic change in water quality is likely due to the elimination of carp in the system.  

With the increased water clarity, we are starting to see more aquatic plant growth on the lake bottom.  This type of plant growth increases the ecological stability of Casey Lake.  If you take a stroll and stop at the access points in Casey Lake Park, you will see a few bluegill spawning “beds” about 10-15 feet off the shoreline.  These beds are clear circles in the sand about 10-12” in diameter.  This is a good indication that the stocked bluegill survived and are actively reproducing.  The U of MN research team will be electro-fishing in the next couple of weeks to come up with data on the fish community in Casey Lake. 

Please stay tuned for another update this fall!


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