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North Pond Update 8/20/20

Updated: Aug 25, 2020

We are continuing to have some relief from the algae on North Pond. The most recent Secchi disk measurement (taken by Dr. Whitney King from Colby College on 8/19) was 8 ft, indicating that this particular bloom is over for the time being. Depending on the weather conditions, another bloom may occur before the end of the summer season. If weather stays cool and windy like the past few days, we may be lucky! But if we get hot stagnant weather again, there is a good chance of the lake stratifying and going anoxic again, pumping phosphorus out of the sediments and into the water for algae to consume.

Despite less algae in the water, we are continuing with toxin testing. This is because research has indicated that one of the periods in which cyanobacteria produce toxins is when there is high productivity, in other words, when they are growing. So, if a new bloom is forming, we want to measure while it is forming, in addition to after it is in full bloom.

Because the wind was blowing from the NW today, we took samples on the southern shore of North Pond and Little North Pond, along with a sample from Great Meadow Stream at the Rt 225 bridge. There was fortunately still no microcystin toxin detected at any of the sites!

Results from Abraxis Microcystin Rapid Tests. If the sample line is darker than the control line, that means there is no microcystin present.

We tested on the downwind side of the lake because that is where we expect algae to accumulate. But you can help us with picking sampling locations by reporting any scums that might develop on your shoreline using this Google form here:

At the 7 Lakes Alliance, we have an instrument called the FlowCam, which is essentially a microscope attached to a camera. When we compare the algae samples from 8/6 and 8/19 on North Pond, you can see the difference between the cyanobacterial bloom and the conditions now. The long chains on the top are a cyanobacteria called Dolichospermum (formerly Anabaena). Almost all the images from 8/6 are of this type of cyanobacteria! They can form quite long chains, and they can control their buoyancy, so they float to the top and block out light for other algae, basically making it very difficult for anyone else to compete. When we look at the sample from 8/19 on the bottom, you can see there is now a variety of algae in the lake and no Dolichospermum anymore!

FlowCam images from North Pond water samples from 8/6 (top) and 8/19 (bottom).

The North Pond Association is convening the first meeting of their science committee tonight, where we will discuss the measurements that are needed to help identify the most important sources of phosphorus. In the meantime, get in touch with the NPA LakeSmart coordinator to make sure your property isn’t one of the phosphorus culprits!


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