Cyanobacteria 2013

2013 WATER QUALITY REPORT by Jim Martel

Last year was a tough one on lake water quality. The above average rainfall throughout

the summer caused much more runoff to enter the lake carrying with it more sediment and

phosphorus. The sediment lowered the transparency and the phosphorus caused more algae to

grow. The average Secchi disk sighting went from about 12 feet in depth in 2012 to just 10 feet

last year.

For the first time in the 10 years I've been involved in monitoring lake water quality, I

saw two blue-green algae or cyanobacteria blooms last year, both in late August. The good thing

is now I know what they look like. I would describe them as not blue-green in color but more

like a lime green (see pictures ). This bloom was only about a foot wide and occurred along the

shore in calm conditions. I scooped up a sample and brought it to DES for analysis. They found

approximately 1 million cyanobacteria/milliliter, which is quite high. If you see something like

this give me a call (632-7594) and don't swim in it or allow your pets to drink it. Cyanobacteria

can produce a toxin which becomes concentrated during a bloom.

Don't confuse a pine pollen "bloom"with a blue green algae bloom. Although similar in

color, the pine pollen bloom usually occurs in June and the pine pollen is dispersed on land as

well as water. The green dust on your car is pine pollen.

One way to reduce or eliminate algae blooms is to reduce the amount of phosphorus in the lake.

Much of the phosphorus is carried into the lake with the sediment and overland runoff. We can

help to reduce this input by intercepting all overland flow and forcing it to filter through the

ground, where physical, biological and chemical processes capture and hold the phosphorus. See

(http://des.nh.gov/organization/commissioner/pip/publications/wd/documents/nhdes-wd-10-

8.pdf) for information on how you can control runoff from your property.

One piece of good news; Scotts no longer has phosphorus in its lawn fertilizer. Other

fertilizer manufacturers are expected to follow suit. This should be a great help in reducing

phosphorus in lakes. Time will tell.

I'm hoping that the spring snowmelt will be slow this year, for water quality's sake.

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