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The Great North American Secchi Dip-in
By Producer, Kelly Meinhart
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study of lake ecology is quite different from the study of streams
and rivers. Yet both require a team of dedicated scientists
and volunteers to get involved and monitor a variety of indicators
on a regular basis. As with stream studies, the health of lake
waters are subject to environmental changes, human impacts,
and also upon the natural courses of seasonal changes.
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better understand and document these changes, scientists and
volunteers across the country participate in a variety of lake
water quality tests on regular basis. One of these activities
has become some what of a national following, and so, has been
named “The Great North American Secchi Dip-in” and
it’s a procedure that just about anybody can perform and
understand.
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program is run by Kent State University, and the national data
that is collected by the study is combined to create a picture
of the trends in transparency, or clarity, of lake water on
a national scale.
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wondering what the Secchi test is, and why it’s pretty
simple to do? Let’s start with the basics… The Secchi
disk test is a means of surveying the transparency of lake water
by slowly dropping a weighted circular disk into the water.
The disk has two white portions and two black. As you drop the
disk lower and lower into the water, it will become harder to
see the disk due to algal growth, suspended sediments, and other
conditions existing in the water. While lowering it, the observer
notes at what depth he/she lost sight of the disk, and then
again at what depth the disk reappeared. These depths are noted
by using a measured rope to drop the disk. From there, the data
is recorded and entered into the Secchi website for inclusion
into the national data.
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year I had the opportunity to take part in the Great North American
Secchi Dip-in, and so I was off to Pinchot Lake in York County.
Ten of us, including folks from the Pa DEP and Pa DCNR, and
watershed students and specialists headed out on a pontoon boat
to visit different areas and depths of the lake. Our goal was
not only to perform the Secchi dip-in, but also to complete
a variety of water quality tests including temperature and oxygen
profiles, to determine what types of algae might be growing
in the lake by taking chlorophyll samples, and other tests to
determine the overall health of the water in the lake –
both at the surface level and also at the bottom of the lake.
One of the things that we found, and what Barbara Lathrop of
Pa DEP already suspected, was that this lake in particular has
very low levels of dissolved oxygen during the summer months.
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f you watched the video clip offered by Barbara, then I’m
sure you understand the importance of dissolved oxygen….
If you haven’t, please do so; she offers some excellent
insight on why lake water tests are so important. As she explains,
one of the greatest concerns about lake water is the amount
of dissolved oxygen present. A healthy level of dissolved oxygen
(a minimum of 3 mg per liter) is critical for fish and other
species to survive; yet it is difficult to maintain this minimum
during the summer months, at least at this particular lake.
Be sure to listen in to her video clip learn more about the
importance of dissolved oxygen to lake ecology.
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the 2,500 lakes in Pennsylvania only about 200 or so are annually
assessed, and of those, only 10-15 participate in the Secchi
dip-in event. So if you are interested in getting involved in
monitoring a lake near you – contact Diane Wilson or Barbara
Lathrop at Pa DEP Citizen’s Monitoring Lake Program, P.O.
Box 8555, Harrisburg, PA 17105-8555.
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For more information about this issue, check out the following
websites:
 Great
North American Secchi Dip-in
North
American Lake Management Society
U.S.
Environmental Protection Agency’s Water Monitoring Program
Pennsylvania’s
Citizen Volunteer Monitoring Program
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