Tag Archives: meromictic

Stewardship

Green Lakes State Park – Home to a National Natural Landmark and More!

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New York’s State Parks are home to many unique natural features. Green Lakes State Park, near Syracuse, is the home of a National Natural Landmark. The Landmark found here is Round Lake, which is one of 28 such sites found in the state. A National Natural Landmark (NNL) is a natural area that has been designated by the Secretary of the Interior in recognition that the site contains significant examples of the nation’s biological and/or geological features. Round Lake is a rare meromictic lake surrounded by a forest that includes about 20 acres of diverse, old-growth forest. These two components led to Round Lake’s designation as a National Natural Landmark in 1973. The maple-basswood rich mesic forest and the meromictic lakes at Green Lakes State Park have also been recognized as being of statewide significance by the NY Natural Heritage Program (2018) in addition to Round Lake’s designation as a NNL.

NNLPlaqueWQ
The plaque at Round Lake dedicating it as a National Natural Landmark.

You may be asking yourself, what is a meromictic lake? A meromictic lake is a lake that does not have complete mixing of the surface and bottom waters. This is due to the lake being very deep without a large surface area: Round Lake is over 163 feet deep with a diameter of about 700 feet or 36 acres (see below).  The most common type of lake mixing is a dimictic lake which mixes twice a year, once in the summer and once in the fall. To learn more about lakes and their seasons (they have them too!), please see this blog.

MapDEC
This contour map was obtained by NYS DEC

Meromictic lakes remain chemically stratified throughout the year which makes it very hard for organisms to live there especially in the deepest layers of the lake. Chemical stratification refers to the layering of the water within the lake based on chemicals such as dissolved salts and oxygen. Because of this, there is no oxygen and there tends to be lots of dissolved salts in the lower layers as the salts increase the density, or weight, of the water which makes it sink to the bottom of the lake. These conditions make species diversity in a meromictic lake very low. The few fish that occur here are confined to live in the epilimnion, the top layer of water, because that is where there is enough oxygen for them. Snails, zooplankton and phytoplankton (microscopic aquatic critters and plants) are the more abundant species in these lakes.

One exception to the lack of life in the depths of a meromictic lake is the presence of several interesting types of bacteria, for example those in the other lake on the park’s property, Green Lake. Green Lake has a characteristic purple sulfur bacterium that resides in the deep waters. If you pull a water sample from that layer of water, the sample that comes up is this purple-pink color and it smells like rotten eggs. This color and smell comes from the purple sulfur bacteria that resides in the water, which has been studied by many researchers such as those at SUNY College of Environmental Science and Forestry (see picture below). Although Green Lake is also a meromictic lake, it is not included in the Natural Landmark due to the higher use and less natural surroundings than Round Lake.

Sampling_KimSchulzESF
A water sample showing the purple sulfur bacteria at Green Lake. Photo by Kim Schulz, a professor at SUNY-ESF.

The other major component that makes Round Lake a National Natural Landmark is the old-growth forest that surrounds the lake. The Landmark is described as containing 20 acres of “virgin mesophytic forest”. The term “virgin forest” typically describes sites that have never been cut, which is not quite the case here, but the site is exceptional in having minimal cutting over the past few centuries and now supports trees that range from 100 to nearly 400 years old. Mesophytic is an ecological term that describes the vegetation characteristic of rich, moist, well-drained soils. NY Natural Heritage Program describes this forest as a maple-basswood rich mesic forest (2014) and maps roughly 130 acres in the park as old-growth forest – a good place to see some very old trees! There are some particularly old (and very tall) specimens of tuliptrees, bitternut hickory, sugar maple, hemlock and basswood within the Tuliptree Cathedral southwest of Round Lake. The largest tree measured there was 147 ft in 2011, one of the many tuliptrees to be found in this forest.

TuliptreeCathedral_DianeWheelock
Above is a picture of the Tuliptree Cathedral renamed as such following extensive surveys of the old-growth forests in 2001-2002. Photo by Diane Wheelock.

NY State Parks contain many more exceptional sites to see beyond Round Lake! To learn more about other National Natural Landmarks located within State Parks, please see these blogs on the Ellenville Fault Ice Caves and the Iona Marsh.

Post by April Brun, State Parks

Featured Photo taken by Parks Water Quality Unit looking at the western shoreline of the lake.

Resources:

New York Natural Heritage Program. March 2014. Ecological Communities of New York State.

New York Natural Heritage Program. 2018. Significant Natural Community Occurrences. Biotics database. NY Natural Heritage Program Albany NY.

National Park Service. n.d. Round Lake National Natural Landmark.

Flora & Fauna

Lakes Have Seasons, Too

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As the northeast transitions from fall to winter, watch for changes in Parks lakes and ponds nearest you.  You might notice that the water churns more than it did during the summer, or you might even notice ice beginning to form at the surface.  Such phenomena can mean exciting happenings deeper in the water.  One of the most fascinating changes to observe is lake-turnover, or the mixing of cool and warm waters.

Lakes that turn over twice a year are known as “dimictic”: di=twice, mictic= mixing.  They are one of the most common types of lakes on Earth.  Dimictic lakes freeze in the winter and melt completely by summer.  These lakes mix during the spring and fall, after ice melts and before ice forms.  Examples of dimictic lakes are seen across New York State, including Shaver Pond in Grafton Lakes State Park, Moreau Lake of Moreau Lake State Park, Lake George of the Adirondack region, and Lake Erie.

combined spring turnover image
Long Pond at Grafton Lakes State Park during spring turnover: ice melting after winter (top), followed by water mixing into the lake (bottom). Fall turnover is the opposite: water mixing followed by ice forming in early winter. Ice photo by OPRHP. Mixing photo cropped from original by L. Schelling, OPRHP.

Without turnover, aquatic life in different areas of a lake may not have enough oxygen or nutrients to thrive.  Calm waters tend to separate into layers – with denser, “heavier” waters sinking below less dense surface waters, creating an invisible boundary through which oxygen and nutrients cannot pass.  Water is most dense 4 degrees Celsius above freezing (4 OC, or 39OF) and becomes less dense as it cools or warms from this point.  In the summer, this means warmer water is at the surface, closer to the air and thus richer in oxygen for fish.  Meanwhile a layer of cooler, 4oC water settles at the bottom – where many nutrients accumulate, but also where decomposition of dead animals and plants can lead to little to no oxygen in the water.

adapted figure of dimictic temperatures
Dimictic lake temperature throughout the seasons, with the layering (“stratification”) and mixing of warmer (red) and cooler (blue) waters. Spring turnover results from ice melting, and fall turnover results from wind chilling and mixing surface waters. Image adapted from Figure 44.10 in “Ecology and the Biosphere” (Candela Learning).

 

As chilly, windy fall weather kicks in, some of the oxygen-rich surface water can cool, sink into the lower levels of the lake, and push the deeper, nutrient-rich waters up closer to the surface.  The result is a well-mixed habitat for fish.  In dimictic lakes, this turnover happens again in the spring, when the surface ice melts to that heavier, 4oC water and mixes into the deeper waters.

Why are some lakes dimictic and others not?  One reason is lake location — dimictic lakes are more common in temperate regions with warm summers and cold winters, where lakes may freeze over completely.  Another factor is lake size.  Two lakes that are famous for not having complete mixing are Round Pond and Green Lake in Green Lakes State Park.  These are the rare “meromictic” (mero=part) lakes which mix in the upper waters but are too deep to allow surface and bottom waters to mix.  Alternatively, some lakes may be so shallow that they mix frequently (“polymictic”). NY Natural Heritage Program describes 7 different types of lakes in the state.

Seasonal turnover is important for lake recreation as well as for fish and plant life within lakes.  Fishing can improve near the end of mixing periods in lakes that experience turnover, since now oxygen and nutrients will be better distributed throughout the water.  Many fish and aquatic life are sensitive to changes in their habitat – oxygen and nutrient levels, as well as temperature changes. Keeping an eye on the changes in the water is useful to biologists and park enjoyers alike.

Post by Erin Lennon, State Parks Water Quality Unit.

Sources and Further Reading

NY Natural Heritage Program Conservation Guide on oligotrophic dimictic lakes

New York Natural Heritage Program’s “Ecological Communities of New York State” 2014 edition describes all of the lake and pond types in the state

“Ecology and the Biosphere” from Candela Learning.

Green Lake is a rare meromictic type.

Thermal stratification & the effects of a change in temperature on aquatic organisms.