Water clarity is measured with a Secchi Disk. Readings are taken monthly and added to the cumulative chart. The Secchi Disk is a black and white disk about the size of an 8-inch dinner plate. The disk is lowered into the water on a calibrated line until the disk disappears. That depth is the “Secchi Depth”. It is a direct measure of water clarity and an indirect measure of water quality. Water high in nutrients (undesirable) stimulates the growth of microscopic free-floating plants (phytoplankton) which decrease the transparency of the water. As you can see from the Secchi reading chart,
representing many years of measurements, the water clarity varies considerably through the seasons reflecting the growth cycles of plankton. Inflow of silt laden water also decreases the transparency. Since Lake Auman has no inflowing streams, there is no influx of silt, except for the occasional shoreline construction project. So the Secchi depth gives us a good, cheap, easy to measure, indication of nutrient loading. The nutrients are mostly runoff from over fertilization of lawns and gardens or defective septic systems. This is why we have a mandatory septic pumping program and ask residents to be careful with the use of fertilizers.
Water Temperature & Oxygen Levels
and dissolved oxygen values
were measured from the surface to the bottom of Lake Auman each month in 2001-2002 and again in 2008-2009. These data were plotted on graphs showing how the values change with depth. As expected, the follow up testing up in 2009 confirmed that values found earlier were cyclic and repeat themselves throughout the respective months every year. Rather than publish each monthly chart, composite data curves were created and grouped into spring warming changes and fall cooling changes. These charts should be valid in predicting what the temperature and oxygen values in the water are likely to be at any time of the year.
One of the practical uses of these data is in determining what species of fish can survive in the lake and where they can and cannot live at various times of the year. Most fish (like bass and bluegills) need 5 mg/L of dissolved oxygen to live. Trout need more. Catfish can survive with less. The charts show that during winter months there is ample dissolved oxygen for fish anywhere from the surface to the deepest waters. But in summer there is virtually no oxygen below the thermocline which lies between 25 and 30 feet below the surface. Furthermore, that shallow surface layer is very warm – above 73 degrees F. Therefore, only “warm water species” like bass and bluegills can survive in the lake. Cold water species like trout, pike and walleye could not survive our summer, because down deep where the water is cool enough for them, there is not enough oxygen.
Occasionally we experience significant periods of extreme summer temperatures. There has been some speculation that with high summer temperatures there would be low amounts of dissolved oxygen in the coves and possibly cause a fish kill. All the fish in our lake thrive at oxygen values at or above 5.0 mg/L. Tests measuring the dissolved oxygen content were performed and the results showed that coves had more oxygen than anywhere else in the lake, probably because of the abundance of oxygen producing aquatic vegetation in the shallows. Bluegills in the weedy coves were abundant and active. Bluegills can survive temperatures up to 96.8, bass up to 95.9 and catfish up to 95. Of course the water temperature cools significantly at depths below 10 ft., so our fish population is not likely to be threatened by extreme summer conditions.
Lake Auman Water Chemistry
Periodically, water samples are taken from various areas around the lake. The results of the latest (2019)
can be found here Water Chemistry Data
Plankton in Lake Auman
Plankton are tiny drifting organisms that play an important role in the health and well-being of Lake Auman. A wide variety of plankton is important because it provides the basis of the food chain in the lake.
A study of the plankton found in Lake Auman was conducted by Dr. Paul Kirst with the help of Dr. Patricia “Trish” Sellers of UNC-Pembroke and Dr. Gordon Robinson of the University of Manitoba. Dr. Sellers made possible the collection, photography and preliminary identification of our samples and Dr. Robinson confirmed the identification of the plankton - particularly the identity of the phytoplankton. The results of this plankton study
can be found using this link.