Resident Q&A

Tug Lake District, an Aeration System and Harmful Blue Green Algae

Questions and Answers

August 2020

Why do we need a Lake District and Aeration System – the lake has been clear almost all summer?

No two lakes are the same and no lake behaves exactly the same from year to year.

The frequency and intensity of algal blooms varies greatly from year to year and there are many reasons for this. It is most often the result of varying amount of nutrients available to algae in the lake. For lakes that receive the majority of nutrients from the surrounding landscape (e.g. Lake Mendota) the level of bloom activity is correlated well with the amount of nutrients entering the lake in Spring from rainfall, snowmelt, and rivers.

In Tug Lake, the majority of nutrients feeding algal blooms appears to come from bottom waters and sediment. This is not unusual. The release of phosphorus from sediments is highly dependent on a sustained level of anoxia (no oxygen) in the bottom waters. The duration of complete oxygen depletion and volume of water that is anoxic can vary from year to year. Released phosphorus in anoxic bottom waters must get mixed into the sunlit layers of the lake where the algae can grow through photosynthesis. Those nutrients can be mixed into the upper layers of the lake during storms or high wind events or during changes in the thermal structure of the lake as in fall when cooling surface waters sink. Then water temperatures need to be warm enough to allow rapid growth. The timing and interplay of all these factors changes from year to year resulting in frequent blooms in one year and few blooms in a different year.

Observations of bloom activity or lack thereof are helpful. However, lack of a bloom usually means algae have not accumulated at the surface where people can see them from shore. That doesn’t mean there isn’t an abundance of algae in the lake distributed throughout the water column. You would only know that by taking samples for laboratory analyses. It is also important to recognize that there isn’t always a correlation between the amount of algae observed in the lake and the amount of algal toxins in the lake. Some algae can’t make the toxins, others can, but are not in a physiological state that allows them to do so. Then there are cases where the algae may be in low abundance, but every cell is induced to produce a lot of toxin. In that case it doesn’t take a bloom to raise toxin levels in the lake to unsafe levels.

Since Tug has a history of producing blooms, I wouldn’t assume the problem just went away. I wouldn’t be surprised to see a bloom later in August or in September when the lake begins to mix.

Dr. Todd Miller, UW-Milwaukee (2020 08 16)

Improving the Eco-System Health of Tug Lake: How Should We Proceed?

During the summers of 2015 and 2016, Tug Lake residents have observed that algae blooms on the lake have increased, especially during the months of June and July. Tug Lake Task Force water testing research has indicated that phosphorus and chlorophyll are above normal healthy lake levels, and this condition can contribute to increased harmful blue green algae proliferation. The TLTF has determined that establishing a Lake District to fund an aeration system to decrease blue green algae is the best strategy to improve the eco-system health of Tug Lake over time.

What sort of research has the TLTF done?

Over the last three years, we have done considerable research and consulting with Dr. Todd Miller of UW-Milwaukee, Cason and Associates, and John Hinde of Air Diffusion Systems. Also, nine members of the TLTF have collected six months of water samples for Dr. Miller’s data collection research. On the table now is the Aeration System proposal and Lake District proposal. Between 60-70% of Tug Lake residents contributed to the funding of Dr. Miller and Cason for the work they did.

Why does the lake get harmful blue green algae?

Dr. Miller presentation theorized the lake goes anoxic (low or no oxygen) in the summertime. His theory is we have phosphorous trapped in the sediment of the lake. The bottom of the lake will give up phosphorous which feeds the blue green algae bloom. In spring and fall, turnover disrupts that process and what stabilizes and capture phosphorous in the lake bottom. We’ve also done testing on iron levels (which we have) and iron helps trap the phosphorous in the sediment, making it unavailable for blue green algae.

What about the role of wetlands contributing to more nutrients in the lake?

Cason and Associates has consulted with the TLTF to check the wetlands in the immediate area of the lake and has determined no significant nutrient loading was attributed to the stream or wetlands and felt it was more of an in-lake situation over time.

Where can I find out more information and research about the status of Tug Lake?

Dr. Miller has a website with all his data along with his buoy check-ins regarding chlorophyll, phosphorous, cyano-bacteria and other measures.

If the aeration system Does not make any difference, is there a way to dissolve the Lake District?

Yes, a certain number of petitions would need to be submitted at the annual meeting. A majority vote of the residents at the annual meeting would decide the future of the Lake District.

What is the life expectancy of the aeration system?

About 10 years with annual maintenance. Parts can be replaced at a lessor amount than the original cost of the aeration system over time.

How long do the compressors last?

Vertex compressors have the longest life of any rocking piston compressor on the market. However, compressor life depends on the frequency of maintenance. Filters need to be changed every three months. With regular maintenance, compressors may run 4-6 years before needing a maintenance rebuild (about $250 labor and materials). Without regular maintenance, they may need a rebuild after 18 months. Compressor life with regular maintenance should be about 10 years. Replacement compressors are about $700.

The air-stations (diffusers) should last a decade or more. Annual cleaning is advised to remove hard water deposits – though this shouldn’t be a concern for acidic Tug Lake. The air-stations could potentially be damaged by boat anchors. Fortunately, replacement parts are relatively inexpensive.

Bottom-line tubing is a heavy rubber air hose that should last for decades. It even withstands being hit by boat props. The only issues we see with rubber air hose is due to heat stress near the compressor cabinet. Vertex avoids this issue by installing 3 feet of heat resistant hose between the compressor and the rubber air hose.

Other issues we see with aeration systems (regardless of brand) are compressor and cooling fan damages due to power surges. At least once every year we end up repairing systems damaged by power surges due to nearby lightning strikes. Vandalism is very rare thanks to the locking cabinets; however, compressor cabinets getting damaged after being struck by lawn tractors is not uncommon. For these reasons, we recommend having insurance on your aeration system.

Cason & Associates does offer maintenance service agreements for aeration systems.

How long do the compressors last?

If we run the aeration system for six months, John Hinde estimated that power for the compressor would cost about $3,100/year. Compressor life could be up to 10 years if we are running it six months out of the year.

Does the aeration system have any warranties?

Vertex aeration systems have the following warranty specifications:

Cabinets – lifetime warranty against rust

Compressors – 3-year warranty (does not include filters and maintenance rebuild kits)

Air-stations – 5-year warranty

Bottom-Line tubing – 15-year warranty

HOW DOES IRON MITIGATE BLUE GREEN ALGAE IN THE LAKE?

The amount of iron in sediments of the lake determines the capacity of the sediment to sequester phosphorus (mainly phosphate) under aerobic conditions. Phosphate is largely bound by Fe3+ (ferric iron or iron oxides). When Fe2+ (ferrous iron, soluble iron) in the water column is oxygenated to Fe3+ it precipitates out as a floc and can capture dissolved phosphate on the way down, thus precipitating it out of the water column into the lake sediments. So, having some iron of any kind in the lake water can help in removing dissolved phosphate.

In the case of Tug Lake, most of the phosphorus feeding algal blooms appears to be coming from the sediments during periods of anoxia in summer. This is phosphate released from Fe3+ when it is reduced to Fe2+. Bacteria are heavily involved in this process but that is another story. So as long as we prevent bottom waters from becoming anoxic I would hypothesize that this would prevent phosphorus (in the form of phosphate) release from sediments and subsequently reduce algal blooms.

The ratio of total iron to total phosphorus in the bottom waters of Tug would be a pretty good indicator for the capacity of Tug bottom waters to capture and hold onto the phosphate under aeration conditions. A higher ratio means higher capacity for sequestering phosphorus in bottom waters and sediment. I can certainly make those measurements for you or you can ask Cason. Is it necessary to make these measurements? In my opinion, if there wasn’t enough iron (or other metals) to sequester the phosphate then we would see a constant release of phosphate throughout the season, but that’s not what we observed. We observed phosphate release only when bottom waters were anoxic. Measurements of Fe2+ vs Fe3+ would be interesting, but I’m not sure it is important in this context since aeration will favor Fe3+. Other metals can also bind phosphate, like manganese, aluminum, calcium, but probably play a lesser role here. Sulfate is also important since it can compete for binding of iron to phosphate. It gets more complicated than this, but this is a start!