Part I of this article series explained how creating a governing body like a lake district would necessary to fund and coordinate the kinds of efforts explained in today’s installment.
Locals know there is something wrong with the water in lakes Tainter and Menomin in Menomonie. It’s not immediately evident when the ice melts each winter that the water is in trouble, but by late June and into early July, the lakes become green and the water can often put off a pungent odor.
No one wants to swim in those waters and only the bravest souls venture out on tubes and water skis. When the water changes mid-summer, boats still glide through the muck so anglers can fish or so boat riders can enjoy a recreational ride, but most avid water enthusiasts abandon the local lakes to seek clearer water somewhere else.
Folks are hesitant about dipping into the glowing green water and their fears are valid. The green water comes from the blooms of cyanobacteria (often referred to as blue-green algae) that grow out of control long before the traditional dog days of summer each year. Cyanobacteria are toxic species, and when they grow to a level visible in the water, it is an indication that the water is indeed toxic. Stagnant and/or shallow waters collect and retain growth at the highest levels and the health threat is legitimate.
“Cyanobacteria put a variety of toxins in the lake,” says researcher and UW-Stout lecturer Dr. Scott McGovern. “It’s been shown in studies that they do bio-accumulate in fish and they do cause problems. The toxins cause health problems in humans, pets and livestock. It’s all been well documented.”
McGovern has been studying cyanobacteria for nearly a decade and for the majority of his research he has worked with the water in Lake Menomin.
There are a number of factors that contribute to the excess growth of cyanobacteria in the lakes, including high levels of phosphorous and an imbalanced ecosystem.
Phosphorous pours into the water ecosystem from a variety of sources. Because both Tainter and Menomin are impounded by the dams in Cedar Falls and Menomonie, the phosphorous-rich sediment that flows in is collected and contained in the lakes. Where the water doesn’t flow well in bays and shallow water, the sediment settles there, creating a high level of concentrated phosphorous in the water. Once present in the lakes, the imbalanced ecosystem is not prepared to combat the high levels of phosphorous and in fact may contribute further to the breeding ground for cyanobacteria.
McGovern contends that large bottom-dwelling fish play a major role in contributing to the high levels of phosphorous. They are also a culprit in destroying plants that would be able to absorb the phosphorous nutrients. If bottom dwellers such as carp, buffalo, fresh water drum and sucker populate the lakes, they need to be controlled by a balanced level of predator fish. Otherwise they contribute to an overabundance of cyanobacteria.
Following the life cycle of bottom dwelling fish, there are a number of ways those fish wreak havoc on the balance of a lake’s ecosystem.
Bottom dwelling fish spawn in the spring, and “when those eggs hatch,” McGovern says, “you have a small fish fry that needs a source of protein. What do they eat? They eat crustaceans such as water fleas, copepods, and seed shrimp.”
The crustaceans that become fuel for the young bottom dwellers are the species of animals that graze on cyanobacteria. With a depleted population, there are not enough consumers of the green.
“During the spring hatch,” McGovern says, “bottom dwellers can absolutely devastate that population of animals.”
As the bottom dwellers grow they continue to cause problems. They stir up the sediment looking for food on the bottom of lakes and this behavior results in even more phosphorous being released into the water. Phosphorous would stay tied up in the organic sediment at the bottom of the lake, except the bottom-dwelling fish ingest plenty of it as they feed.
McGovern explains, “Bottom-dwellers search the sediment for insects to eat. When they search the sediment they stir up the sediment increasing the phosphate in the water. They eat some of the sediment, and it’s going to be in the water again.”
The fish digestion results in a water soluble phosphorous byproduct that is easier for cyanobacteria to use as fuel.
Bottom-dwellers also uproot plants from the lake bottom making it nearly impossible for the plants to fully develop and for the water to clear.
“The large plants have the capability of precipitating the phosphorous into the sediment where they can use it. They have the ability to clarify the water altogether,” McGovern says.
Plant coverage is essential to the health of a lake and if bottom dwellers dominate the ecology, the plants cannot do their job.
A first step in mitigating change in the water quality would be to manage the fish. A more up-to-date comprehensive fish study would need to be done to determine the current make-up of fish in the water.
Once the fish populations have been identified, decisions can be made about how to best add balance back to the ecosystem. A study on Menomin has not been done since 1999 — and it primarily focused on game fish. Once a comprehensive fish study has been completed, including a survey of bottom-dwelling fish, decisions can be made about how to balance out the ecosystem.
Bio-manipulation is a method that has been successful in reintroducing a balanced ecosystem back to affected waters. In Lake Wingra near Madison, carp were removed from the lake to address their cyanobacteria problem. Evidenced in their carp project poster, water clarity was achieved after the removal of the bottom dwellers.
The results of the fish study would determine what could be accomplished with the introduction of predator fish. Introducing more predator fish like northern, walleye and large-mouth bass could help manage the spawn of fish that are disruptive to the ecosystem. With more predators in the water, the bottom-dwelling fish wouldn’t necessarily eat the most important animals in the lake, and it would be possible to increase the growth of large aquatic plants.
Increase large aquatic plants
“When lakes are overrun by bottom dwellers,” McGovern says, “they will lose the beneficial large aquatic plants. But as soon as you can remove the bottom dwellers, oftentimes that alone will clear the lake and allow the sediment to settle enough for these large plants to take off.”
The water has to be clear enough for the plants to thrive, but when they do, they can further clarify the lake and increase biodiversity.
According to McGovern, “The plants have the ability to hold the phosphate nutrients over the growing season when normally cyanobacteria would be most prevalent. They also provide habitat for the fish to lay their eggs as well as animals that eat cyanobacteria. These large plants can do a lot to balance the ecological state of a lake.”
Simultaneously reducing bottom dwellers and increasing predators will ensure a healthier variety of fish and the essential plant life will have a better chance to thrive.
Besides absorbing the phosphorous present in the water, plants could also be utilized as a natural filtration in areas where high levels of phosphorous enter the lakes. There are efforts upriver to decrease the amount of phosphorous depositing in the local waters, and McGovern believes those efforts are also necessary.
Bio-manipulation, mitigating erosion, and water basin clean-up are all necessary efforts that if used together would complement one another. Several of the world’s foremost experts in limnology, the study of freshwater science, argue that when loads of sediment impact the clarity of a lake, simply controlling the deposits of that sediment doesn’t achieve clear water. (Sondergaard, 2003) (Scheffer, 2007)
“The research states that reducing external phosphorous alone is very often not enough to get a lake that has this green cyanobacteria to go back to the clear water state. That is a concern of mine,” McGovern says. “I feel that we should try to coordinate in efforts, and at the same time use biomanipulation along with the DNR efforts of reducing external phosphorous. It may be that a two-tiered system could be used with filtering plants and harmless calcium-based compounds such as lime and quick-lime could be used in isolated areas to precipitate phosphorous.”
The compounds McGovern mentions would be strategically placed in areas where water enters and leaves the lakes as well as where the water is most stagnant. Possible sites would include the convergence of the Hay River and Lake Tainter, just before the dam at Cedar Falls, and/or in the cut-off north of Lake Menomin.
If the water can be clarified long enough, the large aquatic plants can take over. The plants will be nourished by the nutrients in the water instead of the cyanobacteria. The plant coverage would need to be extensive in order to effect change in the water. “With the amount of nutrients we have coming in,” McGovern says, “We should aim for 40-60 percent aquatic plant coverage on the bottom of the lake.”
Part of how McGovern would like to demonstrate this process would be to continue an ongoing experiment that started with clearing up a barrel of Lake Menomin water last summer.
“If I blocked off the Wolske Bay and removed the fish that would interfere with the water fleas, the copepods and the seed shrimp, they would graze down the cyanobacteria. Plants would come in because the water would clear and that is what I would like to do there, but we would have to accept it as a heavily planted area.”
McGovern would love to have access to Wolske Bay, but it has not yet been approved by the DNR or Menomonie’s City Council for this summer’s work.
Biomanipulation will likely be an important part of the process to remove phosphorous from the water so the clear water state can be restored and retained. In order to accomplish this, however, it is going to take leadership, organization and money. Friends of the Red Cedar Basin, a nonprofit group, has dedicated itself to developing a lake district to fund clean-up efforts.