A Breath of Fresh Air
In Olancha, CA, a manmade recreational lake that was usually a source of recreational pleasure had become, instead, a font of foul odors. Water-quality problems had plagued the lake, owned by Craig Vasquez, president of the Excel Bridge Manufacturing Corp., and his two brothers.
“There were problems with pond weed and a lot of sludge buildup in the prevailing wind side of the lake. The water was stagnant,” says Vasquez. “Late in the summer when winds die down and the days are longer and hotter, the water heats up [and] the lake would start stinking really bad.”
Vasquez met Michael McGee, president and general manager of EP Aeration in San Luis Obispo, CA, at golf-related trade shows—the company provides aeration for water features on golf courses among other applications—and asked him about solutions for the problem.
“He explained how his system could turn the water over 70 to 80 times a day by moving cold water from the bottom up to the surface and thus would make it move on an outward motion,” he says.
Aeration systems are used to address everything from water-quality challenges to odor elimination to preventing winter fish kills by improving oxygen circulation and mimicking natural water systems.
As Vasquez did his homework, golf course superintendents spoke highly of the EP Aeration system.
“I’m thinking it’s got to do the same thing it does for a golf course as it does for us,” he says. “It’s nothing different—it’s a body of water that doesn’t have water coming in and water going out, so we need to put breath into this thing. I went with the recommendations from people who have used it.”
The solution seemed cost-effective and simple enough for Vasquez that he had EP Aeration help him set up a system in his family’s lake.
Vasquez was particularly pleased with the easy installation process. “I put in the underground air lines. It wasn’t a big deal; it was like putting in garden sprinklers. I trenched from one end of the lake to the other, buried some lines, had some shut-off valves put in, and got several half-horsepower compressors and a pump shed,” Vasquez says.
Vasquez says the reason he chose the solution was that while fountain-type aeration systems are effective at major parks, he didn’t see a similar application at his family’s lake, since recreational water vehicles are always moving about the lake.
“We wanted something non-obtrusive—something that was laid out in a long garden hose–type form from end to end with weighted line that takes it to the deepest part of the lake and once you laid that in there, all you would see is a little trail of bubbles,” he says.
EP Aeration systems employ diffusion tubing that is keel-weighted to sit atop a sludge layer. On the top of the tubing surgically cut slits sit at regular intervals. The slits are opened through 2 psi of airflow and control the size and rate of the rise of the air bubbles. This guarantees laminar (without turbulence) flow of bubbles from the bottom of the surface and the same quantity of air is available throughout the length of the tubing.
The installation took place five years ago. Vasquez says the approach has taken care of about 90% of the lake’s problems. “Every once in a while—if it’s a really extreme heat situation with no wind—we will get a little glaze of algae formation,” says Vasquez.
 |
Photo: Aeration Safety |
| Aeration systems go beyond traditional fountains. |
For that, Vasquez uses Bacta-Pur, bacteria developed to remove unwanted solids and soluble pollutants from lakes and ponds in the presence of oxygen. The bacterial strains, dispersed from the bottom of the water column, help control ammonia, solubilize organic deposits, and convert waste into natural fish food.
The fish love the aeration/bacteria solution, Vasquez notes. “It’s brought new life to the lake,” he says. “The stench has gone away and everything is breathing because there’s air. It’s like a situation of a stream running in and out of it, where there always is movement. We didn’t have that condition because the lake is manmade—it’s just a big pool with no drain.”
Easy maintenance is another factor Vasquez favors about the system. He has the compressors rebuilt every 18 months for about three times before scrapping it to buy another. EP Aeration charges one-quarter the price of a new one for the rebuilt one. “We have four lines and eight compressors, so when one starts slowing down, I take it offline, have the company rebuild it, and put on a new one,” Vasquez says of the rotation maintenance.
The solution has brought water-quality improvements in a cost-effective manner, Vasquez notes. “For a 2,000-foot lake, it costs between $75 and $100 a month in electricity for the aeration system,” he says.
Cleaning Up a Manmade Mess
Elsewhere in California, Mary Lake sits in the heart of Redding, a city of about 100,000 residents nestled in hills within 60 square miles of varying topography. Mary Lake had been a “swampy” 6-acre lake that was basically a depression in the ground in the midst of a subdivision, according to Gerry Kersten, director of support services for Redding, CA. A small creek runs into the lake, and the construction of a small dam created the 6-acre pond that is 10 feet deep in the center. The lake is home to a great deal of wildlife, including turtles, bass, geese, cranes, ducks, and beavers.
“As more development was growing around the lake, there was more runoff into it, with more nutrients going into the lake that caused some algae and aquatic weed problems,” Kersten says.
In an effort to address the problem, Kersten met with Jim Keeton of Keeton Industries in Wellington, CO, and they began experimenting with approaches. “Over time, we’ve fine-tuned the formula that keeps it natural yet cleans it up considerably for aesthetic purposes,” Kersten says.
Aeration is only one arrow in the quiver, Kersten says. “One of my goals was to not treat it with chemicals for a variety of reasons,” he says.
Among those reasons: discharge issues associated with runoff requirements in the small creek that runs in and out of the lake and ends up in the Sacramento River. Because Kersten wanted a natural approach to treating the lake’s problems, he uses microbes he bought from Keeton Industries in conjunction with the aeration.
“The theory behind the microbes is that it competes with the algae for nutrients, so even though there is a heavy nutrient load going into that lake, the microbes we use soak up the nutrients before the algae has a chance to feed,” he says.
Because dying algae can cause problems with oxygenation in the lake, Kersten chose to pair up the microbes with aeration. “We wanted to complement that particular treatment with an aeration system that keeps the water turning over,” explains Kersten.
The system consists of six diffusers, along with a pump that pushes air into the water to oxygenate the lake and help it maintain healthy levels to support the fish and other life forms that live beneath the surface.
Kersten says the approach has been successful.
Another part of the solution involves the use of blue dye to help reduce photosynthesis, which aquatic weeds and vegetation need to grow. “Those weeks of treatment can be a bit unsightly from time to time,” notes Kersten, “but with the combination of those several approaches, that has helped the lake to remain healthy.”
One Lake, Multiple Contaminants
The combination of aeration and microbes also has been applied with success in Inglewood, CA, at the Hollywood Park race track. There, horses are washed down every day and the water is directed to the onsite wastewater treatment plant, where it is treated and pumped to a lake. From that lake, the reclaimed water is used to irrigate the turf track horses use to race. In addition to the grooming runoff, the lake must contend with its population of ducks, geese, and flamingos and a large amount of fertilizer.
According to David Kessinger, general foreman for plumbing with the Hollywood Park race track, the bottom of the lake “looked nasty.
“You could put your arm in it, pull it out, and it would be covered with little crawling bugs. The water was so nasty, it wasn’t worth using to irrigate,” he says.
The turf track needed to be maintained because racing was being conducted on the turf track as well as the dirt track, Kessinger explains. “Our engineers were telling us we needed to get some aeration going,” he says.
 |
Photo: Aeration Safety |
| Aeration in Minnesota lakes combats winter fish kill. |
Kessinger explored the options and chose the AIRE-O2 Series II aeration system from Aeration Industries International Inc. in Chaska, MN. The system creates a partial vacuum under the water, dispersing air that is drawn through the shaft horizontally into the water. The rotating propeller induces a flow of atmospheric air through the air intake ports on the shaft above the water surface. The air is drawn through the shaft, past the propeller, and exits in a high-velocity stream of high bubbles as it is diffused in the water.
Kessinger uses aeration in conjunction with a BioAmp microbe system, which mixes microbes with water and spins them for 24 hours before releasing 30 trillion microbes into the lake. As a result, the horse track can produce live, active microbial culture onsite to enable “good bugs” to break down organic matter—bugs that are typically decreased in numbers due to heat, fungicides, pesticides, and compaction, among other factors.
“The microbes and aeration in conjunction turned the lake right around in a few months,” says Kessinger. “It’s fantastic now. The pH levels are balanced. It took care of a lot of the metal problems we were having in the water. You can see the bottom and I hadn’t ever seen the bottom.”
The effectiveness of the combination approach initiated in January 2005 was driven home when one of the race track’s employees had stopped using the microbes for several months and the water reverted to a bad state again. The microbe treatment resumed, and so did the quality of the water.
“The water is more usable now and the grass looks a lot better,” says Kessinger.
Fish Kills on Thin Ice
Controlling winter fish kill is one of the prime uses of aeration in Minnesota, among other states.
“People have tried to improve water quality by aerating, and the idea behind it is that by creating a current, the water would come into contact with air and would have exchange of gases—oxygen would come in, carbon dioxide would go out—and that would be the idea behind trying to prevent winter fish kill in making sure there’s a higher amount of oxygen,” says Marilyn Danks, who heads up Minnesota’s aeration safety and permitting program.
David Wright, a supervisor with Minnesota’s Division of Ecological Services of the Department of Natural Resources (DNR), explains that game fish and minnow populations are subject to winter kill, which occurs in a significant decline in oxygen during a long period of ice cover.
Aeration helps by adding oxygen to the water through bubbles and agitation and diffusion of oxygen from the air into a pond.
“We’ve used all sorts of ways to add oxygen during the winter, either by disrupting ice cover or by finding a way to disrupt the ice cover to increase the amount of exchange between the atmosphere and the water and keep fish alive in basins where they would normally winter kill,” Wright says.
 |
Photo: Aeration Safety |
| Traditional aeration methods use a fountain-like system. |
In addition to being used as a fish management tool, the state also permits aeration to be used to protect structures from ice damage and to minimize damage to shorelines from ice movement by creating open water between the ice and the shore.
But Wright says aeration technology needs to be regulated in the state to reduce public risk as a result of the drowning or near-drowning associated with thin ice and open water for which the technology is responsible.Minnesota requires a permit for the use of the aeration systems to keep track of where they are and how they’re being used and to require a certificate of insurance or a bond accepting financial responsibility in case of an accident. Enter Danks, whose job it is to oversee aeration safety. In using aeration for preventing winter fish kills, some safety issues surfaced, she says.
“They create a hole in the ice and some people want to use the surface of a lake in winter for recreational opportunities, so there’s a potential for liabilities,” she says. “In Minnesota, we require a permit be acquired for aeration systems of any kind operating in a public water.”
Those using aeration systems are required to post “thin ice” signs around the area of open water near the thin ice they create and notify the public by publishing notices in newspapers.
Minnesota not only has examined the safety issues associated with aeration but also has looked into the systems’ effectiveness. Wright’s office conducted a study regarding claims by aeration proponents that aeration has a positive effect on water quality as well as claims about the impact of aeration sediments on the bottom of the pond or lake being aerated. During a two-year period, the state compared similar basins, some of which had running aeration systems and some of which did not. The impact of water quality in an individual basin when an aeration unit was operative and when it was turned off was not studied, Wright says.
“It was clear to me the aeration system altered the temperature pattern in the lakes and changed the oxygen distribution,” says Wright. “In the deep lakes, the currents tended to bring nutrients up into the surface water.”
Wright says he and his staff made generalizations about water-quality changes associated with aeration, not knowing with “great confidence” that those changes truly could be attributed to the aeration.
Wright says natural lakes were studied as opposed to manmade drainage ponds that were isolated and protected or ornamental basins. The only type of aeration system studied was a ‘bubbler system” that was installed on the bottom of a lake, designed to circulate the entire basin. Wright did not study aeration systems placed at the surface that are designed to increase the oxygen content of the surface waters.
In looking at shallow natural lake basins normally well-mixed by the wind, the DNR could see no water-quality changes associated with the operation of an aeration system.
“The shallow lakes that were mixed with wind looked just like the shallow lakes that were mixed with wind and the aeration system,” Wright notes.
Where Minnesota DNR officials did note water-quality changes was in deep basins that normally stratify and where the wind energy was insufficient to keep them well-mixed during the summer.
“In those basins, if you added aeration, it made major changes in water quality,” Wright notes. “It warmed up the bottom water and made it more oxygen-rich, but it also tended to elevate the nutrient levels in the surface water and, as a result, the lakes tended to be greener and have more algae, which we measured as chlorophyll, and there was some indication they had less blue-green algae, which might be viewed as a water-quality benefit.”
Another question studied was whether aeration changes the rate or type of sediment accumulation.
“There were claims being made that if you install an aeration system, it would increase the oxidation of organic material in the bottom of the lakes and the lakes would get deeper,” Wright says.
To test this, researchers took a core test of aerated and non-aerated lakes.
“In those cores, they could compare both between lakes and the top of the core when aeration was happening with deeper parts of the core that represented strata before the aeration system was turned on,” says Wright. “We sliced the core into little pieces and dated the pieces so we could look at today and a number of years ago, comparing within one lake and then between other lakes.”
Researchers concluded aeration systems operating in Minnesota did not dramatically change the rate or composition of the sediment that built up in the bottom of the lakes. Wright says his findings confirm what other studies have shown.
A variety of aeration systems operate in Minnesota: systems that agitate the surface; systems that pump water, create fountains, and use the movement of water, spraying it into the air to add oxygen; bubble systems designed to enhance water circulation and enable a normal interchange of oxygen between the air and the water to aerate the water, with the bubbles moving the water around at a faster rate; and systems that pump the water out of a lake and cascade a series of steps and aerate it back into the lake.
Of the approximately 300 aeration systems that run in Minnesota, one-tenth of them continue to run in the summer, Wright says. And while Minnesota’s DNR continues to issue aeration permits for summer use, officials haven’t decided about the systems’ benefits as such.
Still, Wright is not totally opposed to summer aeration use. He concedes aeration can reduce the frequency or abundance of blue-green algae blooms and some systems’ ongoing turnover reduces noxious odors.
“There may be shallow protected basins where it produces other aesthetic benefits, but anytime you change the temperature, oxygen, and mixing patterns of lakes during times when they normally would be stratified, you generate other biological changes, which may be viewed as beneficial or not,” Wright says. “Our experience in Minnesota is that some of our lakes may be under-aerated and we got into problems where our desire was to completely mix the water column and add enough energy and we only partially mixed the water column, though I do not have any firm studies to back that up.”
There are a few cases in Minnesota where aeration is being used to improve water quality.
“We have some aeration systems in the state that are not aerating the surface of the lake but are designed to aerate the deep strata of the lake below the thermocline with a goal of trying to maintain the higher oxygen and minimize the release of nutrients—particularly phosphorus—out of the lake sediments as a water-quality enhancement tool,” says Wright.
St. Paul’s water utility has a reservoir of natural lakes, and Wright says the utility aerates the deep strata of the main water supply reservoir as part of a strategy to minimize the amount of phosphorus in the system.
“The goal is to keep the lake sediments—or at least the surface of them—oxygenated so less phosphorus would be released into the lake,” Wright says. “Less phosphorus would mean less growth of algae and less taste and odor problems they would have to deal with in their treatment process.”
Advertisement
In the end, Wright says, “We understand this technology pretty well in terms of its ability to keep areas ice-free and enhance circulation of water to keep lakes from winter kill. Our ability to modify the biology of systems to change algae growth or how green the water gets is an area of science we understand less well, and the experience has been that sometimes it works and sometimes it doesn’t.
“There are probably good reasons for why it works in some cases and not in others, but I don’t know that we necessarily understand the relationship between how changing aeration or circulation patterns affects the biological communities we are trying to manage.”
Author's Bio: Journalist Carol Brzozowski lives in Coral Springs, FL.
May-June 2007
A Breath of Fresh Air
In Olancha, CA, a manmade recreational lake that was usually a source of recreational pleasure had become, instead, a font of foul odors. Water-quality problems had plagued the lake, owned by Craig Vasquez, president of the Excel Bridge Manufacturing Corp., and his two brothers.
“There were problems with pond weed and a lot of sludge buildup in the prevailing wind side of the lake. The water was stagnant,” says Vasquez. “Late in the summer when winds die down and the days are longer and hotter, the water heats up [and] the lake would start stinking really bad.”
Vasquez met Michael McGee, president and general manager of EP Aeration in San Luis Obispo, CA, at golf-related trade shows—the company provides aeration for water features on golf courses among other applications—and asked him about solutions for the problem.
“He explained how his system could turn the water over 70 to 80 times a day by moving cold water from the bottom up to the surface and thus would make it move on an outward motion,” he says.
Aeration systems are used to address everything from water-quality challenges to odor elimination to preventing winter fish kills by improving oxygen circulation and mimicking natural water systems.
As Vasquez did his homework, golf course superintendents spoke highly of the EP Aeration system.
“I’m thinking it’s got to do the same thing it does for a golf course as it does for us,” he says. “It’s nothing different—it’s a body of water that doesn’t have water coming in and water going out, so we need to put breath into this thing. I went with the recommendations from people who have used it.”
The solution seemed cost-effective and simple enough for Vasquez that he had EP Aeration help him set up a system in his family’s lake.
Vasquez was particularly pleased with the easy installation process. “I put in the underground air lines. It wasn’t a big deal; it was like putting in garden sprinklers. I trenched from one end of the lake to the other, buried some lines, had some shut-off valves put in, and got several half-horsepower compressors and a pump shed,” Vasquez says.
Vasquez says the reason he chose the solution was that while fountain-type aeration systems are effective at major parks, he didn’t see a similar application at his family’s lake, since recreational water vehicles are always moving about the lake.
“We wanted something non-obtrusive—something that was laid out in a long garden hose–type form from end to end with weighted line that takes it to the deepest part of the lake and once you laid that in there, all you would see is a little trail of bubbles,” he says.
EP Aeration systems employ diffusion tubing that is keel-weighted to sit atop a sludge layer. On the top of the tubing surgically cut slits sit at regular intervals. The slits are opened through 2 psi of airflow and control the size and rate of the rise of the air bubbles. This guarantees laminar (without turbulence) flow of bubbles from the bottom of the surface and the same quantity of air is available throughout the length of the tubing.
The installation took place five years ago. Vasquez says the approach has taken care of about 90% of the lake’s problems. “Every once in a while—if it’s a really extreme heat situation with no wind—we will get a little glaze of algae formation,” says Vasquez.
|
Photo: Aeration Safety |
| Aeration systems go beyond traditional fountains. |
For that, Vasquez uses Bacta-Pur, bacteria developed to remove unwanted solids and soluble pollutants from lakes and ponds in the presence of oxygen. The bacterial strains, dispersed from the bottom of the water column, help control ammonia, solubilize organic deposits, and convert waste into natural fish food.
The fish love the aeration/bacteria solution, Vasquez notes. “It’s brought new life to the lake,” he says. “The stench has gone away and everything is breathing because there’s air. It’s like a situation of a stream running in and out of it, where there always is movement. We didn’t have that condition because the lake is manmade—it’s just a big pool with no drain.”
Easy maintenance is another factor Vasquez favors about the system. He has the compressors rebuilt every 18 months for about three times before scrapping it to buy another. EP Aeration charges one-quarter the price of a new one for the rebuilt one. “We have four lines and eight compressors, so when one starts slowing down, I take it offline, have the company rebuild it, and put on a new one,” Vasquez says of the rotation maintenance.
The solution has brought water-quality improvements in a cost-effective manner, Vasquez notes. “For a 2,000-foot lake, it costs between $75 and $100 a month in electricity for the aeration system,” he says.
Cleaning Up a Manmade Mess
Elsewhere in California, Mary Lake sits in the heart of Redding, a city of about 100,000 residents nestled in hills within 60 square miles of varying topography. Mary Lake had been a “swampy” 6-acre lake that was basically a depression in the ground in the midst of a subdivision, according to Gerry Kersten, director of support services for Redding, CA. A small creek runs into the lake, and the construction of a small dam created the 6-acre pond that is 10 feet deep in the center. The lake is home to a great deal of wildlife, including turtles, bass, geese, cranes, ducks, and beavers.
“As more development was growing around the lake, there was more runoff into it, with more nutrients going into the lake that caused some algae and aquatic weed problems,” Kersten says.
In an effort to address the problem, Kersten met with Jim Keeton of Keeton Industries in Wellington, CO, and they began experimenting with approaches. “Over time, we’ve fine-tuned the formula that keeps it natural yet cleans it up considerably for aesthetic purposes,” Kersten says.
Aeration is only one arrow in the quiver, Kersten says. “One of my goals was to not treat it with chemicals for a variety of reasons,” he says.
Among those reasons: discharge issues associated with runoff requirements in the small creek that runs in and out of the lake and ends up in the Sacramento River. Because Kersten wanted a natural approach to treating the lake’s problems, he uses microbes he bought from Keeton Industries in conjunction with the aeration.
“The theory behind the microbes is that it competes with the algae for nutrients, so even though there is a heavy nutrient load going into that lake, the microbes we use soak up the nutrients before the algae has a chance to feed,” he says.
Because dying algae can cause problems with oxygenation in the lake, Kersten chose to pair up the microbes with aeration. “We wanted to complement that particular treatment with an aeration system that keeps the water turning over,” explains Kersten.
The system consists of six diffusers, along with a pump that pushes air into the water to oxygenate the lake and help it maintain healthy levels to support the fish and other life forms that live beneath the surface.
Kersten says the approach has been successful.
Another part of the solution involves the use of blue dye to help reduce photosynthesis, which aquatic weeds and vegetation need to grow. “Those weeks of treatment can be a bit unsightly from time to time,” notes Kersten, “but with the combination of those several approaches, that has helped the lake to remain healthy.”
One Lake, Multiple Contaminants
The combination of aeration and microbes also has been applied with success in Inglewood, CA, at the Hollywood Park race track. There, horses are washed down every day and the water is directed to the onsite wastewater treatment plant, where it is treated and pumped to a lake. From that lake, the reclaimed water is used to irrigate the turf track horses use to race. In addition to the grooming runoff, the lake must contend with its population of ducks, geese, and flamingos and a large amount of fertilizer.
According to David Kessinger, general foreman for plumbing with the Hollywood Park race track, the bottom of the lake “looked nasty.
“You could put your arm in it, pull it out, and it would be covered with little crawling bugs. The water was so nasty, it wasn’t worth using to irrigate,” he says.
The turf track needed to be maintained because racing was being conducted on the turf track as well as the dirt track, Kessinger explains. “Our engineers were telling us we needed to get some aeration going,” he says.
|
Photo: Aeration Safety |
| Aeration in Minnesota lakes combats winter fish kill. |
Kessinger explored the options and chose the AIRE-O2 Series II aeration system from Aeration Industries International Inc. in Chaska, MN. The system creates a partial vacuum under the water, dispersing air that is drawn through the shaft horizontally into the water. The rotating propeller induces a flow of atmospheric air through the air intake ports on the shaft above the water surface. The air is drawn through the shaft, past the propeller, and exits in a high-velocity stream of high bubbles as it is diffused in the water.
Kessinger uses aeration in conjunction with a BioAmp microbe system, which mixes microbes with water and spins them for 24 hours before releasing 30 trillion microbes into the lake. As a result, the horse track can produce live, active microbial culture onsite to enable “good bugs” to break down organic matter—bugs that are typically decreased in numbers due to heat, fungicides, pesticides, and compaction, among other factors.
“The microbes and aeration in conjunction turned the lake right around in a few months,” says Kessinger. “It’s fantastic now. The pH levels are balanced. It took care of a lot of the metal problems we were having in the water. You can see the bottom and I hadn’t ever seen the bottom.”
The effectiveness of the combination approach initiated in January 2005 was driven home when one of the race track’s employees had stopped using the microbes for several months and the water reverted to a bad state again. The microbe treatment resumed, and so did the quality of the water.
“The water is more usable now and the grass looks a lot better,” says Kessinger.
Fish Kills on Thin Ice
Controlling winter fish kill is one of the prime uses of aeration in Minnesota, among other states.
“People have tried to improve water quality by aerating, and the idea behind it is that by creating a current, the water would come into contact with air and would have exchange of gases—oxygen would come in, carbon dioxide would go out—and that would be the idea behind trying to prevent winter fish kill in making sure there’s a higher amount of oxygen,” says Marilyn Danks, who heads up Minnesota’s aeration safety and permitting program.
David Wright, a supervisor with Minnesota’s Division of Ecological Services of the Department of Natural Resources (DNR), explains that game fish and minnow populations are subject to winter kill, which occurs in a significant decline in oxygen during a long period of ice cover.
Aeration helps by adding oxygen to the water through bubbles and agitation and diffusion of oxygen from the air into a pond.
“We’ve used all sorts of ways to add oxygen during the winter, either by disrupting ice cover or by finding a way to disrupt the ice cover to increase the amount of exchange between the atmosphere and the water and keep fish alive in basins where they would normally winter kill,” Wright says.
|
Photo: Aeration Safety |
| Traditional aeration methods use a fountain-like system. |
In addition to being used as a fish management tool, the state also permits aeration to be used to protect structures from ice damage and to minimize damage to shorelines from ice movement by creating open water between the ice and the shore.
But Wright says aeration technology needs to be regulated in the state to reduce public risk as a result of the drowning or near-drowning associated with thin ice and open water for which the technology is responsible.Minnesota requires a permit for the use of the aeration systems to keep track of where they are and how they’re being used and to require a certificate of insurance or a bond accepting financial responsibility in case of an accident. Enter Danks, whose job it is to oversee aeration safety. In using aeration for preventing winter fish kills, some safety issues surfaced, she says.
“They create a hole in the ice and some people want to use the surface of a lake in winter for recreational opportunities, so there’s a potential for liabilities,” she says. “In Minnesota, we require a permit be acquired for aeration systems of any kind operating in a public water.”
Those using aeration systems are required to post “thin ice” signs around the area of open water near the thin ice they create and notify the public by publishing notices in newspapers.
Minnesota not only has examined the safety issues associated with aeration but also has looked into the systems’ effectiveness. Wright’s office conducted a study regarding claims by aeration proponents that aeration has a positive effect on water quality as well as claims about the impact of aeration sediments on the bottom of the pond or lake being aerated. During a two-year period, the state compared similar basins, some of which had running aeration systems and some of which did not. The impact of water quality in an individual basin when an aeration unit was operative and when it was turned off was not studied, Wright says.
“It was clear to me the aeration system altered the temperature pattern in the lakes and changed the oxygen distribution,” says Wright. “In the deep lakes, the currents tended to bring nutrients up into the surface water.”
Wright says he and his staff made generalizations about water-quality changes associated with aeration, not knowing with “great confidence” that those changes truly could be attributed to the aeration.
Wright says natural lakes were studied as opposed to manmade drainage ponds that were isolated and protected or ornamental basins. The only type of aeration system studied was a ‘bubbler system” that was installed on the bottom of a lake, designed to circulate the entire basin. Wright did not study aeration systems placed at the surface that are designed to increase the oxygen content of the surface waters.
In looking at shallow natural lake basins normally well-mixed by the wind, the DNR could see no water-quality changes associated with the operation of an aeration system.
“The shallow lakes that were mixed with wind looked just like the shallow lakes that were mixed with wind and the aeration system,” Wright notes.
Where Minnesota DNR officials did note water-quality changes was in deep basins that normally stratify and where the wind energy was insufficient to keep them well-mixed during the summer.
“In those basins, if you added aeration, it made major changes in water quality,” Wright notes. “It warmed up the bottom water and made it more oxygen-rich, but it also tended to elevate the nutrient levels in the surface water and, as a result, the lakes tended to be greener and have more algae, which we measured as chlorophyll, and there was some indication they had less blue-green algae, which might be viewed as a water-quality benefit.”
Another question studied was whether aeration changes the rate or type of sediment accumulation.
“There were claims being made that if you install an aeration system, it would increase the oxidation of organic material in the bottom of the lakes and the lakes would get deeper,” Wright says.
To test this, researchers took a core test of aerated and non-aerated lakes.
“In those cores, they could compare both between lakes and the top of the core when aeration was happening with deeper parts of the core that represented strata before the aeration system was turned on,” says Wright. “We sliced the core into little pieces and dated the pieces so we could look at today and a number of years ago, comparing within one lake and then between other lakes.”
Researchers concluded aeration systems operating in Minnesota did not dramatically change the rate or composition of the sediment that built up in the bottom of the lakes. Wright says his findings confirm what other studies have shown.
A variety of aeration systems operate in Minnesota: systems that agitate the surface; systems that pump water, create fountains, and use the movement of water, spraying it into the air to add oxygen; bubble systems designed to enhance water circulation and enable a normal interchange of oxygen between the air and the water to aerate the water, with the bubbles moving the water around at a faster rate; and systems that pump the water out of a lake and cascade a series of steps and aerate it back into the lake.
Of the approximately 300 aeration systems that run in Minnesota, one-tenth of them continue to run in the summer, Wright says. And while Minnesota’s DNR continues to issue aeration permits for summer use, officials haven’t decided about the systems’ benefits as such.
Still, Wright is not totally opposed to summer aeration use. He concedes aeration can reduce the frequency or abundance of blue-green algae blooms and some systems’ ongoing turnover reduces noxious odors.
“There may be shallow protected basins where it produces other aesthetic benefits, but anytime you change the temperature, oxygen, and mixing patterns of lakes during times when they normally would be stratified, you generate other biological changes, which may be viewed as beneficial or not,” Wright says. “Our experience in Minnesota is that some of our lakes may be under-aerated and we got into problems where our desire was to completely mix the water column and add enough energy and we only partially mixed the water column, though I do not have any firm studies to back that up.”
There are a few cases in Minnesota where aeration is being used to improve water quality.
“We have some aeration systems in the state that are not aerating the surface of the lake but are designed to aerate the deep strata of the lake below the thermocline with a goal of trying to maintain the higher oxygen and minimize the release of nutrients—particularly phosphorus—out of the lake sediments as a water-quality enhancement tool,” says Wright.
St. Paul’s water utility has a reservoir of natural lakes, and Wright says the utility aerates the deep strata of the main water supply reservoir as part of a strategy to minimize the amount of phosphorus in the system.
“The goal is to keep the lake sediments—or at least the surface of them—oxygenated so less phosphorus would be released into the lake,” Wright says. “Less phosphorus would mean less growth of algae and less taste and odor problems they would have to deal with in their treatment process.”
In the end, Wright says, “We understand this technology pretty well in terms of its ability to keep areas ice-free and enhance circulation of water to keep lakes from winter kill. Our ability to modify the biology of systems to change algae growth or how green the water gets is an area of science we understand less well, and the experience has been that sometimes it works and sometimes it doesn’t.
“There are probably good reasons for why it works in some cases and not in others, but I don’t know that we necessarily understand the relationship between how changing aeration or circulation patterns affects the biological communities we are trying to manage.”