Hypolimnetic Aeration

Hypolimnetic Aeration

The most common type of lake and reservoir aeration taught in Europe today is hypolimnetic aeration. This process brings water from the bottom to the surface to be oxygenated and then returned to the bottom without mixing the bottom water with the surface water. The reason for oxygenating only the hypolimnion in contrast to complete mixing or inversion of the water body is because it is believed that mixing bottom water with surface water will cause a fish kill by warming the bottom water. Sport fish prefer cooler water. This concept that mixing is bad for fish is completely false. First, warming the bottom water by inversion simultaneously cools the surface water. Second, fish cannot go to the bottom unless the bottom water is oxygenated and is free of toxic gases, particularly hydrogen sulfide, ammonia and carbon dioxide that exist at high levels in the hypolimnion in water devoid of oxygen. While hypolimnetic aeration may put oxygen in the bottom water, it has not been effective in removing carbon dioxide. Third, it is well known that if fish have any of the three toxic gases in their bloodstream, the warmer surface water will cause these gases to make bubbles that will either kill the fish or make them lethargic and sickly.

So the ultimate question is, which type of aeration system, hypolimnetic or inversion, is the most effective in getting the desired oxygenation of the bottom water and in ridding the bottom and the entire water body of toxic gases? Obviously, hypolimnetic aeration does not rid the water above it of toxic gases, or oxygenate it, while artificial inversion is effective in accomplishing both goals. A huge amount of energy is required to move enough water with hypolimnetic aeration as compared to the Clean-Flo Continuous Laminar Flow Inversion and Oxygenation System. Inversion of water bodies is a common natural event that is typically not associated with fish kills.

While some companies report successful results of hypolimnetic aeration, there are also several reports of unsuccessful results, two of which are Gächter and Müller, 2002 and Jaeger, 1994.

The hypolimnetic aerator has a dubious record. Union Carbide installed one in Lake Waccubuc in New York in 1972. There was no significant increase in oxygen after two years (Fast, 1979), and hypolimnetic phosphorus increased. It is our understanding that Union Carbide then dropped interest in hypolimnetic aerators, but certainly other attempts by other companies have been more successful.

Several million dollars were spent in the 1980s on hypolimnetic aeration of eight lakes in Minnesota. These were lakes Marie, Augusta, and Louisa in Annandale, Minnesota, Lake Como and Lake Vadnais in St. Paul, Round Lake in Eden Prairie, Ryan Lake in Robbinsdale and Moore Lake in Fridley (a lake which was already restored by Clean-Flo and became the top fishing lake in seven counties before the Clean Flo inversion and oxygenation system was removed). CLEAN-FLO International tested dissolved oxygen 20 feet from the outlet of the hypolimnetic aerator in Moore Lake after it operated through the winter, and found it to be 0.0 mg/l.

Within a few weeks of installation, the hypolimnetic aerators froze and ruptured through the ice in Lakes Augusta and Marie in Annandale, Minnesota, when the temperatures dropped and were shut down after a few weeks of operation.

In objecting to an article published in NALMS LAKE LINE, a publication of the North American Lake Management Society (Vol. 6 No. 4, July, 1986, p. 27), Christopher Taggert, a biologist at McGill University, Montreal, Canada wrote, "I was surprised by the recent anonymously authored article concerning hypolimnetic aeration that refers the reader to a company which has a vested interest in the idea that eutrophic lakes can be restored by the use of 'Limno' aerators. I am concerned that LAKE LINE has chosen to publish what appears on inspection to be an advertisement under the guise of a pseudo scientific article. Readers familiar with the literature concerning lake restoration (none of which were cited in the article) will know that the 'story' is neither as simple, nor as inexpensive, nor as promising as the article would lead one to believe (...) suitable biological conditions for cold water fish production may be limited by the presence of an anoxic, hydrogen sulfide rich metalimnion." (Existing above the hypolimnetic water being oxygenated.)

A news article in the Annondale, Minnesota Advocate on September 2, 1987 describes the dissatisfaction of the citizens with their hypolimnetic aerators. Part of the article says, "At a public hearing regarding proposed assessments for the CRWD's (Clearwater River District) Chain of Lakes Restoration Project, lakeshore residents complained about three lake aerators that were installed nearly two years ago, and never have worked properly. The aerators one each in Lakes Augusta, Louisa, and Marie have been plagued by mechanical malfunctions, overheating, excessive noise, and inadequate power, the lakeshore residents said. And one after another, the property owners stood up to insist that, before a maintenance assessment is approved, the aerators should be in good working condition.

"We've been fooling with this for almost two years," one lakeshore resident said, "and now we're about to be assessed for it. And then we're stuck with it." ... "The aerators are not working now.”...

"But the aerators, Wenck (the consultant) admitted, have not worked particularly well. Recent testing of the aerators showed that they did not meet the CRWD performance specifications, that they only worked sporadically, and that when they did work they tended to overheat and create objectionable noise levels."

Other news reports tell that citizens from Moore Lake complained about their problems with their lake. Round Lake filled with weeds and algae. St. Paul citizens have continuously complained about the taste and odor problems in the water coming out of Lake Vadnais.

While most hypolimnetic aeration systems provide limited amounts of oxygen to the lake bottom, they are by nature limited in their performance abilities. By their construction, they can only move a fraction of the volume of water that the Clean-Flo inversion and oxygenation system moves, and the amount of oxygen that can be transferred to the water.

The following five tables compare the characteristics of hypolimnetic aerators with Clean-Flo Continuous Laminar Flow Inversion and Oxygenation System.

Kobe Steel apparently previously sold the Lake Lyfter, later manufactured by Kaiyo. A search on the Internet indicated that both companies have apparently quit making hypolimnetic aerators, with Kaiyo now making a lake destratification system. A comparison was made between Kobe Steel's report, "Restoration of Urakami Reservoir 1978 to 1985" and the Clean Flo design for the same 27.6 hectare, 13 meter deep reservoir, to achieve better results.

Characteristic	Kobe	Clean-Flo
Number of diffusers	6	2
Cost of Equipment	$480,000	$57,000
Horsepower	45	5
Rollover rate	Not given	3.3 days
Hypolimnetic dissolved oxygen	3 mg/l	8mg/l*
Hypolimnetic Percent of Saturation	40 - 100% hypolimnion only	90 - 100%* surface to bottom
Hypolimnetic ammonia (N), mg/l	0 - 3	0.01*
Temperature difference surface to bottom	0 - 1.7 C	0 - 1 C*
Diffuser height	From bottom to near-surface	5 cm above bottom
Bubble size	Very large	Very small
Air line	Lifts off bottom near diffuser	Lies on bottom
Non-toxic alum-free phosphate precipitant available	Not given	Yes
*Anticipated results based on other projects.

A comparison has been made between Kaiyo's report on Shimonohara Reservoir and the Clean Flo design for the same reservoir, to achieve better results.

Characteristic	Lake Lyfter	Clean-Flo
Number of diffusers	3	2
Cost of Equipment	$ **	$69,000
Horsepower	22.5	14
Rollover rate	Not given	3.5 days
Hypolimnetic dissolved oxygen, mg/l	Not given	8mg/l* surface to bottom
Hypolimnetic dissolved oxygen, %	Not given	90 - 100%*
Temperature difference surface to bottom	2 C	0 - 1 C*
Diffuser height	From bottom to near-surface	5 cm above bottom
Bubble size	Very large	Very small
Air line	Lifts off bottom near diffuser	Lies on bottom
Buffered alum available	No	Yes
*Anticipated results based on other projects.
** Not given. $240,000 based on Kobe Steel's prices

A comparison has been made between Kaiyo's report on 28.3 hectare, 20 meter deep Honjo Reservoir and the Clean‑Flo design for the same reservoir, to achieve better results.

Characteristic	Lake Lyfter	Clean-Flo
Number of diffusers	6	2
Cost of Equipment	$ **	$63,130
Horsepower	60
Rollover rate	not given	3.3 days
Hypolimnetic dissolved oxygen	not given	8 mg/l*
Percent of Saturation	20 hypolimnion only	90 - 100* surface to bottom
Temperature difference surface to bottom	0 - 3.5 C	0 - 3 C*
Diffuser height	From bottom to near-surface	5 cm above bottom
Bubble size	Very Large	Very small
Air line	Lifts off bottom near diffuser	Lies on bottom
Non-toxic alum-free phosphate precipitant available	No	Yes
* Anticipated results based on other projects.
** Not given. $480,000 based on Kobe Steel's prices.

A comparison has been made between Kaiyo's report on 45 hectare 20 meter deep Ube Maruyama Reservoir and the Clean‑Flo design for the same reservoir, to achieve better results.

Characteristic	Lake Lyfter	Clean-Flo
Number of diffusers	6	6
Cost of Equipment	$ **	$116,890
Horsepower	42.5	46
Rollover rate	not given	3.5 days
Hypolimnetic dissolved oxygen	8 - 10 mg/l	8 mg/l*
Percent of Saturation	90 – 100 hypolimnion only	90 – 100 surface to bottom
Temperature difference surface to bottom	7 C	0 - 3 C
Diffuser height	From bottom to near-surface	5 cm above surface
Bubble size	Very Large	Very small
Air line	Lifts off bottom near diffuser	Lies on bottom
Non-toxic alum-free phosphate precipitant available	No	Yes
*Anticipated results based on other projects.
** Not given. Less than $480,000 based on Kobe Steel's prices.

A comparison has been made between Kaiyo's report on Sakuna Reservoir and the Clean‑Flo design for the same reservoir, to achieve better results.

Characteristic	Lake Lyfter	Clean-Flo
Number of diffusers	2	1
Cost of Equipment	$ **	$33,120
Horsepower	10	8
Rollover rate	Not given	2.9 days
Hypolimnetic dissolved oxygen	5 mg/l hypolimnion only	8 mg/l* surface to bottom
Percent of Saturation	63	90 - 100
Temperature difference surface to bottom	3 C	0 - 3 C
Diffuser height	From bottom to near-surface	5 cm above bottom
Bubble size	Very large	Very small
Air line	Lifts off bottom near diffuser	Lies on bottom
Non-toxic alum-free phosphate precipitant available	No	Yes
*Anticipated results based on other projects.
**Not given. Less than $160,000 based on Kobe Steel's prices

References

Fast, A.W., 1979. Artificial aeration as a lake restoration technique. Lake Restoration, Proc. of a Natl. Conf. Aug. 22 24, 1978. USEPA 440/5 79 001, p. 121 31.

Gächter, René and Beat Müller. No effect of hypolimnetic aeration on the P cycling of Lake Sempach: A re-evaluation of a well-accepted concept. Goldshcmidt Conference Abstracts 2002. (http://www.the-conference.com/2002/gold2002/abstracts/Authors_G.pdf)

Jaeger, Dieter. Effects of hypolimnetic water aeration and iron-phosphate precipitation on the trophic level of Lake Krupunder. Hydrobiologicia, Vol. 275-276 Number 1/February 1994.(http://www.springerlink.com/content/k7gu20841422r0h2)