Cottage Q&A
QUESTION
What is a lake-water circulation system and how does it work? Are there any available in Canada?
Cathy Cyr, via e-mail
ANSWER
There are two types of lake-water circulation systems: lake mixers, which destratify a lake, disturbing stagnant water; and selective layer treatments, which focus on oxygenating just the bottom or middle layer of the lake without mixing with the surface. One of the goals of both systems is to reduce nutrient levels in the water, particularly phosphorus and ammonia, in part by increasing oxygen levels. Lake mixers are occasionally used to churn the water so algae blooms can’t take hold.
Almost 10 years ago, Cottage Life profiled a Canadian selective layer treatment, called a lake lung, that was rejuvenating Chesley Lake, Ont., through a process called hypolimnetic aeration. A buildup of rotting vegetation and pollutants was depleting the lake of oxygen, affecting the fish population and causing algae blooms. Andy Gemza, a Toronto-based biologist and lake-regeneration scientist, had a solution: Draw, oxygenate, and return water that sits in the lake’s cold lower layer without mixing the layers of the lake. This creates a healthy habitat for zooplankton, which eat algae and provide a food source for young fish. An inverted U-tube, or lung, within which the lake water is treated, is housed under a raft and connected to an onshore oxygen generator. The lake lung generated immediate benefits, but after three years the raft was caught in a winter gale and damaged beyond repair by ice.
Similar systems operate successfully today but are taken out of the water before winter. Gemza is now finalizing a new design with a submerged unit not susceptible to the dangers of heavy winds and ice. The technology isn’t appropriate for all lakes; it works best in smaller cone-shaped or kettle lakes between nine and 30 metres deep. Costs depend on a number of factors (size of lake, length of operation, etc.) but range from $50,000 to $400,000, with additional operating and maintenance costs of up to $10,000 per year. (Systems currently in use are paid for by private individuals or companies.) For more information, contact Andy Gemza at andygem@sympatico.ca. Eco-Guide International also manufactures water circulation and aeration systems and consults on lake management and restoration. Visit its website for more information www.lake2000.com
Lake mixers, including bubblers, propellers, and jets, mix cold lower water with warmer upper water. These systems add oxygen and reduce algae growth by increasing the water’s contact with air, and need to be customized to your lake. Although cheaper than selective layer treatments, they may adversely affect fish and zooplankton habitats in deeper lakes and, in some cases, can actually promote growth of algae by warming the lake and releasing additional nutrients from the bottom.
Before installing either system, you’ll need permits from various government bodies, depending on the scale of your remediation efforts.
Steve Brearton
Published in the April/May ’07 issue of Cottage Life.
