Learn | Algae and aquatic weed control

Control of milfoil with aeration, water circulation, & bacteria

Control of milfoil by combining aeration, water circulation, & bacteria

Canadianpond aeration systems are made up of:

Control of milfoil can be very difficult These aeration systems will emit thousands of tiny air bubbles which rise to the surface pulling a column of water up with them. While adding much needed oxygen, this system will create a laminar flow of water. Gallons per minute of water moved are in direct relation to the depth and type of device used. The result is well oxygenated water circulating through a Milfoil bed. Once aerated and circulated, beneficial bacteria should be added – reason to follow.

A system must be designed to the specific needs of each location allowing for individual conditions such as:

  • Density of Milfoil growth
  • Size of area to be cleared
  • Lake bottom condition – bottoms of Milfoil beds are usually made up of decaying organic matter – silt and muck.
  • Water depth

Let’s look at an example of a typical system. Assume we have a cottage with a Milfoil bed spread across its waterfront – the bed is 60 ft. along the shoreline and extends out into the lake 60 ft.- total 3600 sq. ft. The Milfoil growth is dense; the bottom is heavily silted; and water depth averages 10 ft. This probably would require 4 air diffuser stations (2 disc model) each providing 3000 gallons of circulation per minute for a total of 12 000 gallons of water now well oxygenated and spreading throughout the bed. The cost of the system would be in the area of $2500, if self-installed (installation is easy). Bacteria costs would be on top of this. Also keep in mind 3600 sq. ft. is a large area and probably greater than many cottagers would have to clear.

How does this system works?

Milfoil requires an abundant supply of lake nutrients or it perishes. Fundamentally the system operates by starving the Milfoil of nutrients. It does this in several ways:

  • Circulating water attracts and holds some of the lake nutrients, thus tending to deprive the Milfoil of some of its normal food availability.
  • Well oxygenated water acts to oxidize the bottom silt so there is not the usual release of nutrients. Silt has a heavy content of nutrients.
  • The decaying process of the bottom silt is accelerated by the addition of more bacteria, and oxygen combining with the nutrients already there to hasten the decomposition process but also to further reduce the silt content.
  • As the Milfoil thins out, other water plants, which were crowded out by the aggressive growth of the Milfoil which took up all the sunlight due to the Milfoil`s extensive surface mat, start to reappear and fight for what nutrients are still available.

Milfoil in a pondThe annual Milfoil growth cycle starts in the spring / early summer as the water starts to warm. Growth as most of us well know is rapid and extensive through the summer and early fall. Eventually stems and surface mats die leaving the roots to survive the winter and provide new growth in the spring. Circulation and aeration extend the fall life of the tops and leave the roots less able to survive the long freeze up period.

A word of warning – the Milfoil eradication program described above is not instantaneous. It can be very substantial very quickly, or it may take longer than one season to do the job. We do, however, have growing testimonials on its ultimate success.

There are many compensating advantages to the deployment of an aeration system water and bacteria approach. Just a few would be:

  • The cost of buying and operating the system is not great when you consider the benefits – being able to swim in front of the cottage and backing the boat out without having to pull up the motor to clear the propeller of the tangled Milfoil weeds. System cost is between $2000 and $3000, bacteria included. Hydro costs will be about $15 per month for the approximate 9 months a year it will operate.
  • Ongoing control efforts are easy. Once you have cleared your area the system will keep it clear even if Milfoil remains in your bay or in the vicinity.
  • Many other eradication methods are labour intensive and never ending. Like mowing grass it comes back in a few weeks, and again, and again, both this year and next.
  • System maintenance is easy; to start in the spring just plug in the compressor and open 3 valves, reversing this process in December. You cannot operate the system once ice starts to form because you will have open water above the diffusers and the ice will be thin in the surrounding area. This is hazardous for surface traffic such as ATVs, snowmobiles, etc.

The process is lake friendly. It returns, albeit a small part of the lake, from its eutrophic state, rich in nutrients supporting abundant plant growth including Milfoil and algae, to an oligotrophic state, rich in oxygen and scarce plant growth. The type of conditions normally found in a lake with a steep rocky shoreline and clear deep water.

We may also want to read the case studies on Invasive Aquatic Plant Management in our case study section.

If you have questions about the foregoing, or about alternate approaches to eradication, or wish to talk about a system for your cottage and get a specific quote give us a call.