Aeration of Waterloo Lake

Aeration of Waterloo lake

Let’s start with the fact that all lakes are favorable environments for the growth of aquatic plants but also phytoplankton and cyanobacteria. These three types of living things are naturally present in various places in these ecosystems and need phosphorus (P) to initiate their summer growth.

Phosphorus comes from two sources, the first being runoff from the watershed. But there is also a second source of phosphorus already in the lake, generated by these successive layers of organisms which die year after year, and which precipitate in organic sedimentary layers. I invite you on a trip to the bottom of the lake to understand how aeration will help Waterloo lake.

Lac WaterlooImagine in the fall, all the plants, algae, phytoplankton and cyanobacteria die and fall to the bottom of the lake to form the newest layer of organic sediment. As the biological activity naturally slows down during winter, this compost will wait for the water to heat up to begin its decomposition. In the spring when the water reaches 10 Celsius or higher, the so-called benthic microorganisms (called benthos that live on the seabed) will begin recycling nutrients. Often not well known, this benthic fauna is the essential basis of a healthy ecosystem capable of recycling most of the seasonal organic load.

The main enemy of our friends of the benthic fauna is “episodic anoxia” or lack of oxygen. Some use the term ‘anaerobic conditions’. Imagine all those layers of organic matter that have built up on the bottom of the lake over the years. As biological activity develops, our countless, invisible benthic fauna partners will need oxygen to digest, recycle, and do their beneficial decomposition work.

In a eutrophic lake, there are times when we can measure the gradual and complete disappearance of the oxygen level just above the sediments. When this fateful moment arrives, when the organic layer is finally found without dissolved oxygen, it is then in anoxia! The Herculean labors of our benthic fauna then come to an abrupt end because they can no longer breathe. One misfortune often attracts another, and in the absence of oxygen, phosphorus (P), nitrogen (N), iron (Fe) and manganese (Mn) which were insoluble in the sediments, become soluble again and reappear in the water column in a form available to plants, algae, phytoplankton and cyanobacteria. This phenomenon is called anaerobic phosphorus release.

Without maintaining the oxygen level above the sediments, the window of opportunity to decompose this organic layer closes and before long a new organic layer is added to it once fall returns. The lake therefore loses a few millimeters of depth each year and this is called bio-accumulation. This process eventually becomes exponential and the lake produces more and more organic load and its episodes of anoxia become more frequent. In this type of habitat, fish are becoming increasingly rare, and aquatic grass beds are expanding. This is the start of hyper-eutrophication and the predicted death of a lake.

Studies show that approximately 50% of the phosphorus input from eutrophic lakes comes from the release caused by anoxia in organic sediments. The homogeneous distribution of aeration in the bottom of a lake aims to control this anoxia. Bubble Tubing® expertise is aeration from the bottom of a lake where it matters most, near sediment. It is a recognized and precise method which is the basis of the biological management of nutrients. Aeration is also there to keep the bacterial fauna aerobically and to avoid sediment anoxia, two essential factors for Waterloo lake.

LACTIONAeration of upper sedimentary layers sometimes gives spectacular results. The eutrophication process can even be reversed and we will see the process that we call bio-dredging. In these lakes, which typically accumulate organic sediments, the direct effect of maintaining the dissolved oxygen level will finally allow the benthic fauna to do its job of composting the accumulated organic sediments. Properly ventilated over the years, a lake will become deeper and deeper and less and less productive in plants like algae and cyanobacteria. In the event that the lake is mechanically dredged, this lake will still need aeration to maintain an optimal benthic fauna and avoid the problem of the anoxia of the lake ecosystem. For ten years now, Waterloo lake has only been partially and temporarily aerated. This viable technique has not yet had a chance to gain traction. Plans exist to add ventilation that will have a positive and measurable impact.

Here is an article (available only in french), written by Mario Paris, president of Canadian Pond Products Limited and BubbleTubing.com.  It is published in the Journal LACTION des Ami (e) s du Bassin Versant du Lac Waterloo, Number 2 – Spring 2014, page 3.