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How can Aeration Help a Lake Such as Lac Waterloo?

Understanding Lake Bottom Aeration for Lac Waterloo.

Comprendre l’aération pour le lac Waterloo (Understanding Lake Bottom Aearation for Lac Waterloo), is an article first written in French by Mario Paris, president of Canadianpond.ca Products Ltd., and published in the journal LACTION des Ami(e)s du Bassin Versant du Lac Waterloo (LACTION: Friends of the Watershed of Lac Waterloo), Number 2 – Spring 2014, page 3.

Let’s start with the fact that all lakes are suitable environments for the growth of aquatic plants, phytoplankton and cyanobacteria. These living organisms are naturally present in different parts of a lake ecosystem and each requires different levels of Phosphorous (P) to begin their seasonal growth.

Phosphorous comes to the lake from two sources, the first being water runoff from the watershed. The second comes from the lake itself as year after year dying plants, fish, microorganisms form layers of phosphorous rich organic sediment. I invite you to take a trip with me to the lake bottom to better understand how aeration will help Lac Waterloo.How can aeration help a lake?

Imagine the lake in the fall, when all plants, algae, phytoplankton and cyanobacteria die and precipitate to the bottom to form the latest layer of organic sediment. The biological activity is naturally slowed down during the winter, so the composting process will be waiting for warmer water to start its decomposition. In the spring when the water reaches 10 Celsius or warmer, the benthic organisms (benthos, organisms living at the bottom of sea or lake) will start recycling nutrients. Often unknown, the benthic fauna is nevertheless essential to a healthy ecosystem capable of recycling the majority of a seasonal organic load.

The main enemy of our rich benthic fauna is a condition called anoxia or a deficiency of oxygen. Some use the term anaerobic to describe this same condition. Imagine all those layers of organic material that have accumulated on the lake bottom over the years. When the biological activity resumes in Spring, our countless invisible partners of the benthic fauna will need oxygen to digest, recycle and do their beneficial work of decomposition of the nutrient rich organic sediments.

In an eutrophic lake, there are periods when we can measure the gradual or complete disappearance of the oxygen just above the sediments. When that fateful moment arrives, the organic layer without dissolved oxygen is considered anoxic! The Herculean labors of our benthic community then come to an abrupt end because they cannot breathe. One evil often attracts another; in the absence of oxygen, phosphorus (P), nitrogen (N), iron (Fe) and manganese (Mn), which were insoluble in sediments when oxygen was present, now become soluble and release into the water column in a form available to plants, algae, phytoplankton and cyanobacteria. This phenomenon is called the anaerobic release of phosphorus.

Without maintaining the oxygen level above the sediment, the window of opportunity to break down this organic layer closes and before long a new organic layer has been added after the fall. Every year the lake loses a few millimetres in depth as sediments accumulate in a process known as bioaccumulation. This accumulation eventually becomes exponential as the lake produces more and more organic debris resulting in more frequent anoxic episodes. In this type of habitat the fish become increasingly rare while beds of aquatic plants expand. This is the beginning of hyper-eutrophication, a death sentence for a lake.

Studies show that approximately 50% of the phosphorus from eutrophic lakes is released from anoxia conditions at the organic sediment level. The homogeneous distribution of aeration on the bottom of a lake is to control the anoxic conditions. Our firm Etang.ca has extensive expertise in lake-bottom aeration and aerating on the lake floor is a recognized and effective method for biological nutrient management. Aeration helps maintain the aerobic bacterial flora and prevents anoxic conditions at the sediment level, two key factors in Waterloo Lake.LACTION logo: Friends of the Watershed of Lac Waterloo

Aerating the upper sedimentary layers produces spectacular results. The eutrophication process can even be reversed over time; this is what I refer to as bio-dredging. In lakes that typically accumulate organic sediments the direct effect of maintaining dissolved oxygen levels is a functioning benthic layer that efficiently composts organic deposits. Properly aerated, over the years, the lake will deepen, and be less and less productive in plants, algae and cyanobacteria. Even if the lake is dredged one day, the lake will still need aeration to maintain optimal benthic fauna and to prevent anoxic conditions in the future. For 10 years now, Lac Waterloo was only partially and temporarily aerated. This viable technique has not yet had the chance to fully prove itself. Plans exist for adding even more aeration that will have a favourable and measurable impact.

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