Lake Aeration for Nutrient Control

By David Ernes – Lake Management Committee

As many of you know, our lake is stratified. This means that below about fifteen feet, the lake temperature drops rapidly, as does the level of dissolved oxygen. Under these low oxygen conditions, the phosphorous normally bound to other minerals in the sediment, predominantly iron, is released into the water just above the lake bottom. During the spring and fall lake turnover, and other conditions of increased agitation, this phosphorous mixes with the water throughout the lake, resulting in a surge in nutrients. This can eventually result in an algae bloom. In recent article, we discussed the use of alum to cap the sediment, preventing the release of this phosphorous. Another method that can be used to minimize this release is aeration.

Aeration, also referred to as circulation, involves the use of compressors to force air through weighed tubes connected to bubblers situated on the lake bottom. The released air bubbles add oxygen and, with sufficient pressure, mix the lake water, disrupting the stratification.  The subsequent increased oxygen content restores the balance between phosphorus and the sediment minerals keeping it trapped. Also, an increase in lake bottom oxygen accelerates the breakdown of the organic matter (leaves, dead vegetation, etc.) by beneficial bacteria. The fish can also access the improved lake oxygen levels, which is beneficial to their health.

Aeration is best done on the deep areas of a lake where it is stratified, so this type of aeration does not directly impact the coves or the smaller inlets. Over time, aeration may be felt more broadly, as the lake reaches equilibrium.

This past fall, representatives from EverBlue Lakes visited our community to make a presentation, which included an overview of their system optimized for larger lakes. The presentation also included their systems for “muck” digestion and for watershed remediation.

In the past few articles, we have presented some of the options being evaluated for our lake. There are many more options out there. But to control algal blooms, which many consider as our main objective, the most common involve the use of chemicals to kill the algae or options to control the nutrients from the lake sediment using alum, and aeration.

Another option not discussed is to control the nutrients from the watershed. This is more complicated. However, remember that our property is part of this watershed. So, do your part so that you can say that you too are trying to ….

BE LAKE RESPONSIBLE