Diffused Aeration: How Starting from the Bottom can Help Avoid a Winter Fish Kill

The same pond that is healthy and beautiful for most of the year has the potential to be thrown off balance during the coldest part of the year.  Changes in sunlight availability and temperature alter the energy input and usage in your pond ecosystem, changing the strategies you should take to care for it. With ice potentially sealing the surface of your lake for up to months at a time, surface aeration is no longer an option, but diffused aeration has an opportunity to help your pond survive the winter and be ready to thrive come the spring thaw.

We have already introduced the importance of aeration in our previous post about beautiful decorative aerators, but that looked at everything in high-productivity, warmer months. Algae received sunlight for most of the day, fish had plenty of food, and there was plenty of mixing at the surface to provide oxygen for the ecosystem.

But what happens when the weather turns cold? Everything in your pond slows down. The angle of sunlight hitting the surface is less direct, resulting in greater reflection and less energy for photosynthesis. Organisms from bacteria to fish do not regulate their own body temperature, so their metabolisms slow down. With sustained air temperatures below freezing, ice will form on the surface, sealing your pond off from the atmosphere.

An Icy Threat

This barrier limits the oxygenation of the water below in several ways as highlighted in Figure 1. First, it acts as a physical barrier to the atmosphere where oxygen would normally come from. Additionally, ice and snow on top of a lake prevent light from reaching algae and aquatic plants.

The combination of these two factors leads to a cycle of oxygen depletion that could result in a fish kill. With very limited light, plants and algae are unable to produce oxygen as normal. While the algae and the root systems of plants usually survive to the spring, the leaves do not. As they are decomposed, byproducts such as methane and carbon dioxide build up as oxygen is used (this can lead to amazing phenomena like this or this.)

If you combine this with the lack of mixing with the air that ice causes, a pond becomes a closed environment with a timer, similar to a scuba diver who needs to surface before their oxygen tank runs out of air.

The Benefits of Bubbles

A simple and direct way to supplement your pond’s oxygen supply is with diffused aeration. With this system, a compressor on the shore pumps air to the diffuser at the bottom of the pond. The diffuser releases the air, allowing oxygen to enter the water.

Some of this oxygen will become dissolved and available for aquatic respiration, while some of it will bubble to the surface. This is not wasted, however, because the displacement of water by the bubbles circulates what would otherwise be stagnant and stratified water.

Lake Source LLC has several options for diffused aerators that can fit your needs. Systems can be set up with multiple diffusers for larger ponds and some can even be run with solar power, reducing your operating costs! A typical setup would include an inconspicuous housing unit for the compressor on the shore with the diffuser at the bottom, out of site and keeping your pond beautiful.

 While diffused aerators are particularly effective in the winter because they can add oxygen from beneath the surface, they are equally effective in the warmer seasons too! Increasing available oxygen is useful regardless of season and the increased mixing will help avoid hot spots and stagnant water in the summer heat. If you think a diffused aerator could help you manage the health of your pond, or have any other questions about pond management, give Lake Source LLC a call today (833.800.5253)!