Aeration

Aeration increases dissolved oxygen in the deeper parts of a lake.  This allows aerobic bacteria to act on organic sediment.  It also helps bind sediment phosphorus so that it is less available to algae.

Article: Aeration Alternatives and Tips on Sufficiency, e.g. don't undersize!

Providing aeration for a lake is one of the fundamental approaches to a healthy lake.  The idea is to ensure there is adequate dissolved oxygen (DO) at the sediment level.  DO should remain above 4 mg per liter all season to ensure effectiveness of the aeration program.  The objective of aeration is to maintain sediment level DO to bind the phosphorus in the sediment.  This will reduce internal nutrient loading and help prevent algae blooms.

There are basically two types of aeration: Inversion aeration and hypolimnetic aeration.  Inversion aeration features diffusers in the lake bottom which release tiny bubbles.  The bubbles bring cold water from the deep allowing it to be mixed by wind action at the surface.  This process breaks the thermocline, the layer between warm water on top and cold water at the bottom.  Hypolimnetic aeration brings the cold water up from the bottom, then aerates it, but returns it directly to the bottom so as not to break the thermocline.

The diffusers in the lake area are fed by on shore compressors and air lines in the lake bottom.  A nice feature of an aeration system is that there is no electric in the water; all you are doing is blowing air into the lake bottom.  Keep in mind, you are not aerating by blowing oxygen into the deep, it is the wind action that gets the oxygen into the cold bottom water that is brought to the surface and then drops to the bottom again.  Aeration is most effective in the deep end of the lake.

There is a distinction between aeration and “mixing.”  Aeration is a vertical process, whereas mixing via water movers is a horizontal process.  Aeration improves deep water dissolved oxygen; mixing prevents stagnation of water in coves.

It is imperative to adequately size an aeration system.  An undersized system will lose DO in the hottest months.  Thus it will still mix the water but not bind the phosphorus.  This will tend to bring up nutrient rich bottom water, defeating the purpose of the aeration system by contributing to algae growth.

 

Alan Fedeli, Chairman of Cupsaw Environmental Committee and NJCOLA Board member