Taken from Diet for a Small Lake 

Algal blooms are among the most significant and common lake problems encountered in New York State lakes and, therefore, algae management is discussed first. Techniques are grouped by physical, chemical and biological control. 

The three management techniques that control most algae through physical means all involve lake stratification. Lakes in New York State may stratify in summer and winter. When a lake is stratified, colder, heavier water sinks to the bottom and lighter, warmer water rises to the top. This creates distinct layers that do not mix easily. In relatively deep lakes, these layers become less distinct during the spring and fall months and mix together in the process known as destratification or turnover. 

During stratification, the bottom water, or hypolimnion, receives little or no exposure to the atmosphere, which can lead to oxygen depletion. This is usually much more severe in the summer stratification, during the four warmest months of the year. The hypolimnion is the location for reactions with the sediment, degradation of organic materials that have settled out of the water column, and significant biological activity. This combination of oxygen depletion and chemical reactions can lead to deoxygenated, high-nutrient conditions. 

Artificial circulation Principle Artificial circulation is the process which injects compressed air from a pipe or ceramic diffuser into the hypolimnion. With some circulators, water is moved through the use of solar-powered impellors. Either method can eliminate thermal stratification and improve the flow and movement of water within a lake. 

This may improve fisheries and reduce taste and odor problems associated with ammonia, iron and manganese by changing them to a reduced state. It may also lower algae levels by inhibiting the release of phosphorus from oxygen-depleted bottom sediments. A reduced state is the opposite of an oxidized state, changing the oxidation state of an atom by gaining electrons. 

There are several ways that artificial circulation can correct algae problems. Lake sediments may release bound phosphorus under low-oxygen conditions, which encourages algal blooms when the lake turns over in the fall. Increased circulation will restore sufficient oxygen to bottom waters and minimize this nutrient release. 

In a lake with light-limited algae, mixing that extends to the lake bottom will decrease the time that individual algae cells are exposed to light, thus restricting their growth. This is referred to as the “critical depth” concept. Circulation may improve zooplankton survival and increase predation, which can reduce algae levels. Algae species may shift from blue-green to less noxious green algae from the increased surface water contact with the atmosphere, a lowering of the pH and incorporation of carbon dioxide-rich bottom waters. The rising column of bubbles from the aerator, if sufficiently powered, will produce lake-wide mixing that eliminates temperature differences and results in a constant temperature throughout the water column. The disintegration of the thermal layers allows mixing that exposes bottom waters to the atmosphere. When the temperature and density differences between upper and lower layers are nearly eliminated, wind and other natural mixing mechanisms will assist in maintaining well-mixed conditions.

Examples of Aerators / Diffusers 

AirPro Pond Aerator Kit by Living Water - Rocking Piston Pond Aeration System for Up to 1 Acre 

EasyPro PA6SWN Single Diffuser Shallow Pond Aeration Kit 

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