Why Aeration Is Important
Aeration is an important part of many lake management and restoration
efforts. Naturally, most ponds will undergo two stratification periods
annually. Stratification creates two distinct layers of water that are
separated by a transitional layer (thermocline). Because of the density
differences between the layers, the lower layer (hypolimnion) is isolated
from nearly all input of atmospheric oxygen while stratification persists.
Without aeration, many ponds will develop an oxygen-deprived hypolimnion
throughout the summer. The same ponds may also run the risk of oxygen
depletion under periods of extended ice cover. Ponds that undergo periods
of oxygen depletion may be influenced to different degrees ranging from a
decline in ecosystem efficiency to the extreme of experiencing episodes of
fish kills. By disrupting the pond's stratification, the pond's ecosystem
is supplied with adequate oxygen, preventing the suffocating effect that
would have otherwise occurred.
Aeration is also an important tool for reducing the accumulation of organic
muck that builds up on the pond bottom. Under low oxygen conditions,
decomposition takes place at a much slower rate than under oxygenated
conditions. As a result, organic material is decomposed at a very slow
rate, in fact, usually slower than the rate that new organic material is
being created. The end result...a pond that is rapidly becoming shallower
as it fills with organic material. Simultaneously, gases bubble up from the
muck, producing the foul rotten egg smell. Proper aeration can actually
reverse the build-up of organics in the short-term (natural succession
dictates that a pond will naturally fill in) and eliminate the foul odors as
a result of the accelerated decomposition of organic material under
Aeration is also instrumental in managing nutrients. Under anaerobic
conditions, phosphorous compounds become soluble allowing the phosphorous to
be assimilated by other organisms (i.e. Algae). However, by maintaining an
adequate supply of oxygen it can be retained in the sediments where it is
unavailable for algae growth.
What types of aeration are available?
Although there are many variations in the types of aeration systems
available, most can be classified as either surface or bottom aeration.
Surface aeration systems, such as fountains and agitators, work by pumping
water into the air or by mixing surface water. These surface aerators can
operate effectively in ponds less than eight feet deep, but are typically
ineffective at aerating deeper bodies of water. Efficiency is also
sacrificed in fountain systems as a result of having to pump water into the
air. Maintenance also tends to be higher on these units and issues of
safety arise with the need to run electric lines through the water.
Although the fountains may be aesthetically pleasing, owners must also deal
with the inconvenience of the floating unit, which may restrict water usage
in certain situations.
Bottom aeration is the second category of aeration devices. Although design
and materials vary, most bottom aerators incorporate the same principle;
releasing compressed air or oxygen through a diffuser located near the
bottom of the pond (use of pure oxygen is not usually practical or necessary
in most pond situations). The greatest advantage of bottom aeration over
other types is that the positioning of the aerator allows for the
oxygenation of the entire water column. As the bubble plume rises through
the water column, it also moves a column of water with it. This water
movement disrupts the stratification and creates uniform oxygen
concentrations throughout the pond. In addition, bottom aerators operate
efficiently, present few safety hazards, and pose little concern for water
The critical difference between bottom aerators arises from the type of
diffuser used. Much emphasis is placed on the efficiency at which oxygen
from the air bubbles diffuses into the water column. Although an important
consideration in some aquatic applications, it is not a great concern for
pond management. However, it is important to note that
smaller diameter bubbles produce better oxygen diffusion, but more
importantly, move a greater volume of water within the bubble plume. By
maximizing water circulation within the pond, the oxygen that diffuses into
the upper layer of the pond from the atmosphere and from photosynthesis,
gets mixed with the anaerobic waters in the hypolimnion. The result is a
uniformly aerated pond that is operating efficiently and is aesthetically
Proper aeration can make considerable improvements in a pond ecosystem.
By circulating water within the pond, stratification is eliminated and
dissolved oxygen levels rebound. Higher oxygen levels yield greater biotic
growth, including fish growth. However, aeration is just one of the tools
needed for holistic pond management. To maintain a balanced ecosystem,
other tools including beneficial microbes and physical removal need to be
used in conjunction with aeration. Implementing this multi-faceted
approach allows managers to work with Mother Nature to meet their goals.