The most important factor
in ensuring the success of a large pond or lake is proper aeration. Dissolved oxygen is a critical component
in the ecology of a pond. It is
what makes the pond go and what keeps the inhabitants healthy and keeps the
water clean. This article will discuss the consequences of poor aeration and low
dissolved oxygen levels and the numerous benefits of proper pond aeration and
healthy dissolved oxygen levels.
To be
technical, dissolved oxygen is gaseous oxygen dissolved in an aqueous solution.
So basically it is the amount of oxygen available in the pond water. Generally speaking 5 ppm is the baseline
for what is good for a pond or lake.
Anything below that can lead to problems.
So what
are these problems associated with low dissolved oxygen and what causes them?
The most critical problem associated with low oxygen levels is a fish kill. Fish require a certain ppm of dissolved
oxygen to live and without it…well, they die. Poor oxygen levels can also lead to
noxious odors coming from the pond as the break down of organic waste will shift
from an aerobic process to a slower anaerobic process that results in the
production of hydrogen sulfide. Also, in the case of deeper ponds, the lack of
oxygen will lead to stratification meaning there becomes a layer at the bottom
of the pond that becomes un-usable as it is extremely oxygen deficient. This in turn reduces the available
living space of the fish, placing more strain on the still oxygenated
water
The
issues that cause oxygen levels to become low are numerous. Probably the most common is an over
abundance of aquatic plants, particularly algae. Aquatic plants are good in
moderation as they do release oxygen into the water. In the case of algae, planktonic algae
make up the base of the food chain in a pond and are therefore critical. However, many of these plants that
release oxygen during the day, also consume oxygen at night. So when you have a pond with a heavy
algal bloom or thick aquatic vegetation, oxygen can be rapidly consumed
overnight and even on cloudy days, causing a fish kill.
Other
factors that contribute to poor dissolved oxygen levels and the need for pond
aeration is a high organic waste load.
Organic waste in a pond can come from a variety of sources including dead
vegetation, fertilizer run-off, fish food and fish waste. All of those examples are naturally
broken down in a pond, but to do so efficiently and without further detriment to
the water quality, oxygen is needed.
So when you have a high waste load to be degraded, you will require a
large amount of oxygen to do so.
So, by
now you may be concerned that these issues could affect your pond and you want
to prevent them from happening, but are not sure how to select pond aeration
system.
True,
there are varying types of pond aerators
to choose from, but to keep things simple, you basically have two types of
aeration systems: surface aeration and bottom based aeration. A good rule of thumb for figuring out
which one would be best is to use the average depth of your pond as a
barometer. If your pond is less
than 6 feet deep, than a surface aeration system will probably work well, while
deeper ponds will benefit more from a bottom based aeration system.
What is
the difference between the two you may be wondering. Surface aerators are generally floating
aeration units that pull in water from the top foot or so of the pond and splash
it into the air. As the water
crashes back down onto the pond, oxygen transfer takes place as well as the
venting of gases. Because the oxygen transfer is taking place just at the
surface, these aeration systems or best suited for shallower ponds. Surface
aeration units can also be equipped with different spray patterns for more
aesthetic appeal, however the more extravagant the spray, usually the less
efficient it is at aerating.
Bottom
based aeration systems or diffused aeration involves pushing air down to the
bottom of a pond or lake and allowing the bubbles to naturally rise to the
surface. These aeration units are
the most efficient for aerating deeper pond and lakes as the bubbles are
providing the bulk of the work. However,
diffuser systems can be used in shallower ponds, but in those cases more units
will be needed and installed evenly throughout the pond, thus adding more cost
into the system. As
the bubbles rise, they destratify the water eliminating the oxygen poor zone at
the bottom and mixing it with the oxygen rich water above creating a healthier
water column. These systems also create very little surface agitation other than
a gentle rolling action therefore providing no aesthetic appeal.
It is
important to note that unless you have a very round even depth pond, you should
look for assistance in sizing a proper aeration unit to meet the needs of your
pond. Having an undersized aeration
system can actually lead to problems instead of helping them.
Now you
have a properly sized pond aeration system. What can you expect now? The benefits to expect from a good
aeration systems are numerous.
- Fish kills(due to low oxygen) can be prevented
- Beneficial
pond bacteria is stimulated to efficiently break down waste and reduce the
bottom muck layer. Aerobic
bacteria will out proliferate problematic anaerobic bacteria to control
odors
- Key nutrients such as phosphates are rendered unavailable
and metals like iron are precipitated out
- Algae blooms will be less severe and less problematic due to
the lack of available nutrients
- Pond water is destratified leading to the prevention of
turnovers and improved overall water quality
- Gasses such as carbon dioxide and hydrogen sulfide can be
vented
- The need for maintenance products are reduced to the ponds
naturally ability to regulate itself.
- In the case of northern states, aeration systems will also
help prevent winter fish kills be preventing the pond’s surface from freezing
over and allowing the venting of gasses.
Pond
aeration systems can be a significant financial investment, depending upon the
size of the pond being aerated.
However the costs associated with monthly water treatments, regular
maintenance and the constant worrying about the quality of water are far greater
than the long term benefits and peace of mind associated with a good aeration
system.
