Aeration As A Lake And Pond Managment Tool
Aeration As a Pond & Lake Management Tool:
The most important water quality parameter for lakes and ponds is dissolved oxygen. Oxygen is essential to the metabolism of all aerobic (air breathing), aquatic organisms. Oxygen is measured in parts per million (ppm). 5 ppm is like a drop of food coloring in a 55 gallon drum. 5 ppm is what I'll term as the threshold to support a healthy aquatic eco-system. Here are some basics about dissolved oxygen in fresh water:
The air we breathe is 20.9% dissolved oxygen, the rest is essentially nitrogen.
Oxygen concentration is temperature dependent. Warmer water holds less oxygen. And it is in warmer months when metabolic activity is the greatest in ponds when oxygen demand is typically greatest. Heat is also the reason more oxygen related fish kills are likely to occur during the dog days of summer.
Oxygen is affected by: initial dissolved oxygen levels, barometric pressure, water temperature, water purity and elevation. In nature, oxygen is produced in water by: a) Wind action. b) Diffusion at the air water interface. c) Photosynthesis from aquatic plants. Oxygen levels in your pond's water typically fluctuate throughout the day. During clear, bright days plants utilize the sun's energy to produce oxygen so that peak oxygen levels occur in late afternoon. Typically, the weather tends to be
breezier during the mid-day so oxygen exchange at the water's surface is also greater. As the sun sets, the winds tend to calm. The same plants that were just producing oxygen reverse themselves and are now consuming it. Typically, in the early morning hours just as the sun rises, oxygen levels will be at their lowest point of the day. Without oxygen present or with minimal oxygen:
Ponds and lakes can stratify (layer). The organic muck layers on the bottom degrade much more slowly. Phosphorous can stay in solution making it readily available for plant growth. Oxygen breathing — sediment consuming organisms such as bacteria can be stressed and die. Conditions become favorable for the formulation of harmful gases such as ammonia, hydrogen sulfide and carbon dioxide. The effective living space for fish and many of their food choices is reduced. Lakes and ponds which contain a large volume of cold, "bad" bottom water are candidates for an unwanted "turnover".
During late spring, summer and early fall many lakes become stratified. This is the horizontal layering of water with warmer water at the surface and cooler water at the bottom. Because cold water is denser than warm water, a natural density barrier exists that restricts water movement between the layers. Since most oxygen is produced or enters the water in the top layer it is unable to mix with the colder bottom layer. When these stratified conditions to an extreme state a couple
things can happen. A summer storm occurrence which is typically preceded by several days of calm, cloudy days could cause a pond or lake to turnover. Those calm cloudy days have reduced sunlight which influences oxygen production from plants. Dissolved oxygen levels in the water tend to drop. Heavy wind action coupled with colder rainwater deepens the possibility of being strong enough and cool enough to mix the entire body of water and cause a fish kill. When the cold stagnant bottom layer mixes with the healthy warm water on top, the bottom water absorbs much of the oxygen while releasing its harmful gasses. The consequence of this event is a rapid fish kill. In fall as water surface temperature drops naturally, it will eventually equal the same temperature as the bottom water. Once the temperatures are equal there will no longer be density barrier which will allow the whole lake or pond to mix. If the bottom was extremely stratified a fish kill could result just as described above.
So what is a person to do to prevent a fish kill due to low or no oxygen conditions? If you fertilize your pond or lake, do so carefully as to not cause to strong of a "bloom." Specifically, blue-green algae are more susceptible to die offs than more stable green algae. Manage your pond for secchi-disc reading of 24" or greater. Managed algae have a dramatic effect on fish as well as water quality and plant species composition. Some people prefer clear water in which they can see all the way to the bottom. Clear water is better for a swimming hole than a fishery. Fertilizing correctly results in a more productive pond in terms of carrying capacity expressed in pounds of fish per acre. Keep in mind certain species of blue-green algae can add to fish "off-flavor" if you are thinking of eating what you catch.
Create a berm and swale around the bank to allow water to be filtered through the soil prior to entering your pond. Try to encourage native vegetation around the perimeter of your pond to assist filtering incoming water. Rooted plants are more stable than algae. Algae come in two forms. Planktonic (microscopic) algae that tint the water green and Filamentous algae which, are typically referred to as "moss" or "horsehair." Rooted plants are more stable as they won't die off as fast as algae on cloudy days.
If you use grass carp for rooted aquatic plant control, be careful to not stock too many. Grass carp preferred choices of meals are higher order vascular plants. If stocked too heavily these exotic vegetarians eliminate all vegetation cover in a pond. Those nutrients are then released back into the water column, increasing the fertility and leading to a pea green soup of planktonic algae. Grass carp won't eat planktonic algae. Stocking rates vary by the amount of vegetation and type found in you pond as well as length of growing season. Rate from 3-30 fish per acre have been used successfully but depend on many variables. Ask for help on this one. Do not overfeed your fish with fish food. Use a floating extruded feed. Extruded feed has been researched to give your fish the greatest cost per unit gain. It is the most digestible (hence little waste to cause oxygen demand). Extruded feed floats on water's surface. Don't feed more than fish consume within five minutes. Uneaten feed drops to the bottom and adds to the oxygen demand of the system.
Supplement natural occurring oxygen with an aeration system of some type. There are several types of aeration systems that add oxygen to ponds. No single one of them is going to work for every type of lake or pond. Each pond/lake must be viewed as its own individual living system and aeration needs are determined based on the site specific parameters for the body of the water and the goals of the pond owner. With a properly designed aeration system you can expect:
- Greater densities of this can be achieved
- Spring and fall turnovers can be eliminated
- Winter-kills can be prevented in the northern Unites States and waterfowl can be protected from bird eating predators
- Water quality can be improved
- Organic muck decomposition on the bottom can be accelerated
- The body of water can be chemically and thermally de-stratified
- Circulation currents create more favorable conditions for desirable algae to out-compete blue greens. Algae blooms and die offs should be less severe
- Oxygen insurance for fish you have invested time and money on
For pondmeisters in the Northern part of North America I would be remiss for not mentioning using aeration to prevent winterkill. A combination of thick ice, heavy snow and high concentration of decaying plants under the ice is a recipe for fish kills in shallow lakes and ponds. Heavy ice and snow cover do not allow sunlight to penetrate water to any significant depth. As a result there is little or no photosynthetic activity to produce oxygen. If this condition is severe enough a fish kill could result because oxygen is used up by decaying plants as well as the living creatures. One solution is to install some type of aerator/circulator that creates a small opening at the surface to allow oxygen to absorb into the water. Colder water holds more oxygen and metabolic activity is at the yearly low so only a small hole is required. An area of about 3% of the surface should be should be fine. Do not splash the water because that will cool the water and actually thicken the ice.
Article By: Bob Robinson (Fisheries Biologist) Kasco Marine, Inc. Reproduction of this article is prohibited without written consent.