Aeration has a number of benefits for dugouts and ponds.
- It helps prevent taste and odour problems by ensuring that oxygen concentrations remain high enough throughout the entire water column to prevent conditions of little or no oxygen (anaerobic).
- It also helps prevent the release of phosphorus from sediments. This limits algae growth and reduces the amount of plant material present to ultimately die and decompose.
- It prevents the release of iron from the sediments and the problems associated with high iron concentrations such as damage to water treatment systems, water distribution systems and drip irrigation systems.
Artificial aeration augments the natural process of oxygen replacement. This is accomplished by injecting air into the deepest part of the dugout producing a non-turbulent mixing action; lifting the oxygen-depleted water from the bottom to the top to circulate with the oxygenated water.
How anaerobic conditions happen
In the summer, warm temperatures produce very high levels of biological activity, resulting in increased oxygen demands. The rate of oxygen diffusion cannot keep up with the rate of oxygen consumption. This results in the quick depletion of oxygen levels in the water. This occurs most frequently when warm temperatures produce very high levels of biological activity which can very rapidly consume the oxygen.
This is the most common cause of summer fish kills in dugouts and lakes.
In the winter, once ice forms on a dugout it seals the surface and prevents very little new oxygen from diffusing into the water. Under these sealed conditions, algae decay quickly consuming any available oxygen.
Once oxygen levels become low, anaerobic organisms take over the decomposition process resulting in the release of unpleasant smelling gases such as methane and hydrogen sulfide.
The absence of oxygen in the water also allows plant nutrients (nitrogen, phosphorus) and metals (iron, manganese) trapped in the dugout sediment to dissolve into the water. A layer of poor quality water that is high in nutrients and metals begins to form at the bottom of dugout. As long as anaerobic conditions exist, the amount of poor quality water grows quickly and moves upward.
In the summer, anaerobic conditions may go undetected if water intake is near the surface of the water. However water conditions near the bottom of the dugout may be anaerobic. In the winter, anaerobic conditions are present when the water turns black (may be caused by dissolved iron, manganese and other dissolved or decomposed material) and has a rotten egg smell (caused by hydrogen sulfide gas).
| Parameter (milligram per litre, mg/L) | Aerated | Non-aerated |
|---|---|---|
| Dissolved oxygen | 14.3 | 0.4 |
| Iron | 0.04 | 1.5 |
| Phosphorus | 0.05 | 0.15 |
For quality water year-round
Continuous year round aeration produces the best water quality. In fact, data indicates that water quality continues to improve for up to five years after a continually operating aeration system is installed in a dugout.
Dugout aeration helps cycle oxygen and nutrients, improving water quality in reservoirs throughout the year.
Summer
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Aerated
- The sun heats the surface water, but the aeration system and the wind keep the dugout well mixed, oxygen (O2) levels high, and the temperature uniform.
- A small supply of plant nutrients limits algae growth floating on the water’s surface, allowing the light to reach the bottom of the dugout. This encourages the growth of rooted weeds at the bottom.
- A small amount of algae eventually dies and falls to the bottom of the dugout where it decomposes and consumes oxygen. However, the aeration system keeps oxygen concentrations high and the dugout well mixed.
- Water quality remains good.
Unaerated
- The sun heats the surface water which floats on top of the colder, deeper water. This reduces the ability of the wind to mix the water at the bottom of the dugout, limiting the mixing to the top few feet.
- Conditions are suitable for algae growth. Surface algae bloom becomes thick, preventing light from reaching the bottom of the dugout. Rooted weed growth is limited to the edges of the dugout.
- Green algae consume all of the available nitrogen, die and fall to the bottom of the dugout where they decompose and use up oxygen which is not replaced.
- The absence of oxygen in the water allows plant nutrients (such as, nitrogen and phosphorus) and metals (such as, iron and manganese) that were trapped in the sediment to dissolve into the water. Hydrogen sulfide forms and produces a "rotten egg" smell.
- Water quality deteriorates at the bottom.
Fall
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Aerated
- As the water temperature cools, the algae die and fall to the bottom of the dugout.
- The aeration system and wind continue to maintain high concentrations of oxygen (O2) throughout the dugout.
- The algae decompose in a well-oxygenated environment.
- Water quality remains good.
Unaerated
- The surface water temperature cools, creating a uniform temperature throughout the dugout.
- The algae die and fall to the bottom, consuming oxygen while decomposing at the bottom of the dugout.
- The uniform temperature allows the wind to mix the waters, increasing oxygen concentrations throughout the dugout and temporarily improving water quality.
Winter
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Aerated
- The circulating water carries oxygen (O2) to the bottom of the dugout. Oxygen is supplied by the aeration system and the atmosphere. Dead organic material decays aerobically at the bottom of the dugout.
- Water quality remains good.
Unaerated
- Very little oxygen diffuses through the surface ice. Water quality near the surface remains good.
- At the bottom, algae decay quickly consumes the available oxygen and becomes anaerobic. Water quality deteriorates at the bottom of the dugout.
- Nutrients (such as nitrogen and phosphorus) and metals (such as, iron and manganese) move from the sediment and into the water
- Hydrogen sulfide (H2S) forms and produces a "rotten egg" smell.
- Water quality continues to deteriorate. The poor quality water at the bottom quickly grows and moves upwards, spreading through the dugout.
Spring
Description of the above image
Aerated
- Dugout water becomes a constant temperature as the heat of the sun melts the ice.
- Oxygen diffuses into the water from the atmosphere and is carried to the bottom of the dugout by the circulating water.
- Nutrients and minerals (such as, nitrogen, phosphorus, iron and manganese) remain trapped in the sediment.
Unaerated
- Dugout water becomes a constant temperature as the heat of the sun melts the ice.
- Wind blowing over the dugout surface causes the turnover of the water, mixing poor quality water throughout the dugout.
- Nutrients released from the sediment rise to the surface.
- The smell of hydrogen sulfide (H2S), which started to form in the winter, continues to grow.
Related links
- Powering an aeration system
- Components and installation of an aeration system
- Ponds and dugouts
- Farm surface water management