Key takeaways for pond aeration
Aerating stormwater ponds provides:
- Oxygenation of the water.
- Air movement throughout the water column creates circulation that eliminates and prevents water stratification the leading cause of fish kills.
- Nutrient management by balancing the trophic state and reducing nutrients available to algae and aquatic weeds.
- Diffused aeration that circulates the pond assists with managing nutrients in the water and prevents the harmful effects of stagnant water.
Diffused aeration systems are the most efficient way to circulate the water. Similar to an aquarium, an air compressor pumps air to the bottom of the pond and the diffusers break the air into micro-bubbles. As the bubbles rise, they expand and create a current that lifts bottom water to the surface.
Surface fountains are the least efficient way to aerate ponds, and they do not eliminate stratification. Fountains are floating devices that draw surface water using a shallow pump and spray the water above the surface. Fountains circulate water that is already oxygenated and do not break up the stratified layers in the water. Fountain pumps are inclined to clog with vegetation, require frequent maintenance, and have high electricity costs.
- The only way to prevent chronic algae regrowth is to reduce nutrients washing into the pond. Chemical herbicides provide only temporary control of algae blooms and require circulation and aeration to prevent fish kills when the algae die.
- Homeowners should tolerate some algae in the warmer months. Some amount of algae in stormwater ponds helps capture nutrients and contaminants from polluting downstream waters.
- Large algae mats that cover more than 20% of the surface limit the oxygen transfer from the atmosphere and lead to fish kills. They also contribute to stagnation and noxious odors, clogged outfalls, and localized flooding.
Homeowners and HOAs, to prevent and control algae blooms:
- Don’t over-fertilize lawns—soil test first.
- Don’t apply fertilizers to roads, driveways, and sidewalks. Instead, sweep or blow fertilizers off impervious surfaces to prevent washing into storm drains.
- Don’t fertilize bank slopes of ponds.
- Clean up yard waste and lawn clippings to prevent them from entering storm drains.
- Wash cars on lawns using phosphorus-free soap.
- Don’t feed the wildlife. Creatures turn food into fertilizer!
- Pick up after your pets.
- Plant location-appropriate wetland plants along the shoreline to filter runoff and absorb nutrients.
- Add a circulation and aeration system to increase oxygen in ponds.
- Consider aquatic dyes to shade the water and suppress algae growth.
Submerged Aquatic Plants
- Stormwater ponds are susceptible to submersed plant growth because, due to their shallow nature, sunlight can reach the bottom. They are also subject to repeated nutrient inputs from lawn and roadway runoff with each rain event. The combination of nutrients, shallow water, and sunlight makes stormwater basins susceptible to submerged vegetation.
- Submerged plants are beneficial and provide oxygenation of the water, shelter for wildlife, and absorption of nutrients and pollutants.
- Submerged vegetation should be limited to the littoral zone and should not cover more than 20% of the pond.
- An excessive amount of submerged plants can impede circulation and reduce pollution-mitigating benefits, block inlets and outlets, cause noxious odors and fish kills from vegetative decay and low oxygen and increased sediment that accelerates the pond’s dredging requirements.
Homeowners and HOAs should employ an integrated approach to weed management:
- Consider using Triploid Grass Carp (LINNE Industries note: This solution is controversial and highly jurisdictional. The use will likely require a permit and may not be allowed in stormwater basins. Consult your state and local authorities before considering this option.)
- Perform manual and mechanical harvesting.
- Use aquatic dyes to shade plants and reduce the growth rate. Unfortunately, this solution requires early spring application and repeated applications throughout the growing season. This may not be a viable solution if your pond is regularly flushed during rain events. Dyes will not work for shallow ponds.
- Use a licensed applicator for submerged plants requiring chemical treatment.
- Educate your residents.
- Many invasive plants are introduced by residents tossing aquarium and water garden plants into ponds. Prevent introduction by properly disposing of unwanted hobbies.
- Nutrients from daily activities can contribute to plant growth. (Reduce fertilizer applications and avoid fertilizers on roads, driveways, and sidewalks. Sweep or blow fertilizers off impervious surfaces to prevent washing into storm drains. Pick up pet waste and don’t feed ducks, fish, and turtles.)
Although floating plants may be attractive, they are not appropriate for stormwater ponds and can cause serious problems. Stormwater ponds are designed to manage water runoff to prevent flooding and limit movement of pollutants to rivers and beaches. Free-floating plants are highly mobile and can clog outfalls. This can prevent water from flowing out of the pond and cause flooding around the pond. Submerged- floating plant leaves impede the flow of water through the pond and can cause areas of accumulated sediment and stagnancy. With stagnation, the pond’s ability to trap and treat pollution is impaired and raises the risk of pollution being discharged to downstream waters. All floating plants can create a barrier to the surface to atmosphere oxygen exchange that will lead to low dissolved oxygen and increase the potential for fish kills.