Keep your pond pristine with aeration
If you have a pond, or if you are considering installing one, proper aeration will alleviate most problems before they begin. Ponds and lakes are beautiful and soothing but, if not properly maintained, they quickly can turn on you. Proactive approaches to water-quality management are your best bet.
A pond's lifecycle Natural forces of succession constantly try to transform your pond back to land. A pond in pristine condition is said to be in its oligotrophic state, which means that it has low nutrient levels (nitrogen, phosphorus and potassium) and the dissolved oxygen is relatively high.
As nutrient-laden runoff enters your pond from surrounding areas, aquatic plant matter decomposes and tree leaves or other organic debris enter the pond and decompose; thus water's nutrient level begins to rise. Green algae responds to the increased nutrient levels and they begin to proliferate. Blue-green algae begin to grow on the water surface. Acceptable levels of dissolved oxygen still remain in the pond. Now your pond is in a mesotrophic state.
As the green algae continue to bloom they eventually block sunlight to aquatic plants on the bottom. These plants and algae die, robbing oxygen from the water to fuel the decomposition process. The decomposed matter adds even more nutrients to the water and sludge builds up on the bottom. These conditions stimulate blue-green algae to flourish. Your pond now looks like pea soup and is said to be in a eutrophic state, characterized by low-dissolved oxygen and high nutrient levels in the water.
The benefits of oxygen Aerobic bacteria use oxygen to cleanse ponds and lakes of excess nutrients and require oxygen for life. Oxygen supports the process of aerobic digestion, which lowers the available nutrients for algae and weed growth while helping to retard the growth of (or even reduce) the sludge bed. Your goal is to add as much oxygen to the water as you can to promote aerobic bacteria. Aeration, viewed as a "holistic" approach, supports the natural ecosystem of your pond. The ecosystem relies on oxygen for the health and growth of all its components. Thus, the addition of more oxygen does not cause ill effects on desirable plant life.
Aeration accomplishes this goal as it adds oxygen to water. Waterfalls and certain types of fountains are helpful, but they do not have sufficient mixing and aeration capabilities to be used as stand-alone tools. Therefore, you must use supplemental aeration.
Aeration systems Three types of mechanical-aeration systems are available: surface sprays, horizontal aspirators and bottom diffusers. Several non-mechanical aerators also are on the market. However, these units typically are not tested for oxygen-transfer rates; therefore, their efficiency is not well defined.
* Surface-spray aerators are the best choice when the basin is less than 12 feet deep or irregularly shaped. You can adjust the surface spray in different styles or patterns. Because surface-spray aerators shoot water into the air, they create soothing sounds via splashing and bubbling and resemble fountains (see photo, page C 6).
* Horizontal aspirators, which create strong currents and are available as submerged or floating units, have a directional flow. When you want to avoid surface spray, for long, narrow bodies of water or canals, horizontal aspirators are the best choice (see top and middle photo, below).
* Bottom-diffused aeration is effective in water over 12 feet in depth. This system consists of an air compressor (typically mounted on the shore) and one or more air diffusers that lie on the pond floor. The diffusers connect to the air compressor via weighted tubing to minimize visibility. The air bubbles rise to the surface, transfering oxygen into the water (see bottom photo below).
Bottom-diffused aeration systems require a minimum depth of 12 feet for peak operation. Studies indicate that for every 3-foot decrease in depth, the system's relative efficiencies drop 50 percent. They are ineffective in less than 8 feet of water and you must never use them in less than 5 feet of water. Because bottom-diffused systems typically involve no electricity or mechanical parts in the body of water, they are the safest of the three types of aerators for ponds where swimmers and their pets may play.
These systems' pumping rates and oxygen-transfer rates vary. Manufacturers have these specifications readily available and are happy to share them with you.
Aeration-system safety Safety is a major concern when you decide to install a water-aeration system. Systems must be tested for safety and approved as a complete package (unit, electrical-power center and cable) by a certified-testing laboratory. Such labs include: Electrical Testing Lab (ETL), Electrical Testing Lab-Canada (ETL-C), Communities of Europe (CE), Underwriter's Laboratory (UL) or Canadian Standards Association (CSA). These laboratories, recognized worldwide for their product-safety approving methods, affix a stamp or sticker on the products that meet their safety standards. Look for such stamps or stickers before you purchase your system. In addition, if you plan to install an aeration system in a body of water used for recreation, optional ground-fault-circuit interrupters (available from the manufacturer) offer extra protection. These devices detect voltage leaks to a ground and interrupt or "break" the power source, offering protection from electrocution and power surges.
Installation First, you must ensure that your system is durable and easily maneuverable to your site.
After placing and positioning floating aerators in the water, you must anchor them or moor them to the shoreline. You typically place horizontal aspirators in the water (near the shore of the pond) and anchor them from behind. The electrical-power unit is shore-mounted, connected by cables that you bury (trench) in the ground.
Installation requirements for bottom-diffused aeration systems are a little different. You situate the compressor on shore, then strategically place the diffusers on the pond bottom. A line of tubing runs from the air compressor to each of the diffusers. If you opt not to use weighted tubing, you must secure the tubing to a heavy, solid object before connecting it to the diffuser. To aid in the removal of these units, you may want to run an additional tubing line to the surface of the water during installation and anchor it to the shore. You then can use it to pull the diffuser to shore.
Operating times Operating times vary according to the climate and the severity of water-quality problems. General guidelines for surface and sub-surface aerators in moderate climates are to operate the unit for 12 hours a day during the spring, summer and fall, and remove the unit during winter. Bottom-diffused systems can operate 24 hours a day all year.
Servicing To remove the unit for servicing or at the end of a season, simply use the mooring or anchor line to bring the unit to shore and then remove it from the water. As mentioned above, an additional tubing line acts as a pulley for removal of the diffusers.
Final determinants Aeration naturally supports the ecosystem of a pond, and when you use it as a preventive tool, it can deter many of the problems that plague unmanaged bodies of water. Have a qualified specialist determine which system is right for you based on your specific pond. You can contact a pond- and lake-management specialist by looking in the Yellow Pages or by calling a water-aeration manufacturing company. Some manufacturers have worldwide networks of distributors that specialize in this field and offer free on-site evaluations of ponds and lakes.
Heather Schwabe is regional marketing and public-relations manager for Otterbine Barebo Inc. (Emmaus, Pa.).
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