A Breath of Fresh Aeration
By Steve Carbol, Lake & Wetland Management Senior Biologist
How Pond & Lake Aeration Systems Work
Simply, aerators are machines that circulate water in lakes and ponds. Aerator models have been developed to work in and benefit various levels of lakes and ponds and function in different ways.
Surface aerators, as their name implies, function in the upper layers of a water body to agitate and circulate water mostly near the water’s surface. A pump takes in water in the lake’s upper strata and spouts it out in a bell- or mushroom-shape at the surface, refreshing and pushing the pumped water out and away from the unit. These types of aerators operate in a fashion rather similar to a fountain except that with surface aerators the emphasis is in moving the water out and away from the unit rather than upward for aesthetic purposes.
Submersed Diffused Aerators
Submersed diffused aerators operate in the lower levels of a water body, typically just above the lake bottom, and pump air down from the surface to plates that break the airstream up into tiny diffuse bubbles that dissolve in the water column, charging it with dissolved oxygen, and also rise to push the surrounding water vertically toward the surface.
The effect of a submersed diffused aerator on a pond is somewhat like that of an Alka-Seltzer on a glass of water into which it’s been dropped. The mechanics are wildly different, of course, but in both instances, effervescent bubbles are released into the bottom of a water column to rise to the top for beneficial purposes.
Why Do You Aerate a Lake or Pond?
Lake and Pond Aerators are an effective strategy to remedy a laundry list of problems faced by troubled waterways. One of the most common issues faced by water bodies is thermal stratification, a condition in which the water in a basin separates into layers or zones of markedly different temperatures, with the warmest water at the surface and the coolest in the deepest part of the basin. This typically happens from late spring to late autumn when the upper water layers (known as the epilimnion), constantly mixed by surface wind and waves, are warmed by longer, hotter days with plentiful sunlight.
Meanwhile, deep down in the lower levels of the basin (the hypolimnion), untouched by wind and at such depths that the sun only weakly penetrates (or doesn’t at all), the water remains cool, dense, and unmixed. This lowest zone is often hypoxic, exhibiting very low levels of dissolved oxygen and noxious gasses produced by slowly decomposing benthic sludge. As a result, the hypolimnion is home to very little life.
These two drastically different zones are separated by a thin middle layer characterized by a steep gradient in temperature. This middle layer (the metalimnion) acts as a barrier, effectively preventing the mixing and exchange of heat and oxygen between the epilimnion zone above and the hypolimnion below.
During seasonal atmospheric temperature fluctuations, such as when autumn passes into winter and the days become cooler, the upper zone cools as well. As the upper and middle zone temperatures drop and more closely match the temperature of the deep hypolimnion zone, the sharp demarcation between the layers begins to blur, the layers become more homogeneous, and they begin to mix.
When this phenomena occurs, that deep, hypoxic, oxygen-starved bottom water begins to move upward and spread throughout the basin, resulting in what’s known in the lake industry as a pond turnover.
How Pond Turnover Affects Aquatic Life
A turnover can pose some deleterious problems for aquatic life in the pond. In addition to having to contend with the seasonal temperature drop, fish and other aquatic creatures must also survive the low-oxygen conditions that result from the hypolimnion dispersing through the water column. These conditions can culminate in fish kills, sometimes affecting thousands of individual fish at a time. In Florida, some of the fish species most susceptible to lake turnover include:
- American Gizzard Shad (Dorosoma cepedianum)
- Florida’s State Freshwater Fish
- The Largemouth Bass (Micropterus salmoides)
American Gizzard Shad (Dorosoma cepedianum)
The American Gizzard Shad is a very important part of the food chain and can often be the most abundant fish species in some large systems. A close relative of the familiar herring and sardine, the flashy, metallic silver American Hickory Shad swims in large schools, feeds largely on plankton, and can grow up to 18.8 inches and 3.4 pounds. Despite its abundance, decent size, and bright silver scales, pond owners may never see shad in their system until a pond turnover and resulting fish kill occurs. This is because shad live out in the open water in the middle of lakes where schools have plenty of room to ceaselessly cruise for plankton.
The Largemouth Bass (Micropterus salmoides)
Not quite as susceptible to turnover as shad, the Largemouth Bass may still often perish in significant numbers during a turnover event. This can result in a decidedly large loss of investment for some lake owners, as the Largemouth is one of the most intensively stocked and managed gamefish the world over. In addition to simply losing the fish and monetary investment in a turnover event, there’s the resulting fallout to contend with.
The abundance of fish corpses can create an unsanitary silver-white drift along a lake’s shoreline. And if not collected and removed quickly, there’s the overpowering, foul stench of all those piscine corpses decomposing along the shoreline that often attract legions of vultures, storks, ibis, egrets, and other wildlife that take advantage of the sudden abundance of food.
How to Prevent Pond Turnover
The installation of an aeration system into a lake can help prevent the water from thermally stratifying by constantly circulating, aerating, and blending the water so that thermally distinct zones do not form. If water doesn’t stratify, it can’t turnover, saving the lake’s fish community and the owner’s investment. Beyond preventing catastrophic turnovers, aerators help to oxygenate stagnant, nutrient-laden water, creating a healthier environment for fish and other aquatic life as well as cutting down on harmful, explosive toxic algal blooms, noxious gasses created by benthic bacteria, and any resulting offensive odors.
Further, when coupled with the application of sludge-reducers and beneficial bacteria, aerators can be even more effective in improving water quality and breaking down accumulated unwanted benthic nutrient stores.
Contacting Lake & Pond Professionals
Lake & Wetland Management offers complimentary site surveys and proposals to best tailor the style and size of our aerator systems to the needs and dimensions of your water body. Call today for your free survey and to treat your lake to a fresh, healthy breath of fresh aeration.
For the best lake and pond fountains and aeration service, contact Lake and Wetland.