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Lake Tips: Aquatic Plant Management - Part II
Controlling Nuisance Vegetation
Best management practices (BMPs), such as conservation tillage, grassed waterways, filter strips, sediment control/retention basins, grade stabilization structures, and many others, can be used to prevent sediments from entering the lake.
Local ordinances may be considered that restrict tree and vegetation removal or limit boating in certain areas of the lake where nutrients could be stirred up.
Educational programs about proper lawn care and fertilization also can help generate interest, and remind landowners that excessive nutrient inputs can negatively impact the lake, as well as property values, recreational opportunities and irrigational uses.
Here is a list of common in-lake techniques that have been used (with varying degrees of success) for plant and algae removal:
Herbicides that kill targeted species of nuisance aquatic plant growths have been successfully applied in lakes, particularly those with exotic plant infestations. Due to societal concerns regarding the use of chemical agents in the environment, all cost-effective and efficient alternatives to herbicide use also should be considered.
Mechanical harvesters are used to mow and remove aquatic plants from the lake. Harvesters are labor intensive and cannot be used in shallow areas where stumps or other obstacles are present. Harvesters may help promote the spread of some plants able to reproduce from plant fragments broken off and left in the lake. They may also remove small fish along with plants. Hand cutting and removing aquatic plants, using scuba gear, with other control techniques has been applied in some limited plant growth areas.
Dredging for the purpose of aquatic plant management is most effective in targeted areas where increasing water depth and nutrient-rich sediments are limiting plant growth. Removing sediments will create a major disruption throughout the lake systems and can become a particular problem when heavy metals or other toxins are present in the spoils.
Drawdown of lake water levels exposes plants to freezing and drying conditions, and is obviously more applicable in reservoirs and lakes with water level control structures. Some aquatic plants are not affected by drying, so it is important to understand the biology of the plant species present in your lake. Lake-level drawdowns usually are conducted for some other purpose, such as dam repairs or fisheries management, and coordination with all lake users is important.
Biocontrols or biological controls means introducing an organism into an ecosystem for the purpose of controlling a nuisance species. For example, natural predator of a nuisance exotic species is introduced into the ecosystem to control the nuisance. Know your predator and any possible side effects to the ecosystem. An ideal balance at a non-nuisance level between the predator and nuisance species is the theoretical target. Grass carp are an example of biological control. These plant-eating fish have been used with success in several southern lakes. They can cause problems by eradicating all plants, not just nuisance species. Loss of fish habitat and introduction of nutrients into the water column often limit the use of grass carp to golf course ponds or other single-use ponds, where ecological balance is not a priority.
Sediment covers form a barrier to prevent plant growth, and usually are used in swimming or boat access areas. These barriers should be gas permeable, and carefully secured to the lake bottom to prevent them from breaking up and posing a problem to swimmers, wildlife and boat propellers.
Aluminum sulfate (Alum) treatments are perhaps the method used most often used to alleviate algal blooms. Alum is applied to the lake surface, where it bonds with phosphorus and settles into the lake sediments. This is not an effective method for controlling rooted vegetation, since plants will continue to use the phosphorus available in the soil.
Aeration or destratification alters nutrient and gas concentration in a lake to decrease algae growth. A thorough understanding of the chemistry and circulation of a lake is necessary for the successful application of these techniques.
Other techniques for reducing algal blooms include adding liquid dyes to reduce sunlight needed for algae growth, using algaecides (copper sulfate), introducing biocontrols (algae-eating zooplankton or fish), physically removing algae, applying calcium compounds, and removing or aerating oxygen-depleted bottom sediments to prevent phosphorus release into the water column.
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