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Aquatic Plant Problems

As nutrient concentration increase, aquatic vegetation growth can become a serious problem in lakes and ponds.

A wide range of aquatic plants can be found growing in, on, and around a body of water. Based upon their various adaptations, some will be found rooted in swiftly flowing streams while others can only survive in placid, stagnant ponds. Within a natural, well-balanced system, these plants provide food and cover for fish, waterfowl, and aquatic invertebrates. They produce oxygen, plus help to stabilize bottom sediments.

Like terrestrial plants, aquatic vegetation requires a carbon source, sunlight, and nutrients. Dissolved carbon dioxide, bicarbonates and carbonates, typically quite abundant in water, provide a source of carbon for the growth and food production process known as photosynthesis. The energy driving this process is derived from sunlight. Therefore, the depth of sunlight penetration will limit the depth to which aquatic plants can grow. At the same time, the amount of nutrients available (mainly nitrogen and phosphorous) will limit the quantity of vegetation which can grow.

Aquatic plants derive their nutrients from the sediment and/or the water column. These nutrients are cycled between the sediment and the water on an annual basis. Adding to this nutrient enrichment of lakes and ponds, a process known as eutrophication, are inputs from external sources. Nutrients and sediments are contributed by man’s agricultural, domestic, and industrial activities through sources such as cropland and feedlot runoff, factory and cannery effluents, domestic waste discharges, construction site erosion, lawn and garden fertilizer runoff, and septic tank leachate. The most noticeable symptom resulting from eutrophication is the development of prolific aquatic plant growth.

The point at which aquatic vegetation becomes a nuisance is closely associated with the primary uses of a body of water. By common usage, all aquatic growth is often clumped under the general heading “weeds”. A “weed” has been defined in various ways, depending upon the “eye of the beholder”. A simple definition is a “plant growing out of place”. A more optimistic view is “a plant whose true value has not been realized”.

For the purposes of this text, an aquatic plant problem is defined as “undesirable plants that grow so profusely as to crowd out more desirable growth or detract in some way from the usefulness, value, and/or appearance of an area”. Therefore, overabundant vegetation that adversely affects aquatic life; impedes industrial, agricultural or domestic water use; interferes with recreational activities and/or destroys economic values, all fall under this definition.

Therefore, overabundant vegetation that adversely affects aquatic life; impedes industrial, agricultural or domestic water use; interferes with recreational activities and/or destroys economic values, all fall under this definition.

Aquatic Plant Control Methods
Waters clogged with aquatic vegetation are usually rendered useless for their intended purposes. Correctional methods are available, but before choosing a technique, consider the following interrelated factors:

1. What is the intended use of the water?
It is usually not necessary to eliminate all of the growth, but rather to control the vegetation which is creating a nuisance. The degree of aquatic plant control is determined by water use.

2. How safe is the method?
This should not only include human hazards, but also the environmental impacts. Seemingly harmless alteration in the aquatic environment can sometimes result in severe ecological damage such as loss of all fish and plant life.

3. How effective is the method?
Various control methods offer varying degrees of effectiveness. Assess how long it will take to obtain control and how long control will last.

4. What method is least costly?
This question must be judged on a long-term basis. Capital investment and labor must be included in these costs. Safety and effectiveness are also factors to be evaluated.

Advantages and Disadvantages of Aquatic Control Techniques

• Physical Removal
Hand harvesting of aquatic vegetation by pulling, raking, cutting or digging can be accomplished in small shoreline areas. Specialized rakes and cutters have been designed to increase efficiency. Neighborhood youth groups might want to designate a lake or pond “clean-up day” as a community project. Be aware, however, that working underwater is a cumbersome and tiring task, and regrowth from seeds and remaining underground plant parts can be expected.

• Mechanical Removal
Specialized mechanical equipment has been developed for both cutting and harvesting (removing) aquatic weed growth. Units range in size from toothed blades which attach to a rowboat up to large harvesters equipped with retrieval and unloading conveyors.

Harvesting facilitates removal of a certain amount of nutrients and organic material from the lake in the form of plant tissue. Unless done intensively, noticeable reduction of nutrient concentrations and sediment build-up will not occur.

Harvesters are sometimes utilized for offshore weed removal, supplementing a chemical treatment program along hard to reach shoreline areas. Another effective approach involves harvesting a week or so prior to chemical treatment. This enhances chemical effectiveness since many plants are quite vulnerable in their active “regrowth” stage.

When harvesting, remove all plant fragments to avoid their re-establishment throughout the lake. Harvesting does have its drawbacks and these must be considered:

  • Initial investment is high plus maintenance is expensive.
  • Mobility and effectiveness are limited around developed shorelines and over uneven bottoms.
  • Hedgerows of weeds, left several feet below the water, can branch out and regrow at greater densities.
  • Several cuttings will be required per season.
  • Fragmented plants can establish themselves in new areas.
  • Harvested weeds should not be left on shore to dry and hauling can be costly since fresh weeds are quite bulky. (NOTE: Gardeners and farmers will sometimes take aquatic weeds and utilize them for mulch materials.)
  • Harvesting is ineffective in removing algae and duckweed.
  • Cutting bars can disturb valuable spawning areas.

• Biological Controls
Plant consumers (herbivores), microbial bio-augmentation (micro-organisms), plant pathogens (diseases) and competitve species are under study as “natural” approaches to controlling noxious vegetation. While some have shown promise, the introduction of exotic organisms carries with it unknown, long-term ecological consequences.

Plant-eating fish, such as the grass carp or white amur (Ctenopharygodon idella Val.), have been stocked in lakes, ponds and canals to consume aquatic vegetation. Although banned in many states, sterile (triploid) stocks may be introduced in some areas. Long-term effects upon native fish and plant populations are still unpredictable. Questions exist on suitable stocking rates, competition with game fish and potential for habitat destruction. Feeding by these fish is initially selective. However, as sources of preferred plants become scarce, feeding will continue on other types of growth. This can lead to the eradication of all rooted vegetation, the habitat required by desired game fish species. Furthermore, the short intestine of these fish results in incomplete digestion of plant materials and rapid recycling of nutrients. Algal blooms, not controlled by these fish, can result.

A dragline equipped with a clam bucket can deepen shoreline areas around ponds. Be sure to remove dredge spoils from the area to prevent them from washing back into the water.

Similarly, Tilapia have been stocked in waters to feed upon algea. These fish are highly successful at reproducing in warm waters and have been known to overpopulate. They are sensitive to cold water and do not survive if water temperatures fall below 50°F(10°C). They are not a preferred sport species and are of questionable quality for food.

Microbial bio-augmentation consists of adding concentrated populations of non-pathogenic, naturally-occurring microorganisms and enzymes to accelerate organic decomposition and to either create or augment an essential component of an ecosystem’s food web. Specially formulated products contain several different microorganisms to degrade complex organic material (bottom “muck”). The byproducts produced (gases) are released to the atmosphere and/or are similiated into the microorganisms biomass. Reductions in soluble nutrients and organic soft sediments have been seen in field trials by applicators. Decreased suspended organic solids may also be affected. It is necessary to note that reduction of incoming nutrients through proper watershed management practices and installation of sufficient aeration systems are necessary for the overall success of microbial bio-augmentation. Without reducing incoming nutrients, addition of microorganisms will have minimal impact. Many of the microorganisms currently available have cultures that will only function efficiently in aerobic (oxygen present) environments. The use of this method requires careful evaluation of the water body and surrounding terrain as a whole to rectify influences on its ecosystem prior to its implementation.

Insects have been introduced with some success to selectively feed upon aquatic plant populations. Adults and/or larvae of certain moths and weevils, taken from their native areas, have been introduced where exotic plant populations have become established. Some success has been achieved in controlling Water Hyacinth, Eurasian watermilfoil and Alligatorweed. Various agencies and institutions are currently conducting research on native and exotic species to determine their effectiveness and possible impacts on non-target species. Extreme caution must be taken to ensure these insects will not feed upon native plants or agricultural crops.

Competitive plant species, introduced in some areas in an attempt to overtake existing species, has had limited success. Without control over numerous environmental factors, it is difficult, if not impossible, for man to dictate what should grow where within the aquatic environment. “Aquatic gardening”, unlike terrestrial farming, contains too many uncontrolled variables.

Plant diseases or pathogens such as bacteria, viruses, fungi and other microorganisms which infect aquatic plants are being examined as selective control agents. Isolation and culturing of these organisms must be perfected and their effects upon native aquatic plants, terrestrial species and animals must be carefully looked at before they are “seeded” into new environments.

NOTE: State, Federal and International regulations prohibit and/or regulate the transportation and introduction of exotic organisms discussed above. Consult your local authorities.

Drawdown or periodic lowering of water levels to expose bottom sediments, where physically possible, is an effective tool for controlling some aquatic weed species.

• Habitat Manipulation
Drawdown or periodic lowering of water levels to expose bottom sediments, where physically possible, is an effective tool for controlling some aquatic weed species. Desiccation (drying-out) of underwater weeds and compaction of bottom mud results. Freezing of the ground during drawdown will also kill the roots and underground stems of certain aquatic plants. Encroachment by emergent shoreline plants, seed survival, and destruction of fish habitat can present a problem if drawdown is improperly timed.

Dredging has the benefit of removing existing rooted plants and nutrient rich sediments plus increasing water depths. If the bottom is properly contoured, underwater weed growth can be reduced or eliminated. Draglines with clam buckets are used for small pond work. Large hydraulic dredges are employed on large bodies of water. Disposal of spoils presents the biggest problem since water contained in the saturated muck should be prevented from re-entering the watershed.

Dilution or flushing a water body with fresh water from a nutrient-free source can aid in lowering nutrient concentrations. As a result, some aquatic plant growth will be reduced. Rooted aquatic plants utilizing nutrients contained in bottom sediments will remain unaffected.

Chemical treatment provides an effective means of controlling nuisance plants.

Bottom Barriers made of plastic, rubber, fiberglass screen or nylon are available for placement in beach or shoreline areas or small ponds. They are intended to inhibit or prevent rooted growth within selective areas. They are best installed during pond construction, drawdown, or during periods when growth is not present. Algae and free-floating vegetation are unaffected. Build-up of even slight amounts of sediment on the liner will provide substrate for new growth.

Bottom Barriers made of plastic, rubber, fiber-glass screen or nylon are available for placement in beach or shoreline areas or small ponds.

Fertilization of ponds to produce platonic algal blooms that shade out rooted vegetation and increases fish production is a method commonly used by commercial catfish farmers in the South. Most ponds, however, are fertile enough to support an abundance of life. The addition of more nutrients can compound existing problems by stimulating additional noxious weed and algae growth. Blooms detract from the recreational and aesthetic value of the pond and can create taste and odor problems.

Physical shading of water areas with black plastic sheeting, artificial structures, or overhanging shoreline vegetation has been attempted to inhibit aquatic plant growth. Sheeting makes the water inaccessible for a period of several weeks. Man-made structures and bank vegetation serve only to partially limit light penetration. Shade tolerant aquatic species will still develop.

• Chemical Shading
Shading water areas with soluble dyes can successfully inhibit aquatic plant growth. Specially made aquatic dyes such as Aquashade can inhibit plant growth by limiting sunlight penetration to bottom areas where the majority of aquatic growth begins. The product works especially well in clear water ponds and lakes with high nutrient levels. It should be noted that soluble dyes have limited effect in waters less than two feet deep.

Aquashade is a blend of blue and yellow dyes scientifically formulated to absorb the wavelengths of light (red-orange and blue-violet) required for aquatic plant and algae growth. This action effectively inhibits photosynthesis in young, bottom growth and may prevent development altogether if applied early enough in the season. Inhibition of planktonic (suspended) algal blooms has also been proven through the use of this product. Desirable, floating-leaf plants such as lilies are unaffected by it if they have already surfaced and concentrated product does not contact leaves directly.

Aquashade is the only “colorant” product of its kind that is registered by the U.S. Environmental Protection Agency for aquatic plant growth control. Therefore, it is the only formulation that has gone through the necessary testing to meet these criteria. Aquatic plant growth control claims made by other dye manufacturers are illegal under both Federal EPA regulations and U.S. patent laws. Furthermore, aquatic treatments with non-registered dyes, even as a colorant, are illegal in some states. Environmental and regulatory concerns warrant prudent use of properly labeled aquatic treatment products.

• Chemical Control
The use of chemicals is the most common and versatile management strategy for controlling nuisance aquatic plant populations. Chemicals offer longer lasting control than mechanical methods; involve minimal labor and equipment; provide flexibility and predictability; plus, ultimately cost less. From the range of products available, spot control within particular areas or selective control of specific plant species can be achieved. Applications can be made to sites that cannot or might not be reached by other methods. Algaecides and aquatic herbicides will not disrupt the ecological balance and in many cases can be used to restore some balance to a system. Ingredients are non-persistent. They will degrade or become deactivated within a relatively short period of time after controlling target plants. Therefore, no build-up occurs within the fish food chain.

Products currently allowed for use are somewhat limited due to the stringent government registration process. Millions of dollars and years of research have gone into testing these compounds on a broad spectrum of target and non-target organisms. Evaluations are made not only by the manufacturers themselves, but also by universities, government agencies, private consultants and commercial applicators.

The use of chemicals is the most common and versatile management strategy for controlling nuisance aquatic plant populations.

The registration process requires a battery of short-term (acute) and long-term (chronic) testing under a variety of environmental and laboratory conditions. Toxicity to rats, fish, aquatic invertebrates, desirable vegetation (crops, ornamental plants, turf, etc.) and other potentially exposed organisms must be determined. Screening tests and multiple generation studies on test animals are conducted to determine effects on cell function and growth, fetal development and pregnancy. Chemical residues and breakdown products are examined to trace the pathway of the compounds within the environment. Effects from altering water temperature, light intensities, water qualities and other factors are also investigated. Determinations are made as to the application rates and frequencies required to control the target aquatic plant species.

The outcome of this testing is the drafting of a product label designed to provide instructions for applying the product effectively and to help prevent product misuse. Specific directions are provided for handling, application, container storage and disposal, and water use restrictions following application. Use instructions and precautionary wording are clearly stated on the label. Additional product data is available from the manufacturer providing additional insight into product toxicology, environmental effects and use.

Proper use of these products may entail temporary restrictions on use of water for swimming, fish consumption, drinking, irrigation or domestic use. These restrictions vary with the different chemicals used. Local permits and/or licensing may be required on public waters. Varying water, weather and/or plant growth conditions could interfere with product effectiveness. With proper planning, timing, application and follow-up it’s possible to achieve safe, effective and economical control of nuisance aquatic plants. L&W

Excert from book How to Identify and Control Water Weeds and Algae.

For more information contact Applied Biochemists, W175 N11163 Stonewood Dr., Ste 234, Germantown, WI 53022, (262)255-4449, (800)558-5106, fax (262)255-4268, e-mail: info@appliedbiochemists.com, web site: www.appliedbiochemists.com.

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Monday, March 25, 2002 - http://www.landandwater.com/features/vol46no1/vol46no1_1.html