Aquatic Weed Control

Aquatic weeds are necessary to support a thriving aquatic ecosystem. However, weeds can become detrimental if their growth is accelerated because of high nutrient loading. Aquatic weed problems are caused by excessive phosphorus and nitrogen concentrations in water bodies, stimulating excessive algae growth. The nutrients come from various possible sources: wastewater effluent, decaying organic matter, fertilizer runoff, and animal waste.  

Aquatic weed control reduces weeds in ponds, lakes, reservoirs, fish farms, and other artificial or natural bodies of water. It can include mechanical removal, herbicide applications, and natural or biological approaches.  

Clean-Flo advocates for the use of natural weed control methods and advises against the use of herbicides in all but the most extreme cases of weed infestation. Below, we will explain a little more about different types of aquatic weeds and how to deal with them.  

What are the best methods for aquatic weed control?

As mentioned above, there are three main ways of addressing weed infestations: mechanical, chemical, and biological. Mechanical approaches use nets, rakes, harvesters, and other machinery to physically remove vegetation from the lake. In cases where the weeds are so overgrown that it is impossible to operate a boat in the lake, this approach may become necessary. One advantage of mechanical methods is that they can remove a great deal of biomass – and the embedded nutrient load – from the water column, thus making it unavailable for future plant growth. One drawback is that the vegetation must be disposed of, which can be costly. Also, mechanical methods do not address the root causes of rampant weed growth.  

The second and most common method to control and destroy unwanted vegetation is chemical application. There are hundreds of chemicals available that disrupt plants’ biology in various ways. They are commonly sprayed into the water, but they will sometimes be injected below the surface or distributed throughout the lake in granular or pellet forms. Herbicides typically act quickly to kill plant life and improve the aesthetic appeal of the lake. But as with mechanical methods, they do not address underlying causes and may, in fact, worsen the situation. More on that later.

The third way of addressing weed growth is approaching the problem from an ecosystem perspective. The most critical driver of plant growth is nutrients. When nutrient concentrations are high, dissolved oxygen concentrations tend to be lower. A healthy, balanced ecosystem has high dissolved oxygen and moderate nutrient levels. With high nutrients, plants proliferate and add to the nutrient stockpile in the lake year after year. Without dissolved oxygen fueling a thriving community of zooplankton and fish, there is no check on the growth of plants, and the system is unbalanced. Reversing this process by re-oxygenating the water and removing excess nutrients is essential to solving this problem. This is the Clean-Flo approach.

Another method worth mentioning is the use of triploid grass carp. This fish is genetically engineered so that it cannot reproduce. It is a voracious consumer of plants and called a “floating weed remover.” Grass carp are stocked at a rate of approximately two fish per acre. At the time of stocking, they are 10”-14” long. They eat and grow the most rapidly in the first five years of life and effectively suppress the growth of submerged vegetation. Generally, they should only be considered when weed infestations are severe. Stocking a pond or lake with grass carp requires a state-issued permit, and the fish must come from a licensed hatchery. 

The Drawbacks of Using Chemicals

• Chemicals are expensive.
• Chemicals need to be applied frequently.
• Chemicals are restricted by federal and state regulations and can only be applied by certified individuals or companies.
• Chemicals contribute to the problem rather than addressing the root causes of excessive weed growth. By destroying plants year after year, the stockpiles of organic matter in lakes grow, and the nutrients available to plants and algae increase over time.  
• Calculating and applying herbicides can be tricky. The applicator could cause more harm than good if you get the dosage wrong.
• Herbicides and aquatic pesticides can be dangerous for the environment.
• There can be no guarantee that a particular herbicide or pesticide will be effective, yet their potential adverse environmental impacts remain.

Inversion Oxygenation for Aquatic Weed Control

The primary way to reverse the process that leads to excessive weed growth is to move the lake toward a better balance of oxygen and nutrients. This helps promote nutrient uptake throughout the entire food chain and reduces the food sources for aquatic weeds.  

The concept of aeration has been around in the aquaculture industry since the 1970s. It is the method of increasing the dissolved oxygen content of water by pumping air into the water column and circulating the water to increase its interaction with the atmosphere. Aeration was initially intended to control disease in fish; however, it was found to help treat algae buildup on ponds and the surface of tanks over time. 

Aeration systems must be properly designed to be effective. There are no “one-size-fits-all” solutions.  Buying inexpensive equipment from companies advertising off-the-shelf products should be avoided. Design is complex and must take into account the water body’s size, average and maximum depths, nutrients present, residence time, and other factors.

Can bioaugmentation be used for aquatic weed control?

Bioaugmentation is the practice of adding beneficial microbes, enzymes, or mineral nutrients to a pond, river, or lake to improve their quality. The technique has been used to enhance water quality, promote the growth of beneficial algae and plants, and suppress others.

Clean-Flo has successfully combined inversion oxygenation with bioaugmentation for years to achieve exemplary results. Nutrients have been reduced throughout the systems’ operation, and product applications and ecosystems have been restored to a healthy balance. This has driven back levels of nuisance aquatic weeds and algae and replaced them with beneficial microorganisms, zooplankton, diatoms, and fish.