In any ecosystem, when you combine water, sunlight and nutrients, you get plant growth. When that ecosystem is a recreational lake, the result is all too often a waterbody so covered with green filamentous algae that from a distance, it blends in with the surrounding environment. This situation is not only aesthetically displeasing; it is also potentially dangerous as some algae are toxic and bad for the ecosystem, limiting the lake’s ability to function properly. Mitigating these conditions without the continual need for algaecides can be challenging unless you implement environmentally sustainable approaches for lake algae control.
There are circumstances and considerations that may limit the feasibility of algaecide use in the maintenance of a body of water. Public concern over chemical use if your lake is used for swimming or fishing, regulatory limitations, and environmental conditions that limit product effectiveness are all factors that might make the use of certain products inappropriate in some situations. Also, some times, recreational lakes are water sources for irrigation, which puts even greater limitations on the types of products that can be applied to those waterbodies. As a park manager, this can be very frustrating, as you are trying to balance beauty and functionality of your waterbodies.
The best way to deal with algae is to prevent it. Deploying a sustainable, Integrated Pest Management (IPM) strategy which focuses on prevention and nutrient mitigation, utilizing tools such as beneficial bacteria, aeration, vegetative buffers and phosphorus binding minerals, could also limit the amount of chemicals that are needed to prevent or control algae problems.
Every lake has bacteria present. There are many “good” or beneficial bacteria that are a natural part of aquatic life. These bacteria are responsible for breaking down organic matter such as grass clippings, leaves, sediment, and waste created by aquatic life, as well as metabolizing excess nutrients such as nitrogen and phosphorus. When these bacteria are in low supply, and the introduced nutrient load is high, an algae bloom can occur.
One way to help prevent an algae bloom is by aerating the water. Beneficial bacteria need oxygen to be productive and aeration will actively introduce dissolved oxygen to your lake’s water column. Both submersed aeration systems and floating fountain aerators will increase the oxygen in your lake. Many times the depth, shape, or aesthetic look desired will guide your decision as to which type of aeration is best for your lake.
Another factor that promotes algae growth, is excess sunlight to a body of water. Controlling the amount of light that your lake receives can eliminate the ideal environment for algae to grow. The application of a non-toxic and environmentally friendly blue or black dye to the water will reflect a tremendous amount of sunlight that would otherwise be available in the water column for photosynthesis and subsequent growth of algae. An important note to this strategy is that dye must be applied regularly throughout the year as the dye does degrade over time and the goal is to maintain a constant UV screen. In addition to being an environmentally sustainable approach that helps prevent conditions that would be conducive for algae to grow, many lake owners like the aesthetic enhancement that a dye adds to a lake.
Managing the availability of nutrients for plant growth can be more challenging than affecting the water’s oxygen level or controlling the amount of light it receives, but ultimately may be the single most effective means of controlling algae. In most freshwater ecosystems like lakes, the nutrient of greatest concern is phosphorus. Nitrogen can cause problems from time to time, but by and large, if a lake is greener than it should be, there is probably too much phosphorus.
Phosphorus is both transported into lakes as surface runoff, usually bound to some particle of sediment, and available in the nutrient-rich layer of muck at the bottom of the lake. Limiting the amount of sediment flowing into lakes is best accomplished by establishing a “buffer” area around the perimeter of a lake and within any sources of flowing water that feed into the lake. If the landscape permits it, leave the area around a lake un-mowed or landscape with beneficial plants and grasses. Both options will slow overland flow and let nutrient-laden runoff settle out before it reaches the aquatic environment. For parks especially, a great side benefit to establishing buffers is that they discourage geese, which can be a major nuisance both on shore within your park and in the aquatic ecosystem as introduced phosphorous from their waste.
If a buffer area on shore is not an option or preferred by park management, emergent vegetation can be established in the shallow water just off of the bank. Sediment can then settle near the edge where these beneficial plants can absorb the nutrients and prevent algae from gaining access to it. Some attractive native plants that are useful in this regard include Three Square Rush and Pickerelweed.
After addressing how to reduce introduced phosphorus load, the next source to manage in your park lakes is the naturally occurring phosphorous. The first, and arguably most important step, is to test the water and sediment chemistry. Knowing the nutrient levels and the ratios between different nutrients is critical to bring nutrients into a healthy balance. Even for lakes that appear healthy, having water chemistry data on file is extremely useful. If a problem develops in the future, such as an unusual algae bloom for instance, tests taken at that time can be compared against this baseline data to determine if a chemistry change is responsible for the adverse event.
The nutrient-rich layer of organic muck on the bottom of lakes continuously releases available phosphorus into the water column. The most extreme and expensive measure to remove phosphorus from the bottom of a lake is to bring in equipment and dredge. However, this can usually be avoided or postponed through regular lake maintenance. In addition, beneficial bacteria and enzymes can be added to process this organic matter naturally. Combining these biological measures with aeration can, over time, bring down the amount of organic muck in the bottom of a lake and make the environment less hospitable for algae growth.
Probably the most immediate and most effective way to reduce phosphorus in a lake is to sequester it in the water column. There are a number of environmentally conscious products that bind with phosphorus to make it unavailable to fuel algae growth. Choosing the best product for a particular lake, as well as its dosage and means of application, will depend on the conditions of the site and the results of a comprehensive water chemistry analysis. Re-treatment may be necessary from time to time depending on the rate at which phosphorus is deposited in the lake through future inputs like fertilizer runoff, sedimentation, etc.
When your park is trying to avoid “green lakes,” there are several year-round environmentally sustainable strategies to deploy, however it is best to prevent algae before it grows. Every lake’s ecosystem is different, so it is rare for one single technique to be the “silver bullet” that prevents an algae problem.
Proper lake maintenance is an ongoing process that requires regular observation and adjustment. Extreme cases may still require occasional treatment with chemical products, but improving the overall health and balance of the ecosystem will dramatically reduce the frequency of required treatment and make those minimal treatments more effective. A doctor will tell you it is much easier to treat an otherwise healthy patient than one with chronic health problems. Likewise, doing as much as possible to improve the general health of a lake will yield a better looking lake and ease the treatment of any future problem. After all, the only green vegetation at your park should be the leaves on the trees and the grass on the ground.
Gavin Ferris is an experienced Ecologist with SOLitude Lake Management, an environmental firm providing full service lake, lake, and fisheries management services throughout the Eastern United States. Gavin can be reached through the website www.solitudelakemanagement.com.