What is Lake Management?
Aquatic Resource Consulting
The term "limnology" is derived from the ancient greek word λίμνη (limne) meaning lake or pond.
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Natural ponds form over the course of time in depressions and basins on the Earth’s surface. Many factors lead to their formation such as tectonic movement, meandering rivers, former glacial zones and sinkholes. Not all naturally occurring depressions become lakes however, some become wetlands, swamps, or temporary ephemeral/vernal ponds. Factors that affect their formation are regional geology and soils, climate and weather as well as the local flora and fauna (including humans). Regardless of how a lake is formed, even if it is man-made, it will eventually fill in with sediment and become a meadow through a natural lake/pond lifecycle called eutrophication.
The simplified explanation of eutrophication is that, as time passes, water bodies receive nutrient laden sediments from storm water and irrigation runoff, erosion, and even from the atmosphere. The addition of these nutrients (primarily nitrogen and phosphorous), in turn, increase the amount of vegetation, algae and other organisms growing in the pond. Every growing season, as these organisms grow and die off, they add a layer of sediment to the bottom of the pond/lake. These nutrient rich sediments give rise to the next season’s growth, and a positive feedback loop develops, ultimately leading to the lake filling in completely and becoming a meadow.
All lakes succumb to eutrophication and are classified by how much eutrophication has occurred. The trophic state index classifies a lake as: oligotrophic, mesotrophic, eutrophic, and hypereutrophic. An example of an oligotrophic lake is Lake Tahoe, while an example of a hypereutrophic lake would be... your typical Stormwater detention basin. Lake Tahoe has clear water (200+ feet of visibility) with very little vegetation and algae growth. This is because the surrounding granite watershed that feeds the lake has very little nutrient laden runoff. Shallow detention basins on the other hand have so much vegetation and algae you typically can’t see more than a few feet during the growing season.
Both of these example lakes, if left alone, will become meadows. Lake Tahoe will progress on a geologic timescale and take hundreds of thousands of years, while a detention basin will likely be gone in the several decades or even a single decade. Mankind relies on lakes for many reasons and we typically think of them as a natural resource that, if left alone, will find and equilibrium and exist in harmony. From day to day, or week to week, this appears to be empirically true, but when observing a water feature over time, like all things on earth, it is following its natural lifecycle, eutrophication.
Manmade lakes by definition are of course not naturally occurring. If a geographic location was conducive to the formation of a lake, there would likely already be one there. This means that manmade lakes are already in an even greater struggle against their surrounding environmental conditions for their continued existence from the moment they were excavated. Therefore, if the owner of a lake wishes for the lake to be kept in a given state (oligo, meso, eutrophic), maintenance activities to reduce/inhibit sedimentation, nutrient loading, and other factors, will be required to suspend the progression of eutrophication.
Lake management can be best understood as a form of Integrated Pest Management. Physical weeding and mowing, cultural practices to reduce nutrient loading and counter other inputs, pest monitoring and prevention, biological controls, and chemical controls are all part of the best lake management practices. The scope and scale of activities required in an IPM program are based on the function and/or form of a water feature as well as its intended uses. Decorative ponds on estates or near wine tasting rooms are more labor intensive; owners often desire specific levels of water clarity and strict thresholds for vegetation and algae control, while irrigation ponds merely require enough labor to ensure they function as intended without clogging pumps, causing mal odors, or harboring vectors of disease.
All lakes, regardless of how they were formed or made, become part of the local ecosystem. A Lake Manager’s actions need to find a balance between the owner’s desired condition, and the wildlife that have not only become dependent on the lake but area also an integral part of the ecology that keeps the lake healthy. Many owners tend to see themselves as separate from their lake and separate from the nature surrounding their house, when in fact, they are an integral part of the ecosystem of the pond and even the food chain within it. As an owner of a lake, on which so much life is dependent, thoughtful and knowledgeable stewardship requires understanding the impacts of their day to day activities on the property, from their landscaping design and practices, to the detergents and cleaning products they use.
For these reasons, it is prudent for a lake owner to seek out or develop the necessary knowledge to properly manage a lake. Understanding the ecological ramifications of their actions while constantly evaluating and adjusting both short and long-term goals. There are numerous products on the market to achieve the biological, cultural and chemical control portions of an IPM. Understanding which of these are best suited for a specific location, and which products work well together or counteract is vital to a successful sustainable management plan.
IPM in Practice
Mechanical control activities involve the removal of emergent, floating and submersed aquatic vegetation. Limiting emergent plants such as cattails (Typha), bulrush (Scheonoplectus) and other shoreline growth is particularly important as it can encroach far out into a lake to the point where a major and expensive restoration project may be required. While many of these emergent plants are an important feature for wildlife, and provide needed shoreline stabilization, when left unmonitored, overly dense growth can restrict the intended uses of the water, reduce capacity, and potentially create habitat for pests or vectors of disease such as mosquitos.
Regularly scheduled annual maintenance based on control thresholds might involve thinning and removal of dead and dying emergent plants, tree skirting and pruning (especially of thirsty willows or other species that drop abundant leaf litter into the lake). These actions reduce amount of decomposition of organic biomass in the lake which helps stem the growth of aquatic plants and algae.
Submersed vegetation can be controlled through the use of a variety of tools. Removal of submersed vegetation periodically provides a number of benefits including: removal of nutrients from the system, preventing seed dispersal, reduction of additional sedimentation buildup when plants die off in fall and winter, and reducing structures for filamentous algae to grow on during the growing season. Mechanical tools such as a lake-mowing devices, not to be confused with an aquatic weed harvester, Weed Razors ™ , throwing rakes, and many other devices are available to perform this work from shore or a boat.
Algae, floating plants, and other accumulated surface debris should also be collected manually through the use of pool nets, debris booms, or by hand. A good rule of thumb per the IPM approach is to collect as much as is reasonably possible (50% to 80%) before relying on chemical control. While manual control is labor intensive and sometimes costly, it is important to remember it has long-term benefits and cost savings through removal of nutrients from the system and reducing sediment buildup.
Cultural controls include the installation of aeration and circulation devices such as fountains, water jets, or bottom diffusers. These systems are typically designed to mix the water column vertically or horizontally. Mixing can bring oxygen rich surface waters to the depleted bottom (hypolimnion). Low oxygen at the lake bottom will allow the release of nutrients from sediments into the water column, creating conditions that stimulate growth of plants and algae. The aggressive mixing of the water column by many of these systems also interferes with the ability of many algae species to regulate their buoyancy at the surface, inhibiting the development of potentially harmful algal blooms. More information can be obtained by the manufacturers to identify which type of system is right or your site.
Use of dye is also a cultural control method that is effective at reducing plant and algae growth through limiting sunlight penetration. The reduced sunlight shrinks the photic zone, which is the area of the lake where photosynthesis occurs. This will restrict the growth of submersed plants to a narrower band around a lake’s shoreline (the littoral zone) and because many algae species also form in the benthic zone (the bottom) their populations will also be reduced.
Other cultural activities include establishing vegetated buffers around the shores to reduce erosion and trap sediments from runoff. Depending on the site-specific conditions of the lake, reducing flow rates from creeks, or other sources will also reduce inputs of suspended sediments. The feasibility of these options should be evaluated as a management program is developed.
Biological controls usually bring to mind stocking herbivores fish in a lake, but this can be hit or miss and there are several cons to consider. Stocking carp is a frequent question lake managers receive. Often permits are required for your use of these fish species which will depend on whether or not it is likely for them to escape downstream or over a spillway. High numbers of these fish are often required to have an impact on vegetation, and the fish may also not prefer eating the vegetation you wanted them to control. Additionally, if the carp are too successful in removing vegetation, juvenile fish and other aquatic organisms that require plant life for habitat, shelter, and food will be left vulnerable. It is also important to consider that one way carp do reduce vegetation is that they will root in the mud for food causing turbidity. This turbidity acts like a dye shrinking the photic zone, however, if the pond is used for irrigation, specifically drip irrigation, the owner may have to deal with more clogged emitters and sprinkler heads.
Alternatively, stocking fish with a mix of species will help by creating a more robust food chain whereby the nutrients used by the autotrophs (plants and algae) and secondary consumers (insects and small fish) will bioaccumulate their way up the chain to become part of the tissue of the tertiary consumers (piscivorous fish like trout, bass, and bluegill). When birds, wildlife and even humans catch and remove these fish, it is removing nutrients from the system. Risks and rewards associated with herbivores fish may not pan out for every lake, but developing even a modest fishery can be a simple and cost-effective part of a biological control strategy.
Newer strategies of biological control rely on the use of products that augment and support the naturally occurring organisms within the ponds that can compete with plants and algae for nutrients (Nitrogen, Calcium, Magnesium, Iron, and Phosphorous). Many of these products are made of food grade class one microorganisms including several Bacillus Spp. bacterium. These species are well documented for their ability to inhibit potentially harmful cyanobacteria blooms, aka blue-green algae (Wright, S.J.L. and Thompson, R.J. 1985).
The primary purpose for the addition of these organisms is to strip the water column of nutrients and to reduce sediment buildup. The sediment layer in a pond is where a majority of the nutrients for algae and plants is stored. Products that speed up the decomposition of organic debris (leaves, pollen, etc.) An added benefit of the addition of these organisms is that when using the treated water for irrigation, the bacteria have antifungal properties and also can increase nutrient uptake through the roots in many crops (Fiddaman, P. J. and S, Rossal, 1993).
Chemical Control with pesticides (typically aquatic herbicides and algaecides) can be used to treat infestations, but there are many regulations and real potential for negative consequences. Compared to terrestrial pesticides, there are fewer products available for use in aquatic environments, and knowing which one, or combination, is highly dependent on the specific plant you want to control. In addition, if the water is being used for irrigation, the choice in product is even more restricted. A major concern when applying a pesticide is possibility for the decaying biomass to deplete the dissolved oxygen in the lake with lethal consequences to aquatic biota. If manual removal is not possible, follow pesticide label instructions carefully and only treat portions (1/4 to 1/2) of the system at a time to avoid depleted oxygen problems and a ‘fish kill’.
Water quality monitoring should be performed from time to time to develop benchmarks and to evaluate the effectiveness of your management strategies and any products you may have applied. Measuring physical properties at varying depths throughout a lake such as: pH, dissolved oxygen (DO), salinity, total dissolved solids (TDS), specific conductivity, visibility/turbidity, and temperature can help in selecting between different control methods at different times. Sometimes they can tip a manager off to problems that are starting to develop. Collecting a representative sample of water from across a lake to analyze for chemical constituents such as nitrogen, phosphorous (at a minimum), and other trace elements will provide adequate data for evaluation purposes. These parameters can be tested using bench top or portable equipment or sent to a lab for analysis. Conventional test strips (typically for aquariums) do not usually provide the reporting limits or accuracy needed to have reliable data.
Monitoring is part of any IPM approach. A good manager will be able to identify plants and organisms and sort out the good from the bad. New arrivals to the pond, be it plants, algae, or even snails, may pose a significant risk and may require a rapid response before an infestation occurs. A knowledgeable manager should have a rapid response plan ready when these organisms arrive. In addition, a management plan should include treatment thresholds of known problems to reduced labor and product costs by addressing problems early.
Anyone can become a lake manager, learning the technical aspects of lake management best practices and applying an IPM approach is not difficult. It requires some experience and a willingness to study and devote time to the lake. For this reason, many lake owners choose to hire a professional in the field. Professionals can be consultants who make recommendations for existing staff or specialty landscape companies that assume complete control of the feature. Whatever approach is taken, a lake owner should ask themselves “do I have a plan?”