Excessive aquatic plant growth is a common complaint and may interfere with desired uses of ponds. Phosphorus and nitrogen typically drive aquatic plant growth, which may persist while nutrient levels remain elevated. This publication will assist landowners, pond managers, farmers, producers, and municipalities how (a) land-based actions throughout the watershed can reduce external nutrient and sediment loadings, and (b) in-pond actions can assist in managing plant growth, slowing the release of nutrients, and encouraging more sustainable conditions. Additional Land-Grant Press pond publications are available on lgpress.clemson.edu: Ponds in South Carolina, Recreational Ponds in South Carolina, and An Introduction to Stormwater Ponds in South Carolina.
A “healthy” pond contains a variety of plant species that may cover about 20% of the surface.1 Unless they are rapidly expanding or particularly problematic, the plants are likely providing benefits, including habitat for fish and other organisms, stabilization of soils, and uptake of the nutrients in the water.1 Rapid or excessive aquatic plant growth is a common concern and can interfere with the intended uses of a pond.
Excessive plant growth is a symptom of a pond’s underlying high nutrient levels.2 Nutrients are essential, but high levels (especially phosphorus) will encourage excessive plant or algae growth in freshwater systems.3 Nutrients are often carried from land into waterways, so actions on the land that drains into the pond have a tremendous influence on conditions within the pond. Common sources of nutrients include fertilizer, soil erosion, sewer overflows or leaks, improperly functioning septic tanks, and animal waste (figure 1).4
Pond management begins with preparation. First, identify your main goals and uses for the pond. Then develop an integrated plan to determine cost-effective strategies for meeting those goals. The plan should include (1) land-based actions to protect your pond, (2) in-pond practices to manage problems, and (3) aquatic weed identification to determine efficient treatment options.
Land-Based Solutions to Protect Your Pond
It is often less work to prevent nuisance weeds from establishing than to control them.5 Reducing the source(s) of nutrients entering the pond and implementing best management practices is critical to managing nuisance weeds. Evaluating the land surrounding your pond may identify sources of pollutants. Additional tools, such as SCDHEC’s Watershed Atlas, provide a variety of information that may help identify probable sources of pollutants to waterways. Some best management practices to consider include
- Use fertilizer wisely. Fertilizer contains nutrients that drive plant growth on land and in water. Use only what is recommended from soil testing results and don’t apply if heavy rain is forecast.6 The Clemson University Ag Service Lab’s website provides additional information on soil testing.
- Practice landscape management. Do not allow grass clippings or other yard waste to migrate into the pond where they can decompose and contribute to nutrient pollution.7 Instead, use as mulch or compost them to return the nutrients to your landscape and further reduce fertilizer needs.7
- Use native plants. These plants are adapted to South Carolina regional climates and soils and typically do well with minimal maintenance or fertilizer.8 The Carolina Yards Plant Database provides information on plant options.
- Cover bare soil with plants or mulch. When exposed to the elements, soil particles can move across the landscape with stormwater runoff and enter waterways as sediment.9 The soil particles may carry pollutants, such as nutrients, with them. Many plants, such as native grasses, provide excellent erosion control of upland areas and can be grown from seed to cover large areas.10 Seed selection, mixes, and application rates vary significantly based on the location, time of year, and land use. Use a seed mixture that includes annual seeds (that will germinate quickly to provide temporary stabilization) and perennial seeds (that are slower to establish but will provide long-term stabilization). The SC Department of Transportation provides a technical document for seed recommendations that includes several native types of grass suitable for South Carolina. The USDA Natural Resource Conservation Service (NRCS) job sheet South Carolina 327 (Conservation Cover) Technical Guide provides recommendations, including seed mixtures specific for South Carolina, for establishing vegetation on sites expected to have high erosion rates.
- Improve the shoreline (or buffer) area with vegetation. Plants along a shoreline can slow stormwater runoff and remove pollutants, including nutrients, before entering a waterway (figures 2 and 3).11 Clemson Cooperative Extension’s Home & Garden Information Center (HGIC) offers multiple factsheets including Shorescaping Freshwater Shorelines for installation guidance, Maintaining Your Shoreline for healthy shorelines maintenance (excluding the dam area), and Life Along the Salt Marsh: Protecting Tidal Creeks with Vegetative Buffers for coastal-specific planting suggestions. Greenville County’s comprehensive guide to riparian buffers, the Riparian Buffer Design and Maintenance Manual, provides a plant list suitable for the Upstate area. Partnering with upstream or downstream neighbors can make a more significant impact.
- Manage animals and their waste. Animal waste contains nutrients and bacteria and can contaminate nearby waterways. Pick up pet waste. Do not feed wildlife near ponds. The HGIC factsheet, Resident Canada Geese: Management Options, details the types of shoreline buffers that will deter geese from congregating near a pond since they need ease and visibility when entering a pond. Fence livestock out of ponds and provide an alternate water source.12,13
- Stabilize slopes. The steeper the slope, the greater the risk of erosion and runoff of soil and nutrients. Options for preventing erosion vary by steepness; vegetation has a good chance of success on moderate slopes (gentler than 3:1), additional techniques such as erosion control blankets may become necessary for medium slopes (3:1 to 2:1), and structures or special techniques are typically required on steep slopes (steeper than 2:1).14 Consider using terraces to minimize surface runoff from steep slopes (2:1).14 Use proper livestock densities in pastures to prevent over-grazing and rotate animals to other pastures during wet periods.15
In-Pond Management Strategies
The HGIC factsheet Aquatic Weed Control Overview lists various management options that can be effective, depending on the specific plant targeted for control. An integrated pest management (IPM) approach prioritizes prevention and best management practices to prevent weeds from establishing and is a cost-effective strategy for controlling aquatic weeds.16 The success of a particular control method can be dependent on the pond’s chemistry. Some details regarding each control method are described below.
Physical Control is the removal of nuisance plants or changes to the physical conditions within the pond.
- Physically remove plants. This can provide immediate control of some plant species and reduces the chances of problems from plant decay; however, it should be avoided if the plants regrow from plant fragments. Physical removal may require large equipment and can be expensive. Removal should be done carefully to prevent shoreline damage during the process. In addition, proper disposal of the removed plant material is necessary.17 The University of Florida plant management website provides information on mechanical control.
- Add oxygen. Subsurface aeration uses bottom diffusers to add oxygen to the system and circulate water throughout the pond (figure 4). Circulation promotes consistent water temperatures, and aeration increases oxygen levels. Increasing dissolved oxygen in the water column supports fish and aerobic bacteria, which help degrade organic debris and prevent buildup.18 Oxygenating bottom sediments may slow the release of nutrients from the sediments and help prevent excessive aquatic plant growth.19
- Install floating wetlands. Also known as floating islands, plants in floating container gardens take up nutrients from the water column (figure 5) and may reduce weed growth and algae blooms and prevent fish kills. These are effective when they cover at least 20% of the water surface and are most suitable for smaller ponds.20 Refer to the HGIC factsheet Floating Wetlands: Container Gardens for Your Pond to learn more.
- Dredge sediment. Sediment should be removed as needed or required (by applicable stormwater management ordinances) to restore water storage capacity, reduce in-pond nutrients, and deepen your pond to help prevent plant growth by avoiding increased water temperatures and sunlight penetration. The removal process can be expensive and may require permits.21
- Drawdown water levels. Reducing the water level is an extreme measure that may kill plants. It should be conducted during the winter and is most suitable for ponds over an acre with functioning control structures that allow water levels to be manually adjusted. If fish are present, this will put stress on the population.17
- Add pond dye. The colorant limits the movement of light through the water and reduces photosynthesis while leaving the upper two feet productive. This method can be effective for up to six months.17
- Bind phosphorus. The application of phosphorus-binding materials, such as alum or other specifically developed products, makes it unavailable to aquatic plants. Repeated applications of the process may be necessary since the phosphorus remains in the pond bottom sediments.22 Past applications may not control future phosphorus inputs into a pond.22
- Install benthic barriers. Covering portions of the pond bottom with natural or synthetic substances blocks rooted plant growth and makes conditions less suitable for weed growth. This is an expensive but effective option for submerged weeds.17
- Biological Control provides long-term control of some aquatic weeds by using certain types of fish, and the results can be relatively quick – within a few weeks or months.
- Stock recommended fish species. Certain types of fish, such as carp or tilapia, will eat specific weeds.23,24 Refer to the HGIC factsheet, Biological Control of Aquatic Weeds for more information. The SC Department of Natural Resources maintains a list of commercial aquaculturists for purchasing these fish in South Carolina. A free permit may be required and should be provided by the fish supplier.25
Chemical Control involves using commonly available herbicides labeled for aquatic use to control specific vegetation rapidly. Refer to the HGIC factsheet Chemical Control of Aquatic Weeds for more information. Critical considerations when using chemical control include:
- Follow regulations! The HGIC factsheet The Label is the Law provides guidance on the proper application of herbicides. Before applying any approved herbicide to a waterbody, confirm if a Pesticide Applicator License or permitting is required. A license can be obtained through the Department of Pesticide Regulation within Clemson University’s Regulatory Services, and their website provides guidance and resources. Additional information on regulations and permitting can be found on the SC Department of Health and Environmental Control NPDES Pesticide Permit Information website. There may be restrictions on the pond and water use after an application.26 For large infestations, treat only up to one-third of the pond’s surface area at a time to protect aquatic life, such as fish.27
- Avoid downstream impacts. Chemical control may only provide short-term results, and repeated applications may be necessary. Do not apply before rain events or in ponds with significant outflow, as the herbicide may wash downstream prior to uptake and could be harmful to downstream waters.27
- Check pond water chemistry. Certain water parameters, such as pH, influence fish and plant health and the effectiveness and toxicity of herbicides. The HGIC factsheet Recreation Pond Chemistry outlines how to maintain pond health. An irrigation water sample and a pond bottom sample should be collected and analyzed before implementing any management strategies. Learn more about how to collect and analyze irrigation water and pond bottom samples on the Clemson University Ag Service Lab Irrigation Water website and the Soil Testing website. You can also purchase water testing equipment to analyze samples. Check the label of the specific herbicide to be sure your pond’s water is within the acceptable range(s).28
Identify Your Aquatic Weed
It is essential to accurately identify the nuisance plant to determine the best combination of management strategies. You may be able to quickly identify your aquatic weed using these helpful resources:
- Aquaplant is an online diagnostic tool developed by Texas A&M Extension,
- Aquatic Plants is an app for your mobile device, developed by NC State University.
If you would like additional assistance identifying your aquatic plant, you can submit a plant sample to the Clemson Plant & Pest Diagnostic Clinic. Information on submitting samples is available on their website. Instructions for collecting samples are provided in a sampling guidelines handout for aquatic weeds and the HGIC factsheet Submitting an Algae Sample for Identification. You can also contact your local Clemson Cooperative Extension Agent for help. Contact information for county offices and staff is available on the Clemson Cooperative Extension website. Pictures can be extremely helpful in identification; they must be clear and with the plant in focus (figure 6). Please see the HGIC factsheet Tips for Taking Good Photos to Send to Your Extension Agent to ensure sufficient quality.
Professional pond management companies can assist with severe aquatic plant problems, equipment purchases (e.g., aerator, benthic barrier), and regular maintenance to prevent future problems. The SC Department of Natural Resources provides a list of Lake Management Consultants throughout South Carolina, and Clemson University provides a list of certified Master Pond Managers.
In conclusion, ponds are complex ecosystems that must be managed holistically to achieve the desired results for their intended purpose. Weed prevention is an essential factor to consider when managing a pond for your desired use.
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- Nutrient Cycling in Aquatic Ecosystems. Reston (VA): US Geological Survey; [accessed 2021 Jun 22]. https://www.usgs.gov/centers/umesc/science/nutrient-cycling-aquatic-ecosystems?qt-science_center_objects=0#qt-science_center_objects.
- Correll DL. Phosphorus: a rate limiting nutrient in surface waters. Poultry Science. 1999;78(5):674–682. https://www.sciencedirect.com/science/article/pii/S0032579119409917#bbib195.
- Nutrient Pollution: Sources and Solutions. Washington (DC): US Environmental Protection Agency; [accessed 2021 June 22]. https://www.epa.gov/nutrientpollution/sources-and-solutions.
- Whetstone J, Heaton W. Aquatic weed control overview. Clemson (SC): Clemson Cooperative Extension Home & Garden Information Center; 2015 Dec. HGIC 1714. https://hgic.clemson.edu/factsheet/aquatic-weed-control-overview/.
- Pesticides, Herbicides, and Fertilizers. Greenville (SC): Greenville County Soil & Water Conservation District; [accessed 2021 June 22]. https://greenvillesoilandwater.com/pesticides-herbicides-fertilizer/.
- Yard Waste. Greenville (SC): Greenville County Soil & Water Conservation District; [accessed 2021 Aug 30]. https://greenvillesoilandwater.com/yard-waste/.
- A Guide to Native Plant Gardening. Austin (TX): The University of Texas at Austin, Lady Bird Johnson Wildflower Center; [accessed 2021 June 22] 2021. https://www.wildflower.org/learn/guide-native-plant-gardening.
- Erosion. Greenville (SC): Greenville County Soil & Water Conservation District [accessed 2021 Aug 30]. https://greenvillesoilandwater.com/erosion/.
- NRCS. Conservation cover (native grasses and forbs). Columbia (SC): USDA NRCS (Natural Resources Conservation Service); 2015 Jan. SC Practice Job Sheet 327. https://efotg.sc.egov.usda.gov/references/public/SC/SC327_Conservation_Cover_JS_Natives_January_2015.pdf.
- Nieswand GH, Hordon RB, Shelton TB, Chavooshian BB, Blarr S. Buffer strips to protect water supply reservoirs: a model and recommendations. Journal of American Water Resources Association. 1990 Dec;26(6):959–966. doi:10.1111/j.1752-1688.1990.tb01430.x.
- Water quality protection – pet waste. Providence (RI): Rhode Island Department of Health and University of Rhode Island Cooperative Extension Department of Natural Resources Science; 2004 Mar. https://web.uri.edu/safewater/files/Pet-Waste.pdf.
- Zaimes GN, Schultz RC, Isenhart TM. Streambank soil and phosphorus losses under different riparian land-uses in Iowa. Journal of the American Water Resources Association. 2008 Jul; 44(4):935–947. doi:10.1111/j.1752-1688.2008.00210.x.
- Prevent soil erosion on your property: a homeowner’s guide to erosion control. Davis (CA): USDA Natural Resources Conservation Service; [accessed 2021 June 22]. https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_063808.pdf.
- Clary WP, Kinney JW. Streambank and vegetation response to simulated cattle grazing. Wetlands 2002 Mar. 22(1):139–148. doi:10.1672/0277-5212(2002)022[0139:SAVRTS]2.0.CO;2.
- Stallings KD, Seth-Carley, Richardson RJ. Management of aquatic vegetation in the Southeastern United States. Journal of Integrated Pest Management. 2015 Mar. 6(1). doi:10.1093/jipm/pmv002.
- Plant Management in Florida Waters. Gainesville (FL): University of Florida. [accessed 2021 June 23]; https://plants.ifas.ufl.edu/manage/.
- Oakes PL, Gullett K, Bobowick R. Technical Note No. AEN-3: aeration of ponds used in aquaculture. Washington (DC): USDA Natural Resource Conservation Service. 2011 Jul. https://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=33946.wba.
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- Alum Treatments to Control Phosphorus in Lakes. Madison (WI): Wisconsin Dept. of Natural Resources. 2003 Mar. https://dnr.wi.gov/lakes/publications/documents/alum_brochure.pdf.
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