Phytoplankton, or algae, give water its green appearance and provide the base for the food chain in ponds. Tiny animals called zooplankton use phytoplankton as a food source. Large aquatic plants (aquatic macrophytes) can grow rooted to the bottom and supported by the water (submersed plants), rooted to the bottom or shoreline and extended above the water surface (emersed plants), rooted to the bottom with their leaves floating on the water surface (floating-leaved plants), or free-floating on the water surface (floating plants).
These different types of aquatic macrophytes can have different functions that protect water quality. Aquatic plants growing on a littoral shelf may help protect receiving waters from the pollutants present in surface water runoff. In open areas, floating-leaved and free-floating plants suppress phytoplankton because they absorb nutrients from the pond water and create shade. For more information on managing aquatic plants and algae in ponds in Maryland, see Urban and Stormwater Pond Management and see Plants Recommended for Stormwater Ponds for Maryland-specific native aquatic plant recommendations.
Best Management Practices
- Ponds are more resistant to problems if they have a narrow fringe of vegetation along the edge, instead of highly maintained turfgrass.
- In ponds with littoral plantings, problem plants should be selectively controlled without damaging littoral shelves.
- Encourage clumps of native emergent vegetation at the shoreline.
- A comprehensive management plan should include strategies to control the growth of nuisance vegetation that can negatively affect a pond’s water quality and treatment capacity.
- Frequently remove filamentous algae by hand and/or frequently apply algaecide to small areas of algae (spot treatment). The use of algaecides requires a permit from MDE and must be applied by a licensed applicator.
- To reduce the risk of oxygen depletion, use an algaecide containing hydrogen peroxide instead of one with copper or endothall.
- To control excessive aquatic plant growth, mechanical methods can be used that include the placement of barriers such as plastic mesh to block sunlight penetration into the pond, and physically pulling, raking, and cutting weeds.
- Aquatic herbicides, if used to control excessive aquatic plant growth, require a permit from MDE.
- Do not use grass carp to control aquatic plants, as this fish is not legal in Maryland.
Next: Water Quality Monitoring