Common Aquatic Plants of Howard County
Aquatic plants are a beneficial and necessary part of the ecology of lakes and ponds. Without them, most other organisms could not survive. Aquatic plants keep the water oxygenated, provide food, cover and nesting sites for wildlife, absorb excess nutrients, aid in the removal of suspended sediments from the water column and stabilize the shoreline and pond bottom.
The Natural Resource Management Division of the Department of Recreation & Parks receives numerous inquiries regarding vegetative growth in and around ponds, mostly during the growing season (April-September) and particularly when excessive amounts of aquatic plant growth reach levels that are aesthetically unappealing to residents. The purpose of this article is to help citizens of Howard County correctly identify aquatic plants they may observe in their community ponds, become familiar with possible plant control methods, and most importantly encourage greater tolerance for aquatic plants and understanding of the role they play in pond ecology and the maintenance of water quality.
Categories of Aquatic Plants
There are five categories of aquatic plants.
1. Algae: non-vascular plants that are found throughout the water column in three basic forms: microscopic, filamentous (strand-like), and macrophytic (visible with the eye.
2. Free-floating plants: vascular plants whose roots are not anchored in the sediment so the plants are floating on the water surface. Duck weed, water meal, water fern, and water hyacinth are examples of free-floating aquatic plants.
3. Submerged plants: vascular plants that are rooted in the sediment and found completely submerged underwater and lack rigid structure. Examples include Hydrilla, Brazilian elodea, and water milfoil.
4. Emergent plants: vascular plants that are rooted in the sediments, found floating at and extending above the surface of the water, and have rigid structure. Examples include pickerel weed, creeping willow primrose, and water lily.
5. Marginal plants: vascular plants that are rooted in the sediments, found along the fringes of a pond typically in less than two feet of water and have rigid structure. Examples include cattail, sedges, rushes, and reeds.
Prevention and Watershed Management
Unfortunately, aquatic plants can spread to “nuisance” levels and can interfere with aesthetics and pond uses such as recreational pursuits like boating and fishing. Abundant overgrowth of aquatic vegetation is generally attributed to excessive nutrients (particularly nitrogen) present in the water. How does the extra nitrogen get in the water? Sources of nitrogen include the atmosphere (air & rain), storm drains, runoff from impervious surfaces in the watershed such as streets, sidewalks, and rooftops, over land surface runoff from lawns, and ground water recharge. It is difficult, if not impossible, to single out the sole source contributing to the excess load of nutrients. It is the combination of all sources.
Prevention is the best solution to aquatic plant problems. It is often less expensive and easier in the long run to prevent weed growth than to control abundant aquatic vegetation. To start, ponds should be properly designed. Ponds constructed with steep slopes can prevent aquatic weeds from taking root. In addition, sediment basins installed upstream of a pond will trap sediment, help to maintain pond depth, and reduce nutrient transport. Soil erosion and nutrient runoff are the two major causes of abundant aquatic weeds. Soil erosion not only makes a pond shallower, but it allows rooted weeds to invade quickly and the suspended soil particles aid in nutrient transfer that further stimulates plant growth.
When trying to remedy existing problems, selecting the best treatment option or combination of treatments depends upon many factors.
- Proper plant identification
- Extent of the problem
- Economic considerations
- Local environmental conditions
- Pond uses
Various methods exist to deal with aquatic vegetation and they range widely in terms of costs, frequency of application, and the amount of manpower to implement. They include:
- Dredging to deepen the pond and reduce accumulated sediments
- Manual or mechanical harvesting of plant material
- Manipulation of water levels
- Applying dyes to water
- Installing pond bottom liners
- Biological controls
- Chemical herbicides
Dredging is a major activity and involves de-watering of the entire pond and the use of large equipment such as bulldozers to remove pond-bottom sediments. Dredging can also occur hydraulically; however, this type of dredging operation is too expensive for use in small ponds. Dredging reduces aquatic plant problems directly by removing the plants, bottom sediment, and associated nutrients.
Manual or mechanical harvesting
Harvesting aquatic vegetation consists of three essential steps. The first step involves cutting or uprooting the vegetation, then collecting it, and finally removing the plant material. Depending upon the size of the area, harvesting can be accomplished with hand tools and physical labor or with the aid of cutting machines. Success with this method depends upon prompt and complete removal of all cut plant material. Haphazard removal of cut material can actually increase the problem because some plant fragments have the potential to re-establish on site.
Manipulation of water levels
Pond drawdowns, particularly in the winter, have the potential to suppress vegetation growth because the pond-bottom soils are exposed to harsh conditions such as freezing, desiccation, wind and compaction. Vegetation exposed during the drawdown should be removed, or the rotting vegetation will contribute nutrients that will permit new, vigorous re-growth of vegetation when the water level is restored. In ponds without drain structures, water pumps can be used. In addition, this management option is not feasible if the pond is an active fishery.
Applying dyes to water
Commercially available nontoxic water dyes are used to color the water to suppress light penetration and shade out aquatic growth. These products mainly target algae; however, some submerged plants are susceptible to them. To be effective, the dyes must persist for several weeks. These products should be used in early spring at the start of the growing season prior to the vegetation getting firmly established. Some individuals are of the opinion that water dye products make a pond look unnatural because of the usually bright green or blue appearance of the water after treatment. These products also need to be reapplied as needed, depending on the flow rate of the pond.
Installing pond bottom liners
Covering the bottom sediments of small ponds with either plastic sheeting (4 mil or thicker), a layer of mineral soils or both can control aquatic vegetation growth. Although this method is not applicable to large areas, it has worked well surrounding boat docks, ramps and piers.
Some pond managers promote the use of non-native, herbivorous (plant eating) Chinese grass carp to control aquatic vegetation. At this time, the Maryland DNR prohibits the release of this species in Maryland and it is not an option.
Another form of a biological control of algae is the use of submerged bales of barley hay directly into the pond. Although the exact mechanism of control is not fully understood at this time, it appears that the break down of the barley hay emits a compound that inhibits the growth of algae.
Various herbicides labeled for aquatic use are available to suppress aquatic vegetation and in some situations is the only practical method of control. However, treatment with herbicides should only be considered a temporary control method. Long-term control methods need to address the real issue of excess nutrients in the water. In order to use aquatic herbicides, permits from the Maryland Department of Environment need to be secured and the individual applying the chemicals need to be certified by the State. Other precautions need to be adhered to because herbicides can be toxic to fish and other aquatic life. Some aquatic herbicides also require restrictions on water use or fish consumption after treatment.
Whichever method(s) are ultimately employed, one always needs to consider proper plant identification, treatment for intended use of the water, timing of treatment, water movement in the system, weather events, and permitting issues.
Since many of the ponds that occur in Howard County function primarily as storm water management facilities, the Bureau of Environmental Services, Storm Water Management Division, has the primary responsibility of pond maintenance. They ensure that all storm water management ponds in the county are functioning as engineered, maintain drain structures, and mow vegetation growth on earthen dams. Currently, there are well over 800 storm water management facilities to maintain in the County.
The Bureau of Parks, Natural Resource Division is responsible for managing, protecting, and enhancing the natural resources of all county-owned park and open space lands. Efforts are made to manage these areas in a way that both conserves their ecological integrity and makes them available for recreational and educational uses. This Division works in partnership with the Storm Water Management Division to enforce County storm water regulations, establish riparian buffers surrounding ponds and stream banks where applicable, and enforce against encroachments onto park land such as illegal mowing down to the edge of ponds.
What Can a Homeowner Do to Help?
The entire burden cannot solely rest on the shoulders of the local government. Water quality is important to everyone and there are some key land stewardship practices that homeowners can implement on their own property to contribute to the protection of our precious water resources.
The Alliance for the Chesapeake Bay and the U.S. Fish and Wildlife Service teamed up to create an environmental education initiative called BayScapes. BayScapes are environmentally sound landscapes benefiting people, wildlife and the Chesapeake Bay. BayScaping advocates a “holistic” approach through principles inspired by the relationships found in the natural world. Some examples of how a homeowner can protect water resources include:
- Controlling runoff from your yard by installing a rain garden or rain barrel
- Replacing lawn areas with alternative landscapes
- Providing mulch cover over bare spots in your yard
- Aerating your lawn
- Recycling water to your garden and yard
More detailed information can be found at the Alliance for the Chesapeake Bay or the U.S. Fish & Wildlife Service.