Chapter 8 - A Citizen's Manual for Developing Integrated Aquatic Vegetation Management Plans

Map Aquatic Plants (Step F)

What is an Aquatic Plant Survey

Depending on a water body's size, depth, and other characteristics, aquatic plant growth can be extensive or occur in small localized areas. In order to design an effective management program specific to your water body, the types of aquatic plants growing there, their location and the extent of growth must first be determined. This can be accomplished by performing an aquatic plant survey. A survey involves systematically traveling around the water body and shoreline and noting aquatic plant conditions. An important part of the survey is collecting samples of aquatic plants to verify the species. This is especially important if invasive, nonnative macrophytes are suspected to be present.

Tip: Staff with Ecology's Freshwater Aquatic Weeds Management Program can guide you in designing a survey of your water body. In addition, grants are available for aquatic plant surveying projects through Ecology's Aquatic Weeds Management Fund.

How to Map Aquatic Plants

Mapping aquatic plants in your water body involves the following tasks:

1. Conduct a systematic survey of the water body.
2. Produce an aquatic plant survey map.

1.  Conduct a systematic survey of the water body. Aquatic plant surveys are usually conducted in critical stages in the growth cycle of plants. Ideally, surveys should be performed early in the growth season (spring), at mid-season (summer), and late in the growth season (fall). But this often can't be done because of time and financial limitations. A survey at the height of the growth season (August), when plants are most obvious, provides a practical and valid alternative. A simple aquatic plant survey consists of:

1. Identifying major types of aquatic plants.
2. Drawing a map of aquatic plant types and locations in the water   body.
3. Estimating relative abundance of aquatic plant types.
4. Collecting samples of plant species.
5. Identifying sediment types.

A. Identifying major types of aquatic plants.

Before you start your survey, you will need to become familiar with various types of aquatic plants. There are generally four kinds of aquatic plants that inhabit freshwater. The types are characterized according to how they are attached to the sediments. The four groups are emergent (such as cattails), freely-floating (such as duckweed), rooted, floating-leaved (such as water lilies), and submersed forms (such as milfoil). The four plant types may occupy different regions of the lake, with emergents and floating-leaved plants confined to shoreline margins, while submersed and free-floating plants can extend to deeper, open water areas. In general aquatic plants tend to inhabit shallow, near-shore areas of the water body. In shallow water bodies, profuse aquatic plant growth may occur throughout the system.

How to Recognize the Four Types of Aquatic Plants

Emergent aquatic plants grow rooted in saturated soils around the shoreline or in water up to about 2 feet deep. Mature emergents stems, leaves, and flowers extend well above the water surface. Many look like terrestrial plants. Soft rushes, bulrushes, cattails, and iris are typical emergent species.

Freely-floating aquatic plants float on or under the water surface. Their root systems, if present, generally hang beneath the plant and are are not attached to the bottom. This diverse group ranges from large plants like coontail and water hyacinth to very small surface-floating plants like duckweed. They are usually found in protected areas or where water currents are very slow. Since they absorb nutrients entirely from the water column, these aquatic plants are frequently found where nutrient content is high.

Rooted floating-leaved aquatic plants grow attached to the sediments in water depths from 1.5 to 10 feet. They are recognized by oval or circular leaves that float on or project just above the water surface. The floating leaves are connected to the bottom by long, flexible, fairly rigid stems. Water lilies are common floating-leaved plants.

Rooted submersed aquatic plants grow at water depths where light is sufficient. Submersed plants grow with stems and leaves underwater, although some forms also have differently-shaped leaves (e.g. broad-leafed pondweed). Submersed species usually have long, thin, flexible stems that are supported by the water. Submersed plants show a variety of leaf forms, from long ribbons (long-leaf pondweed) to feathery whorls (milfoil). Most submersed aquatic plants produce flowers above the water surface.

All the aquatic plant line drawings are the copyright property of the University of Florida Center for Aquatic Plants (Gainesville). Used with permission.

B. Drawing a map of aquatic plant types and locations in the water body.

You will need the following basic supplies and equipment for your survey:

• A map of your water body
• A rope marked off in feet to measure water depth
• A weighted rake with rope attached for collecting samples
• A notebook, pencils, and waterproof marker
• Plastic bags for samples, with labels
• An anchor

Keeping the four basic plant types in mind, tour the entire water body by boat, noting where plants are near or at the water surface. You may also find it helpful to walk around the shoreline, especially if near-shore areas are clogged by weeds and make boat passage difficult. Sketch the locations of plant growth for the four types on a large-scale map of the lake, preferably one that indicates water depth intervals and includes major landmarks for reference.

C. Estimating relative abundance of aquatic plant types.

The relative abundance or prominence of the aquatic plant types often indicates how well the system is in balance. A healthy aquatic system usually has a variety of types and species of plants. The presence of only a few species of plants in a water body may occur where shoreline areas have been disturbed (by an influx of sediments or other contaminants) or have been invaded by exotic species.

In order to determine relative amounts of aquatic plants, you will need to look at the plant beds at representative points within the water body. Before leaving shore, establish survey lines, called transect lines, at appropriate points along the shoreline. For a small lake, you can mark off transects, say every 300 feet, all the way around the shoreline. Draw these lines on the lake map extending them perpendicularly from shore out to where the water is about 20 feet deep (typically the outer limit of growth).

In a boat, follow each of these lines looking at the submersed plants through an underwater viewer. These can be obtained at diving shops or recreational supply stores or built (contact Ecology staff for ideas on constructing your own viewer). At regular points along the transect (e.g. at increments of 3 feet of water depth), make an estimate of plant abundance by counting the number of plants per unit area of lake bottom. Estimate plant abundance as sparse (a few plants per square yard), moderate (5-10 plants per square yard), or dense (more than 10 plants per square yard).

D. Collecting samples of plant species.

Identifying aquatic plant species is important for several reasons. For one thing, different species often respond differently to the same control techniques. A technique that is very effective on one species may not work at all on a different species. It is also important to determine whether any rare or sensitive plants are present. These species are protected and some control technologies are prohibited. Finally, it is crucial to find out whether any invasive, nonnative plant pests are present, because the presence of these plants calls for fast, aggressive action. To help acquaint you with some important exotic plant invaders, an illustrated plant identification key in Appendix B portrays six exotic species of concern in Washington waters.

RED FLAG - If an invasive, exotic species is present in your water body, notify staff at Ecology's Freshwater Aquatic Weeds Management Program . A more intensive survey should be conducted to determine the precise locations of the exotic plant populations. In addition, special measurements should be taken to deter the status of the infestation, regardless of whether it is in a beginning or advanced stage.

If an endangered, rare, or sensitive aquatic plant is present in your waterbody, a more intensive survey is recommended to determine the precise locations. See the discussion on the DNR Natural Heritage Program in Appendix C.

Samples of aquatic plants should be collected at points along the survey transects. From the boat or shoreline you can cast a weighted rake to the lake bottom and pull up aquatic plants. Be sure to note the transect line number, the location on the transect, and the depth from which the sample was taken (use your calibrated rope to measure depth). Specimens collected in this manner can be bagged and sealed for later shipment to a specialist for identification.

It is also advisable that you preserve a sample of the important plant species in your water body for permanent record. Staff with Ecology's Aquatic Weeds Management Program can help you with ideas on preserving plant specimens.

Tip: Be sure to keep all plant fragments on the boat for proper disposal later on, as many problem plant species can reproduce and spread by fragments.

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How to Collect and Prepare an Aquatic Plant Sample for Verification

Step 1. Obtain an aquatic plant sample by dropping a weighted rake to the lake bottom and pulling up the vegetation snagged by the rake. Remove the plants from the rake, sorting out the different plant types. To keep the plants from drying out, sort them in a shallow pan filled with water.

Step 2. Rinse a few healthy specimens of the plant types of concern with water from the lake. Carefully lay the plants between two pieces of damp paper towel, place them in a plastic bag and seal the bag securely. Label the bag clearly with the date, name of the water body, location and depth of sample, and your name and telephone number.

Step 3. Mail the samples to a recognized aquatic botanist for identification as soon as possible. Damp plant specimens in a plastic bag can easily be mailed in a regular envelope.

Step 4. If delivering a fresh (wet) sample in person, store it in a plastic jar filled with lake water in the refrigerator in the interim, and then transfer it to a small cooler with an ice pack for transport to an aquatic plant expert. Plant samples can usually be kept fresh in this way for up to five days.

To whom do I send an aquatic plant sample for identification?

Contact Jenifer Parsons (509) 457-7136 or Kathy Hamel (360) 407-6562.

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E. Identify sediment types.

Sediment types are generally classified as:

• mucky, organic
• sandy
• compact, clayey
• gravely

Sediments in the water body can be identified by either collecting a bottom sample with a small sampling dredge, by shoving a PVC pipe into the bottom, or by examining sediment brought up with an aquatic plant sample.

2. Produce an aquatic plant survey map of the water body.

Using field notes and maps from the aquatic plant survey, construct and aquatic plant map of the water body. The aquatic plant map should show:

• Water depth contours, in feet or meters (this type of data is presented on bathymetric maps).
• Approximate locations of each of the four types of macrophytes.
  • emergents
  • free-floating types
  • rooted, floating-leaved types
  • submersed types
• Highlighted locations of exotic, invasive aquatic plant species, if present.
• Highlighted locations of rare, sensitive, or endangered aquatic plant species, if present.
• Locations of wetlands/conservancy areas.
• General sediment types
• mucky, organic
• sandy
• compact, clayey
• gravely

• Tributaries/outlets
• Open areas

Tip: Preparing an aquatic plant map for your water body will save you valuable time later in the planning process as you explore certain recommended treatment options. The above information and aquatic plant map can be used when completing an Application for Stocking Grass Carp with Fish and Wildlife.

Reference and Resources on Aquatic Plant Identification

• Ecology's Freshwater Aquatic Weeds Management Program Coordinator^A
• Aquatic plant Identification and Herbicide Use Guide¹⁰
• Wetland Plants of the Pacific Northwest¹⁷
• Common Marsh, Underwater, and Floating-leaved Plants²
• County Noxious Weed Control Boards

Example of  an Aquatic Plant Map

The following is an example of an aquatic plant survey map produced for Lake Tranquil.

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