GUIDANCE FOR DELINEATING INVASIVE AQUATIC PLANTS FOR MANAGMEMENT
Objectives
1. Delineating and qualifying boundaries of invasive aquatic plants for management purposes.
2. Collect additional information on the geographic locations, size (boundaries), and relative
abundance of invasive aquatic plants for management purposes.
3. Identify native aquatic plants and their locations in proximity to invasive aquatic plants to
inform management decisions including buffering treated areas.
Introduction
Delineating vegetation is critical for natural resource planning, management and protection. A map
provides a physical representation of where plants occur. By classifying vegetation, selected properties
of the plants (e.g. species identity or relative abundance) can be used to describe and differentiate areas
for management purposes. For example, the map can depict areas where invasive plants occur and
distinguish areas with native plants.
There are multiple needs for data on aquatic plant beds or stands. The MN DNR Invasive Species
Program, lake groups and local units of government are interested in mapping stands of invasive and
native aquatic plants for management activities (e.g. Eurasian watermilfoil, curly-leaf pondweed
flowering rush or starry stonewort control as well as native plant protection), assisting in rapid response
planning, evaluating and tracking populations over time.
An aquatic plant surveyor must delineate invasive aquatic plants before management actions are
undertaken. If a contractor or lake group completes a delineation, some effort by the DNR to verify the
results is required. Generally, large beds or stands of invasive vegetation should be mapped as
contiguous areas for management (polygons) and isolated plant occurrences mapped as points.
Aquatic plant definitions and classifications
Delineation: a specific type of survey recognized by the MN DNR that is used to identify areas of
vegetation either targeted for control or identified for protection.
Polygon: a shape, usually drawn with GIS or GPS, which describes the area of a plant stand or bed to be
controlled or protected/buffered from management activities.
Waypoint: a sample point or survey point taken with a GPS unit where plant observations are recorded.
Stand or Bed: an area of vegetation that is identified based on distinctiveness and uniformity. It is
mapped or delineated as a polygon based on the target species’ presence and abundance.
Treatment: management activities used to control an invasive plant species generally through
mechanical, chemical or biological means. Note – MN DNR permits are required in most instances.
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Target Plant: the plant species (invasive or native) identified as the primary concern for the delineation
(e.g. for control or protection purposes).
Associated Plants: plants that are observed in a bed or stand but are not dominant. Both native and
invasive plant species should be noted during the delineation as well as their respective relative rake
fullness or visual abundance (see definition for Relative Rake Fullness or Visual Abundance below).
Rake Coverage or Visual Abundance: an abundance ranking (0-4) based on the number of plants or
percent plant coverage observed at a sampling point (waypoint). For invasive plant delineations these
rankings are used to determine potential management areas for control purposes. Determining
abundance is subjective and estimates may differ across surveyors. MN DNR Invasive Species Program
uses ranking of 0-4 based on rake coverage and/or visual abundance. (See Table 1 below for
clarification). For visual abundance assessments, it is important to conduct the assessment over a
uniform sized area (e.g. entire side of boat, the area immediately around the boat or 5-10 square
meters) to consistently rank abundances of the target plant.
Table 1. Quantitative ranking (0-4) used to estimate plant abundance based on rake coverage and/or
visual observation. A zero (0) ranking indicates no target plants were retrieved or observed in a sample.
Stand Density: an overall abundance ranking for a target species within a larger plant stand or bed.
Stand density can be used as an assessment tool by comparing stand densities over time or before and
after management. See Table 1, for visual abundance descriptions and appropriate stand density
rankings.
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Equipment
A checklist of recommended field equipment is provided in Appendix.
Data can be recorded on paper forms or electronically. If there are historic maps of target invasive
plants or previously controlled areas, surveyors should review them and make copies on waterproof
paper (e.g., ‘Rite-in-the-rain®’) to bring in the field or input them into their GPS devices.
If mapping with a hand-held or boat-mounted GPS unit (e.g. Garmin Map 76 or GPS Map 78), surveyors
must collect a series of waypoints, boat tracks and notes to identify the plant species associated with
each delineated plant bed or stand. Post-processing of data generally occurs with a desktop computer
using a GIS mapping program such as ArcMap or Google Earth to create delineated polygons (i.e.
treatment polygons, or native species beds or stands) from the boat tracks and waypoint observations.
Processed data should be submitted to the DNR including GIS files and associated invasive/native plant
data (as a tabular electronic spreadsheet) so that a map can be recreated if needed.
Delineation timing and purpose
A field delineation is simply the process of mapping the extent (edges) of invasive and native aquatic
plant stands or beds. Surveys are best done under low to moderate wind conditions (< 20 km/h or 12
mi/h). Surveyors should time pre-treatment delineations when the target aquatic plant is actively
growing and observable.
The distribution and abundance of plants can change dramatically throughout the growing season and
from year to year. For this reason, delineations are generally performed during the season in which
management has been planned for the target plant. To schedule early season delineations (typically
applies to curly-leaf pondweed), communication with lake residents/users can be helpful as they may
have knowledge of when plants are present.
To evaluate effectiveness of management efforts, a follow-up delineation can be performed after
treatment or the subsequent year depending on the management strategy. Lastly, additional surveys,
such as point-intercept surveys, may be appropriate to identify changes in a plant community over time
and at a lakewide scale. The objective of a point-intercept survey is distinct from a delineation and these
surveys are not ideal to identify areas for invasive plant control (i.e. delineate polygons).
Conducting the delineation
Delineation of a target plant occurs through field observations generally made via three methods. These
methods are often combined during a delineation and include: visual observations, SONAR (fishfinder)
observations, and thrown or spun rake observations. The ability to visually identify the boundaries of
submersed plant stands varies with water clarity, depth, wind, plant height and plant cover. If water
clarity is limited, a surveyor must use a sampling rake or other below-water sampling device to identify
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plants. A metal rake head attached to a rope can be thrown and dragged along the lake bottom, or a
rake head attached to a long pole pushed to the lake bottom and spun (rotated). The surveyor then
records each plant species collected on the rake and quantifies rake fullness to characterize relative
plant abundance. SONAR can assist in below water plant observations but must be verified by a
sampling rake.
Delineation field process
1. Pre-survey: gather previous year’s delineation or polygons and upload this information on the
GPS unit for reference. If helpful, review bathymetric maps (lake contours) to get an idea where
submersed invasive plants may grow.
2. Record the track of the boat with the GPS receiver.
3. Beginning at one end of the first area to delineate, run transects (paths) perpendicular from
shore lakeward, using a zig-zag pattern for narrow littoral zones (See Figure 2 below).
Figure 1. Example of delineation process. Polygon indicates an invasive plant treatment area, dotted line
indicates boat track, and waypoints indicate abundance observations.
4. Along the transect, take waypoints at regular intervals noting target and associated plant
observations (see below Sampling Waypoints for more information). If the target area is
narrow, make the intervals short and vice versa.
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NOTE: A general rule could be applied which allows for points to be spaced 10-25 meters
apart on small lakes (100-400 acres), 35m on medium lakes (400-1000 acres) and 50m on
large lakes (1000+ acres). Additionally, one hundred (100) waypoints is a general minimum
number of survey points to be taken on a small waterbody. However, number of survey
points will vary depending on the size of survey area, extent of infestation, and whether the
stands are monocultures or are composed of a diverse mix of plant species.
5. As sampling progresses to deeper depths, stop when the target plant is no longer observed.
6. Repeat this process until the entire littoral zone or targeted area has been surveyed. Postprocessing of collected data is then completed using GIS software to edit polygons and create a
map.
7. As an option, surveyors can assign a qualitative stand density rating for each delineated plant
stand based on the target plants (see figure 6). Surveyors can sample random points within the
stand by rake toss and use the average rake-collected relative abundance of the target plant
(the scale 1-4 noted below) to characterize stand density.
Sampling Waypoints: (At each sample point)
1. If visibility is adequate, record visual plant observations or use a sampling rake if inadequate or
to verify plant species present.
• Use SONAR to assist in detecting plant presence, especially at deeper depths.
• Record and estimate the range in depths where target invasive plant occurs.
2. Record water depth at all sample points (if available).
3. Record an estimate of relative abundance of the target plant at each sample waypoint (use the
abundance scale of 0-4 and see Figure 1 for rake abundance clarification).
4. Record observations of native plants when present and their relative abundance (i.e. rake
fullness).
• Early season native plants may be sparse, small and more difficult to detect.
• Note the presence and location of stands of floating leaf and emergent vegetation.
5. Other parameters or observations to consider:
• Water temperature: Record 1-3 observations of water temperature below surface at
dispersed locations around the lake including GPS location and depth of temperature
reading. Some observers record temperatures from different depths: surface, mid
depth, and near lake bottom.
• Water clarity: record at least one observation and GPS location of Secchi disk
transparency during survey at a lake depth that exceeds the Secchi observation.
Other observations: it may be helpful to include the weather and conditions of your
survey day. Additionally, any other notes that may be helpful to your delineation
assessment.
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Figure 2. Example field data recording sheet for delineation surveys.
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Figure 3. Example field data recording sheet for delineation survey on Middle Cormorant Lake. Abundance ranking represented as 1-4, zeros (0) not listed.
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Figure 4. Example delineation map with proposed treatment polygons for Eurasian watermilfoil. Points courtesy of Anoka Conservation District.
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Figure 5. Example delineation map of Eurasian watermilfoil. Lake Josephine, Ramsey County, MN.
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Figure 6. Example map inset of delineated polygons of Eurasian watermilfoil with qualitative density ranking.
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APPENDIX
Example Field Delineation Equipment List
☐Clipboard
☐Lake Access point / Map
☐Data sheets on waterproof paper (Rite-in-the-rain®) or electronic data collection device
☐Bathymetric map of lake
☐Pencils
☐Double sided rake on rope or metal garden rake with handle
☐Plant ID books/ AIS identification sheets
☐Polarized sunglasses
☐Plastic bags/collection containers
☐Sharpie® marker
☐Sorting trays for plants and invertebrates (white or light color)
☐Hand lens
☐Digital camera
☐Depth Pole or SONAR fishfinder
☐Boat / Canoe
☐Life Jackets [1 each wearable (USCG Type 1, 2, 3, or 5) and 1 throwable (USCG Type IV)]
☐GPS Unit with historical data/polygons uploaded
☐Secchi disk
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