Download assessment of the milfoil weevil

ASSESSMENT OF THE MILFOIL WEEVIL
(EUHRYCHIOPSIS LECONTEI) FOR BIOLOGICAL
CONTROL OF EURASIAN WATERMILFOIL
(MYRIOPHYLLUM SPICATUM) IN DEVILS LAKE
(LENAWEE COUNTY, MI)
December, 2010
ASSESSMENT OF THE MILFOIL WEEVIL
(EUHRYCHIOPSIS LECONTEI) FOR BIOLOGICAL
CONTROL OF EURASIAN WATERMILFOIL
(MYRIOPHYLLUM SPICATUM) IN DEVILS LAKE
(LENAWEE COUNTY, MI)
December, 2010
Prepared for:
Mr. Charles Jarrett, Supervisor
Woodstock Township
730 Manitou Road
Manitou Beach, MI 49253
Mr. John Jenkins, Supervisor
Rollin Township
730 Manitou Road
Manitou Beach, Michigan 49253
Prepared by:
Lakeshore Environmental, Inc.
803 Verhoeks Road
Grand Haven, Michigan 49417
TABLE OF CONTENTS
SECTION
PAGE
LIST OF FIGURES....................................................................................................................................... i
LIST OF TABLES ....................................................................................................................................... ii
LIST OF APPENDICES ............................................................................................................................. iii
1.0
EXECUTIVE SUMMARY ............................................................................................................ 6
2.0
DEVILS LAKE AQUATIC VEGETATION COMMUNITIES ................................................... 8
2.1
3.0
The GPS Point-Intercept Method ....................................................................................... 9
THE PROBLEM: EURASIAN WATERMILFOIL (EWM) ....................................................... 12
3.1
Methods for Control of EWM .......................................................................................... 15
3.1.1 Biological Control ................................................................................................... 15
3.1.2 Aquatic Herbicides and Algaecides ........................................................................ 17
3.1.3 Benthic Barriers ....................................................................................................... 18
3.1.4 Suction Harvesting .................................................................................................. 18
4.0
EVALUATION OF WEEVILS IN DEVILS LAKE (2010) ....................................................... 19
4.1
In Situ Methods................................................................................................................. 19
4.1.1 Weevil Stocking Site Selection ............................................................................... 19
4.1.2 Weevil Stocking ...................................................................................................... 21
4.1.3 Milfoil Stem Collection ........................................................................................... 22
4.1.4 Milfoil Stem Density Assessment ........................................................................... 22
4.2
Laboratory Methods and Analyses................................................................................... 22
4.2.1 Rinsing and Separation of EWM Stems ................................................................. 23
4.2.2 Measurement of EWM Stem Parameters................................................................ 23
4.2.3 Analysis of EWM Stems for Weevil Damage ........................................................ 23
5.0
DEVILS LAKE 2010 WEEVIL DATA ....................................................................................... 24
5.1
6.0
Results and Discussion by Site......................................................................................... 24
DEVILS LAKE 2010 WATER QUALITY DATA ..................................................................... 26
6.1
Results and Discussion by Site......................................................................................... 27
7.0
FUTURE WEEVIL STOCKING RECOMMENDATIONS AND COST ESTIMATES .......... 34
8.0
LITERATURE CITED ................................................................................................................. 36
FIGURES
NAME
PAGE
Figure 1. Variable-Leaved Pondweed................................................................................................. 12
Figure 2. Eurasian Watermilfoil Plant ................................................................................................ 13
Figure 3. Eurasian Watermilfoil Canopy ............................................................................................ 14
Figure 4. Native Milfoil Beds ............................................................................................................. 14
Figure 5. Milfoil Weevil (Euhrychiopsis lecontei) ............................................................................. 16
Figure 6. Aerial Photo of Devils Lake 2010 Weevil Stocking Sites ................................................... 21
Figure 7. Degree of Weevil Damage on EWM Stems among Sites ................................................... 25
Figure 8. EWM Stem Density for All Sites ........................................................................................ 26
TABLES
NAME
PAGE
Table 1. Devils Lake Exotic Aquatic Plants (2010).............................................................................. 8
Table 2. Devils Lake Native Aquatic Plants (2010) ........................................................................... 10
Table 3. Data Table of Weevil Stocking Sites (2010) ........................................................................ 25
Table 4. MDNRE Lake Trophic Status Parameters ............................................................................ 27
Table 5. Devils Lake Spring 2010 Water Quality Data ...................................................................... 33
Table 6. Devils Lake Late Summer 2010 Water Quality Data ........................................................... 33
Table 7. Devils Lake Weevil Program Budget for 2011..................................................................... 34
APPENDICES
NAME
PAGE
APPENDIX A. Devils Lake GPS Grid Data 2010 ............................................................................. 39
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Devils Lake 2010 Annual Report
December, 2010
Page 6
ASSESSMENT OF THE MILFOIL WEEVIL (EUHRYCHIOPSIS LECONTEI) FOR
BIOLOGICAL CONTROL OF EURASIAN WATERMILFOIL
(MYRIOPHYLLUM SPICATUM) IN DEVILS LAKE
(LENAWEE COUNTY, MI)
December, 2010
1.0 EXECUTIVE SUMMARY
This report evaluates Eurasian Watermilfoil stem and weevil data collected during the late summer of
2010 in an effort to determine the efficacy of the weevil (Euhrychiopsis lecontei) on Eurasian
Watermilfoil (Myriophyllum spicatum) growth characteristics within Devils Lake, Lenawee County,
Michigan in sections 26, 27, 34, and 35 of Woodstock Township (T. 5S, R. 1E) and sections 2,3,4,9
and 10 of Rollin Township (T. 6S, R1E). Devils Lake was previously surveyed in July of 2007 and
determined to be infested with approximately 2 acres of M. spicatum that was concentrated around
the littoral zone of the lake. An additional survey during June of 2009, detected approximately 154.6
acres of Eurasian Watermilfoil. During that survey, it was also determined that approximately 81.8
acres of Eurasian Watermilfoil was present in Woodstock Township and 72.8 acres of Eurasian
Watermilfoil was present in the Rollin Township portions of the lake. Recent surveys conducted
during late spring of 2010 determined that the Eurasian Watermilfoil population in the Woodstock
Township portion of the lake was out-competed by a sudden overgrowth of the native milfoil species,
Myriophyllum heterophyllum (Variable Watermilfoil) which grows in very dense beds, yet does not
exhibit the fragmentation risk of the Eurasian Watermilfoil species. As a result of this discovery, the
stocking of the weevils was recommended to occur in areas of the lake which contained a highly
robust population of Eurasian Watermilfoil (Myriophyllum spicatum) to ascertain a high probability
of successful colonization by the weevil and resultant healthy population. The areas of Devils Lake
which contained robust Eurasian Watermilfoil beds included an area near the south portion of the
lake and in an area offshore from the public access site as well as near the lake outlet at the north
section.
Approximately 41,500 weevil units were applied to the three treatment sites (SE1, W1 and
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December, 2010
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W2) located at the southeast and west areas of the lake. The weevil stocking density used for these
sites was greater than 200 weevils m-2, which was recommended by Newman and Biesboer (2000)
for optimal weevil damage. Data on Eurasian Watermilfoil stem characteristics and weevil damage
was collected at the treatment sites during October of 2010. It is suspected that Devils Lake contains
a significantly lower population of hybridized milfoil, especially in the Rollin Township section of
the lake. In all areas, the clear visual distinction between the native and exotic milfoil species can be
made. This may indicate that hybridization of exotic milfoil with M. heterophyllum is less likely
than that of M. sibiricum (Northern Watermilfoil). The majority of the native milfoil populations in
Devils Lake consist of M. heterophyllum (Variable Watermilfoil).
The highest densities of Eurasian Watermilfoil (over 118 stems per square meter) were located in the
area offshore from the public access site (Site W1). Stem densities which ranged from 89-110 stems
m-2 were noted at the SE1 and W2 sites, respectively.
A collection of approximately 40 Eurasian
Watermilfoil stems from the 3 total stocking sites has confirmed that the weevil populations are
thriving at all stocked locations as indicated by weevil damage, especially at the NW1 site. The
majority of the Eurasian Watermilfoil in Devils Lake exists in water with adequate depth to avoid
fragmentation from boat propellers. There is some concern, however, that Eurasian Watermilfoil
fragments produced from high wave action are spreading to areas outside of the weevil stocking
zones and are thus in the process of more Eurasian Watermilfoil bed formations. In areas with these
characteristics, it may be advantageous to spot-treat the Eurasian Watermilfoil with registered aquatic
herbicides or suction harvesting to prevent further spread. Vulnerable areas generally include near
docks and shorelines.
The long-term benefits from the weevil may take years to be fully realized
because the feeding action of the weevil on the Eurasian Watermilfoil stems requires adequate time
for the structural integrity of the stems to decline and eventually result in stem mortality.
Water quality data collected from Devils Lake during the spring and summer of 2010 indicates that
the lake is meso-eutrophic (moderate in nutrients and high in transparency), and contains an
abundance of planktonic green algal species.
During the summer, the dissolved oxygen
concentration of the lake drops below the recommended concentration of 5.0 mg L-1 which makes the
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December, 2010
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hypolimnion (bottom depths of the lake) uninhabitable to fish. This reduction in dissolved oxygen is
a normal phenomenon in lakes since the demand for oxygen at the lake bottom is high due to the
respiration by microbes which are actively breaking down organic matter.
2.0
DEVILS LAKE 2010 AQUATIC VEGETATION COMMUNITIES
The aquatic plant sampling methods used for lake surveys of macrophyte communities commonly
consist of shoreline surveys, visual abundance surveys, transect surveys, Aquatic Vegetation
Assessment Site (AVAS) Surveys, and GPS Point-Intercept Grid surveys. Other less common and
more costly surveys that involve bioacoustic monitoring and/or side-scan sonar imaging are used to
determine biomass density in very large bodies of water (i.e. Chesapeake Bay, US). The Michigan
Department of Natural Resources and Environment (MDNRE) protocol consists of an Aquatic
Vegetation Assessment Site (AVAS) Survey which assigns a percentage of cover to each sampled
quadrat based on visual estimates (Table 1), whereas the U.S. Army Corps of Engineers utilizes a
GPS Point-Intercept Grid survey for inland lakes following large-scale lake improvement treatments
to assess the changes in aquatic vegetation structure and to record the relative abundance and
locations of native aquatic plant species. Due to the shallow mean depth and large size of Devils
Lake, a bi-seasonal GPS Point-Intercept Grid survey is preferred to assess all aquatic species.
MDNRE Species
Abundance Meaning
% Coverage of AVAS
Abundance Code
Interpretation
Surface Area
a
Found
<2
b
Sparse
2 - 20
c
Common
21 – 60
d
Dense
> 60
Table 1. MDNRE AVAS species relative abundance codes used in AVAS surveys
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December, 2010
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2.1
The GPS Point-Intercept Grid Survey Method
While the MDNRE AVAS protocol considers sampling vegetation using visual observations in areas
around the littoral zone, the Point-Intercept Grid Survey method (Appendix A) is meant to assess
vegetation throughout the entire surface area of a lake (Madsen et al. 1994; 1996). This method
involves conducting measurements at Global Positioning Systems (GPS)-defined locations that have
been pre-selected on the computer to avoid sampling bias. Furthermore, the GPS points are equally
spaced on a map. The points should be placed together as closely and feasibly as possible to obtain
adequate information of the aquatic vegetation communities throughout the entire lake. At each GPS
grid point location, two rake tosses are conducted and the aquatic vegetation species and abundance
are recorded. In between the GPS points, any additional species and their relative abundance are also
recorded using visual techniques. This is especially important to add to the GPS Point-Intercept
survey method, since M. spicatum and other invasive plants may be present between GPS points but
not necessarily at the pre-selected GPS points. Once the aquatic vegetation communities throughout
the lake have been recorded using the GPS points, the data can be placed into a Geographic
Information System (GIS) software package to create maps showing the distribution of a particular
species. The GPS Point-Intercept method is particularly useful for monitoring aquatic vegetation
communities through time and for identification of nuisance species that could potentially spread to
other previously uninhabited areas of the lake. For this particular survey, a total of 630 GPS grid
points were sampled throughout Devils Lake. This number of grid points was selected to dramatically
increase the sample size necessary to reduce variability among lake sampling sites and to yield an
accurate estimate of M. spicatum acreage. A table of all aquatic plant species observed in Devils Lake is
shown below in Table 2.
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December, 2010
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Aquatic
Aquatic Macrophyte
Aquatic Macrophyte
Macrophyte
Common Name
Growth Form
Species
% of
Quadrats
Present
(of 630)
Myriophyllum spicatum,1
Eurasian Watermilfoil
Submersed
31.0
Potamogeton crispus,2
Curly-leaf Pondweed
Submersed
1.3
Chara vulgaris (macroalga), 3
Muskgrass
Submersed
23.0
Potamogeton pectinatus,4
Thin-leaf Pondweed
Submersed
5.4
Potamogeton zosteriformis, 5
Flat-stem Pondweed
Submersed
3.5
Potamogeton gramineus,7
Variable-leaf Pondweed
Submersed
23.2
Potamogeton richardsonii, 9
Clasping-leaf Pondweed
Submersed
13.2
Potamogeton illinoensis,10
Illinois Pondweed
Submersed
3.8
Vallisneria americana,15
Wild Celery
Submersed
3.7
Myriophyllum sibiricum, 17
Northern Watermilfoil
Submersed
1.7
Myriophyllum heterophyllum,18
Variable Watermilfoil
Submersed
2.9
Ceratophyllum demersum, 20
Coontail
Submersed; Non-rooted
1.1
Elodea canadensis, 21
Common Waterweed
Submersed
4.1
Utricularia vulgaris, 22
Common Bladderwort
Submersed; Non-rooted
0.2
Utricularia minor,23
Small Bladderwort
Submersed;Non-rooted
1.6
Najas guadalpensis, 25
Southern Naiad
Submersed
4.1
Potamogeton pusillus ,26
Small-leaf Pondweed
Submersed;Rooted
9.4
Nymphaea sp., 30
White Waterlily
Floating-leaved
2.5
Nuphar sp., 31
Yellow Waterlily
Floating-leaved
0.8
Arrow arum, 36
Arrowhead
Emergent
2.7
Pontedaria cordata, 37
Pickerelweed
Emergent
0.5
Typha sp.,39
Cattails
Emergent
0.3
Decodon verticillata, 42
Swamp Loosestrife
Emergent
5.4
Lythrum salicaria, 43
Purple Loosestrife
Emergent
1.9
Table 2. Aquatic plant species and their relative abundance in Devils Lake (October, 2010).
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December, 2010
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The grid survey determined that approximately 41.3% of the surveyed areas (i.e. littoral zone area)
were unvegetated and contained bare sand and/or marl. The presence of bare areas was more
apparent in 2010 than in 2009 and the reasons are unclear. During the 2010 survey, a total of 15
native submersed, 2 floating-leaved, and 4 emergent aquatic plant species were found for a total of
21 species.
The most dominant native aquatic plant species within Devils Lake were in the
Potamogetonaceae family, which included the Pondweeds such as Variable-leaf Pondweed (P.
gramineus; Figure 1). Chara vulgaris was present in 23.0% of the grid points sampled and thus was
the most dominant rooted native submersed aquatic plant (actually a macroalga) in the littoral zone.
Chara vulgaris often carpeted the lake bottom in areas where it grew and formed a thick layer which
makes it difficult for newly formed M. spicatum fragments to take root in the lake bottom sediment.
Thus, preservation of this and other low-growing species are critical for the long-term control of M.
spicatum and other nuisance species that spread through fragmentation. Clasping-Leaf Pondweed
occupied approximately 13.2% of the littoral zone, which represents a significant increase in this
plant from 2009. The pondweeds serve as excellent cover for fish and macroinvertebrates and should
be preserved to the extent possible to support a healthy fishery. The majority of the native aquatic
plant species in Devils Lake were sparse in abundance and do not currently threaten the balance of
the ecosystem or the safety of recreationalists on the lake. In fact, protection of these native aquatic
plant species is critical for the ecological balance of Devils Lake.
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December, 2010
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Figure 1. Variable-Leaf Pondweed (P. gramineus), a common native
pondweed present in Devils Lake.
3.0
THE PROBLEM: EURASIAN WATERMILFOIL
Eurasian Watermilfoil (Myriophyllum spicatum; Figure 2) is an exotic aquatic macrophyte first
documented in the United States in the 1880’s (Reed 1997), although other reports (Couch and
Nelson 1985) suggest it was first found in the 1940’s. M. spicatum has since spread to thousands of
inland lakes in various states through the use of boats and trailers, waterfowl, seed dispersal, and
intentional introduction for fish habitat. M. spicatum is a major threat to the ecological balance of an
aquatic ecosystem through causation of significant declines in favorable native vegetation
communities within lakes (Madsen et al. 1991; Boylen et al. 1999), and may limit light from reaching
native plant species (Newroth 1985; Aiken et al. 1979; Figure 3). Additionally, M. spicatum can
alter the macroinvertebrate populations associated with particular native plants of certain structural
architecture (Newroth 1985). Within the past decade, research has been conducted on the genotype
of hybrid watermilfoil species (Moody and Les, 2002; 2007) which are commonly a result of cross-
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pollination between M. spicatum and other native species such as Northern Watermilfoil (M.
sibiricum), and Whorled Watermilfoil (M. heterophyllum). The majority of native milfoils do not
form dense canopies, but may instead form dense beds that reach near the surface of the lake (Figure
4). Since the introduction of Eurasian Watermilfoil, many nuisance aquatic plant management
techniques such as chemical herbicides, mechanical harvesting, and biological control have been
implemented. Thus, biological control may be a preferred method to that is chemical-free and targetspecific, and will not cause fragmentation of M. spicatum. Alternative strategies are discussed in
more detail in section 2 below.
Figure 2. The submersed exotic aquatic macrophyte, Eurasian Watermilfoil, Myriophyllum spicatum,
L. © Superior Photique, 2008
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Devils Lake 2010 Annual Report
December, 2010
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Figure 3. A dense canopy of Eurasian Watermilfoil which reduces light availability to favorable
native aquatic plant species.
Figure 4. Native Watermilfoil species, (above) can also grow in thick beds, but tend not to canopy
across the lake surface.
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Devils Lake 2010 Annual Report
December, 2010
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3.1
Methods of Control for Eurasian Watermilfoil
The management of exotic aquatic plants is necessary in nutrient-enriched aquatic ecosystems due to
accelerated growth and distribution.
Management options should be environmentally and
ecologically sound and financially feasible. Options for control of exotic aquatic plants are limited
yet are capable of achieving strong results when used properly. Implementation of a management
program which protects native aquatic plants (especially the submersed pondweeds and the
macroalga Chara) in Devils Lake to continue to provide for a healthier fishery is recommended.
However, exotic aquatic plant species should be managed with solutions that will yield long-term
results and with minimum harm to the aquatic environment.
3.1.1
Biological Control
The use of the aquatic weevil, Euhrychiopsis lecontei to control M. spicatum has become a popular
option for many inland lakes. The weevil naturally exists in many of our lakes; however, the lack of
adequate populations in many lakes requires that they be implanted or stocked for successful control of
the Eurasian Watermilfoil. The weevil feeds almost entirely on M. spicatum and will leave native
aquatic species unharmed. The weevil burrows into the stems of the Eurasian Watermilfoil and removes
the vascular tissue, thereby reducing the plant’s ability to store carbohydrates (Newman et al. 1996).
Eventually, the Eurasian Watermilfoil stems lose buoyancy and the plant decomposes on the lake
bottom. Recent research has shown that the weevils require a substantial amount of aquatic plant
biomass for successful control of M. spicatum. In addition, the weevils require adequate over-wintering
habitat since they over-winter within shoreline vegetation. Lakes with sparse Eurasian Watermilfoil
distribution and abundant metal and concrete seawalls are not ideal candidates for the milfoil weevil.
Although there is heavy developmental density around the Devils Lake shoreline, an abundance of metal
seawalls, and heavy boat traffic, there is adequate overwintering vegetation around the Devils Lake
shoreline.
Late-summer (October, 2010) surveys of Devils Lake revealed favorable Eurasian
Watermilfoil stem densities (89-118 stems m-2) to support a sustainable weevil population.
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The native weevil, Euhrychiopsis lecontei (Coleoptera: Curculionidae; Figure 5) has been shown to
cause detrimental impacts on the exotic aquatic macrophyte M. spicatum (Creed et al. 1992, Creed
and Sheldon 1995, Newman et al. 1996). The weevil life cycle consists of larval, pupae, and adult
life stages, which all are involved in the destruction of the Eurasian Watermilfoil plants. Completion
of a single life cycle generally occurs in 17-30 days and is dependent upon water temperature
(Newman et al., 1997). In the initial stages of biological control, larvae are applied to the apical (top)
portions of stems and destroy the vascular tissue (Creed and Sheldon 1993, 1994a, Newman et al.
1996), which significantly hinders stem elongation. During the pupation stage, stem vascular tissue
is further destroyed during the construction of the pupal chamber (Creed and Sheldon 1993). During
the adult phase, mature weevils feed on the Eurasian Watermilfoil leaves and stems (Creed and
Sheldon 1993).
Figure 5. The milfoil weevil, Euhrychiopsis lecontei,
Enviroscience, Inc., used with permission.
Observed impacts include the devascularization of stem tissue which causes buoyancy loss (due to a
loss of stored CO2 gases in stem epithelial cells) and photosynthetic growth inhibition of Eurasian
Watermilfoil plants (Creed et al. 1992; Newman et al. 1996). Cofrancesco et al. (2004) summarized
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that the primary mode of weevil damage to the stem includes inhibition of stem elongation. The
weevil is a native herbivore to the waters of the north temperate region, and will feed on native
milfoil populations if the invasive milfoil is not present, though it prefers the invasive milfoil over
native species. Other herbivore species such as Phytobius leucogaster and Acentria ephemerella
showed negligible results in the reduction of Eurasian Watermilfoil (Sheldon 1995; Creed and
Sheldon 1994). It is possible that many water physical, chemical, and biological variables could
affect the success of the E. lecontei control method. As a result, weevil evaluation treatments should
minimize variables to the extent possible. In situ evaluations have the advantage of eliminating
manipulation effects (a form of variable reduction) of transferring plants from a field site to the
laboratory or mesocosm. Conversely, many field evaluations are scrutinized by the presence of
multiple variables that can vary considerably in the field and confound experimental results. Some
studies have assessed the impacts of the weevil on Eurasian Watermilfoil biomass (Scribailo and
Alix, 2003); however this method is more amenable to reviewing long-term impacts of the weevil on
Eurasian Watermilfoil growth.
In the past, the Devils Lake Yacht Club (DLYC) and Lakes
Preservation League (LPL) requested an evaluation to estimate an effective weevil density given the
observed Eurasian Watermilfoil growth within Devils Lake. During 2010, public hearings were held
to gain a measure of support from the public. As a result of the demonstrated support, Rollin and
Woodstock Townships has been working with Lakeshore Environmental, Inc. to assess the efficacy
of the weevils as more are added to the Devils Lake ecosystem.
3.1.2
Aquatic Herbicides and Algaecides
The use of aquatic chemical herbicides is regulated by the MDNRE under Part 33 (Aquatic Nuisance) of
the Natural Resources and Environmental Protection Act, P.A. 451 of 1994, and requires a permit from
the Michigan Department of Natural Resources and Environment (MDNRE). The permit contains a list
of approved herbicides for a particular body of water, as well as dosage rates, treatment areas, and water
use restrictions. Furthermore, residents that reside within 100 feet of the proposed treatment area must
be notified at least seven days, but not more than forty-five days prior to the initial treatment date. A
certified herbicide applicator usually notices the residents in advance of the proposed treatment date, and
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during the day of treatment. Contact and systemic aquatic herbicides are the two primary herbicide
types used in aquatic systems. Contact herbicides cause damage to leaf and stem structures; whereas
systemic herbicides are assimilated by the plant roots and are lethal to the entire plant. Wherever
possible, it is preferred to use a systemic herbicide for longer-lasting aquatic plant control. There are
often restrictions with usage of some systemic herbicides around shoreline areas that contain shallow
drinking wells. Systemic herbicides such as Triclopyr (Trade Name: Renovate OTF®) could be used to
successfully treat localized or widely dispersed beds of Eurasian Watermilfoil. The current infestation
of Devils Lake could be spot-treated with systemic herbicides such as Triclopyr as an alternative to 2,4D for selective long-term control, with little negative impacts to the native aquatic vegetation
communities within the lake.
3.1.3
Benthic Barriers and Weed Rollers
Benthic barriers or mats are generally placed onto the lake bottom of beach areas in early spring after
ice-off to prevent the germination of various aquatic plants, including Eurasian Watermilfoil. The
barriers generally come in sizes which are practical only for small areas (i.e. 12’x12’). If used after
the aquatic vegetation has grown, they will generally require a month for the underlying vegetation to
decay (Madsen 1997). In addition, the mats generally require a use permit from the MDNRE prior to
installation.
For more information on the mats and where to order them, visit the website:
http://www.lakemat.com.
3.1.4
Suction Harvesting (Diver Assisted)
Diver-assisted suction harvesting is a labor-intensive method where individual aquatic plants are
hand-pulled from the sediment by a SCUBA diver and fed into a large suction tube which offloads
the suctioned vegetation onto a barge where they are bagged in biodegradable bags and disposed of
properly. Although this method is time-consuming, it has the benefit of being chemical-free and is
very selective in the vegetation that is removed based on the selectivity of the diver. As long as the
bottom of the lake is not disrupted, the benthic communities are usually unharmed. This strategy has
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been used on both Devils and Round Lakes in 2010 and may be used again to control sparse Eurasian
Watermilfoil populations from spreading outside of weevil stocking areas and near docks and
beaches.
4.0
AN EVALUATION OF WEEVILS IN DEVILS LAKE, LENAWEE
CO, MI
During the summer of 2010, approximately 41,500 weevil units were placed into the southeast and
west sections of Devils Lake. Efforts were made to assure that weevil density studies followed
recommendations by (Newman and Biesboer, 2000), with current weevil stocking densities of ≥ 200
weevils m-2.
4.1
4.1.1
In Situ Methods
Weevil Stocking Site Selection
Devils Lake is a 1,337-acre lake located in sections 26, 27, 34, and 35 of Woodstock Township (T.
5S, R. 1E) and sections 2,3,4,9 and 10 of Rollin Township (T. 6S, R1E), in Lenawee County,
Michigan. The lake has an approximate maximum depth of 63 feet and a mean depth of 14.2 feet.
Although the majority of the lake is deep, there is approximately 350 acres of surface area that is
capable of being colonized by M. spicatum. Nutrient data such as total phosphorus may help to
explain nuisance native aquatic vegetation growth; however, the growth of invasive species such as
M. spicatum is less dependent upon nutrient increases and more dependent on the mode of
introduction and propagation. A review of recent vegetation survey data (October, 2010) by
Lakeshore Environmental, Inc., revealed that the amount of Eurasian Watermilfoil in the littoral zone
areas had increased from 17% to 30% since the 2009 survey. This could be attributed to growth of
the Eurasian Watermilfoil beds prior to weevil implementation. Monitoring of these beds will be
critical in the determination of the weevil efficacy. The majority of this milfoil was present in the
proposed stocking sites.
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Devils Lake 2010 Annual Report
December, 2010
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Devils Lake West Shore and Southeast Shore Sites
The first stocking site (Site W2) was selected at a water depth of approximately 1.5 meters due to the
presence of large, dense healthy M. spicatum beds, and the favorable site protection characteristics
which included large emergent vegetation beds that may serve as overwintering vegetation sites. The
second stocking site (Site W1, out from the public access site) was selected at a water depth of 2-3
meters and had an abundance of thick milfoil beds with a mean stem density of 118 stems m-2. The
third site (Site SE 1) was also selected since other dense areas of milfoil were located there in
approximately 1.5 meters of water depth. Surveys conducted in July of 2010 demonstrated that the
native milfoil species had dominated the northern portion of the lake and the Eurasian Watermilfoil
was sparse in most areas north of the Woodstock township line. As a result, it was recommended to
stock all weevils in places where Eurasian Watermilfoil was dominant and the stem densities were
great enough to sustain viable weevil populations. All of the stocking sites are shown in Figure 6.
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W2
W1
SE1
Figure 6. West and Southeast Shore Weevil Stocking Sites in Devils Lake, Lenawee County, MI.
4.1.2
Weevil Stocking
Milfoil weevils were stocked on June 16 of 2010 in three areas near the west (W1, W2) and southeast
(SE1) shores of Devils Lake. Stocking areas were determined through a combination of previous
Point-Intercept aquatic vegetation surveys conducted during fall of 2009 and spring of 2010.
Approximately 41,500 weevil units were placed among the three sites, with the greatest number of
units (> 20,000) placed at Site W1, since this site had the highest Eurasian Watermilfoil stem density.
All new treatment sites were marked with a GPS unit for future reference in the field. In each of the
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lake treatment areas, a lake bottom area of 625 ft2 (58.1 m-2) was delineated to yield a weevil density
of ≥ 200 weevil units per m-2.
4.1.3
Milfoil Stem Collection
On 22 October, 2010, a total of 120 Eurasian Watermilfoil stems were collected from all of the
current (n=3) weevil stocking sites by skin-divers. Individual Eurasian Watermilfoil stems were
randomly selected and removed at the sediment-water interface and placed into a labeled 2-gallon
ziplock® plastic collection bag for analysis.
4.1.4
Milfoil Stem Density Assessment
On 7 July, 2010, three 0.25 m2 PVC quadrat samples were also collected from each of the three new
treatment sites (W1, W2, and SE1) to measure the stem density in order to estimate the number of
stems per square meter in Devils Lake. The PVC quadrat was placed on the lake bottom and all
plants which were within the square were cut and placed into labeled 2-gallon ziplock® plastic bags
for stem counts. A total of three for each site were collected and a mean was calculated to yield an
average Eurasian Watermilfoil stem density for each weevil treatment (stocking) site.
4.2 Laboratory Methods and Analyses
After Eurasian Watermilfoil stems were collected in the field and transported to the laboratory, they
were cleaned and sorted prior to being inspected under the dissection microscope.
Individual
Eurasian Watermilfoil stems were keyed to the species level of taxonomy using an aquatic vegetation
taxonomic key (Crow and Hellquist, 2000). Individual methods and analyses are explained in the
sections below.
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4.2.1
Rinsing and Separation of Eurasian Watermilfoil Stems
Each Eurasian Watermilfoil stem that was collected at each of the 3 sampling sites was sorted and
untangled prior to analysis under the microscope. In order to avoid washing away any delicate life cycle
stages (i.e. newly laid eggs or larvae) off of the exterior of the Eurasian Watermilfoil stems, washing of
the stems was conducted only after an initial scan of the Eurasian Watermilfoil stem was completed and
any of the associated weevil life cycle stages (if any present) were recorded. Eurasian Watermilfoil
stems that could not be immediately analyzed were placed between moistened paper towels which were
refrigerated to halt tissue degradation. If necessary, stems with thick encrustations of zebra mussels
(Dreissena polymorpha) or other debris were cleaned with deionized water and a steady stream of cold
and lightly pressurized water. Whenever possible, tissue analyses occurred as soon as the dissection
microscope was available after each sample.
4.2.2
Measurement of Eurasian Watermilfoil Stem Parameters
Stem damage parameters such as stem length, stem compression diameter, and number of stem
lateral branches was measured and recorded. Stem length was measured in (cm) with the use of a
calibrated measuring tape 6 meters in length. Stem compressional diameter was measured in (mm)
with the use of a set of calibrated, digital calipers, which was re-calibrated between each reading for
enhanced accuracy. Stem lateral branches were counted as additional meristems that were formed
off of the main axis of the plant stem.
4.2.3
Analysis of Eurasian Watermilfoil Stems for Weevil Damage
The condition of the Eurasian Watermilfoil stems (index of stem damage, Jermalowicz-Jones et al.,
2007) was measured on each of the collected stems. The index of stem damage includes a stem
tissue damage scale that ranges from 0 to 5. The index ranged from 0 - 5 with a value of “0” denoting
no weevil damage visible, a “1” denoting the presence of eggs on an apical meristem, a “2” denoting the
presence of larvae or eggs on or in the stem, a “3” indicated the presence of larvae in the stem tissues
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and vascular tissue damage, “4” indicated the presence of larvae or pupae and severe necrosis of the
stem tissue, and a “5” denoted both severe tissue necrosis, weevil pupae or larvae, and the loss of foliar
leaves. To assess for weevil damage, each individual milfoil stem was placed under the dissection
microscope (first under the 10x objective power and then under the 20x objective power) to look at
the plant from the apical tip to the roots. Both overhead and base-lighting are used to illuminate the
plant specimens and determine if weevil larvae or other life cycle stages are present in or on the
individual stems. If weevil stages were located in or on the stems, they were recorded.
5.0 DEVILS LAKE SUMMER 2010 WEEVIL DATA RESULTS
The assessment of all weevil stocking sites from 2010 (Table 3) allowed for a measure of the
continued efficacy of the weevil on the degradation of milfoil stems and for the determination of
future areas to be re-stocked.
5.1
Results and Discussion by Site
All of the three sampling sites exhibited some extent of weevil damage; however, Sites SE1 and W1
contained the highest amount of weevil stem damage at 2.8 and 2.5 respectively (Figure 6), which was
slightly higher than damage values noted for Round Lake. The weevil damage at Site SE1 1 was
marginally significant (p < 0.055) when compared to the other two sites. Site SE1 contained the lowest
mean stem diameters but these were not correlated with increased weevil damage.
Mean stem length was not significantly different among sites and demonstrated a much more consistent
height of plant relative to those stem lengths observed in the Round Lake sites. The differences in stem
lengths at all three sites will be evaluated again in 2011 to determine if weevils have caused the decrease
in stem lengths as previous research has indicated (Cofranceso et al., 2004; Jermalowicz-Jones et al.,
2008). The number of milfoil stem lateral branches was also not significantly different among sites;
however, Site W2 had the highest mean number of lateral branches and also the second highest mean
stem density.
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Stem density (Figure 7) has been shown to be directly correlated with the survival of the weevil which
depends on a high abundance of Eurasian Watermilfoil stems for population growth. Site W1 had the
highest stem density at 118.0±38.9 stems per m-2, followed by Site W2 with 110.0±42.2 stems per m-2.
Site SE1 had the lowest stem density at 89.0±13.8 stems per m-2.
Sampling Mean Stem
Mean Weevil
Site
Diameter
Mean Stem
Mean Stem
Mean # Lateral
Damage Index Length (cm)
Density
Branches
(mm)
(0-5)
(# stems m-2)
Site W1
2.3±0.4
2.5±1.8
147.2±32.7
118.0±38.9
0.9±1.1
Site W2
2.2±0.5
2.3±1.7
148.3±31.4
110.0±42.2
1.1±1.7
Site SE1
2.1±0.3
2.8±1.6
142.7±34.5
89.0±13.8
1.1±1.0
Table 3. Summary Data Table of All Weevil Stocking Sites (2010). Numbers are means and
standard deviations of n=40 stems collected at each of the 3 sites.
Mean Index of Damage to EWM
Stems
3
2.8
2.5
2.3
2
1
0
SITE SE1
SITE W1
SITE W2
Figure 7. Degree of weevil damage (via the weevil damage index) on milfoil stems among sites
within Devils Lake, Lenawee County, Michigan (based on October, 2010 samples).
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Mean Stem Density per Site
140
120
100
80
60
40
20
0
118
110
89
SITE SE1
SITE W1
SITE W2
Figure 8. M. spicatum stem density (based on July, 2010 samples) for each weevil stocking site within
Devils Lake, Lenawee County, Michigan.
6.0 DEVILS LAKE WATER QUALITY DATA RESULTS
Water quality parameters such as water temperature, dissolved oxygen, total phosphorus, total Kjeldahl
nitrogen, alkalinity, pH, conductivity, among others, appear to not be directly correlated with weevil
abundance within lakes (Jester et al., 2000). However, these metrics were measured in May and October
of 2010 and are compared to the baseline values (Table 4). Devils Lake is considered mesotrophic
based on high water clarity (mean Secchi transparency = 22.5), moderate nutrient levels at depths
beyond 30 feet, and an abundance of aquatic plant growth. The south-central Deep basin 1 was selected
as the major deep basin which was representative of the overall lake health.
The quality of water is highly variable among Michigan inland lakes, although some characteristics
are common among particular lake classification types. The water quality of Devils Lake is affected
by both land use practices and climatic events. Climatic factors (i.e. spring runoff, heavy rainfall)
may alter water quality in the short term; whereas, anthropogenic (man-induced) factors (i.e.
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shoreline development, lawn fertilizer use) alter water quality over longer time periods. Furthermore,
lake water quality helps to determine the classification of particular lakes. Lakes that are high in
nutrients (such as phosphorus and nitrogen) and chlorophyll-a, and low in transparency are classified
as eutrophic; whereas those that are low in nutrients and chlorophyll-a, and high in transparency are
classified as oligotrophic.
Lakes that fall in between these two categories are classified as
mesotrophic. Devils Lake is classified as meso-eutrophic based on its moderate transparency and
high nutrient concentrations.
Lake Trophic Status
Total Phosphorus
-1
Chlorophyll-a
-1
Secchi Transparency
(µg L )
(µg L )
(feet)
Oligotrophic
< 10.0
< 2.2
> 15.0
Mesotrophic
10.0 – 20.0
2.2 – 6.0
7.5 – 15.0
Eutrophic
> 20.0
> 6.0
< 7.5
Table 4. Lake Trophic Status Classification Table (MDNRE)
6.1
Devils Lake Water Quality Parameters
Water quality parameters such as dissolved oxygen, water temperature, conductivity, turbidity, total
dissolved solids, pH, total alkalinity, total phosphorus, total Kjeldahl nitrogen, and Secchi
transparency, among others, all respond to changes in water quality and consequently serve as
indicators of water quality change. These parameters are discussed below along with water quality
data specific to Devils Lake (Tables 5 and 6). Water quality data was collected on May 31, 2010 and
October 12, 2010 over the south-central deep basin in Devils Lake.
Dissolved Oxygen
Dissolved oxygen is a measure of the amount of oxygen that exists in the water column. In general,
dissolved oxygen levels should be greater than 5 mg L-1 to sustain a healthy warm-water fishery.
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Dissolved oxygen concentrations in Devils Lake may decline if there is a high biochemical oxygen
demand (BOD) where organismal consumption of oxygen is high due to respiration. Dissolved
oxygen is generally higher in colder waters. Dissolved oxygen is measured in milligrams per liter
(mg L-1) with the use of a dissolved oxygen meter and/or through the use of Winkler titration
methods. The dissolved oxygen concentrations in Devils Lake were normal and consistent with
increased depth during the May sampling event and ranged between 7.9-9.8 mg L-1. During summer
months, dissolved oxygen at the surface is generally higher due to the exchange of oxygen from the
atmosphere with the lake surface, whereas dissolved oxygen is lower at the lake bottom due to
decreased contact with the atmosphere and increased biochemical oxygen demand (BOD) from
microbial activity. A decline in dissolved oxygen beyond 30 feet during the October sampling (just
before turnover) from 8.8 at the surface to 0.9 at the bottom may cause increased release rates of
phosphorus (P) from Devils Lake bottom sediments which may lead to more algal growth over time.
Water Temperature
The water temperature of lakes varies within and among seasons and is nearly uniform with depth
under winter ice cover because lake mixing is reduced when waters are not exposed to wind. When
the upper layers of water begin to warm in the spring after ice-off, the colder, dense layers remain at
the bottom. This process results in a “thermocline” that acts as a transition layer between warmer
and colder water layers. During the fall season, the upper layers begin to cool and become denser
than the warmer layers, causing an inversion known as “fall turnover”. In general, lakes with deep
basins will stratify and experience turnover cycles. Water temperature is measured in degrees
Celsius (ºC) or degrees Fahrenheit (ºF) with the use of a submersible thermometer. The May water
temperatures of Devils Lake demonstrated nearly isothermic conditions between the surface and
bottom. Late summer water temperatures ranged between 67ºF at the surface and 44.7 ºF at the lake
bottom.
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Conductivity
Conductivity is a measure of the amount of mineral ions present in the water, especially those of salts
and other dissolved inorganic substances.
Conductivity generally increases as the amount of
dissolved minerals and salts in a lake increases, and also increases as water temperature increases.
Conductivity is measured in microsiemens per centimeter (µS cm -1) with the use of a conductivity
probe and meter. Conductivity values for Devils Lake were low and consistent among sampling sites
and similar to most healthy inland lakes in Michigan. Conductivity ranged between 335 µS cm-1 and
360 µS cm-1 for spring and late summer water samples. Baseline parameter data such as conductivity
are important to measure the possible influences of land use activities (i.e. road salt influences) on
Devils Lake over a long period of time, or to trace the origin of a substance to the lake in an effort to
reduce pollutant loading.
Turbidity
Turbidity is a measure of the loss of water transparency due to the presence of suspended particles.
The turbidity of water increases as the number of total suspended particles increases. Turbidity may
be caused from erosion inputs, phytoplankton blooms, stormwater discharge, urban runoff, resuspension of bottom sediments, and by large bottom-feeding fish such as carp. Particles suspended
in the water column absorb heat from the sun and raise the water temperature. Since higher water
temperatures generally hold less oxygen, shallow turbid waters are usually lower in dissolved
oxygen.
Turbidity is measured in Nephelometric Turbidity Units (NTU’s) with the use of a
turbimeter. The World Health Organization (WHO) requires that drinking water be less than 5
NTU’s; however, recreational waters may be significantly higher than that. The turbidity of Devils
Lake was low and ranged from 0.2 – 1.7 NTU’s during the sampling events. The lake bottom is
predominately sandy/marl substrate with some silt, which increases the turbidity values near the lake
bottom.
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pH
The pH is a measure of acidity or basicity of water. The standard pH scale ranges from 0 (acidic) to
14 (alkaline), with neutral values around 7. Most Michigan lakes have pH values that range from 6.5
to 9.5. Acidic lakes (pH < 7) are rare in Michigan and are most sensitive to inputs of acidic
substances due to a low acid neutralizing capacity (ANC). pH is measured with a pH electrode and
pH-meter in Standard Units (S.U). The pH of Devils Lake water ranged from 7.6 – 8.0 during the
late spring and late summer sampling. It is not uncommon for lakes in the northern region of
Michigan to possess pH values slightly lower than those of southern lakes due to the underlying
geological features which help determine pH. From a limnological perspective, Devils Lake is
considered “slightly basic” on the pH scale.
Total Alkalinity
Total alkalinity is the measure of the pH-buffering capacity of lake water. Lakes with high alkalinity
(> 150 mg L-1 of CaCO3) are able to tolerate larger acid inputs with less change in water column pH.
Many Michigan lakes contain high concentrations of CaCO3 and are categorized as having “hard”
water. Total alkalinity is measured in milligrams per liter of CaCO 3 through an acid titration method.
The total alkalinity of Devils Lake is considered above average (> 150 mg L-1 of CaCO3), and
indicates that the water is slightly alkaline. Total alkalinity ranged from 173-188 mg L-1 of CaCO3
during the spring and late summer sampling. Total alkalinity may change on a daily basis due to the
re-suspension of sedimentary deposits in the water and respond to seasonal changes due to the cyclic
turnover of the lake water.
Total Phosphorus
Total phosphorus (TP) is a measure of the amount of phosphorus (P) present in the water column.
Phosphorus is the primary nutrient necessary for abundant algae and aquatic plant growth. Lakes
which contain greater than 20 µg L-1 of TP are defined as eutrophic or nutrient-enriched. TP
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concentrations are usually higher at increased depths due to higher release rates of P from lake
sediments under low oxygen (anoxic) conditions. Phosphorus may also be released from sediments
as pH increases. Total phosphorus is measured in micrograms per liter (µg L-1) with the use of a
chemical autoanalyzer. Mean surface total phosphorus (TP) concentrations for the Devils Lake Deep
Basin sampling site during spring were < 0.020 mg L-1.
Total phosphorus concentrations at the
bottom depths averaged < 0.025 mg L-1.
Total Kjeldahl Nitrogen
Total Kjeldahl Nitrogen (TKN) is the sum of nitrate (NO3-), nitrite (NO2-), ammonia (NH4+), and
organic nitrogen forms in freshwater systems. Much nitrogen (amino acids and proteins) also
comprises the bulk of living organisms in an aquatic ecosystem.
Nitrogen originates from
atmospheric inputs (i.e. burning of fossil fuels), wastewater sources from developed areas (i.e. runoff
from fertilized lawns), agricultural lands, septic systems, and from waterfowl droppings. It also
enters lakes through groundwater or surface drainage, drainage from marshes and wetlands, or from
precipitation (Wetzel, 2001). In lakes with an abundance of nitrogen (N: P > 15), phosphorus may be
the limiting nutrient for phytoplankton and aquatic macrophyte growth. Alternatively, in lakes with
low nitrogen concentrations (and relatively high phosphorus), the blue-green algae populations may
increase due to the ability to fix nitrogen gas from atmospheric inputs. Lakes with a mean TKN
value of 0.66 mg L-1 may be classified as oligotrophic, those with a mean TKN value of 0.75 mg L-1
may be classified as mesotrophic, and those with a mean TKN value greater than 1.88 mg L -1 may be
classified as eutrophic. Devils Lake contained highly variable values for TKN (= 0.50 – 1.00 mg L1
).
Secchi Transparency
Secchi transparency is a measure of the clarity or transparency of lake water, and is measured with
the use of an 8-inch diameter standardized Secchi disk. Secchi disk transparency is measured in feet
(ft) or meters (m) by lowering the disk over the shaded side of a boat around noon and taking the
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mean of the measurements of disappearance and reappearance of the disk.
Elevated Secchi
transparency readings allow for more aquatic plant and algae growth. Eutrophic systems generally
have Secchi disk transparency measurements less than 7.5 feet due to turbidity caused by excessive
planktonic algae growth. The Secchi transparency of Devils Lake averaged 18.5 feet during the 2010
sampling period. This transparency is adequate to allow abundant growth of algae and aquatic plants
in the majority of the littoral zone of the lake. Secchi transparency is variable and depends on the
amount of suspended particles in the water (often due to windy conditions of lake water mixing) and
the amount of sunlight present at the time of measurement.
Total Suspended and Dissolved Solids
Total Suspended Solids (TSS) is the measure of the amount of suspended particles in the water
column. Particles suspended in the water column absorb heat from the sun and raise the water
temperature. Total suspended solids is often measured in mg L-1 and analyzed in the laboratory. The
lake bottom contains many fine sediment particles which are easily perturbed from winds and wave
turbulence. Spring values would likely be higher due to increased watershed inputs from spring
runoff and/or increased planktonic algal communities. In addition, Total Dissolved Solids (TDS) is a
measure of the amount of inorganic and organic solids dissolved in the lake water that may cause a
stained color or increase conductivity. The concentration of TSS in Devils Lake during the spring
and late summer sampling events ranged from < 2.0 mg L-1 to < 15.0 mg L-1. Total dissolved solids
averaged between 20.2 mg L-1 and 43.1 mg L-1. The acceptable standard for drinking water is 100
mg L-1.
Oxidative Reduction Potential
The oxidation-reduction potential (Eh) of lake water describes the effectiveness of certain atoms to
serve as potential oxidizers and indicates the degree of reductants present within the water. In
general, the Eh level (measured in millivolts) decreases in anoxic (low oxygen) waters. Low E h
values are therefore indicative of reducing environments where sulfates (if present in the lake water)
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may be reduced to hydrogen sulfide (H2S). Decomposition by microorganisms in the hypolimnion
may also cause the Eh value to decline with depth during periods of thermal stratification. The E h
(ORP) values for Devils Lake ranged between 142.3 mV and 32.1 mV from the surface to the bottom
within the lake, and thus were within a normal range for meso-eutrophic lakes.
Depth
ft
Water
Temp
DO
mg L
pH
-1
S.U.
Cond.
µS cm
-1
Turb.
ORP
Total
Total
Total Phos.
NTU
mV
Kjeldahl
Alk.
mg L-1
Nitrogen
mgL-1
mg L-1
CaCO3
ºF
0
55.6
9.8
7.5
360
0.2
142.3
< 0.50
182
<0.020
30
48.9
8.1
7.9
354
0.2
89.5
< 0.50
157
<0.020
60
43.5
7.9
7.6
335
0.9
32.1
<0.50
173
<0.020
Table 5. Devils Lake Water Quality Parameter Data Collected over Deep Basin 1 on May 31, 2010.
Depth
ft
Water
Temp
DO
mg L
pH
-1
S.U.
Cond.
µS cm
-1
Turb.
ORP
Total
Total
Total Phos.
NTU
mV
Kjeldahl
Alk.
mg L-1
Nitrogen
mgL-1
mg L-1
CaCO3
ºF
0
67.0
8.8
8.0
354
0.5
113.8
< 0.50
188
< 0.020
30
52.8
4.9
7.9
347
0.8
77.4
< 0.50
176
< 0.020
60
44.7
0.9
7.7
340
1.7
49.5
<1.00
162
<0.025
Table 6.
2010.
Devils Lake Water Quality Parameter Data Collected over Deep Basin 1 on October 12,
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7.0 FUTURE WEEVIL STOCKING RECOMMENDATIONS
AND COST ESTIMATES
The weevil stocking density used during 2010 was estimated to be > 200 weevils per square meter (m-2),
and has been found to be adequate for weevil stem damage. Based on the 2010 seasonal data, it is
recommended that approximately 5,000 weevil units should be placed into each of the three sites during
the late spring or early summer of 2011. After the stocking has taken place, stem parameters similar to
those collected in 2010 should be collected again at all previously stocked sites to assess the efficacy of
the weevils. Parameters such as milfoil stem density, weevil counts per stem, and declines in stem
length should be measured and proposed cost estimates of the 2011 aquatic vegetation management
program are shown below in Table 7.
In addition, regular whole-lake point-intercept aquatic
vegetation surveys should be conducted to determine locations of any new milfoil infestations
throughout Devils Lake and to monitor the distribution and abundance of the native aquatic plant
species. Small colonies of Eurasian Watermilfoil should be removed with suction harvesting or aquatic
herbicides. Recent 2010 data for aquatic plant species in Devils Lake can be found in APPENDIX A.
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Proposed 2011 Management Improvement Item
Estimated
2011 Cost
Biological Control (Weevils @$1.20 per unit)
15,000 units
$18,000
Suction Harvesting or Herbicides (approx. 10 acres@$490 per acre); permits
Professional Limnologist Services (Limnologist surveys/Scientific Annual
$5,700
$14,000
Reports/ WQ Monitoring, Vegetation mapping, Contractor oversight, Riparian
Education); Includes printing and mailing of newsletter (Costs for professional
services will be equally divided among the two townships)
Contingency
TOTAL ANNUAL ESTIMATED COST
$3,770
$42,470
Table 7. Proposed Devils Lake Eurasian Watermilfoil Management Budget for 2011. Note: It is
recommended that the total cost of the program be divided equally among each township.
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8.0 LITERATURE CITED
Aiken, S.G., P.R. Newroth, and I. Wile. 1979. The biology of Canadian weeds. 34.
Myriophyllum spicatum L. Can. J. Plant Sci. 59: 201-215.
Boylen, C.W., Lawrence, W.E., and Madsen, J.D. 1999. Loss of native aquatic plant species in a
community dominated by Eurasian Watermilfoil. Hydrobiologia 415: 207-211.
Cofrancesco, A.F., McFarland, D.G., Madsen, J.D., Poovey, A.G., and Jones, H.L. 2004. Impacts of
Euhrychiopsis lecontei (Dietz) from different populations on the growth and nutrition of
Eurasian Watermilfoil. ERDC/TN APCRP-BC-07.
Couch, R., and E. Nelson 1985. Myriophyllum spicatum in North America. Pp. 8-18. In:
Proc. First Int. Symp. On watermilfoil (Myriophyllum spicatum) and related Haloragaceae
species. July 23-24, 1985. Vancouver, BC, Canada. Aquatic Plant Management Society,
Inc.
Creed, R. P., Jr., S.P. Sheldon, and D. M. Cheek. 1992. The effect of herbivore feeding
on the buoyancy of Eurasian milfoil. J. Aquat. Plant. Manage. 30:75-76.
Creed, R. P., and S.P. Sheldon. 1994. The effect of two herbivorous insect larvae an
Eurasian watermilfoil. J. Aquat. Plant Manage. 32: 21-26.
Creed, R.P., Jr., and S.P. Sheldon. 1995. Weevils and watermilfoil: did a North
American herbivore cause the decline of an exotic plant? Ecol. Appl. 5: 1113-1121.
Creed, R. P., Jr. 2000. The Weevil-Watermilfoil Interaction at Different Spatial Scales: What We
Know and What We Need To Know. J. Aquat. Plant Manage. 38: 78-81.
Jester, L.L., Bozek, M.A., Helsel, D.R., and Sheldon, S.P. 2000. Euhrychiopsis lecontei distribution,
abundance, and experimental augmentations for Eurasian Watermilfoil control in Wisconsin
lakes. . J. Aquat. Plant Manage. 38: 88-97.
Madsen, J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler, and C.W. Boylen. 1991.
The decline of native vegetation under dense Eurasian watermilfoil canopies. J. Aquat. Plant
Manage. 29: 94-99.
Madsen, J.D. G.O. Dick, D. Honnell, J. Schearer, and R.M. Smart. 1994. Ecological assessment of
Kirk Pond, Miscellaneous Paper A-94-1, U.S. Army Engineer Waterways Experiment
Station, Vicksburg, MS.
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December, 2010
Page 37
Madsen, J.D., J.A. Bloomfield, J.W. Sutherland, L.W. Eichler, and C.W. Boylen. 1996. The aquatic
macrophyte community of Onondaga Lake: Field survey and plant growth bioassays of lake
sediments, Lake and Reservoir Management 12, 73-79.
Madsen, J.D. 1999. Point intercept and line intercept methods for aquatic plant
management. Aquatic Plant Control Technical Note MI-02, February 1999.
Newman, R. M., K.L. Holmberg, D. D. Biesboer, and B.G. Penner. 1996. Effects of a
potential biocontrol agent, Euhrychiopsis lecontei, on Eurasian milfoil in experimental tanks.
Aquat. Bot. 53: 131-150.
Newman, R.M., Borman, M.E., and Castro, S.W. 1997. Developmental performance of the weevil
Euhrychiopsis lecontei on native and exotic watermilfoil host plants. J. North Amer.
Benthol. Soc. 16:627-634.
Newman, R. M., and D. D. Biesboer, 2000. A decline of Eurasian Watermilfoil in Minnesota
associated with the Milfoil Weevil, Euhrychiopsis lecontei. . J. Aquat. Plant Manage. 38:
105-111.
Newroth, P.R. 1985. A review of Eurasian water milfoil impacts and management in
British Columbia. Pp. 139-153. In: Proc. First Int. Symp. On watermilfoil (Myriophyllum
spicatum) and related Haloragaceae species. July 23-24, 1985. Vancouver, BC, Canada.
Aquatic Plant Management Society, Inc.
Parsons, J.K., and R.A. Matthews. 1995. Analysis of the associations between macroinvertebrates
and macrophytes in a freshwater pond. Northwest Science, 69: 265-275.
Parsons, J.K., K.S. Hamel, J.D. Madsen, and K.D. Getsinger. 1999. The Use of 2,4-D for Selective
Control of an Early Infestation of Eurasian Watermilfoil in Loon Lake, Washington. J.
Aquat. Plant Manage. 39: 117-125.
Reed, C.F. 1977. History and disturbance of Eurasian milfoil in United States and
Canada. Phytologia 36: 417-436.
Roley, S.S., and Newman, R. M. 2006. Developmental performance of the milfoil weevil,
Euhrychiopsis lecontei (Coleoptera: Curculionidae), on northern watermilfoil, Eurasian
watermilfoil, and hybrid (northern x Eurasian) watermilfoil. Environ. Entomol, 35: 121-126.
Scribailo, R.W., and M.S. Alix. 2003. Final Report on the Weevil Release Study for
Indiana Lakes. Lake and River Enhancement Program, Indiana. 12 pp.
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 38
Sheldon, S.P. 1995. The potential for biological control of Eurasian milfoil
(Myriophyllum spicatum) 1990-1995. Final Report. Department of Biology, Middlebury
College, Middlebury, VT.
Sheldon, S.P., R.P. Creed, Jr. 1995. Use of a native insect as a biological control for an
introduced weed. Ecol. Appl. 5: 1122-1132.
Sutter, T.J., and R.M. Newman 1997. Is predation by sunfish (Lepomis spp.) an
important source of mortality for the Eurasian milfoil biocontrol agent Euhrychiopsis
lecontei? J. Freshw. Ecol. 12: 225-234.
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 39
APPENDIX A
DEVILS LAKE AQUATIC VEGETATION DATA BY GPS
LOCATION (OCTOBER, 2010)
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 40
GPS Sample Quadrat
Macrophyte Species and Abundance Present
711
1c,5b,6b,3b,7b
712
1d,5b,7b,6a,3b
713
3b
714
None
715
1a,31b,5b,21b
716
3b,7a
717
1d,11b,9b,7b,3a
718
None
719
None
720
None
721
39b,31b,7b,3a
722
3b,5b
723
1d,11a,9b,6a,5b,3c
724
1d,9b,26b,7b,10a
725
1d,21a,5b,23b,7b
726
1d,11a,9b,26c,7b
727
1d,11b,21b,9a,6c,7b,3a
728
1c,21a,11a,9a,26c,3b,7b
729
1c,11a,9b
730
1d,11a,21a,9a,3b,10b
731
1d,11a,21b,6b,9b,3b
732
1d,3b
733
1d,11b,6a,7b
734
1d,9a,6c,26c,7b,3b
735
1c,10b,6b,7b,3b
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 41
GPS Sample Quadrat
Macrophyte Species and Abundance Present
736
1d,9a,8a,21b,23a,6b
737
1d,9a,8a,21a,6b
738
1d,8a,21a,6b
739
1c,21a,15a,6b,26b
740
None
741
31b
742
31a
743
None
744
1d,8a,6a,26b
745
1d,23a,8a,21a,5a,6b
746
1d
747
1d,8b,6b
748
1d,8b
749
1d,8a,6a
750
1d,8a,6a,26b
751
1d,8b,5a,6b
752
1c,5b,8a,6c,26b
753
1d,8a,6c,26b
754
1c,8a,5a,21a,6c,26b
755
1b,8a,5a,26c,6c
756
1d,8a,6c,26b
757
1d,8a6b,26b
758
1d,8a,21a,6b,26b
759
1d,8a,6b
760
None
761
1c,8a,11a,21a,6b
762
1d,8a,11a,21a,6b
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 42
GPS Sample Quadrat
Macrophyte Species and Abundance Present
763
1d,8b,6b,7b,18b
764
4b,3b,7b,6a
765
1d,26b,9b,7a,3b
766
1b,26b,9b,3a
767
3a
768
39b, 3a,7a
769
39c,3b,7b,9a
770
1d,21b,6b,7a
771
1d,3b
772
1d,3b,8a,7b
773
3b,7a
774
1d,8a
775
1c,8a
776
1b,8b,3b,4a
777
1c,4b,3a
778
15b,4b,10a,7b
779
7b,6a,9b,4b,3b
780
6b,3b,7a
781
6a,9b,7b,3a
782
6b,10b,7a,8a
783
1b,7b,3b
784
1c
785
1c,8b,9a,7c,3b,11b
786
1c,8a,26c
787
1a,26b,3b
788
15b,7b
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 43
GPS Sample Quadrat
Macrophyte Species and Abundance Present
789
1d,21a,8a,6b
790
3a
791
1d,9a,6b
792
1d,8a,6a
793
21b,8a
794
1c
795
39d (shore)
796
8a,9a,21a
797
1d,8a,21a,6b
798
1d,8a,21a,6b
799
1d,8a,9a,21a,6b
800
None
801
1d,6a
802
1a,9c
803
1b,9a,8a,6b
804
9a,8b,1a
805
1a,8a,6b
806
8a,1c
807
1d,8a
808
1c,8a,5a
809
1d
810
1d,8a,9a,6b
811
1c,8a,9a,6c
812
1d,5a,8a,9a,21a,20a,6c
813
1b,8a,9a,21a,6b
814
8a,9a,21a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 44
GPS Sample Quadrat
Macrophyte Species and Abundance Present
815
1d,7b,9b
816
3b
817
3a,7a
818
1a
819
1c,3c,7b
820
9b,7b,11a,10a
821
6b,9a,26a
822
5b,26b,6b
823
1a,5b,7a
824
None
825
39a,3b,7b
826
39a,7b
827
3a
828
1c,21a,26c,6b,9b,7b
829
1c,7c,3b
830
1c,7b,10b,9a
831
1a,9c,8a,6c,26b
832
1a,9c,26b
833
1c,3b
834
1b,3c,7b,26b
835
3c
836
3a,7a
837
1d,8b,9b,7c
838
3c
839
7a
840
26a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 45
GPS Sample Quadrat
Macrophyte Species and Abundance Present
841
3c,7b,21b
842
9b,3b,7a
843
7b
844
None
845
None
846
None
847
1c,7b,9a
848
1d,9c,7a,3b
849
1b,9b,11a,26a
850
1c,15b,9b,6b,3a
851
4a
852
39a
853
39a
854
3a
855
1c,8a,6b,26c
856
1a,6c,26b,23a
857
1b,7c,3b
858
1d,7a,9b
859
1c,9a,7b,3a
860
3a
861
None
862
None
863
1d,9b,6b,26a
864
1c,9a,26b
865
3b,26a
866
7c,26a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 46
GPS Sample Quadrat
Macrophyte Species and Abundance Present
867
None
868
None
869
None
870
1d,6c,7b,3b
871
1d,26b,9b,7a,3b
872
23a,26b,3b
873
4b,7b
874
15b,3c,7b
875
9b,8a,7b,3b
876
3a,15b
877
3b,7a
878
1b,3b,7a
879
6a
880
1a
881
1a,7a
882
3b
883
None
884
None
885
39a,3c,7b
886
None
887
None
888
None
889
None
890
None
891
None
892
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 47
GPS Sample Quadrat
Macrophyte Species and Abundance Present
893
3c
894
1b,3c,7b,18b
895
1b,18b,7b
896
1c,18a,3b,7b
897
None
898
None
899
8d,7b,3b,9a
900
None
901
None
902
None
903
1c,7b,9b,3b,26a
904
1d
905
1a,10b,26b
906
None
907
1a,3b,7b
908
3b
909
3b,7a,6b
910
1d,9b,3b,7b
911
1a
912
None
913
None
914
None
915
None
916
None
917
None
918
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 48
GPS Sample Quadrat
Macrophyte Species and Abundance Present
919
None
920
None
921
None
922
None
923
None
924
None
925
None
926
None
927
None
928
7b,3b,9a
929
7a
930
3a
931
None
932
None
933
None
934
6b,26a,7b,9b,3a
935
1b,4b,6a
936
7b,10a,4b
937
3a
938
None
939
None
940
None
941
None
942
None
943
None
944
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 49
GPS Sample Quadrat
Macrophyte Species and Abundance Present
945
None
946
1a,26b,7a
947
None
948
None
949
None
950
1c,9b,26b
951
1d, 26c,8b,7b,3b
952
1c,8b,39a,26b
953
3b,7b,9a
954
1c,7b,10a
955
1a,9b,10a
956
3b
957
None
958
None
959
1b,7b,8a
960
3b,7b
961
None
962
None
963
None
964
None
965
None
966
6b,8b,1a,4b
967
1b,7b,6a
968
7b,6b,9b,3a
969
1b,8a,10a,4b,6c
970
4b,7a,9b,1a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 50
GPS Sample Quadrat
Macrophyte Species and Abundance Present
971
None
972
1c,9b,26a,3b,7b
973
3a
974
3a
975
1c,9a,8b,4b,7a
976
None
977
None
978
None
979
10b,7a,9a
980
None
981
None
982
None
983
None
984
None
985
None
986
None
987
None
988
None
989
8b,3a
990
1c,6a,7b,10a
991
1b,8b,9a
992
1b,7b
993
3a
994
None
995
1c,3b
996
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 51
GPS Sample Quadrat
Macrophyte Species and Abundance Present
997
None
998
39b,3b,7a
999
39b,7b
1000
None
1001
None
1002
None
1003
None
1004
None
1005
None
1006
None
1007
None
1008
None
1009
None
1010
None
1011
None
1012
None
1013
None
1014
None
1015
None
1016
None
1017
None
1018
None
1019
1d,6b,9b,21b,26b
1020
1d,18b,7b,4b,20a
1021
1b,4b,7v,18b,9b
1022
39a,3a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 52
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1023
1d,9b,6a,7b
1024
1c,3b
1025
3b
1026
None
1027
None
1028
None
1029
None
1030
None
1031
None
1032
None
1033
None
1034
None
1035
None
1036
None
1037
None
1038
None
1039
None
1040
None
1041
None
1042
23b,26b,7b,3b,4a,10a
1043
3b
1044
3a
1045
39a,3b,7a
1046
39a,26a
1047
None
1048
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 53
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1049
3b,7b
1050
3b,7b
1051
None
1052
7a
1053
3a
1054
3b,7a
1055
None
1056
None
1057
None
1058
None
1059
None
1060
None
1061
None
1062
None
1063
21a,5a
1064
3b,20a,8a
1065
3a,4b,7a
1066
3b,7b,9a
1067
1d,26b,23a,4b,3a
1068
1d,3b,7a,9b,20a
1069
3b
1070
None
1071
None
1072
None
1073
1c,26b,7b,9b,15a
1074
1c,15a,26a,7a,3a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 54
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1075
3b
1076
4b
1077
3a,7a
1078
None
1079
None
1080
None
1081
None
1082
None
1083
None
1084
None
1085
None
1086
None
1087
None
1088
None
1089
None
1090
3a,8a
1091
None
1092
None
1093
None
1094
None
1095
39a,3b,7a
1096
39a,3b
1097
3a
1098
None
1099
None
1100
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 55
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1101
4b,7a
1102
3a,4a
1103
7a
1104
7a
1105
None
1106
39a, 3a
1107
39a
1108
3b
1109
None
1110
None
1112
None
1113
None
1114
None
1115
39a, 7a
1116
39b
1117
None
1118
None
1119
None
1120
None
1121
None
1122
None
1123
None
1124
None
1125
None
1126
39a,7b,3a
1127
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 56
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1128
3b
1129
39a, 3b
1130
3b,7a
1131
7b
1132
3a
1133
None
1134
None
1135
None
1136
39b,3a
1137
39b,7a
1138
39b
1139
None
1140
None
1141
None
1142
None
1143
1b,8b,9a,6b,26a,15a
1144
1b,6b
1145
1b,5a,9b,7b
1146
3a
1147
None
1148
None
1149
1c,6b,9b,5a,15a,4b,7b
1150
1d,26b,10a,9b,7c
1151
3a
1152
None
1153
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 57
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1154
1a
1155
1b,9b,26b,15a,20b,4b,7a,25b
1156
1d,5b
1157
None
1158
10a
1159
None
1160
10b,6b,4a,25b
1161
8b,4a,7a
1162
None
1163
None
1164
None
1165
None
1166
None
1167
None
1168
3a
1169
8a,3a,9a
1170
7b,3a
1171
None
1172
None
1173
None
1174
1b,7b
1175
1c,21b,8a,6b,26b,25a
1176
1d,5b,9b,18a,21a,6b,26b,25b
1177
1d,5b,15b,18b,6b,26c,25b
1178
1d,6b,18b,26b,25b
1179
39c,7a,3b
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 58
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1180
None
1181
None
1182
None
1183
None
1184
1d,7b,3b,9b,15a,18b,26a,23a
1185
4b,7b
1186
None
1187
None
1188
None
1189
None
1190
None
1191
None
1192
39a,4b,7a
1193
39a, 7a
1194
1a,4b,7a
1195
1b,9a,7b
1196
3b
1197
3a,7a
1198
None
1199
None
1200
None
1201
None
1202
1d,9b,26b,23a,15a,18b,5a
1203
1d,6b,9b,7b,3b
1204
1d,9b,6b,3b
1205
1b,3c
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 59
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1206
1b,6b,9b,7a
1207
1b,6a,9a,7b
1208
3c,7b
1209
1b,6a,9a,7b
1210
1d,9b,4b
1211
1d,3b,9b,11a,2a
1212
1d,6b,9b,4a
1213
1b
1214
None
1215
None
1216
None
1217
3a
1218
None
1219
1b,26c,4b,7b,9a,2a
1220
1c,23a,15b,26b,7a,2a
1221
3b
1222
3a
1223
1d,26b,9a,7b,3a
1224
1b,3b
1225
1b,3b,6c,4b,26c,2b
1226
1b,6b,26b,2b
1227
1a ,6b,2b
1228
1b,9a, 6b,26b
1229
6b,3b,7b
1230
1a,6b,21a,7b
1231
7b,21a
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 60
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1232
1b,7b,3a,6a
1233
1d,6a,7b
1234
1b,7b,9b,15a,20a,22b
1235
1c,23b,26b,3b,7c
1236
7b,6a
1237
3b,7b
1238
1b,6a,3b
1239
1c,9b,3b,7b
1240
1d,5b,6b,15b,26b
1241
1c,5b,15b,18a
1242
1b,9b,6b,26b
1243
1d,9b
1244
None
1245
None
1246
None
1247
None
1248
1a,6b
1249
1b,23a,3b,7a
1250
1d,7b,3a
1251
1b,3b,7b,6b
1252
1b,15a,6b,26b,2c
1253
1a,9b,6a,4b,26a,2c
1254
None
1255
None
1256
None
1257
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 61
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1258
None
1259
1b,15a,18b,3b,7a
1260
8a,7b,3a
1261
3b,7b,11a
1262
1d,6b,3b,10a
1263
1b,3a,9b,10a,4b
1264
1b,15a,11a
1265
1b,15b,18b,7a
1266
1c,3a
1267
1a,3b,7a
1268
1b,6b,9a,3b
1269
None
1270
None
1271
None
1272
1c,6b,7a,9a
1273
1a,7a,3b
1274
1b,7b,9a,10a
1275
None
1276
3b,26a,7b,4a
1277
3b,7a
1278
None
1279
None
1280
18b,3c,7a
1281
None
1282
None
1283
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 62
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1284
3b,7b
1285
7a
1286
None
1287
39a,4a,7a
1288
7a
1289
None
1290
None
1300
None
1301
None
1302
None
1303
None
1304
None
1305
None
1306
None
1307
None
1308
None
1309
None
1310
None
1311
None
1312
None
1313
None
1314
None
1315
None
1316
None
1317
None
1318
None
Lakeshore Environmental, Inc.
Devils Lake 2010 Annual Report
December, 2010
Page 63
GPS Sample Quadrat
Macrophyte Species and Abundance Present
1319
None
1320
3a