Aquatic Plant Surveys for Orchard Lake, Lakeville ... - City of Lakeville

Chet Reneson: Tight Line, undated
Aquatic Plant Surveys for Orchard Lake,
Lakeville, Minnesota, 2008
Summer Surveys: May 30 and September 1, 2008
Prepared for:
City of Lakeville
Lakeville, Minnesota
Prepared by:
Steve McComas and Jo Stuckert
Blue Water Science
St. Paul, Minnesota
Submitted January 2009

Aquatic Plant Surveys for Orchard Lake,
Lakeville, Minnesota, 2008
Summary
Two aquatic plant surveys were conducted on Orchard Lake (234 acres) in 2008 The early
summer survey on May 30, 2008 occurred before the aquatic weed harvester finished
harvesting curlyleaf pondweed on Orchard Lake. The May 30 survey evaluated the distribution
and abundance of curlyleaf pondweed. The late summer survey of September 1 characterized
any changes in the plant community and there were checks for Eurasian watermilfoil.
Early Summer Survey: In early summer, the most abundant plant in Orchard Lake was
curlyleaf pondweed and it was found at 96% of the 26 stations (Table 1). In the past, curlyleaf
pondweed has been growing to the surface producing recreational nuisance conditions in water
depths out to 10 feet. Harvesting in 2004, 2005, 2006, 2007, and 2008 has drastically reduced
nuisance curlyleaf growth (defined as curlyleaf growing to the surface). Overall aquatic plants
grew to a depth of 10 feet in 2008. No Eurasian watermilfoil was found in this survey.
Late Summer Survey: The dominant plant in September of 2008 in Orchard Lake was coontail
(Table 1). No Eurasian watermilfoil was found in this late summer survey. Overall, aquatic
plants grew out to a depth of 10 feet around much of the lake except in the southeast end of the
lake. Aquatic plants covered about 120 acres, representing 51% of the 234 acre lake. Coontail
was the dominant plant in the September survey occurring at 82% of the stations. Significant
amounts of benthic filamentous algae rose to the surface and washed up on the south side of
the lake in July and August of 2008.
No Harvesting Post Harvesting Post Harvesting
Conditions Conditions
Pre Harvesting Pre Harvesting Pre Harvesting
Conditions Conditions Conditions
Figure 1. The coverage of aquatic plants in early summer from 2003 to 2008 is shown in pink and nuisance
curlyleaf pondweed is shown in red. An estimated 70 acres of nuisance curlyleaf growth was found in 2003.
Mechanical weed harvesting was conducted on Orchard Lake in May of 2004 through 2008. An estimated 41
acres of nuisance curlyleaf growth was found prior to mechanical harvesting. The area of nuisance
coverage after harvesting was completed was less in 2004 through 2008 compared to 2003 conditions.
-i-

Table 1. The percent occurrence of aquatic plants for Orchard Lake in 2008. Percent
occurrence is calculated based on the number of times a plant species occurs at a
sampling station on transects divided into the number of total stations for the survey.
For example, if milfoil was found in 25 out of 50 stations, its percent occurrence would
be 50%.
Duckweed
(Lemna sp)
Spatterdock
(Nuphar variegatum)
W hite waterlily
(Nymphaea sp)
Marigold
(Bidens Beckii)
Coontail
(Ceratophyllum demersum)
Chara
(Chara sp.)
Star duckweed
(Lemna trisulca)
Northern watermilfoil
(Myriophyllum sibiricum)
Naiads
(Najas flexilis)
Cabbage
(Potamogeton amplifolius)
Curlyleaf pondweed
(P. crispus)
Claspingleaf pondweed
(P. richardsonii)
Narrowleaf pondweed
(P. sp)
Buttercup
(Ranunculus sp)
Water celery
(Vallisneria americana)
Water stargrass
(Zosterella dubia)
May 30, 2008
(% occur)
September 1, 2008
(% occur)
Changes from
May to September
0 4 +
0 14 +
12 11 0
4 4 0
35 82 +
12 25 +
4 4 0
8 36 +
0 4 +
4 7 +
96 11 -
4 4 0
8 0 -
0 0 0
0 4 +
0 11 +
Filamentous algae 35 68 +
Number of Submerged Species 9 11 +
The City of Lakeville has sponsored annual aquatic plant surveys since 1999. A summary of
the percent occurrence of individual species on a lakewide basis is shown in Table 2. Since
1995, it appears that eight submerged species have increased and three submerged species
have decreased. Six species are found sparingly or have not changed in abundance. The
number of species found in Orchard Lake has remained about the same since 1995 (Table 2).
-ii-

Table 2. The percent occurrence of aquatic plants for Orchard Lake for 1995 and 1999 through 2008. Mechanical harvesting has occurred from 2004 to 2008
(blue shading). Changes in plant abundance are rated as: + = increase, -- = decrease, 0 = no significant change (1995 data are from Barr Engineering Company,
Diagnostic Study of Orchard Lake, 1999).
Duckweed
(Lemna sp)
Spatterdock
(Nuphar variegatum)
White waterlily
(Nymphaea sp)
Marsh marigold
(Bidens beckii)
Coontail
(Ceratophyllum
demersum)
Chara
(Chara sp.)
Star duckweed
(Lemna trisulca)
Northern watermilfoil
(Myriophyllum
sibiricum)
Naiads
(Najas sp)
Nitella
(Nitella sp)
Cabbage
(Potamogeton
amplifolius)
Curlyleaf pondweed
(P. crispus)
Illinois pondweed
(P. illinoensis)
Stringy pondweed
(P. pusillus)
Claspingleaf
pondweed
(P. richardsonii)
Narrowleaf
pondweed
(P. sp)
Flatstem pondweed
(P. zosteriformis)
Buttercup
(Ranunculus sp)
Sago pondweed
(Stuckenia
pectinatus)
Water celery
(Vallisneria
americana)
Water stargrass
(Zosterella dubia)
Number of
submerged species
June 16,
1995
% Occur
(based on
57
stations)
June 5,
1999
% Occur
(based on
39
stations)
May 26,
2000
% Occur
(based on
39
stations)
June 8,
2001
% Occur
(based on
39
stations)
May 31,
2002
% Occur
(based on
42
stations)
May 17,
2003
% Occur
(based on
39
stations)
June 7,
2004
% Occur
(based on
24
stations)
May 21,
2005
% Occur
(based on
26
stations)
May 26,
2006
% Occur
(based on
30
stations)
May 22,
2007
% Occur
(based on
26
stations)
May 30,
2008
% Occur
(based
pm 26
stations)
Aug 20,
1995
% Occur
(based on
57
stations)
-- – -- -- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- 3 -- -- 4 0
-- 5 10 5 5 8 13 15 10 12 -- -- 10 8 8 10 8 12 13 10 12 14 0
-- 5 3 3 7 5 4 -- 7 12 12 -- 8 13 12 10 13 27 17 17 19 11 +
-- -- -- -- 5 -- -- -- -- -- 4 -- -- -- -- -- -- -- -- -- -- 4 0
12 18 28 74 38 38 88 62 13 27 35 74 85 56 88 90 90 100 90 93 88 82 +
12 13 13 28 12 10 4 15 10 8 12 18 26 8 27 10 5 19 13 17 19 25 +
-- -- -- -- -- -- -- -- 7 8 4 -- -- 3 -- 5 5 8 17 17 15 4 +
18 23 3 41 12 3 25 19 33 12 8 21 5 23 46 33 13 54 33 27 27 36 +
-- -- -- -- -- -- -- -- -- -- -- 13 -- -- -- -- 3 -- 3 -- -- 4 0
-- -- -- -- 2 3 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 0
5 8 3 13 14 10 13 19 33 31 4 8 3 13 23 10 8 27 27 27 19 7 -
98 74 95 92 74 100 92 96 100 100 96 55 -- 23 4 5 26 -- 7 -- 4 11 -
-- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- -- -- -- -- -- -- -- 0
-- -- -- 10 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 0
9 5 -- 10 5 -- -- -- 7 4 4 18 3 5 8 3 8 8 -- 7 4 4 0
-- -- -- -- -- -- -- -- -- -- 8 -- -- -- -- -- -- -- -- -- -- --
2 -- -- 5 -- -- 4 -- 7 -- -- 13 5 -- 4 8 -- 4 3 -- -- -- 0
-- 8 3 -- -- 3 4 12 3 8 -- -- -- -- -- -- -- 8 -- -- -- -- -
4 -- -- -- -- -- -- -- -- -- -- 8 -- 8 4 -- -- 8 3 3 -- -- 0
-- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- 3 13 12 13 3 12 4 +
4 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 3 27 13 3 8 11 +
9 7 6 8 8 7 7 6 9 8 9 9 6 10 8 9 10 11 11 9 9 11
Aug 14,
1999
% Occur
(based on
39
stations)
Oct 6,
2000
% Occur
(based on
39
stations)
Sept 17,
2001
% Occur
(based on
39
stations)
Sept 8,
2002
% Occur
(based on
39
stations)
Aug 20,
2003
% Occur
(based on
39
stations)
Aug 29,
2004
% Occur
(based on
26
stations)
Aug 22,
2005
% Occur
(based on
30
stations)
Aug 21,
2006
% Occur
(based on
30
stations)
Aug 26,
2007
% Occur
(based on
26
stations)
Sept 1,
2008
% Occur
(based on
28
stations)
Change
from 1995
to 2007
(spring
and fall)
-iii-

Summary of Orchard Lake Water Quality: Summer averages for clarity (using a Secchi
disc), phosphorus, and algae (using chlorophyll analysis) were some of the best on record in
2008 (Table 3). Orchard Lake is not in the impaired status category. Impaired criteria are
shown in Table 4.
Table 3. Water quality summary for Orchard Lake. Data are May-September averages from the
Met Council CAMP program. Blue shading represents years of significant curlyleaf pondweed
harvesting.
Secchi Disc
(m)
Total Phosphorus
(ppb)
Chlorophyll a
(ppb)
1980 2 40 16
1981 3 26 11
1983 2.9 31 11
1987 1.8 -- --
1988 2.3 -- --
1989 2.1 28 14
1990 1 -- --
1991 1.9 -- --
1993 2 35 17
1995 1.3 44 31
1996 2.3 28 15
1998 1.9 38 24
1999 2.1 34 30
2000 2 39 20
2001 2.3 25 13
2004 2.6 38 17
2005 2.4 32 12
2006 2.2 34 14
2007 1.6 41 23
2008 3.0 24 11
Table 4. MPCA nutrient criteria for impaired lakes (MPCA 2005). Orchard Lake is a deep lake.
Water quality results indicate Orchard Lake is not in the impaired category.
Secchi Disc
(m)
Total Phosphorus
(ppb)
Chlorophyll a
(ppb)
Shallow Lake >1.0

Orchard Lake Dakota County (ID: 19-31)
Size: 234 acres; Littoral area: 177 acres (MnDNR)
Maximum depth: 33 feet (MnDNR map)
Introduction
Orchard Lake is a 234 acre moderately fertile lake in Lakeville, Minnesota. In 2008, the
average summer water clarity was 3.0 meters (9.8 feet) and the total phosphorus
concentration was 24 parts per billion (source: CAMP, Met Council).
The plants of Orchard Lake were sampled to evaluate curlyleaf pondweed and to look for
Eurasian watermilfoil. Eurasian watermilfoil has not been found in Orchard Lake (as of
September 1, 2008). Steve McComas, Blue Water Science, conducted two aquatic plant
surveys on May 30 and September 1, 2008.
Methods
Thirteen transects were made at different locations around Orchard Lake. A transect
started at the weedline and headed into shore (Figure 1). Two depths (0-5 feet and 6-10
feet) along the transect were sampled with a rake to assess the aquatic plant composition.
The amount of plants on the rake determined the density of each species at that location.
Low density rated a ‘1' and a high density was a ‘5'.
Figure 1. Transects for plant surveys on May 30 and September 1, 2008. Transects 8.5 and 11.5
were not included in statistics in 2008 to stay consistent with previous surveys.
Orchard Lake Aquatic Plant Surveys for 2008 1

Results: May 8 -- Curlyleaf Assessment
In 2007, curlyleaf pondweed grew to nuisance levels quicker than expected and by the
time the mechanical harvesters arrived and curlyleaf growth was well advanced. In 2008,
an early curlyleaf assessment was conducted on May 8, 2008 to evaluate curlyleaf growth
status. In early May, curlyleaf growth was present, but stem length was short, at less than
a foot. Harvesting was scheduled for the second half of May.
It appears the rapid curlyleaf growth in 2007 was not the typical pattern, and curlyleaf
harvesting can generally start about the third week in May.
Figure 2. On May 8, 2008 curlyleaf pondweed was present, but stem lengths were generally less than
12-inches tall. In the southeast side of Orchard Lake, thick bottom mats of filamentous algae were
present.
Orchard Lake Aquatic Plant Surveys for 2008 2

Results: May 30 -- Early Summer Survey
In early summer, the most abundant plant in Orchard Lake was curlyleaf pondweed and it
was found at 96% of the 26 stations. In the past, curlyleaf pondweed has been growing to
the surface producing recreational nuisance conditions in water depths out to 10 feet.
Harvesting in 2004 through 2008 has drastically reduced nuisance curlyleaf growth
(defined as curlyleaf growing to the surface). Overall aquatic plants grew to a depth of 10
feet in 2008. No Eurasian watermilfoil was found in this survey. A summary of the
occurrence and density of aquatic plants is shown in Table 1.
An aquatic plant coverage map is shown in Figure 3. Curlyleaf pondweed coverage is
basically the same as the aquatic plant coverage map with coverage approximately at 180
acres. This is nearly the same coverage of curlyleaf that was surveyed in 2003 (prior to
the start of the harvesting program). However, the area of nuisance curlyleaf pondweed
growth is less in 2008 compared to 2003. Nuisance coverage of curlyleaf pondweed in
2008 is shown in Figure 3 and was sampled prior to harvesting. After harvesting was
completed in early June, there was very little curlyleaf pondweed growth that would be
considered a nuisance.
A summary of plant density and occurrence for individual transects is shown in Table 2.
Curlyleaf pondweed conditions are shown in Figure 4.
Figure 3. Aquatic plant coverage and curlyleaf coverage on May 30, 2008. Pink shading represents
non-nuisance curlyleaf growth along with other plants. Red shading indicates nuisance curlyleaf
growth prior to harvesting.
Orchard Lake Aquatic Plant Surveys for 2008 3

Table 1. Orchard Lake aquatic plant occurrences and densities for the May 30, 2008
survey based on 15 transects and 2 depths, for a total of 30 stations. Density ratings are
1-5 with 1 being low and 5 being most dense. Transect 8.5 and 11.5 were not used in
statistics.
W hite waterlily
(Nymphaea tuberosa)
Marigold
(Bidens Beckii)
Coontail
(Ceratophyllum demersum)
Chara
(Chara sp)
Star duckweed
(Lemna trisulca)
Northern watermilfoil
(Myriophyllum sibiricum)
Cabbage
(Potamogeton amplifolius)
Curlyleaf pondweed
(P. crispus)
Claspingleaf pondweed
(P. Richardsonii)
Narrowleaf pondweed
(P. sp)
Filamentous algae
Depth
0- 5 feet
(n=13)
Occur %
Occur
Depth
6 - 10 feet
(n= 13)
Density Occur %
Occur
All Stations
(n=26)
Density Occur %
Occur
Density
3 23 1.2 -- -- -- 3 12 1.2
1 8 0.5 -- -- -- 1 4 0.5
8 62 1.7 1 8 1.0 9 35 1.6
3 23 1.3 --– --– -- 3 12 1.3
1 8 0.5 -- -- -- 1 4 0.5
2 15 1.0 -- -- -- 2 8 1.0
1 8 1.0 -- -- -- 1 4 1.0
12 92 2.7 13 100 2.8 25 96 2.8
1 8 0.5 -- -- -- 1 4 0.5
2 15 0.5 -- -- -- 2 8 0.5
4 31 2.0 5 38 2.1 9 35 2.0
Figure 4. Aquatic mammals were active
on Orchard Lake in 2008. Here muskrats
have dislodged spatterdock roots. The
roots are a good food source for
muskrats.
Orchard Lake Aquatic Plant Surveys for 2008 4

Table 2. Individual transect data for Orchard Lake for May 30, 2008.
T1 T2 T3 T4 T5 T6 T7
0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10
White waterlily 1
Marigold 0.5
Coontail 2 0.5 1 2 2
Chara 2 1
Star duckweed 0.5
Northern watermilfoil 1
Cabbage
Curlyleaf pondweed 2 2.3 2 1 2 1 2 4.5 2.5 3 3 4 4
Claspingleaf pondweed
Narrowleaf pondweed 0.5 0.5
Filamentous algae 2 1.3 1 2 3
T8 T8.5 T9 T10 T11 T11.5 T12 T13
0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10
White waterlily 1 1.5
Marigold
Coontail 1 1 2 3
Chara 2 2 1
Star duckweed
Northern watermilfoil 1
Cabbage 1
Curlyleaf pondweed 3 1.5 2 4 3.5 5 4 1 3 4 2 2 4 1.5 2
Claspingleaf pondweed 0.5
Narrowleaf pondweed
Filamentous algae 2 1 4 2
Figure 5. Curlyleaf pondweed on
the sample rake at a density of a
‘2'.
Orchard Lake Aquatic Plant Surveys for 2008 5

Results: August 13 -- Filamentous Algae Assessment
In mid-summer of 2008, it was apparent that floating filamentous algae was more
abundant compared to previous years. Although floating filamentous algae was above
average in 2008, widespread benthic filamentous algae has been observed in Orchard
Lake for at least the previous five years. A map of benthic filamentous algae in Orchard
Lake on August 13, 2008 is shown in Figure 6.
An unusual event occurred in Orchard Lake in 2008. The benthic algae on the southeast
side of Orchard Lake, lifted off the bottom and floated to the lake surface. A significant
amount of floating filamentous algae was blown into the shoreline area (Figure 7).
Figure 6. Benthic filamentous algae map for August 13, 2008.
Orchard Lake Aquatic Plant Surveys for 2008 6

In 2008, this was the first year since surveys have been conducted that the benthic algae
came to the surface (Figure 7). A sample was examined under the microscope and
determined to be a blue-green filamentous algae, Oscillatoria.
It may be the exceptional water clarity of 2008 combined with other factors contributed to
this type of event. The sediment release of the benthic filamentous algae is not expected
to occur on an annual basis unless conditions are just right.
Figure 7. [top - left] Some of the floating filamentous algae that collected on the south shoreline of
Orchard Lake in 2008. [top - right] Close-up shot of the filamentous algae. [bottom - left] A rake
sample of benthic (or bottom) filamentous algae. [bottom - right] The algae was examined under the
microscope and magnified 125 times. It was a blue-green algae called Oscillatoria.
Orchard Lake Aquatic Plant Surveys for 2008 7

Results: September 1 -- Late Summer Survey
The dominant plant in the survey of September 1, 2008 in Orchard Lake was coontail
(Table 3). No Eurasian watermilfoil was found in this late summer survey. The
occurrence and density of plants for each transect are shown in Table 4.
Overall, aquatic plants grew out to a depth of 10 feet around much of the north end of the
lake, otherwise growth was out to the 6 or 7 foot water depth (Figure 5). A map of
aquatic plant coverage is shown in Figure 5. Aquatic plants covered about 120 acres,
representing 51% of the 234 acre lake. Coontail continues to grow densely around the
lake. Northern watermilfoil and chara were important plants in Orchard Lake in
September of 2008.
Figure 8. Aquatic plant coverage map for Orchard Lake on September 1, 2008. The green area
shows coverage of aquatic plants.
Orchard Lake Aquatic Plant Surveys for 2008 8

Table 3. Orchard Lake aquatic plant occurrences and densities for the September 1,
2008 survey based on 14 transects and 2 depths, for a total of 28 stations. Density
ratings are 1-5 with 1 being low and 5 being most dense.
Duckweed
(Lemna sp)
Spatterdock
(Nuphar variegatum)
W hite waterlily
(Nymphaea tuberosa)
Marigold
(Bidens Beckii)
Coontail
(Ceratophyllum demersum)
Chara
(Chara sp)
Star duckweed
(Lemna trisulca)
Northern watermilfoil
(Myriophyllum sibiricum)
Naiads
(Najas flexilis)
Cabbage
(Potamogeton amplifolius)
Curlyleaf pondweed
(P. crispus)
Claspingleaf pondweed
(P. Richardsonii)
Water celery
(Vallisneria americana)
Water stargrass
(Zosterella dubia)
filamentous algae
Depth
0 - 5 feet
(n=14)
Occur %
Occur
Depth
6 - 10 feet
(n= 14)
Density Occur %
Occur
All Stations
(n=28)
Density Occur %
Occur
Density
1 7 1.7 -- -- -- 1 4 1.7
4 29 3.0 -- -- -- 4 14 3.0
3 21 1.5 -- -- -- 3 11 1.5
-- -- -- 1 7 1.0 1 4 1.0
11 79 1.6 12 86 1.1 23 82 1.4
4 29 2.5 3 21 1.0 7 25 1.9
-- -- -- 1 7 0.5 1 4 0.5
10 71 2.0 -- -- -- 10 36 2.0
-- -- -- 1 7 1.0 1 4 1.0
2 14 0.8 -- -- -- 2 7 0.8
-- -- -- 3 21 0.4 3 11 0.4
1 7 3.0 -- -- -- 1 4 3.0
1 7 2.0 -- -- -- 1 4 2.0
3 21 0.8 -- -- -- 3 11 0.8
6 43 2.4 13 93 2.9 19 68 2.8
Orchard Lake Aquatic Plant Surveys for 2008 9

Table 4. Individual transect data for Orchard Lake for September 1, 2008.
T1 T2 T3 T4 T5 T6 T7
0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10
Duckweed
Spatterdock
White waterlily 2 1.5
Marigold 1
Coontail 3 0.3 1 1.5 1 3 2.5 1.5 2 1 0.5
Chara 3
Star duckweed
Northern watermilfoil 1 1 3 3 0.5
Naiads 1
Cabbage 0.5
Curlyleaf pondweed 0.5 0.5
Claspingleaf pondweed 3
Water celery 2
Water stargrass 0.5
Filamentous algae 2.5 3 4.5 2 2 2 1 2 2 2.5
T8 T9 T10 T11 T11.5 T12 T13
0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10 0 - 5 6 -10
Duckweed 1.7
Spatterdock 5 2 4 1
White waterlily 1
Marigold
Coontail 2 0.5 0.5 2 0.5 0.3 1 0.5 2 1 2 2
Chara 2 1 3 1 2 1
Star duckweed 0.5
Northern watermilfoil 2 1.5 3.8 2 2
Naiads
Cabbage 1
Curlyleaf pondweed 0.3
Claspingleaf pondweed
Water celery
Water stargrass 1 1
Filamentous algae 2 2 4 3.5 3 4 4 2.3 4
Orchard Lake Aquatic Plant Surveys for 2008 10

Figure 9. [top] Sample rake with claspingleaf pondweed, coontail, and northern watermilfoil.
[bottom] Waterlilies were common in Orchard Lake in 2008.
Orchard Lake Aquatic Plant Surveys for 2008 11

Comparison of Early and Late Summer Plant Surveys in 2008
In the early summer of 2008, curlyleaf pondweed was found around Orchard Lake and out
to about 10 feet of water. The early summer survey in 2008 was conducted prior to
mechanical harvesting and nuisance growth was observed in patches around Orchard
Lake. However, after harvesting in 2008, no nuisance curlyleaf pondweed was observed.
By the beginning of September, curlyleaf pondweed had resprouted in several areas.
Coontail was the most common plant followed by northern watermilfoil (Table 5). The
acreage of aquatic submerged plants in Orchard Lake decreased from early to late
summer. As is typical, coontail increased from May to September. Coontail seemed to
fill in areas where curlyleaf pondweed was found in early summer. Coontail was found to
occasionally grow to heavy conditions in water depths of 4 to 5 feet.
Table 5. The percent occurrence of aquatic plants for Orchard Lake in 2008. Percent occurrence
is calculated based on the number of times a plant species occurs at a sampling station on
transects divided into the number of total stations for the survey. For example, if milfoil was
found in 25 out of 50 stations, its percent occurrence would be 50%.
May 30, 2008
(% occur)
September 1, 2008
(% occur)
Changes from
May to September
Duckweed
(Lemna sp)
0 4 +
Spatterdock
(Nuphar variegatum)
0 14 +
White waterlily
(Nymphaea sp)
12 11 0
Marigold
(Bidens Beckii)
4 4 0
Coontail
(Ceratophyllum demersum)
35 82 +
Chara
(Chara sp.)
12 25 +
Star duckweed
(Lemna trisulca)
4 4 0
Northern watermilfoil
(Myriophyllum sibiricum)
8 36 +
Naiads
(Najas flexilis)
0 4 +
Cabbage
(Potamogeton amplifolius)
4 7 +
Curlyleaf pondweed
(P. crispus)
96 11 -
Claspingleaf pondweed
(P. richardsonii)
4 4 0
Narrowleaf pondweed
(P. sp)
8 0 -
Water celery
(Vallisneria americana)
0 4 +
Water stargrass
(Zosterella dubia)
0 11 +
Filamentous algae 35 68 +
Number of Submerged Species 9 11 +
Orchard Lake Aquatic Plant Surveys for 2008 12

Summary of Previous Aquatic Plant Surveys
The City of Lakeville has sponsored annual aquatic plant surveys since 1999. A summary
of the percent occurrence of individual species on a lakewide basis is shown in Table 6.
Since 1995, it appears that six submerged species have increased and four species have
decreased. Six species are found sparingly or have not changed in abundance. The
number of submerged species found in Orchard Lake has remained about the same since
1995 (Table 6).
The beach at Orchard Lake.
Orchard Lake Aquatic Plant Surveys for 2008 13

Table 6. The percent occurrence of aquatic plants for Orchard Lake for 1995 and 1999 through 2008. Mechanical harvesting has occurred from 2004 to 2008
(blue shading). Changes in plant abundance are rated as: + = increase, -- = decrease, 0 = no significant change (1995 data are from Barr Engineering Company,
Diagnostic Study of Orchard Lake, 1999).
Duckweed
(Lemna sp)
Spatterdock
(Nuphar variegatum)
White waterlily
(Nymphaea sp)
Marsh marigold
(Bidens beckii)
Coontail
(Ceratophyllum
demersum)
Chara
(Chara sp.)
Star duckweed
(Lemna trisulca)
Northern watermilfoil
(Myriophyllum
sibiricum)
Naiads
(Najas sp)
Nitella
(Nitella sp)
Cabbage
(Potamogeton
amplifolius)
Curlyleaf pondweed
(P. crispus)
Illinois pondweed
(P. illinoensis)
Stringy pondweed
(P. pusillus)
Claspingleaf
pondweed
(P. richardsonii)
Narrowleaf
pondweed
(P. sp)
Flatstem pondweed
(P. zosteriformis)
Buttercup
(Ranunculus sp)
Sago pondweed
(Stuckenia
pectinatus)
Water celery
(Vallisneria
americana)
Water stargrass
(Zosterella dubia)
Number of
submerged species
June 16,
1995
% Occur
(based on
57
stations)
June 5,
1999
% Occur
(based on
39
stations)
May 26,
2000
% Occur
(based on
39
stations)
June 8,
2001
% Occur
(based on
39
stations)
May 31,
2002
% Occur
(based on
42
stations)
May 17,
2003
% Occur
(based on
39
stations)
June 7,
2004
% Occur
(based on
24
stations)
May 21,
2005
% Occur
(based on
26
stations)
May 26,
2006
% Occur
(based on
30
stations)
May 22,
2007
% Occur
(based on
26
stations)
May 30,
2008
% Occur
(based
pm 26
stations)
Aug 20,
1995
% Occur
(based on
57
stations)
-- – -- -- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- 3 -- -- 4 0
-- 5 10 5 5 8 13 15 10 12 -- -- 10 8 8 10 8 12 13 10 12 14 0
-- 5 3 3 7 5 4 -- 7 12 12 -- 8 13 12 10 13 27 17 17 19 11 +
-- -- -- -- 5 -- -- -- -- -- 4 -- -- -- -- -- -- -- -- -- -- 4 0
12 18 28 74 38 38 88 62 13 27 35 74 85 56 88 90 90 100 90 93 88 82 +
12 13 13 28 12 10 4 15 10 8 12 18 26 8 27 10 5 19 13 17 19 25 +
-- -- -- -- -- -- -- -- 7 8 4 -- -- 3 -- 5 5 8 17 17 15 4 +
18 23 3 41 12 3 25 19 33 12 8 21 5 23 46 33 13 54 33 27 27 36 +
-- -- -- -- -- -- -- -- -- -- -- 13 -- -- -- -- 3 -- 3 -- -- 4 0
-- -- -- -- 2 3 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 0
5 8 3 13 14 10 13 19 33 31 4 8 3 13 23 10 8 27 27 27 19 7 -
98 74 95 92 74 100 92 96 100 100 96 55 -- 23 4 5 26 -- 7 -- 4 11 -
-- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- -- -- -- -- -- -- -- 0
-- -- -- 10 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 0
9 5 -- 10 5 -- -- -- 7 4 4 18 3 5 8 3 8 8 -- 7 4 4 0
-- -- -- -- -- -- -- -- -- -- 8 -- -- -- -- -- -- -- -- -- -- --
2 -- -- 5 -- -- 4 -- 7 -- -- 13 5 -- 4 8 -- 4 3 -- -- -- 0
-- 8 3 -- -- 3 4 12 3 8 -- -- -- -- -- -- -- 8 -- -- -- -- -
4 -- -- -- -- -- -- -- -- -- -- 8 -- 8 4 -- -- 8 3 3 -- -- 0
-- -- -- -- -- -- -- -- -- -- -- -- -- 3 -- 3 13 12 13 3 12 4 +
4 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 3 27 13 3 8 11 +
9 7 6 8 8 7 7 6 9 8 9 9 6 10 8 9 10 11 11 9 9 11
Aug 14,
1999
% Occur
(based on
39
stations)
Oct 6,
2000
% Occur
(based on
39
stations)
Sept 17,
2001
% Occur
(based on
39
stations)
Sept 8,
2002
% Occur
(based on
39
stations)
Aug 20,
2003
% Occur
(based on
39
stations)
Aug 29,
2004
% Occur
(based on
26
stations)
Aug 22,
2005
% Occur
(based on
30
stations)
Aug 21,
2006
% Occur
(based on
30
stations)
Aug 26,
2007
% Occur
(based on
26
stations)
Sept 1,
2008
% Occur
(based on
28
stations)
Change
from 1995
to 2007
(spring
and fall)
Orchard Lake Aquatic Plant Surveys for 2008 14

Summary of Previous Curlyleaf Pondweed Surveys
Curlyleaf coverage has stayed about the same, going back to 1999 although there may be
a slight decrease in water depths of 6 to 10 feet from 2004 - 2008 (Table 7 and Figures
10-16). The pattern appears to be that curlyleaf pondweed declines from spring to late
summer and coontail increases. The abundance of curlyleaf pondweed nuisance growth
varies from year to year. Nuisance growth was especially heavy in 1999 and 2002 due in
part, to late onset of lake ice, lack of snow, and early ice out. Harvesting from 2004
through 2008 has reduced the acres of curlyleaf nuisance growth (Figures 10-16).
Additional sampling results using scuba diving to quantify stem densities at two locations
show that curlyleaf stem densities decreased with harvesting from 2004 through 2006,
with an increase in 2007 and then a decrease in 2008 (Table 7).
Table 7. Summary of the density of curlyleaf pondweed for the early summer surveys of
1999 through 2008. Blue shading indicates years of mechanical harvesting.
Survey Date
1999
(June 5)
2000
(May 26)
2001
(June 8)
2002
(May 21)
2003
(May 17)
2004
(June 7)
(post harvest)
2005
(May 21)
(pre-harvest)
2006
(May 26)
(pre-harvest)
2007
(May 22)
(pre-harvest)
2008
(May 30)
(pre-harvest)
Average Early Summer Curlyleaf Density
(0-5- scale)
0-5 ft
Depth
6-10 ft
Depth
11-15 ft
Depth
All
Stations
Stem Densities in
Known Dense CLP
Area That Has Been
Harvested (stems/m 2 )
(5-feet) (n=20)
3.4 4.6 3.8 4.0 ND
4.0 3.9 2.2 3.4 ND
2.5 2.8 2.8 2.7 ND
3.8 4.1 2.0 3.6 ND
3.5 4.0 2.6 3.4 436
2.1 2.5 0 2.3 403
2.1 3.1 0 2.6 407
3.6 3.2 0 3.4 341
3.9 2.7 0 3.3 514
2.7 2.8 0 2.8 360
Orchard Lake Aquatic Plant Surveys for 2008 15

Figure 10. 2002 early summer aquatic
plant coverage. Nuisance curlyleaf
pondweed is shown in red.
Figure 11. 2003 early summer aquatic
plant coverage. Curlyleaf was found
growing out to 15 feet of water depth.
Nuisance curlyleaf pondweed is shown
in red and covered about 70 acres.
Figure 12. 2004 early summer aquatic
plant coverage. Nuisance curlyleaf
pondweed is shown in red after
harvesting was completed. Harvesting
significantly decreased the acreage of
nuisance growth.
Figure 13. 2005 early summer aquatic
plant coverage. Curlyleaf was found
growing out to 10 feet of water depth.
Nuisance curlyleaf pondweed did not
appear in 2005 due to the harvesting.
Figure 14. 2006 early summer aquatic
plant coverage. Nuisance curlyleaf
pondweed is shown in red before
harvesting was completed. After
harvesting was completed curlyleaf
pondweed was greatly reduced.
Figure 15. 2007 early summer aquatic
plant coverage. Nuisance curlyleaf
pondweed is shown in red shading before
harvesting.
Figure 16. 2008 early summer aquatic
plant coverage. Curlyleaf was found
growing out to 11 feet. Nuisance curlyleaf
pondweed, shown in red, was present in
two locations.
Orchard Lake Aquatic Plant Surveys for 2008 16

Summary of Curlyleaf Pondweed Densities from 1999 - 2008
The City of Lakeville has sponsored annual early summer aquatic plant surveys on
Orchard Lake for the last ten years, from 1999 through 2008. For each survey, the same
transect locations and depth zones were used (Figure 17). A curlyleaf density was
assigned at each depth on a transect, each year. A density rating of 1 - 5 was used with 5
being the most dense, where plants were matted at the surface.
A summary of curlyleaf pondweed densities for individual depths on all transects for each
survey is shown in Figure 18. This chart shows that Orchard lake has numerous areas of
high density curlyleaf pondweed growth. There is also a fair amount of variability from
year to year as the number of red squares on a survey (indicative of high density) ranges
from 3 to 23. Since harvesting began, the average number of red squares/survey has
averaged 9 for harvesting years verses 17 for pre-harvesting years.
It appears the variability of curlyleaf from year to year is influenced by climatic factors
whereas the variability of curlyleaf within a lake is influenced by the sediment
composition.
Density ratings and growth categories for light, moderate, and heavy growth are shown in
Figure 19.
Figure 17. Orchard Lake aquatic plant transect locations.
Orchard Lake Aquatic Plant Surveys for 2008 17

Curlyleaf Pondweed Density Summary for Plant Surveys
Transect
Depth
1999
Jun 5
2000
May 26
2001
Jun 8
2002
May 31
2003
May 17
2004
Jun 7
2005
May 21
2006
May 26
2007
May 22
2008
May 30
Average
% Red
>50%
Predicted
growth based
on lake soils
S 5 5 2 5 5 2.5 4 3 1.5 2 3.5 50 Moderate
1
M 5 5 2 3.5 4.5 3.5 4 3.5 2.5 3 3.6 40
D 3 2 2 X 4 X X X X 1 2.4 10
S 5 5 4 5 2.5 0 2 4 3.3 0 3.1 50 Moderate
2
M 5 5 4 4 3 2 4 3.8 4 2 3.7 70 Heavy
D 4 2 4 X 3 X X X X 0 2.6 20
S 5 4 2 4 2 0.5 1 4 1 1 2.5 40 Heavy
3
M 0 5 2.5 4 5 2 2 3.3 3 2 2.9 30 Heavy
D 0 3 2.5 4 4 X X X X 0 2.3 20
S 3 3 3 1 3 2 0.5 2 2 1 2.1 0 Heavy
4
M 5 4 3 3.5 4 1 1.3 2.3 3.3 2 2.9 30
D 4 3 3 1 3 X X X X 2 2.5 10
S 5 0 3 4 4 4.5 0 5 5 4.5 3.5 70 Heavy
5
M 5 4 3.5 4.5 4 4 3 3.6 2.5 4 3.8 60 Moderate
D 0 2 3.5 2 3 X X X X 1 1.9 0
S 5 5 0 5 4 4.5 3 2.5 4 1 3.4 60
6
M 0 5 3 4.5 4 3.5 4 2 2.5 4 3.2 50 Heavy
D 0 1.5 3 2 3 X X X X X 1.9 0
S 1 5 0 3 5 0.5 2 5 4.5 4 3.0 50
7
M 4 3 3 4 4.5 2 3.5 4 2 4 3.4 50 Heavy
D 0 2 3 X 2 X X X X X 1.8 0
S 2 3 0 2 1 X 3 5 5 3 2.7 20 Heavy
8
M 5 2 1 2.5 2 X 1.5 2.5 1 2 2.2 10
D 4 2 1 1 1 X X X X 1 1.7 10
S 1 5 1 4 5 1.5 3 5 4.5 4 3.4 60
9
M 4 3 3 4.5 4 2.5 4 3.3 3 4 3.6 50 Heavy
D 4 2 3 X 2 X X X X 3 2.8 10
S 4 2 1 5 4 0 1 4 4 5 3.0 60
10
M 5 2.5 3 5 4 2.5 4 2.5 3 4 3.6 50 Heavy
D 4 2 3 X 2 X X X X X 2.8 10
S 1 1 2 3 4 2 2 4 4 1 2.4 30
11
M 4 4 3 4 4 2 3.5 3.2 2.5 4 3.4 50 Heavy
D 0 3 3 X 2 X X X X X 2.0 0
S 4 5 4 5 4 2 3 2.3 4.5 2 3.6 60
12
M 5 5 4 5 4.5 2 4 2.8 2.8 4 3.9 70 Heavy
D 0 2 4 X 2 X X X X X 2.0 10
S 0 0 2.5 4 2 0.5 1 1 4 1.5 1.7 20
13
M 4 5 1 5 4 3.5 4 4 3 2 3.6 60 Heavy
D 0 2 1 X 3 X X X X X 1.5 0
Number of Reds 23 16 6 20 21 3 8 11 10 11 8 17
Avg CLP Density 4.0 3.4 2.7 3.6 3.4 2.3 2.6 3.4 3.3 2.8
Depth Zones:
S = 0 - 5 feet
M = 6 - 10 feet
D = 11 - 15 feet
Figure 18. Summary of curlyleaf pondweed density for early summer aquatic plant surveys
for Orchard Lake from 1999 - 2008. Curlyleaf density is shown on a scale from 1 - 5 (with 5
being most dense) for each depth zone on all 13 transects for each survey. An “X” in a box
means no sample at that depth. Colors are coded for density. Blue shading for 2004 - 2008
indicates years of harvesting. A sediment survey was conducted on Orchard Lake in 2001
(orange shaded box). Predicted curlyleaf growth (far right column) has been close to actual
curlyleaf growth conditions.
Orchard Lake Aquatic Plant Surveys for 2008 18

Curlyleaf Pondweed Growth Characteristics
Light Growth Conditions
Plants rarely reach the surface.
Navigation and recreational activities
are not generally hindered.
Stem density: 0 - 160 stems/m 2
Biomass: 0 - 50 g-dry wt/m 2
Estimated TP loading: 300 g-dry wt/m 2
Estimated TP loading: >6.7 lbs/ac
MnDNR rake sample density has a scale from 1 to 4. For certain growth conditions where plants top out at the
surface, the scale has been extended: 4.5 is equivalent to a near solid surface canopy and a 5 is equivalent to a
solid surface canopy. Heavy growth conditions have rake densities of a 4 (early to mid-season with the potential
to reach the surface), 4.5, or 5.
Figure 19. Curlyleaf pondweed characteristics for three growth conditions.
Orchard Lake Aquatic Plant Surveys for 2008 19

Summary of Orchard Lake Water Quality
In 2008, summer averages for clarity (using a Secchi disc), phosphorus, and algae (using
chlorophyll analysis) were some of the best on record (Table 8). Orchard Lake is not in
the impaired status category. Impaired criteria are shown in Table 9.
Table 8. Water quality summary for Orchard Lake. Data are May-September
averages from the Met Council CAMP program. Blue shading represents years of
significant curlyleaf pondweed harvesting.
Secchi Disc
(m)
Total Phosphorus
(ppb)
Chlorophyll a
(ppb)
1980 2 40 16
1981 3 26 11
1983 2.9 31 11
1987 1.8 -- --
1988 2.3 -- --
1989 2.1 28 14
1990 1 -- --
1991 1.9 -- --
1993 2 35 17
1995 1.3 44 31
1996 2.3 28 15
1998 1.9 38 24
1999 2.1 34 30
2000 2 39 20
2001 2.3 25 13
2004 2.6 38 17
2005 2.4 32 12
2006 2.2 34 14
2007 1.6 41 23
2008 3.0 24 11
Table 9. MPCA nutrient criteria for impaired lakes (MPCA 2005). Orchard Lake is
a deep lake. Water quality results indicate Orchard Lake is not in the impaired
category.
Secchi Disc
(m)
Total Phosphorus
(ppb)
Chlorophyll a
(ppb)
Shallow Lake >1.0

Recommendations for Curlyleaf Pondweed in Orchard Lake
The aquatic plant community in Orchard Lake is fairly diverse and 11 submerged aquatic
plant species were observed in September of 2008. Native plants cover about 62% of the
lake bottom in summer. If native plant distribution is maintained, water clarity should
remain high as well. Because the curlyleaf pondweed dieback contributes phosphorus
and can increase algal growth, continuing the curlyleaf pondweed control program is
recommended. The harvesting program was initiated in 2004. Harvesting has the
potential to have a positive affect on water quality and would be beneficial to continue. In
addition to harvesting, another curlyleaf control technique was initiated in 2004 which
involved the use of iron filings to control nuisance curlyleaf growth in two one-acre test
plots. The effectiveness of that demonstration project will be evaluated again in 2009. If
iron treatment shows ongoing curlyleaf control and if it is permitted for use, an iron
treatment area should be expanded in front of the city park and landing.
Orchard Lake Aquatic Plant Surveys for 2008 21

Appendix
Transect Descriptions and
Lowrance x-16 Sonar Graphs of Aquatic Plants
A Lowrance X16 sonar was used to record plant canopies on Orchard Lake.

Transect Descriptions
Transect
1 Gray house next to landing.
st
2 1 house north of landing.
3 Big boulder wall, gray house behind.
4 Natural shoreline before peninsula.
5 Head into corner.
Description
6 Fringe of natural area with picnic tables at the back. Right of rock rip-rap.
7 Two willows next to rad house.
8 Gray, 3 story house next to road.
9 Private beach where road goes up.
10 Two tier rock wall.
11 Right of the beach.
11.5 Big boulder wall, tan house 20 feet from shore.
12 Left of house with stone and iron fence.
13 East (left)of spit, going into lily beds.