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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

Pre Harvesting Conditions

Post Harvesting Conditions

Post Harvesting Conditions

Pre Harvesting Conditions

Pre Harvesting 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 waterm ilfoil (Myriophyllum sibiricum) Naiads (Najas flexilis) Cabbage (Potamogeton amplifolius) Curlyleaf pondweed (P. crispus) Claspingleaf pondweed (P. richardsonii) Narrowleaf pondweed (P. sp) Buttercup (Ranunculus sp) W ater celery (Vallisneria americana) W ater stargrass (Zosterella dubia) Filam entous algae Num ber of Subm erged Species

M ay 30, 2008 (% occur)

September 1, 2008 (% occur)

Changes from M ay 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

+

35

68

+

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. M echanical 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). Change Sept 1, Aug 20, Aug 29, Aug 22, Aug 21, Aug 26, Sept 17, Sept 8, Oct 6, May 21, May 26, May 22, May 30, Aug 20, Aug 14, June 7, May 31, May 17, May 26, June 8, June 16, June 5, from 1995 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1995 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1995 % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur to 2007 (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (based (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (spring and fall) 28 26 30 30 26 39 39 39 39 39 57 pm 26 26 30 26 24 39 42 39 39 39 57 stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) 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

--

–

--

--

--

--

--

--

--

--

--

--

--

--

--

--

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

-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. W ater quality summary for Orchard Lake. Data are M ay-September averages from the M et Council CAM P program. Blue shading represents years of significant curlyleaf pondw eed harvesting. Secchi Disc Total Phosphorus Chlorophyll a (ppb) (m ) (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. M PCA nutrient criteria for impaired lakes (M PCA 2005). Orchard Lake is a deep lake. W ater quality results indicate Orchard Lake is not in the impaired category. Secchi Disc Total Phosphorus Chlorophyll a (m ) (ppb) (ppb) Shallow Lake >1.0 <60 <20 Deep Lake >1.4 <40 <14

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 oneacre 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 authorized to use, an iron treatment area should be expanded in front of the city park and landing.

-iv-


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 â&#x20AC;&#x2DC;1' and a high density was a â&#x20AC;&#x2DC;5'.

Figure 1. Transects for plant surveys on M ay 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 M ay 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 M ay 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. Depth 0- 5 feet (n=13) Occur

Depth 6 - 10 feet (n= 13)

% Density Occur Occur

All Stations (n=26)

% Density Occur Occur

% Density Occur

W hite waterlily (Nymphaea tuberosa)

3

23

1.2

--

--

--

3

12

1.2

Marigold (Bidens Beckii)

1

8

0.5

--

--

--

1

4

0.5

Coontail (Ceratophyllum demersum)

8

62

1.7

1

8

1.0

9

35

1.6

Chara (Chara sp)

3

23

1.3

--â&#x20AC;&#x201C;

--â&#x20AC;&#x201C;

--

3

12

1.3

Star duckweed (Lemna trisulca)

1

8

0.5

--

--

--

1

4

0.5

Northern waterm ilfoil (Myriophyllum sibiricum)

2

15

1.0

--

--

--

2

8

1.0

Cabbage (Potamogeton amplifolius)

1

8

1.0

--

--

--

1

4

1.0

12

92

2.7

13

100

2.8

25

96

2.8

Claspingleaf pondweed (P. Richardsonii)

1

8

0.5

--

--

--

1

4

0.5

Narrowleaf pondweed (P. sp)

2

15

0.5

--

--

--

2

8

0.5

4

31

2.0

5

38

2.1

9

35

2.0

Curlyleaf pondweed (P. crispus)

Filam entous algae

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 Coontail

0.5 2

0.5

Chara

1

2

Star duckweed

2

2

1

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 Filamentous algae

0.5 2

1.3

1

0.5 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

Chara

2 2

2

3

1

Star duckweed Northern watermilfoil

1

Cabbage Curlyleaf pondweed

1 3

1.5

2

4

Claspingleaf pondweed

3.5

5

4

1

3

4

2

2

4

1.5

2

0.5

Narrowleaf pondweed Filamentous algae

2

1

4

2

Figure 5. Curlyleaf pondweed on the sample rake at a density of a â&#x20AC;&#x2DC;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. Depth 0 - 5 feet (n=14) Occur

Depth 6 - 10 feet (n= 14)

% Density Occur Occur

All Stations (n=28)

% Density Occur Occur

% Density Occur

Duckweed (Lemna sp)

1

7

1.7

--

--

--

1

4

1.7

Spatterdock (Nuphar variegatum)

4

29

3.0

--

--

--

4

14

3.0

W hite waterlily (Nymphaea tuberosa)

3

21

1.5

--

--

--

3

11

1.5

Marigold (Bidens Beckii)

--

--

--

1

7

1.0

1

4

1.0

Coontail (Ceratophyllum demersum)

11

79

1.6

12

86

1.1

23

82

1.4

Chara (Chara sp)

4

29

2.5

3

21

1.0

7

25

1.9

Star duckweed (Lemna trisulca)

--

--

--

1

7

0.5

1

4

0.5

Northern waterm ilfoil (Myriophyllum sibiricum)

10

71

2.0

--

--

--

10

36

2.0

Naiads (Najas flexilis)

--

--

--

1

7

1.0

1

4

1.0

Cabbage (Potamogeton amplifolius)

2

14

0.8

--

--

--

2

7

0.8

Curlyleaf pondweed (P. crispus)

--

--

--

3

21

0.4

3

11

0.4

Claspingleaf pondweed (P. Richardsonii)

1

7

3.0

--

--

--

1

4

3.0

W ater celery (Vallisneria americana)

1

7

2.0

--

--

--

1

4

2.0

W ater stargrass (Zosterella dubia)

3

21

0.8

--

--

--

3

11

0.8

6

43

2.4

13

93

2.9

19

68

2.8

filam entous algae

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 Coontail

1 3

0.3

1

Chara

1.5

1

3

2.5

1.5

2

1

0.5

2

2.5

3

Star duckweed Northern watermilfoil

1

1

3

3

0.5

Naiads

1

Cabbage

0.5

Curlyleaf pondweed

0.5

Claspingleaf pondweed Water celery

2

Water stargrass Filamentous algae

0.5

3 0.5 2.5

3

4.5

T8

2

2

T9

2

T10

T11

1 T11.5

2 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

White waterlily

1

2

4

1

Marigold Coontail

2

0.5

0.5

2

0.5

0.3

Chara

2

Star duckweed Northern watermilfoil

1

1

0.5

2

1

3

1

2

1

2

2

2.3

4

0.5 2

1.5

3.8

2

2

Naiads Cabbage

1

Curlyleaf pondweed

0.3

Claspingleaf pondweed Water celery Water stargrass Filamentous algae

1 2

2

Orchard Lake Aquatic Plant Surveys for 2008

1 4

3.5

3

4

4

10


Figure 9. [top] Sample rake with claspingleaf pondweed, coontail, and northern watermilfoil. [bottom] W aterlilies 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

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

4

+

0

11

+

35 9

68 11

+ +

Duckweed (Lemna sp) Spatterdock (Nuphar variegatum) White 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) Water celery (Vallisneria americana) Water stargrass (Zosterella dubia) Filamentous algae Number of Submerged Species

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. M echanical 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). Change Sept 1, Aug 20, Aug 29, Aug 22, Aug 21, Aug 26, Sept 17, Sept 8, Oct 6, May 21, May 26, May 22, May 30, Aug 20, Aug 14, June 7, May 31, May 17, May 26, June 8, June 16, June 5, from 1995 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1995 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1995 % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur % Occur to 2007 (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (based (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (based on (spring and fall) 28 26 30 30 26 39 39 39 39 39 57 pm 26 26 30 26 24 39 42 39 39 39 57 stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) stations) 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

--

â&#x20AC;&#x201C;

--

--

--

--

--

--

--

--

--

--

--

--

--

--

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

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/m2) (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 show n 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 show n 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 show n 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

2

3

4

5

6

7

8

9

10

11

12

13

2004 Jun 7

2005 M ay 21

2006 M ay 26

2007 M ay 22

2008 M ay 30

3.5

50

M oderate

3.6

40

2001 Jun 8

S

5

5

2

5

5

2.5

4

3

1.5

2

M

5

5

2

3.5

4.5

3.5

4

3.5

2.5

3

D

3

2

2

X

4

X

X

X

X

1

2.4

10

1

2003 M ay 17

P redicted grow th based on lake soils

2000 M ay 26

D epth

2002 M ay 31

% R ed >50%

1999 Jun 5

Transect

Average

S

5

5

4

5

2.5

0

2

4

3.3

0

3.1

50

M oderate

M

5

5

4

4

3

2

4

3.8

4

2

3.7

70

H eavy

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

H eavy

M

0

5

2.5

4

5

2

2

3.3

3

2

2.9

30

H eavy

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

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

H eavy

M

5

4

3.5

4.5

4

4

3

3.6

2.5

4

3.8

60

M oderate

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

M

0

5

3

4.5

4

3.5

4

2

2.5

4

3.2

50

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

M

4

3

3

4

4.5

2

3.5

4

2

4

3.4

50

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

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

M

4

3

3

4.5

4

2.5

4

3.3

3

4

3.6

50

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

M

5

2.5

3

5

4

2.5

4

2.5

3

4

3.6

50

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

M

4

4

3

4

4

2

3.5

3.2

2.5

4

3.4

50

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

M

5

5

4

5

4.5

2

4

2.8

2.8

4

3.9

70

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

M

4

5

1

5

4

3.5

4

4

3

2

3.6

60

D

0

2

1

X

3

X

X

X

X

X

1.5

0

8

17

N um ber of R eds

23

16

6

20

21

3

8

11

10

11

A vg C LP D ensity

4.0

3.4

2.7

3.6

3.4

2.3

2.6

3.4

3.3

2.8

D epth Zones: S = 0 - 5 feet M = 6 - 10 feet D = 11 - 15 feet

H eavy

H eavy

H eavy

H eavy

H eavy

H eavy

H eavy

H eavy

H eavy

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 stem s/m 2 Biom ass: 0 - 50 g-dry wt/m 2 Estim ated TP loading: <1.7 lbs/ac MnDNR rake sample density equivalent for light growth conditions: 1, 2, or 3.

Moderate Growth Conditions Broken surface canopy conditions. Navigation and recreational activities m ay be hindered. Lake users m ay opt for control. Stem density: 100 - 280 stem s/m 2 Biom ass: 50 - 85 g-dry wt/m 2 Estim ated TP loading: 2.2 - 3.8 lbs/ac MnDNR rake sample density equivalent for moderate growth conditions: 2, 3 or sometimes, 4.

Heavy Growth Conditions Solid or near solid surface canopy conditions. Navigation and recreational activities are severely lim ited. Control is necessary for navigation and/or recreation. Stem density: 400+ stem s/m 2 Biom ass: >300 g-dry wt/m 2 Estim ated 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

<60

<20

Deep Lake

>1.4

<40

<14

Orchard Lake Aquatic Plant Surveys for 2008

20


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

Description

1

Gray house next to landing.

2

1 st house north of landing.

3

Big boulder wall, gray house behind.

4

Natural shoreline before peninsula.

5

Head into corner.

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.


ER_OrchardAquatic