Eurasian water milfoil (Myriophyllum spicatum)

Pre/Post Herbicide and Fall Bed Mapping Surveys

Round Lake – WBIC: 2640100

Burnett County, Wisconsin

2012 Proposed EWM Treatment Areas

Project Sponsored by: Round-Trade Lake Improvement Association, Inc., Short, Elliot

Hendrickson Inc., and the Wisconsin Department of Natural Resources

Canopied EWM Bed

Survey Conducted by and Report Prepared by: Endangered Resource Services, LLC

Matthew S. Berg, Research Biologist

St. Croix Falls, Wisconsin

May 7, July 25, and September 29, 2012

* Round Lake

i

TABLE OF CONTENTS Page

LIST OF FIGURES ………………..……..………………………………………………... ii

LIST OF TABLES.. ………………..……..………………………………………………... iii

INTRODUCTION……….…..……..………………………………………………………. 1

METHODS……………………………………………………………….………………… 2

RESULTS AND DISCUSSION……………………………………………………………. 3

Finalization of Treatment Areas……………………………………………………. 3

EWM Pre/Post Herbicide Survey…………………………………………………... 4

Fall EWM Bed Mapping Survey…………………………………………………… 12

Descriptions of EWM Beds…….…………………………………………………... 14

LITERATURE CITED……….……………………….……………………………………. 16

APPENDIXES……….…….………………………………………………….……………. 17

I: Survey Sample Points and EWM Treatment Areas……..…………………………… 17

II: Vegetative Survey Data Sheet.………………………………………………………. 20

III: Pre/Post Habitat Variable Maps.………………….……………………………...…... 22

IV: Pre/Post Native Species Richness and Total Rake Fullness.………..……………...... 25

V: EWM and CLP Pre/Post Density and Distribution…………………..……………..... 30

VI: Pretreatment Native Species Density and Distribution…...………………………...... 35

VII: Posttreatment Native Species Density and Distribution…...……………………….... 43

VIII: Round Lake Fall 2011 and 2012 EWM Maps.………………………………………. 56

ii

LIST OF FIGURES

Page

Figure 1: Proposed 2012 Spring EWM Treatment Areas.….……………….……….…..… 1

Figure 2: Rake Fullness Ratings……………………………….…….…………………….. 2

Figure 3: 2012 Survey Sample Points and Final Treatment Areas………………………… 3

Figure 4: Treatment Area Depths and Bottom Substrate….………..……………………… 4

Figure 5: Pre/Post Native Species Richness…………………………..…………………… 5

Figure 6: Pre/Post Total Rake Fullness………………………………..…………………… 5

Figure 7: Pre/Post EWM Density and Distribution ……………………….………………. 6

Figure 8: Pre/Post Changes in EWM Rake Fullness………………………………………. 6

Figure 9: Pre/Post CLP Density and Distribution………….…………………………….… 7

Figure 10: Pre/Post Coontail Density and Distribution …….……………………………... 8

Figure 11: Pre/Post Wild Celery Density and Distribution .…………………………….… 8

Figure 12: Pre/Post Macrophyte Change…………………..…………………………….… 9

Figure 13: 2011 and 2012 Fall EWM Bed Maps ……………………………..…………… 12

iii

LIST OF TABLES

Page

Table 1: Spring EWM Treatment Summary – Round Lake – June 12, 2012……………… 3

Table 2: Pre/Post Survey Summary Statistics – Round Lake, Burnett County –

May 7 and July 25, 2012……………………………………………………………………. 4

Table 3: Frequencies and Mean Rake Sample of Aquatic Macrophytes

Pretreatment Survey - Round Lake, Burnett County - May 7, 2012..……………………… 10

Table 4: Frequencies and Mean Rake Sample of Aquatic Macrophytes

Posttreatment Survey - Round Lake, Burnett County - July 25, 2012……………………... 11

Table 5: Fall Eurasian Water Milfoil Bed Mapping Summary –

Round Lake, Burnett County – September 29, 2012……………………………………..… 13

1

INTRODUCTION: Round Lake (WBIC 2640100) is a 208 acre drainage lake in southwest/south-central

Burnett County, Wisconsin in the Town of Trade Lake (T37N R18W S27 NE SW). It

reaches a maximum depth of 27ft in two spots near the eastern shoreline midlake and has

an average depth of approximately 15ft. Round Lake is eutrophic in nature with very poor

to poor water clarity. From 1986 to 2012, summer Secchi readings have ranged from 1.7-

5.5ft with an average of 3.2ft (WDNR 2012). This clarity produced a littoral zone that

extended to 10ft in May 2012. The bottom substrate is predominately muck in the main

basin and in the lake’s bays while the shoreline and midlake bars and humps are

dominated by gravel and sand (Bush et al 1967).

Figure 1: Proposed 2012 Spring EWM Treatment Areas

In 2003, the Wisconsin Department of Natural Resources (WDNR) confirmed the

presence of Eurasian water milfoil (Myriophyllum spicatum) in Round Lake. Since this

time, EWM has been monitored by the WDNR, but not actively managed. Following a

2011 Fall EWM Bed Mapping Survey that found just over 17 acres of EWM beds, the

Round-Trade Lake Improvement Association, Inc. (RTLIA), under the direction of Short,

Elliot, Hendrickson, Inc. (SEH), decided to begin actively managing the infestation using

herbicide treatments. SEH’s evaluation of the 2011 fall bed mapping survey identified

Beds 3, 5, 7, 8, 10, 13, 14 and 20 as candidates for chemical treatment in 2012. All

combined, these 8 areas totaled 6.87 acres or 3.3% of the lake’s surface area (Figure 1).

On May 7th

, we conducted a pretreatment survey to gather baseline data from the

scheduled treatment areas and to allow SEH biologists to finalize treatment plans.

Following the June 12th

herbicide application, we conducted a July 25th

posttreatment

survey to evaluate the effectiveness of the treatment. We also conducted a September 29th

EWM bed mapping survey to determine where EWM control might be considered in

2013. This report is the summary analysis of these three field surveys.

2

METHODS:

Pre/Post Herbicide Survey: SEH biologists generated pre/post survey points based on the size and shape of the

proposed treatment areas. The 100 points they generated for the eight treatment areas

were well over the 4-10 pts/acre required by WDNR protocol, but the lake’s narrow

littoral zone and resulting thin treatment areas justified this extra effort (Appendix I).

We located each survey point using a handheld mapping GPS unit (Garmin 76CSx) and

used a rake to sample an approximately 2.5ft section of the bottom. All plants on the rake

were assigned a rake fullness value of 1-3 as an estimation of abundance, and a total rake

fullness for all species was also recorded (Figure 2). Visual sightings of EWM were also

noted if they occurred within 6ft of the point. In addition to plant data, we recorded the

lake depth using a hand held sonar (Vexilar LPS-1) and the bottom substrate (bottom type)

when we could see it or reliably determine it with the rake.

We entered all data collected into the standard APM spreadsheet (Appendix II). These

data were then analyzed using the linked statistical summary sheet and the WDNR

pre/post analysis worksheet (UWEX 2010). Pre/post treatment differences were

determined to be significant at p

3

RESULTS AND DISCUSSION:

Finalization of Treatment Areas: Initial expectations were to treat 8 beds totaling 6.87 acres with granular 2, 4-D (Navigate)

at a concentration of 3-4 ppm. Following the pretreatment survey, Bed 10 and the western

finger of Bed 3 were excluded due to low spring EWM density (Figure 3). This resulted

in the treatment areas being decreased to 5.96 acres or 2.9% of the lake’s surface area.

This decline of 0.91 acres represented an over 13% reduction from initial expectations

(Table 1) (Appendix I).

Figure 3: 2012 Survey Sample Points and Final Treatment Areas

Table 1: Spring EWM Treatment Summary

Round Lake – June 12, 2012

Bed Number Proposed

Acreage

Final

Acreage

Difference

+/- 3 1.23 0.68 -0.55

5 1.02 1.02 0

7 1.55 1.55 0

8 0.66 0.66 0

10 0.36 0.00 -0.36

13 1.08 1.08 0

14 0.73 0.73 0

20 0.24 0.24 0

Total Acres 6.87 5.96 -0.91

4

EWM Pre/Post Herbicide Survey: The treatment area littoral zone extended to a maximum of 11.5ft during the pretreatment

survey and 6.0ft during the posttreatment survey. Mean and median depths for all plants

were 5.4ft and 5.3ft respectively during the pretreatment survey before declining sharply

to 2.9ft and 2.5ft in the posttreatment survey (Table 2). Most EWM was established over

rock or firm sand (Figure 4) (Appendix III).

Figure 4: Treatment Area Depths and Bottom Substrate

Table 2: Pre/Post Survey Summary Statistics

Round Lake, Burnett County

May 7 and July 25, 2012

Summary Statistics: Pre Post Total number of points sampled 100 100

Total number of sites with vegetation 62 59

Total number of sites shallower than the maximum depth of plants 100 87

Frequency of occurrence at sites shallower than maximum depth of plants 62.0 67.8

Simpson Diversity Index 0.60 0.84

Maximum depth of plants (ft) 11.5 6.5

Average number of all species per site (shallower than max depth) 0.76 1.15

Average number of all species per site (veg. sites only) 1.23 1.69

Average number of native species per site (shallower than max depth) 0.27 0.87

Average number of native species per site (veg. sites only) 1.13 1.52

Species richness 8 12

Mean depth of plants (ft) 5.4 2.9

Median depth of plants (ft) 5.3 2.5

Mean rake fullness (veg. sites only) 1.83 1.27

5

Initial diversity within the beds was moderate with a Simpson Diversity Index of 0.60.

However, this value increased to a moderately high value of 0.86 posttreatment. Mean

native species richness at sites with vegetation was only 1.13/site pretreatment, but this

also increased slightly to 1.52/site posttreatment (Figure 5). Total rake fullness declined

from a low to moderate 1.83 pretreatment to a very low 1.27 posttreatment (Figure 6)

(Appendix IV).

Figure 5: Pre/Post Native Species Richness

Figure 6: Pre/Post Total Rake Fullness

6

We found EWM at 46 total sites during the pretreatment survey. Of these, 20 had a rake

fullness rating of 3, four rated a 2, and 22 a 1 with EWM being a visual at seven additional

points. During the posttreatment survey, we found EWM at 24 total sites. None rated a 3,

two rated a 2, and 22 rated a 1 with two additional visual sightings (Figure 7) (Appendix

V). Our findings demonstrated a moderately significant reduction of total EWM, as well

as rake fullness 3, but no significant change in rake fullness 2 or 1 (Figure 8).

Figure 7: Pre/Post EWM Density and Distribution

Significant differences = * p

7

Curly-leaf pondweed (Potamogeton crispus), another exotic species that was uncommon

throughout the lake, was found at only three points in the pretreatment survey and none in

the post treatment survey (Figure 9). This reduction was not significant and is likely due

to the normal June senescence for this species rather than the herbicide treatment

(Appendix V).

Figure 9: Pre/Post CLP Density and Distribution

Coontail (Ceratophyllum demersum) was the most common native species in both the pre

and posttreatment surveys and showed a significant increase following treatment (Tables 3

and 4) (Figure 10). Although not present in the pretreatment survey, Wild celery

(Vallisneria americana) showed a highly significant increase and filled in many places that

EWM had dominated prior to treatment to become the second most common species

posttreatment (Figure 11). Water stargrass (Heteranthera dubia) and Sago pondweed

(Stuckenia pectinata) also showed significant increases posttreatment (Figure 12). Both of

these species, along with Wild celery, do not normally overwinter but regrow from seeds,

roots or turions. This likely means they were not present at the time of the June 12th

treatment.

Filamentous algae, normally associated with excessive nutrients in the water column, also

showed a highly significant increase posttreatment. This growth may be in response to the

EWM breakdown posttreatment, the extremely warm water temperatures experienced

during the July 2012 growing season, a combination of the two factors, or it may be the

growth is in response to some other nutrient source such as internal loading from sediments.

Maps for all species from the pre and posttreatment surveys are available in Appendixes VI

and VII.

8

Figure 10: Pre/Post Coontail Density and Distribution

Figure 11: Pre/Post Wild Celery Density and Distribution

9

Significant differences = * p

10

Table 3: Frequencies and Mean Rake Sample of Aquatic Macrophytes

Pretreatment Survey Round Lake, Burnett County

May 7, 2012

Species Common Name Total

Sites

Relative

Freq.

Freq. in

Veg.

Freq. in

Lit.

Mean

Rake

Visual

Sightings Myriophyllum spicatum Eurasian water milfoil 46 60.53 74.19 46.00 1.96 2

Filamentous algae 16 * 25.81 16.00 1.81 0

Ceratophyllum demersum Coontail 12 15.79 19.35 12.00 1.25 0

Elodea canadensis Common waterweed 6 7.89 9.68 6.00 1.33 0

Potamogeton richardsonii Clasping-leaf pondweed 4 5.26 6.45 4.00 1.00 0

Potamogeton crispus Curly-leaf pondweed 3 3.95 4.84 3.00 1.00 0

Potamogeton pusillus Small pondweed 3 3.95 4.84 3.00 1.00 0

Nitella sp. Nitella 1 1.32 1.61 1.00 1.00 0

Potamogeton zosteriformis Flat-stem pondweed 1 1.32 1.61 1.00 1.00 0

* Excluded from relative frequency analysis

11

Table 4: Frequencies and Mean Rake Sample of Aquatic Macrophytes

Posttreatment Survey Round Lake, Burnett County

July 25, 2012

Species Common Name Total

Sites

Relative

Freq.

Freq. in

Veg.

Freq. in

Lit.

Mean

Rake

Visual

Sightings Filamentous algae 52 * 88.14 59.77 1.67 0

Myriophyllum spicatum Eurasian water milfoil 24 24.00 40.68 27.59 1.08 7

Ceratophyllum demersum Coontail 23 23.00 38.98 26.44 1.39 0

Vallisneria americana Wild celery 15 15.00 25.42 17.24 1.13 0

Potamogeton richardsonii Clasping-leaf pondweed 9 9.00 15.25 10.34 1.22 0

Elodea canadensis Common waterweed 8 8.00 13.56 9.20 1.00 0

Heteranthera dubia Water star-grass 6 6.00 10.17 6.90 1.00 0

Potamogeton pusillus Small pondweed 4 4.00 6.78 4.60 1.00 0

Stuckenia pectinata Sago pondweed 4 4.00 6.78 4.60 1.00 0

Potamogeton zosteriformis Flat-stem pondweed 3 3.00 5.08 3.45 1.33 0

Potamogeton nodosus Long-leaf pondweed 2 2.00 3.39 2.30 1.00 0

Najas flexilis Slender naiad 1 1.00 1.69 1.15 1.00 0

Nymphaea odorata White water lily 1 1.00 1.69 1.15 2.00 0

* Excluded from relative frequency analysis

12

Fall EWM Bed Mapping Survey: On September 29

th, 2012, we located and mapped a total of 19 beds on the lake ranging in size

from 0.05 acre (Bed 20) to 2.58 acres (Bed 3) (Figure 13) (Appendix VIII). In total, these beds

covered 8.84 acres (Table 5). This represented a decline of 8.17 acres which translated to a more

than 48% reduction over 2011’s 17.01 total acres. Despite this significant change, it should be

kept in mind that at least some of this reduction must be attributed to 2012 growing conditions

which produced a reduced littoral zone.

Areas that were treated in June continued to exhibit much reduced EWM growth in September

compared to both fall 2011 and pretreatment 2012 levels. However, EWM was not eliminated

from the majority of treated areas, and there was evidence of at least some

regrowth/reestablishment in most areas.

Figure 13: 2011 and 2012 Fall EWM Bed Maps

13

Table 5: Fall Eurasian Water Milfoil Bed Mapping Summary

Round Lake, Burnett County

September 29, 2012

Bed Number

2012

Area in

Acres

2011

Area in

Acres

2012

Change in

Acreage

Estimated

2012 Mean

Rakefull

2012 Bed Characteristics/Field Notes

1 0.52 1.91 -1.39

14

Descriptions of EWM Beds: Bed 1 – Density declined from a mean rake fullness of 1 on the east end of the bed to

15

Beds 11 – Another area that may have been better classified as a high density area, Bed

11 had partially merged with the former edge of Bed 10. In general, plants were

monotypic, but widely scattered.

Beds 12 – This area was essentially a high density area in 2011, and plants were further

reduced in 2012. This rocky shoreline will likely continue to be a low density/low

control priority.

Bed 13 – Projecting from the point, Bed 13 was significantly reduced by the treatment in

both density and distribution. At the time of the fall survey, EWM was reestablishing on

the western half of the bed and down the shoreline to the southwest. The area appears to

have the potential for treatment again in 2013.

Bed 14 – Treatment eliminated the majority of the bed although a small patch on the

outer edge of the area/littoral zone survived. As this area is near the public boat landing,

it may again be a candidate for treatment in 2013.

Beds 15-18 – All three of these beds had low density as they were established on

marginal sandy/rocky habitat. They were also on the borderline between a true “bed” and

just an area with high EWM density as their borders were often erratic. “Bed 18” had so

little EWM in 2012 that we didn’t feel it even deserved “High Density Area” status.

Because of this, this area is probably again low on the priority list of places to treat.

Bed 19 – Similar to 2011, Bed 19 grew progressively less dense as we moved northwest

into the bay. Density also tapered quickly as the western shoreline on the south end of

the bed. In the bay, EWM was replaced by Coontail and generally represented 50% of plants, but the towers were widely scattered, and there were

simply few plants growing in general over this rocky/sandy substrate. The “bulge” in the

center of the bed had the highest density, and might be a consideration for treatment.

Bed 20 – Located in the middle of the lake, Bed 20 was again nearly 100% EWM.

Although the bed had shrunk inwards from 2011, it was not clear whether this was from

treatment or just the decrease in the late-season littoral zone. Regardless, the nearly

complete reemergence of this bed following the June herbicide treatment was

disappointing.

16

LITERATURE CITED

UWEX Lakes Program. [online]. 2010. Aquatic Plant Management in Wisconsin. Available from

http://www.uwsp.edu/cnr/uwexlakes/ecology/APMguide.asp (2012, November).

UWEX Lakes Program. [online]. 2010. Pre/Post Herbicide Comparison. Available from

http://dnr.wi.gov/org/water/fhp/lakes/PrePostEvaluation.pdf (2012, November).

WDNR. [online]. 2012. Round Lake - Citizen Lake Water Quality Monitoring Database. Available

from http://dnr.wi.gov/lakes/waterquality/Station.aspx?id=073039 (2012, November).

http://www.uwsp.edu/cnr/uwexlakes/ecology/APMguide.asphttp://dnr.wi.gov/org/water/fhp/lakes/PrePostEvaluation.pdfhttp://dnr.wi.gov/lakes/waterquality/Station.aspx?id=073039

17

Appendix I: Survey Sample Points and EWM Treatment Areas

18

19

20

Appendix II: Vegetative Survey Data Sheet

21

Observers for this lake: names and hours worked by each:

Lake: WBIC County Date:

Site

#

Depth

(ft)

Muck

(M),

Sand

(S),

Rock

(R)

Rake

pole

(P)

or

rake

rope

(R)

Total

Rake

Fullness EWM CLP 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

22

Appendix III: Pre/Post Habitat Variable Maps

23

24

25

Appendix IV: Pre/Post Native Species Richness and

Total Rake Fullness

26

27

28

29

30

Appendix V: EWM and CLP Pre/Post Density and Distribution

31

32

33

34

35

Appendix VI: Pretreatment Native Species Density and Distribution

36

37

38

39

40

41

42

43

Appendix VII: Posttreatment Native Species Density and Distribution

44

45

46

47

48

49

50

51

52

53

54

55

56

Appendix VIII: Round Lake Fall 2011 and 2012 EWM Bed Maps

57

58