Aquatic Vegetation of Lake Groton,

Groton, Vermont

Prepared By

Lawrence Eichler

Research Scientist

&

Charles Boylen

Associate Director

Darrin Fresh Water Institute

5060 Lakeshore Drive

Bolton Landing, NY 12814

(518) 644-3541 (voice) (518) 644-3640 (fax)

eichll@rpi.edu

September 10, 2014

DFWI Technical Report 2014-5

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TABLE OF CONTENTS

Background & Introduction . . . . . . . . . . . 1

Methods . . . . . . . . . . . 2

Species List and Herbarium Specimens . . . . . . . . . . . 2

Point Intercept Survey . . . . . . . . . . . 2

Results and Discussion . . . . . . . . . . . 3

Maximum Depth of Colonization . . . . . . . . . . . 5

Species Lists . . . . . . . . . . . 5

Summary . . . . . . . . . . . 9

References . . . . . . . . . . . 11

Acknowledgements . . . . . . . . . . . 11

Appendix A. Aquatic plant distribution maps . . . . . . . . . . . A-1

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List of Tables

Page

Table 1 Species list for Lake Groton …………………………………………….. 5

Table 2 Percent frequency of occurrence data for Lake Groton …………..…….. 8

Table 3 Species richness comparison for Lake Groton …………………….…….. 10

List of Figures

Page

Figure 1 Bathymetric (depth) map of Lake Groton …………………………….….. 1

Figure 2 Aerial photograph of Lake Groton, Vermont ………………….…………. 2

Figure 3 Map of Lake Groton with point intercept survey points .………………… 3

Figure 4 Depth Distribution of Sampling Points in 1 meter depth classes..……….... 5

Figure 5 Frequency of occurrence summaries............................................................. 7

Figure 6 Species richness summaries........................................................................... 8

Figure 7 Distribution of purple bladderwort, the most common species in Lake

Groton ..........................................................................................................

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1

Background

At the request of the Groton Lake Association, we conducted an aquatic plant assessment of

Lake Groton, Groton, Vermont. The assessment included a quantitative survey of existing

aquatic plant communities and the extent of rare, threatened or endangered species (VT DEC).

The Point-Intercept Rake Toss method recommended by the US Army Corps of Engineers was

employed.

Quantitative aquatic plant surveys were undertaken in July of 2014. All surveys were conducted

to provide identification and distribution data for the aquatic plant populations of the lake. The

surveys consisted of collection of herbarium specimens throughout both lakes for compilation of

species lists, and frequency and density data for points distributed throughout the lakes.

This assessment was partially funded by a grant from the Vermont Department of Environmental

Conservation to the Town of Groton.

Introduction

Lake Groton. Lake Groton is located in Caledonia County, in the town of Groton. The lake has

a surface area of approximately 422 acres with a watershed of 12,006 acres and a total volume of

5486 acre feet. Lake Groton has a single outlet at its south end with a control structure to

maintain lake level. Average water depth is reported to be 13 ft, with a maximum depth of 35 ft

(see Figure 1, VTDEC 2014). Water quality for Lake Groton is described as mesotrophic or

moderate in terms of the concentrations of nutrients or fertilizers which control the growth of

algae in the lake. Secchi disk transparency averages 11.4 ft (3.5 m; VT DEC 2013). Phosphorus

concentrations average 12.8 ug/l during the Summer and 8.5 ug/l in the Spring. Annual

chlorophyll levels average 4.1 ug/l. Based on this data, the majority of the lake bottom will fall

within the littoral zone, defined as the region of rooted aquatic plant growth.

Figure 1. Bathymetric map of Lake Groton, VT

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Methods

Species List and Herbarium Specimens. As the lake was surveyed, the occurrence of each

aquatic plant species observed in the lake was recorded and adequate herbarium specimens were

collected. The herbarium specimens were returned to the Darrin Fresh Water Institute, where

they were pressed, dried, and mounted (Hellquist 1993).

Point Intercept. The frequency and diversity of aquatic plant species were evaluated using a

point intercept method (Madsen 1999). At each grid point intersection, all species located at that

point were recorded, as well as water depth. Species were located by a visual inspection of the

point and by deploying a rake to the bottom, and examining the plants retrieved. A total of 147

points were selected for Lake Groton, based on a 100 m grid (Figure 1). A global positioning

system (GPS) was used to navigate to each point. Surveys were conducted on July 30th

of 2014.

Data presented in the summary are on a whole-lake basis, and have not been adjusted for the

littoral zone only.

Figure 2. Aerial photograph of Lake Groton, Vt.

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Figure 3. Map of Lake Groton with

point intercept survey locations for 2014.

Results and Discussion

In July of 2014, the aquatic plant community of Lake Groton included 25 aquatic plant species

with 22 species collected as part of the point intercept survey. This number of species greatly

exceeds the 15 species typically reported for moderately productive lakes in our region and

indicates good water quality and a variety of habitat types. Two of the species present in Lake

Groton, Purple Bladderwort (Utricularia purpurea) and Northeastern Bladderwort (Utricularia

resupinata) are found on Vermont’s Rare plant list (VT DEC 2012).

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Table 1. Aquatic plant species reported for Lake Groton in 2014, 2003 and 1999.

Species Common Name 2014 2003 1999

Brasenia schreberi J.F. Gmel watershield x x x

Chara/Nitella sp. muskgrass, chara x x

Dulichium arundinaceum (L.) Britt. three-way sedge x x x

Eleocharis acicularis (L.) Roemer & Schultes needle spike-rush x x

Elodea nuttallii (Planch.) St. John waterweed x x x

Equisetum sp. horsetail x x

Eriocaulon septangulare With. pipewort x x x

Fontinalis antipyretica moss x

Isoetes echinospora Dur. quillwort x x

Juncus pelocarpus Mey. rush x x x

Lobelia dortmanna L. water lobelia x x

Myriophyllum farwellii Morong Watermilfoil

Myriophyllum humile (Raf.) Morong Watermilfoil x

Myriophyllum tenellum L. leafless watermilfoil x x

Najas flexilis (Willd.) Rostk. & Schmidt. bushy pondweed x x x

Nuphar variegata Engelm. ex Durand yellow pondlily x x x

Nymphaea odorata Ait. white pondlily x x x

Pontederia cordata L. pickerelweed x x x

Potamogeton amplifolius Tuckerm. broad-leaf pondweed x

Potamogeton epihydrus Raf. ribbon-leaf pondweed x x x

Potamogeton gramineus L. variable-leaf pondweed x x

Potamogeton natans L. Floating-leaf pondweed x x x

Potamogeton pusillus L. narrow-leaf pondweed x

Sagittaria cuneata Sheldon arrowhead x x x

Scirpus sp. rush x x

Sparganium sp. burreed x x x

Typha sp. cattail x

Utricularia purpurea Walt. purple bladderwort x

Utricularia resupinata B.D. Greene Northeastern bladderwort x

Utricularia vulgaris L. giant bladderwort x x x

Vallisneria americana L. wild celery x x x

The aquatic plant survey in 2003 was conducted by Lake Groton Association

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Maximum Depth of Colonization

Maximum depth of rooted aquatic plant growth, defining the littoral zone, extended to a depth of

approximately 4.5 meters. Macroalga (Nitella sp.), was reported for a single sample in a depth of

5 m. Sampling points were evenly distributed across all depth ranges (Figure 4).

Figure 4. Depth Distribution of Sampling Points in 1 meter depth classes.

Species Lists

Maps of the distribution of all aquatic plant species encountered are included in Appendix A.

Species richness was quite high, with a large number of species occurring in more than 5% of

survey points (Table 2). Purple bladderwort (Utricularia purpurea) was the most common

species (43% of survey points) followed closely by muskgrass (Chara/Nitella), present in 41% of

survey points. Other common native species included duck celery (Vallisneria americana, 12%

of survey points), white pond lily (Nymphaea odorata, 11%), burreed (Sparganium sp., 7%),

ribbon-leaf pondweed (Potamogeton epihydrus, 7%), and pickerelweed (Pontederia cordata,

7%). Of particular interest is the fact that purple bladderwort, while currently the dominant

species in the lake, was not reported in prior surveys, including as recently as 2003. Purple

bladderwort was found from the water’s edge to a depth of 4.5 meters (15ft), while dense growth

generally occurred in depths of from 1 to 4 meters (3 to 13 ft).

0%

20%

40%

60%

80%

100%

1 2 3 4 5 6 7 8

Perc

en

tag

e o

f P

oin

ts

Depth (m)

Individual

Cumulative

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Table 2. Percent frequency of occurrence data.

Species

Percent

Frequency

Utricularia purpurea 43%

Chara/Nitella 41%

Vallisneria americana 12%

Nymphaea odorata 11%

Sparganium sp. 7%

Pontederia cordata 7%

Potamogeton epihydrus 7%

Eleocharis acicularis 6%

Sagittaria cuneata 6%

Brasenia schreberi 3%

Elodea nuttalli 3%

Lobelia dortmanna 3%

Najas flexilis 3%

Nuphar variegata 3%

Scirpus sp. 3%

Potamogeton natans 2%

Myriophyllum tenellum 1%

Utricularia resupinata 1%

Eriocaulon septangulare 1%

Isoetes sp. 1%

Juncus sp. 1%

Utricularia vulgaris 1%

A total of 31 species of aquatic plants have been recorded in Lake Groton between all surveys.

Of the 27 species reported in 2003, 21 were reported in 2014 and 22 in the 1999 survey. One of

the species absent in the 2014 survey, horsetail (Equisetum) is an emergent species typically not

captured in point intercept type surveys. Two native milfoil species were also observed in 2003,

but not reported in 2014 or 1999. Myriophyllum farwellii was extremely rare and Myriophyllum

humile was common in 2003, but not reported in other surveys. Two common native

pondweeds, broad-leaf pondweed (Potamogeton amplifolius) and variable-leaf pondweed

(Potamogeton gramineus) were also reported in 2003 but not in 2014. Four species were

reported for the first time in 2014, narrow-leaf pondweed (Potamogeton pusillus), cattails (Typha

sp.), purple bladderwort (Utricularia purpurea) and northeastern bladderwort (Utricularia resupinata).

All are common native species in our region.

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Sixty-one percent of whole lake sampling points were vegetated by at least one native plant

species, 94% of survey points with depths less than 5 m and 100% of survey points less than 2

meters depth yielded native aquatic plants in 2014 (Figure 5). The expected relationship of

greater frequency of occurrence of aquatic plants with shallower water depth is consistent with

other regional lakes.

Figure 5. Frequency of occurrence summaries.

Species richness results are presented in Table 3 and Figure 6. Whole lake species richness

averaged 1.68 species per sample point. Species richness values within this range are typical for

low to moderate productivity lakes in the Northeast. For survey points exclusively within the

littoral zone (depths less than 5 meters), species richness averaged 2.62 species per survey point.

As expected, species richness in the littoral zone and its shallow fringe (3.53 species per survey

point) was higher than whole lake species richness.

Table 3. Species richness comparison between depths for the open-lake survey.

Water Depth Class Summary Statistic Total

Whole Lake Mean 1.68

(all depths) N 147

Std. Error 0.14

Points with Mean 2.62

depths <5m N 94

Std. Error 0.15

Points with Mean 3.53

depths <2m N 43

Std. Error 0.24

0%

20%

40%

60%

80%

100%

All <5m <2m

Freq

uen

cy o

f O

ccu

rren

ce

8

Figure 6. Species richness summaries. Error bars are standard error.

0

1

2

3

4

all <5m <2m

Spec

ies

per

Su

rvey

Po

int

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Summary

Quantitative aquatic plant surveys were undertaken for Lake Groton, in the Town of Groton,

Vermont, in July of 2014. Surveys were conducted to obtain aquatic plant density and

distribution data, with a focus on the discovery of invasive species. Aquatic plant surveys were

designed to be comparable to other regional aquatic plant surveys conducted by the US Army

Corps of Engineers and the Darrin Fresh Water Institute over the last 2 decades. The frequency

and distribution of aquatic plant species were evaluated using a point intercept method based on

a differential global positioning system of grid points.

The aquatic plant community of Lake Groton included eighteen submersed species, three

floating-leaved species, and four emergent species in 2014. A total of 31 species of aquatic

plants have been reported when surveys in 2003 (Spenser 2003) and 1999 (Fitch 1999) are

included. All of the species reported are native to our region, with no exotic or invasive species

encountered. This number of species greatly exceeds the 15 species typically reported for

moderately productive lakes in our region and indicates good water quality and a variety of

habitat types. Two of the species present in Lake Groton, Purple Bladderwort (Utricularia

purpurea) and Northeastern Bladderwort (Utricularia resupinata) are found on Vermont’s Rare

plant list (VT DEC 2012). Comparing the species list to a 2003 survey by the lake association,

twenty one of the species reported were still present, with absent species typically reported as

rare in 2003. These results suggest a highly stable lake system.

Species richness was quite high, with a large number of species occurring in more than 5% of

survey points. Sixty-one percent of whole lake sampling points were vegetated by at least one

native plant species and 100% of survey points with depths less than 2 meters yielded native

aquatic plants. The littoral zone or zone of rooted aquatic plants extended to approximately 4.5

meters, with a macroalgae (Nitella sp.) observed to 5 meters. Native species richness in the

littoral zone was 2.62 species per sample similar to many low to moderate productivity lakes in

the Northeast. Purple bladderwort (Utricularia purpurea) was the most common species (43%

of survey points) followed closely by muskgrass (Chara/Nitella), present in 41% of survey

points. Other common native species included duck celery (Vallisneria americana, 12% of

survey points), white pond lily (Nymphaea odorata, 11%), burreed (Sparganium sp., 7%),

ribbon-leaf pondweed (Potamogeton epihydrus, 7%), and pickerelweed (Pontederia cordata,

7%).

Of particular interest is the fact that purple bladderwort, while currently the dominant species in

the lake (Figure 7), was not reported in prior surveys, including as recently as 2003. Purple

bladderwort was found from the water’s edge to a depth of 4.5 meters (15ft), while dense growth

generally occurred in depths of from 1 to 4 meters (3 to 13 ft). The rapid expansion of this

species warrants scrutiny, with the data presented in this report and the 2003 survey serving as

baseline data. The fact that purple bladderwort occurs on the Vermont Rare Plant List will be a

consideration in any management efforts.

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Figure 7. Distribution of purple bladderwort, the most common species in Lake Groton.

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References

Boylen, C.W., L.W. Eichler and J.W. Sutherland. 1996. Physical control of Eurasian watermilfoil

in an oligotrophic lake. Hydrobiologia 340:213-218.

Crow, G.E. and C.B. Hellquist. 2000. Aquatic and wetland plants of northeastern North America.

2 Volumes. University of Wisconsin Press, Madison, WI.

Fitch, N.J. 1999. Aquatic Plant Survey of Lake Groton, VT. Prepared as part of a Vermont

Watershed Mini-Grant Project, Lyndon State College, VT

Hellquist, C.B. 1993. Taxonomic considerations in aquatic vegetation assessments. Lake and

Reserv. Manage. 7:175-183.

Madsen, J.D. 1999. Point intercept and line intercept methods for aquatic plant management. US

Army Engineer Waterways Experiment Station Aquatic Plant Control Research Program

Technical Note CC-02, Vicksburg, MS.

Madsen J.D., J.W. Sutherland, J.A. Bloomfield, L.W. Eichler and C.W. Boylen. 1991. Decline of

native vegetation under a canopy of Eurasian watermilfoil. J. of Aquatic Plant Manage. 29:94-

99.

Spenser, D. 2003. An aquatic plant survey of Lake Groton, VT; conducted by the Lake Groton

Association, Groton, VT.

Vermont Department of Environmental Conservation. 2011. Vermont waterbodies with

Eurasian watermilfoil (Myriophyllum spicatum L.). Online, May 2014.

http://www.anr.state.vt.us/dec/waterq/lakes/docs/ans/lp_ewm-lakeslist.pdf#

Vermont Department of Environmental Conservation. 2013. Vermont Department of

Environmental Conservation – Lay Monitoring Program. Online, May 2014.

www.anr.state.vt.us/dec/waterq/cfm/lakerep/lakerep_details.cfm

Vermont Department of Environmental Conservation. 2014. Depth charts for Vermont lakes.

Online, May 2014. www.watershedmanagement.vt.gov/lakes htm lp depth harts.htm

Acknowledgements

The authors would like to acknowledge Mr. David Spenser for his assistance in coordinating

the current survey project.

Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A

Lake Groton Aquatic Plant Distribution Maps

Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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Appendix A. Lake Groton Plant Distribution Maps A-

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