Aquatic Vegetation Of Lake Groton, Groton, Vermont

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)
[email protected]
September 10, 2014
DFWI Technical Report 2014-5
TABLE OF CONTENTS
Background & Introduction
...........
1
Methods
Species List and Herbarium Specimens
Point Intercept Survey
...........
...........
...........
2
2
2
Results and Discussion
Maximum Depth of Colonization
Species Lists
...........
...........
...........
3
5
5
Summary
...........
9
References
...........
11
Acknowledgements
...........
11
Appendix A. Aquatic plant distribution maps
...........
A-1
ii
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 ..........................................................................................................
10
iii
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
1
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.
2
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).
3
Table 1. Aquatic plant species reported for Lake Groton in 2014, 2003 and 1999.
Species
Common Name
Brasenia schreberi J.F. Gmel
Chara/Nitella sp.
Dulichium arundinaceum (L.) Britt.
Eleocharis acicularis (L.) Roemer & Schultes
Elodea nuttallii (Planch.) St. John
Equisetum sp.
Eriocaulon septangulare With.
Fontinalis antipyretica
Isoetes echinospora Dur.
Juncus pelocarpus Mey.
Lobelia dortmanna L.
Myriophyllum farwellii Morong
Myriophyllum humile (Raf.) Morong
Myriophyllum tenellum L.
Najas flexilis (Willd.) Rostk. & Schmidt.
Nuphar variegata Engelm. ex Durand
Nymphaea odorata Ait.
Pontederia cordata L.
Potamogeton amplifolius Tuckerm.
Potamogeton epihydrus Raf.
Potamogeton gramineus L.
Potamogeton natans L.
Potamogeton pusillus L.
Sagittaria cuneata Sheldon
Scirpus sp.
Sparganium sp.
Typha sp.
Utricularia purpurea Walt.
Utricularia resupinata B.D. Greene
Utricularia vulgaris L.
Vallisneria americana L.
2014
2003
1999
watershield
muskgrass, chara
three-way sedge
needle spike-rush
waterweed
horsetail
pipewort
moss
quillwort
rush
water lobelia
Watermilfoil
Watermilfoil
leafless watermilfoil
bushy pondweed
yellow pondlily
white pondlily
pickerelweed
broad-leaf pondweed
ribbon-leaf pondweed
variable-leaf pondweed
Floating-leaf pondweed
narrow-leaf pondweed
arrowhead
rush
burreed
cattail
purple bladderwort
Northeastern bladderwort
giant bladderwort
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
wild celery
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
The aquatic plant survey in 2003 was conducted by Lake Groton Association
4
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.
100%
Percentage of Points
80%
60%
Individual
40%
Cumulative
20%
0%
1
2
3
4
5
6
7
8
Depth (m)
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).
5
Table 2. Percent frequency of occurrence data.
Species
Utricularia purpurea
Chara/Nitella
Vallisneria americana
Nymphaea odorata
Sparganium sp.
Pontederia cordata
Potamogeton epihydrus
Eleocharis acicularis
Sagittaria cuneata
Brasenia schreberi
Elodea nuttalli
Lobelia dortmanna
Najas flexilis
Nuphar variegata
Scirpus sp.
Potamogeton natans
Myriophyllum tenellum
Utricularia resupinata
Eriocaulon septangulare
Isoetes sp.
Juncus sp.
Utricularia vulgaris
Percent
Frequency
43%
41%
12%
11%
7%
7%
7%
6%
6%
3%
3%
3%
3%
3%
3%
2%
1%
1%
1%
1%
1%
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.
6
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.
Frequency of Occurrence
100%
80%
60%
40%
20%
0%
All
<5m
<2m
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
Whole Lake
Summary Statistic
Mean
Total
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
Std. Error
43
0.24
7
Figure 6. Species richness summaries. Error bars are standard error.
Species per Survey Point
4
3
2
1
0
all
<5m
<2m
8
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.
9
Figure 7. Distribution of purple bladderwort, the most common species in Lake Groton.
10
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. 29:9499.
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.
11
Appendix A
Lake Groton Aquatic Plant Distribution Maps
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 1
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 2
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 3
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 4
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 5
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 6
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 7
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 8
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A- 9
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A-10
Appendix A. Lake Groton Plant Distribution Maps
August 2014
A-11