Aquatic Plant Mapping in Lake Wononscopomuc, 2007

Prepared By:

Northeast Aquatic Research, LLC

George W. Knoecklein

Summary of Report

The goals of this study were to 1) update and refine the distribution map of the state protected aquatic plant species in the lake, 2) verify the distribution of Eurasian milfoil, and 3) provide additional information about the native plant species inhabiting the lake. 

Prior aquatic plant surveys of Lake Wononscopomuc include a weed survey by Lake Management Consultants in 1989 , a weed management study of public lakes in the Town of Salisbury which included Lake Wononscopomuc, conducted in August 1999 by Aquatic Control Technologies Inc. , a survey of Berkshire Region hardwater lakes by Hinkler and Ludlam in August 2001 .  In addition, in September 2004, the CT Agricultural Experiment Station conducted a three day survey of the aquatic plants in the lake .  

Methods

The aquatic plant surveys were conducted on three dates during the summer of 2007, see Table 2.  Each survey had a different focus.  The goal of the first survey was to locate the rare plant Potamogeton friesii because this plant dies back by the mid July.  The second survey was to review sites of rare plants with ACT, Inc.  The last survey was to map thoroughly the locations and density of all species, focusing on Eurasian milfoil.  Each survey was conducted from surface observations of the plant beds.  Observation of plant beds consisted of making frequent stops at points were plant beds appeared to show changes in vegetation composition.  These stops, or points, were than spatially located as a waypoint by using a Garmin GPSmap 76c.

Aquatic Plant Survey Results

General Plant Distribution Results

There were 17 species of plants noted during the 2007 survey, all of which had been seen in 2004 (Table 3).  The number of sightings and the percent frequency of observation for each species is also given in Table 3.  The most frequently observed plant was Eurasian milfoil which was present at 188 of 274 points or 69%.  This was similar to 2004 when Eurasian milfoil was observed at 73% of the points.  The second and third most observed species in 2007 was Chara at 63 points, and northern milfoil at 59 points.  Northern milfoil is one of the State of CT protected species.  Species #2 - # 8, #9, #12, and #13 were detected at lower frequencies during the 2007 survey than they were in 2004.  The 2 protected species, #19, and #21 were observed at higher frequencies in 2007.  Species #10, and #11, were observed at similar frequencies during both surveys.

The littoral zone is composed of predominantly two types of plant communities.  Between the shoreline and about 10 feet of water depth there is a dense blanket of stonewort (chara sp) covering the bottom with 100% cover.  There is approximately 31 acres of chara beds in the lake (Map 2).  Within this chara bed several native species are also present at varying occurrences and densities.  Between about 10 feet of water depth and the outer edge of the littoral zone at about 20 feet of water depth Eurasian milfoil dominates (Map 3).  In most areas, Eurasian milfoil was found to be at or near 100% surface coverage.  The Eurasian milfoil beds generally began at the outer edge of the chara beds and extended out to about 20 feet of water, although sometimes milfoil could be found growing to 23 feet of water.  Eurasian milfoil was also found mixed in with the natives growing in the chara beds, but typically these plants were a minor part of the assemblage.  The Eurasian milfoil formed a band that extended lake-ward approximately 200 feet along west and south shores.  Dense Eurasian milfoil was observed on the shallow peninsulas extending out 1,300 feet from the north shore and 1,000 feet from the eastern shore, including the area around the rocky island.  Additionally, dense Eurasian milfoil beds were observed on the couple of isolated shallow peaks, 20 feet of depth, in the southwestern quadrant of the central deep basin.  There were about 51 acres of dense Eurasian milfoil beds in the lake. 

Fries’ Pondweed

The Connecticut endangered aquatic plant Potamogeton friesii was found at 12 sites around the lake.  This species was always observed in association with other species in water less than 5 feet deep.  It was typically found as an individual specimen or in small groups or clusters of plants distributed loosely over several square feet.  The plant was not found in dense beds or large contiguous patches.  The plant was found scattered along the west, south and north shores, and between the island the mainland.  No plants were found along the east shore. 

Northern Milfoil

The Connecticut threatened aquatic plant Myriophyllum sibiricum was found at 59 points around the lake.  The species was typically found in water less than 10 feet deep.  Generally it was distributed evenly around the whole shoreline as individual plants, small clusters of several plants and groups of clusters spread over several square feet.  There was one large bed of 2.6 acres found along the east shore.  This bed contained northern milfoil at 100% cover, very dense concentrations, and growing to the surface. 

Conclusions

There were 17 species of aquatic plants observed during the 2007 survey.  All had been recorded during the 2004 survey. 

The area of the lake infested with Eurasian milfoil was found to be approximately 51 acres, very similar to the 48 acres estimated during the 2004 survey.  Eurasian milfoil formed a band around the lake at depths between 10 and 20 feet. This species completely covered the large shallow peninsula that juts out toward the center from the north and also around the island and shallows on the east side.  There were a few small beds of Eurasian milfoil found on the shallow islands in the open water. 

Northern milfoil was found at 59 observation points while Fries’ pondweed was found at 12 observation points.  This represents a significant increase in the abundance of both species in the lake.  One 2.6 acre very dense bed of northern milfoil was found along the east side of the lake.

There is a blanket of chara between the shore and about 10 feet of water around most all of the shoreline.  Within the chara cover several other species were observed.  Eurasian milfoil was present but never dominant in the chara beds.

As in the 2004 survey, curly-leaved pondweed was found at only one site, the cove where Sucker Brook enters the lake.  This plant however generally reaches maturity in the late spring and senesces in early July, so it may have been gone from the water column at the time that this study was conducted.

Between 2004 and 2007, the number of observation points with only Eurasian milfoil increased from 30% to 43%, while the number of sites with 5, 6, 7 and 8 species sharply decreased.