Final Project Report: September 13, 2012 Lake Mansfield 2012 Aquatic Vegetation Survey ======== Prepared For: Town of Great Barrington Attn: Amanda Sewall, Conservation Agent Town Hall, 334 Main Street Great Barrington, MA 01230 Prepared By: 289 Great Road, Suite 105 Acton, MA 01720 www.geosyntec.com
CONTENTS SECTION 1: INTRODUCTION... 2 SECTION 2: AQUATIC VEGETATION SURVEY... 3 2.1 Methodology... 3 2.2 Vegetation Survey Results... 3 2.3 Vegetation Survey Photos... 6 1
SECTION 1: INTRODUCTION Lake Mansfield is a 28.5-acre lake located in Great Barrington, MA. Geosyntec Consultants, Inc. (Geosyntec) was contracted by the Town of Great Barrington to conduct an aquatic vegetation survey of Lake Mansfield during the summer of 2012. The primary goals of this project were: 1. Provide an updated assessment of the composition and distribution Lake Mansfield's aquatic vegetation community, to aide lake management planning efforts. 2. Provide updated information on the status of previous efforts to control the growth of nonnative Eurasian milfoil (Myriophyllum spicatum) with milfoil weevils (Euhrychiopsis lecontei). Milfoil weevils were stocked in the lake during the summers of 1995, 1998 and 2000 to provide a biological control agent for Eurasian milfoil. Town Beach Lake Mansfield Boat Launch 2
SECTION 2: AQUATIC VEGETATION SURVEY 2.1 Methodology On July 11, 2012, Geosyntec conducted a survey of the aquatic vegetation in Lake Mansfield. Plant species were identified at 23 sampling locations (see Figure 1). Plants were identified by visual inspection and by using an aquatic vegetation grappling hook to sample submerged vegetation. At each station, the dominant plant(s) were recorded, as well as estimates of plant growth density and biomass. As categorized in Table 1, plant density is an estimate of aerial coverage when looking down to the lake bottom from the water surface. Biomass refers to the amount of plant matter within the water column. For example, a sampling station with dense growth of low-growing plants may have a high density estimate but a relatively low plant biomass estimate. A station with dense growth of a long, ropey plant with stems reaching the water surface would have both high plant density and high biomass estimates. In addition to recording information from the 23 sampling stations, a running documentation of plant growth density and biomass was estimated throughout the lakewide survey. 2.2 Vegetation Survey Results A listing of plant species present at each of the 23 sampling stations is provided in Table 1, including information on vegetation density, plant biomass, and dominant plants at each station. A summary of major findings and the most common plants species observed during the survey is as follows: Plant growth throughout Lake Mansfield was dominated by an assemblage of native species. Two non-native species, Eurasian milfoil (Myriophyllum spicatum) and curlyleaf pondweed (Potamogeton crispus), were observed growing in small quantities. As discussed below, Eurasian milfoil was distributed around the lake at low growth densities. Trace amounts of curlyleaf pondweed was observed at 4 of the 23 sampling stations. Two other non-native species previously documented in the lake, European naiad (Najas minor) and water hyacinth (Eichornia crassipes) were not observed by Geosyntec during the 2012 survey. Lake Mansfield was observed to have dense to very dense growth of rooted aquatic plants over most of its area. A majority of sampling stations (20 of 23 stations, 87%) were determined to have either dense or very dense plant growth, with 70% of all stations categorized as very dense. A majority of stations (16 of 23 stations, 69%) were also found to have high to very high biomass, with plant growth extending through either most of or the entire water column. Overall biomass appears to have increased since the July 2005 survey, when a majority of stations (78%) had low to moderate plant biomass, with plants growing primarily at the lake bottom or in less than half of the water column. Seventeen (17) species of aquatic plants were observed in Lake Mansfield during the 2012 survey. Emergent wetland plant species (e.g. pickerelweed, cattails) were noted only if they were found emerging from within the perimeter of the pond. Notable observations regarding specific plant species are summarized below: Coontail (Ceratophyllum demersum) has increased in abundance and was the most well distributed and dominant plant in Lake Mansfield during the 2012 survey. Coontail was observed at 22 out of 23 sampling stations and was a dominant plant at 13 stations (57%). This plant was found at 11 stations in 2005 and 4 stations in 2001. 3
Coontail was often found floating freely near the surface or forming a dense canopy near the lake bottom. This beneficial native plant provides habitat for young fish, small aquatic animals and aquatic insects. It also plays an allelopathic role in maintaining water clarity by excreting substances that inhibit growth of phytoplankton (plant algae) and cyanobacteria. Northern waterweed (Elodea canadensis) has increased in abundance and was the second most abundant and welldistributed plant in Lake Mansfield. This plant was found at 18 stations (78%) and was a dominant plant at 7 stations (30%). Northern waterweed had a similar distribution in 2005 but was dominant at only 2 stations. This plant provides food and habitat for fish, waterfowl and other wildlife. Bushy pondweed (Najas flexilis) continues to be well distributed throughout Lake Mansfield (17 stations, 74%) but has declined in abundance and dominance since 2005 when it was the most abundant plant in the lake. Bushy pondweed was a dominant plant at 4 stations in 2012, compared to 13 stations in 2005 and 12 stations in 2001. This plant was particularly abundant along the northwestern shore of the lake, where it was observed growing in a very dense, near-monoculture stand. This plant provides an important food source for waterfowl, which eat the entire plant. It also provides shelter for small fish and insects. Richardson's pondweed (Potamogeton Richardsonii) was observed at 14 stations (61%) and dominant at 7 stations (30%). This plant s abundance was similar to 2005, when it was observed at 11 stations and dominant at 7 stations. This plant provides good food and habitat for aquatic mammals and waterfowl. It has wavy leaves that clasp around the stem. Illinois pondweed (Potamogeton illinoensis) was found at 12 stations (52%) and dominant at 3 stations (13%). This plant has increased moderately in abundance since 2005, when it was present at 9 stations (39%) and dominant at one station (4%). Illinois Pondweed provides both important food and cover for aquatic animals. Pickerelweed (Pontederia cordata) is an emergent wetland plant common to marshes and shallow lakeshore habitats in the eastern United States. This plant was observed at 8 sampling stations (35%) and was a dominant plant at 2 stations (9%). Pickerelweed has showy blue-violet flowers that emerge from a vertical spike in mid- to late summer. The nectar and pollen of this plant attracts bees, butterflies and other insects. Its seeds and foliage provide food for waterfowl and mammals such as muskrats and deer. 4
Stiff water crowfoot (Ranunculus longirostris) was observed at 8 sampling stations (35%) and was a dominant plant at 2 stations (9%). This plant was most abundant in shallow water along the western shoreline of Lake Mansfield, where a significant area of very dense growth was observed. This plant has a small white flower that emerges above the water surface. Non-native Eurasian milfoil was found distributed around Lake Mansfield (17 of 23 stations, 74%) in small quantities, and was not observed to be a dominant plant at any of the sampling stations. The July 2012 abundance of Eurasian milfoil was similar to Geosyntec s 2001 survey and less than Geosyntec s 2005 survey, when milfoil was found at 22 out of 23 stations and was a dominant plant at one station. As in 2001 and 2005, milfoil growth was relatively minor over most of the lake. Many of the milfoil plants were observed to be in poor health and vigor, with significant evidence of insect herbivory that can be attributed to milfoil weevils (e.g. bore holes, hollowed/blackened stems). Other species observed in Lake Mansfield but not dominant at any sampling stations were water star grass (Heteranthera dubia), slender pondweed (Potamogeton pusillus), curlyleaf pondweed (Potamogeton crispus), musk grass (Chara vulgaris), water smartweed (Polygonum natans), greater duckweed (Spirodela polyrhiza), broadleaf cattail (Typha latifolia), chairmaker s rush (Scirpus pungens), and Robbin s Spikerush (Eleocharis robbinsii). Curlyleaf pondweed Summary of Lake Mansfield Aquatic Vegetation Density and Biomass Ratings (July11, 2012) GROWTH DENSITY Sparse: 0-25% density # of stations % of stations 0 0% PLANT BIOMASS 1: Scattered plant growth or primarily at lake bottom # of stations % of stations 1 4% Moderate: 26-50% density 3 13% 2: Less abundant growth, or in less than half of the water column 6 26% Dense: 51-75% density 4 17% 3: Substantial growth through majority of water column 9 39% Very Dense: 76-100% density 16 70% 4: Abundant growth throughout water column to surface 7 30% A vegetation survey tally sheet and vegetation density map from the July 2012 vegetation survey are provided on the following pages. 5
Table 1: Aquatic Vegetation Survey Tally Sheet Location: Lake Mansfield (Great Barrington, MA) Date: 7/11/2012 Surveyed by: R. Hartzel species present species dominant Plant Species (Common Name) Plant Species (Scientific Name) Monitoring Locations 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 coontail Ceratophyllum demersum 22 13 northern waterweed Elodea canadensis 18 7 bushy pondweed Najas flexilis 17 4 Eurasian milfoil * Myriophyllum spicatum 17 0 Richardson's pondweed Potamogeton richardsonii 14 7 Illinois pondweed Potamogeton illinoensis 12 3 pickerelweed Pontederia cordata 8 2 stiff water crowfoot Ranunculus longirostris 8 2 water star grass Heteranthera dubia 8 0 slender pondweed Potamogeton pusillus 6 0 curlyleaf pondweed * Potamogeton crispus 4 0 musk grass Chara vulgaris 3 0 water smartweed Polygonum natans 2 0 greater duckweed Sprirodela polyrhiza 1 0 broadleaf cattail Typha latifolia 1 0 # stations # dominant chair-maker's rush Scirpus pungens 1 0 Robbin's spikerush Eleocharis robbinsii 1 0 Plant Density Rating Plant Biomass Rating 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3 4 3 4 3 2 2 2 3 4 4 3 3 4 3 3 3 4 4 4 3 2 4 3 3 2 3 2 2 1 2 2 * Non-native, invasive plant 1 2 3 4 Key to Density and Biomass Ratings Density Biomass Scattered plant growth; or primarily at Sparse: 0-25% lake bottom Less abundant growth, or in less than Moderate: 26-50% half of the water column Substantial growth through majority of Dense: 51-75% water column Abundant growth throughout water Very Dense: 76-100% column to surface
Legend 1. Scattered plant growth; or primarily at lake bottom Sparse Dense 3. Substantial growth through majority of water column Very Dense 4. Abundant growth throughout water column to surface 12 10 2. Less abundant growth, or in less than half of water column Moderate 11 Biomass Density 9 13 23 8 14 7 15 22 6 16 5 20 4 21 19 3 Q:\GISProjects\BR0079-Oakstreet\Projects\Plume Maps\March2009\TCE_March2009.mxd 17 2 1 18 Lake Mansfield Vegetation Map July 2012 *UHDW %DUULQJWRQ, Massachusetts Figure 300 150 0 300 Feet ACTON, MASSACHUSETTS August 2012 1
2.3 Vegetation Survey Photos The photos below were taken during the Lake Mansfield vegetation survey on July 11, 2012. Coontail (Ceratophyllum demersum) has increased in abundance and was the most well-distributed and dominant plant in Lake Mansfield during the July 11, 2012 vegetation survey. This free-floating aquatic plant is named for its appearance, which is often similar to a raccoon s tail. Northern waterweed (Elodea canadensis) was the second most abundant and well-distributed plant in Lake Mansfield. 8
Bushy pondweed (Najas flexilis) Richardson s pondweed (Potamogeton richardsonii) 9
Illinois pondweed (Potamogeton illinoensis) Stiff water crowfoot (Ranunculus longirostris) 10
Pickerelweed (Pontederia cordata) observed along the lake s eastern shore. Larval bore hole Eurasian milfoil (Myriophyllum spicatum) stem showing damage (larval bore hole) typical of the milfoil weevil (Euhrychiopsis lecontei). Eurasian milfoil was found distributed around Lake Mansfield in small quantities, with stems often in poor condition and/or showing signs of weevil damage. 11
Dense growth of stiff water crowfoot (Ranunculus longirostris) was observed topping out at the water surface near the western shore of Lake Mansfield (view northeast towards Lake Mansfield beach). Water smartweed (Polygonum natans) was observed at two sampling stations along the eastern shore of Lake Mansfield. 12