A Plan for Control
of Nuisance Plants
in Cedar Lake
(August 19, 2003)

Introduction

In response to a survey of plant growth in Cedar Lake by ENSR (Survey of the Submerged Aquatic Vegetation and Vegetation Management Recommendations for Cedar Lake, Chester, Connecticut, November, 2002), a plan is presented with prioritization of areas in which nuisance plants should be controlled and methods for control are proposed. Costs and probable effectiveness have been considered.

Summary of ENSR Report

The ENSR report was based on a survey performed by two experienced aquatic biologists from a small boat. Observation points (sampling stations) were set along Imaginary transects drawn on the lake surface. At each shallow-water observation point water depth and sediment depth were determined using a 10 foot pole and sediment type was determined. Water depths greater than 10 foot were determined with a hand held depth sounder. The plant survey was accomplished by visual inspection, with the aid of an underwater video camera. Plant coverage of the lake bottom and biovolume in the water column were estimated using semi-quantitative ENSR standard methods.

The beach areas around the lake were generally void of vegetation. The greatest areas of plant growth were near the public boat launch, at the outlet from the lake, and along the western shore. Sixty-five percent of the lake was devoid of plants. Submerged vegetation rarely reached the surface except near the boat launch.

Fifteen plant species were identified. Two invasive non-native plants, fanwort (Cabomba caroliniana, Cc) and variable leaf watermilfoil (Myriophyllum heterophyllum, Mh) were found. Cc 'dominated' the macrophyte community. Mh, various bladderwort species, and fragrant waterlillies were also abundant.

Comparison with Previous Reports

A 1985 biological survey reported the presence of 'Milfoil' (probably Mh) (Proposal Cedar Lake Chester, Connecticut, Lycott Environmental Research, July, 1985). Several other species (Nuphar, Potamogeton vaginatus, and Ultricularia geminiscapa) "appeared to be the major species interfering with recreational activities". A 1986 report on plants in Cedar Lake reported dominance by so-called 'Eurasian watermilfoil', probably Mh (Cedar Lake – Chester, CT Lake and Watershed Management Plan Final Report, IEP, 1986). A later report (Report on Water Quality/Biological Survey of Cedar Lake and Vegetation Management Recommendation, Aquatic Control Technology, 1990) reported a change in the dominant species from Mh to Cc. However, the "….overall area of vegetative coverage …did not appear to appreciably change from 1986". The 1990 study was accomplished by visual inspection and dragging a small Danforth Anchor and garden rake at selected locations around the Lake's littoral (shallow water) zone: this approach could have missed substantial vegetation densities in water deeper than 10 feet. The 1990 report showed the most vegetation at the north and northwest end of the lake to be between the shore and the 10 feet depth with some Cc occurring beyond the 10 feet delineation shown on the map in the report. Detailed examination of the ENSR report (Table 2) shows substantial plant coverage (Coverage ratings >1) at depths to 12 feet, with Cc and Mh significant (but not the only) contributors (Sampling stations M-3, M-7, M-8 in the ENSR Report). Some expansion of plant coverage in this area may have occurred in the intervening 12 years, but the apparent extent of expansion is small. Furthermore, the methodologies described in the 1990 and 2002 reports are so different that assessing changes in vegetative distribution over time is problematic.

Along the western shore of the lake, the 1990 report showed spotty plant coverage. Cc was present at the most northern portion of this area, but not consistently observed for the southern 2/3 of this area. The ENSR report shows consistently high density of plant growth between the most-westerly part of the lake and a point just south of the two beaches on the western shore of the lake (Figure 5). Examination of the data shows significant contributions of Cc and Mh to plant coverage in this area (Sampling stations F-14, F-15, G-1, G-2, H-14, H-15, I-1, I-2, I-3, J-13, J-14, J-14, K-1, K-2, K-3). There is an apparent significant increase in plant density along this shore of the lake. As observed in other parts of the lake, the presence of Cc and Mh appears to increase the area of coverage to greater depths. Again, the methodologies described in the 1990 and 2002 reports are so different that assessing change in distribution over time is problematic. However, it seems unlikely that the 1990 report would have missed extensive plant coverage in this area and some expansion of coverage may have occurred.

At the southern end of the lake near the outlet, the 1990 report shows a significant amount of plant coverage at depths between the shore and 5 feet to 10 feet depths with Cc playing a role. No Mh was reported in this area. The ENSR report confirms extensive and intensive coverage in this area with Cc and Mh playing a significant role at some sampling stations. However, other species (bladderworts, pondweeds) are also significant. There may be an increase in plant coverage in this area (Sampling stations B-1 through B-4). Perhaps most disturbing is the presence of Cc and Mh at depths to 15 feet (Sampling stations C-3, C-4, C-5). This may represent a significant occurrence of invasive plant species to an area near the Town Beach. It is unlikely that the 1990 study would have sampled or found subsurface plants in this area.

Along the eastern side of the lake near an unnamed inlet the 1990 report shows both Cc and Mh between depths of 5 feet and 10 feet. The ENSR report confirms this data, but also shows Cc and Mh at depths to 14 feet. Again, the 1990 study probably would not have detected plant growth at this depth. Visual examination of this area has shown expansion of nuisance plant growth during the last 6 years.

In summary there may have been some expansion of nuisance plant growth in the lake between 1990 and 2002. Some of this apparent effect may be due to the more thorough sampling performed by ENSR and the differences in methodology utilized in the two studies.

Areas for which Controls were Considered

Path from Boat Launch to Open Water
This is a high use area, especially in the spring. The new boat launch may increase use of this area. The high density of plant growth, which interferes with paddling and the use of motors, indicates that this is a severe problem area.

North End of Lake between Boat Launch and Inlet
This is the most densely covered area in the lake. High densities of Cc, Mh and other plant species were found in this area. Most people avoid this area, due to the high density of infestation, which makes swimming unsafe, fishing impossible, and paddling difficult. This is a severe problem area.

Inlet at Northwest Corner of Lake
The vegetation in the inlet stream is very dense. This is a severe problem area. However, only a limited number of properties are affected. The area is shallow and subject to sedimentation.

West Side of Lake North of Terrace Association Beach
This area is lined with private docks and swimming areas. This is a high impact area in terms of activity by local residents. The density of nuisance plants is highly variable. This is regarded as a moderate problem area.

An important question is whether the Town should be responsible for cleanup of the area around private docks and beaches. The Town owns the lake and the primary reason for the property owners to live along the lake and pay taxes is the use of the lake. Thus, the Town might bear some responsibility for maintaining this part of the lake. However, this area is not open to all Town residents. Therefore, it seems reasonable for the property owners to share the costs of treatments. An argument can be made that these property owners gain higher property values, but pay higher taxes due to higher assessments because of their proximity to the lake. It can also be argued that tax money should not be used to maintain areas dominated by private docks and beaches.

Town and Association Beaches along the Western Side of the Lake
Local residents use these beaches heavily. Thus, this is a high impact area. The density of nuisance plants is low, but their presence is very noticeable by residents. This is presently a moderate problem area, but could rapidly get worse.

Southwest Corner of the Lake
Local residents, especially sub-adults, use this area for fishing and this area is highly visible. The density of nuisance plants is spotty, but sufficient to interfere with fishing, especially late summer. This is a moderate problem area.

South End of Lake (Pelletier Park/Camp Hazen)
This is a highly visible and heavily used area. There is no clear nuisance plant problem in the swimming areas at this time. However, Cc and Mh were observed in the area just outside of the Pelletier Park swimming area (Sampling station C-5). Prevention of spread of vegetation into the swimming areas is highly desirable.

East Side of Lake
This area is primarily used for fishing. The density of nuisance plants has apparently increased markedly in the last few years, but fishing is still possible. This is a low priority area. Proposed Methods for Control of Plants

Benthic barriers (fabric)—Covering an area of the lake bottom with a fabric barrier can be highly effective in controlling rooted vegetation. However, these barriers require careful installation and annual or biannual maintenance, which consists of removal, cleaning, and re-installation. Otherwise, they become covered with sediment allowing new plant growth. The choice of material and weighting is important to prevent gas buildup underneath the barriers, which causes lifting of the barriers with resultant damage to the barriers as well as interference with boat motors and other activities.

A suggestion was made that we should consider barriers consisting of concrete slabs. Heavy slabs would probably sink into the sediment and be covered by sediment, either immediately or due to sedimentation from the water table. Once covered by sediment, these slabs would not be useful. Therefore, they would have to be cleaned periodically. This approach might require permits from the Army Corps of Engineers, as well as DEP and the Chester Inland Wetlands Agency.

Diver-assisted harvesting – Diver-assisted harvesting consists of scuba divers hand pulling undesirable plants from the bottom and feeding the plants into a stream of water in a flexible pipe, which conducts the plants to a raft on the surface. The plants are collected on a screen and the water is returned to the lake. The collected plants are periodically ferried to the shore and taken away for disposal. This approach is most useful for low-density weed growth or for spot treatment around docks or beaches. This approach can be highly selective, depending upon the skill and care of the personnel carrying out the process. Diver-assisted harvesting may require more than one treatment per year and will require yearly treatment to be effective. This process costs approximately $1000/day for treatment of 0.25 to 1 acre, depending upon plant density. Diver-assisted harvesting may not require DEP permits.

Hydro-raking - Hydro-raking is performed from a self-propelled barge. A rake is lowered into the water at depths to 12 feet and pulled toward the barge. The rake scoops up plants (and any other loose materials) from the bottom of the lake. The material is transferred to the shore where it has to be disposed of by either the landowner or the Town. Hydro-raking does not require DEP permits, but does require an Inland Wetlands Agency permit. Hydro-raking may require more than one treatment per year and will require yearly treatment to be effective.

Drawdown (lowering of water level for the winter) – Drawdown requires the ability to lower water levels by at least several feet. The topography of the Cedar Lake area and the design of the outlet from Cedar Lake make this option impossible.

Dredging – Dredging to a depth that did not allow substantial vegetative growth would be very expensive and require permits from several agencies. Such permits would be unlikely to be granted.

Herbicide treatments - While herbicides would probably be effective in control of nuisance plants, their use may be limited due to the presence of species in or near Cedar Lake that appear on Connecticut's Listing of Endangered, Threatened and Special Concern Species (1998). Consultation with DEP personnel found several such species in the Natural Diversity Data Base maps and files for the Cedar Lake area. Three plant species (bladderwort; Utricularia respinata; Torrey's bulrush; Scirpus torreyi; and clasping-leaved water horehound, Lycopus amplectans) have been reported for the southern part of the lake. While the bulrush and horehound species are emergent and might be resistant to some herbicdes, the bladderwort would probably be susceptible to any herbicide treatment for Cc or Mh. Additionally, a damselfly (little bluet, Enallagma minisculum) has been reported near Cedar Lake and any attempt to control nuisance plants in Cedar Lake with herbicides would have to take the presence of this species into account. Some specific herbicides are discussed below:

Fluridone (Sonar) – This is the only herbicide approved for use and effective against fanwort. Fluridone is slow acting and prolonged (>30 day) exposure is required for it to be effective. Therefore, fluridone is not usually used for spot-treatments (less than 5 acres), unless confined by barriers. Fluridone is relatively non-toxic to mammals and invertebrates and does not require proscription of subsequent water use, except for irrigation purposes.

Trichlopyr – This agent is effective against Mh. According to a manufacturer, some activity has been shown against Cc, especially if applied early in the growing season. However, documentation of this information is not readily available.

Biologic controls
Sterile carp – Sterile triploid carp have been introduced into some lakes, where they eat vegetation. This method is cost effective because a single introduction may produce control of vegetation for up to 8 years. However, sterile carp are indiscriminate herbivores and their introduction may have severe unintended consequences. Furthermore, the presence of endangered plant species in the lake would probably bar the introduction of sterile carp by DEP. Introduction of sterile carp would also require design and installation of barriers to prevent escape of the carp from the lake.

Weevils or other insects – We did not find any such agents for treatment of our major nuisance plants.

Control Methods Suggested for Specific Areas

Treatment of the whole lake with fluridone would the most economical approach to controlling fanwort, the principal nuisance species, throughout the lake. However, this approach would kill plants on the list of threatened, endangered or species of special concern and other desired plants. Therefore, this approach is not viable. No other approach has the potential to control fanwort over most of the lake. Since whole lake treatment is not possible, the following limited areas could be treated.

Path from Boat Launch to Open Water
The most effective treatment would be spot treatment with fluridone, possibly with barriers to control its spread. Treatment with fluridone of the entire north end of the lake would include the area around the boat launch. While the cost of the fluridone would not be great ($2000 for 6 acres for liquid formulation), application could cost between $4000 and $5000. Because prolonged exposure to fluridone is required for effective control, two (or even three) applications might be required. Installation of limnal barriers to prevent spread and/or dilution of the fluridone would be expensive ($1.50/foot for approximately 500 feet => >$7000), but would decrease the likelihood that three treatments would be required for effective control. This treatment might last several years. This treatment may be too expensive for the existing budget and the outcome is too uncertain to predict the total long-term cost.

If the use of fluridone is not permitted, installation of a benthic barrier or hydro-raking may be the only effective treatments. A benthic barrier approximately 14 feet wide and 250 to 300 feet long (to reach open water) would cost more than $3000 and require professional installation and removal each year for cleaning. It would be possible to try a shorter section (14 feet by 100 feet) for one year, then add additional sections if this approach proved satisfactory. Benthic barriers are best used in water more than 6 feet deep, in order to reduce the possibility of interference due to, and interference with boat motors. It might be necessary to do some cutting of growth prior to installation of a benthic barrier in order to reduce the potential for gas generation under the barrier.

Hydro-raking would probably be effective. Hydro-raking costs approximately $170/hour (sufficient to clear an area approximately 25 feet by 75 feet), but has a 16 hour minimum, plus a setup fee. Additional costs might be the cost of fragmentation barriers, if required. Furthermore, the Town would have to dispose of the material deposited by the hydro-raker on the shore.

North End of Lake between Boat Launch and Inlet
The optimal control method in this area would be treatment with fluridone as part of treatment of the area near the boat launch. If the use of fluridone is not justified or not permissible, no treatment is recommended.

Inlet
Chemical treatment to control excessive plant growth in this area may not be possible due to continuous water flow. However, hydro-raking might be an option for this area.

West Side of Lake North of Terrace Association Beach
Manual and diver-assisted harvesting could be useful approaches to nuisance vegetation in this area. Benthic barriers might be useful in some limited areas. Hydro-raking is a possibility (See above for costs). It is possible to use hydro-raking for selected properties. An area approximately 50 feet x 75 feet costs approximately $340. In some towns individual shoreline property owners pay for clearing the area adjacent to their land, while the Town pays for the setup fee. Disposal of the collected material can be the responsibility of the landowners, or performed by the Town. Diver-assisted harvesting costs approximately $1000/day, sufficient to clear between ¼ and 1 acre, depending upon plant density. The Town would have to remove the collected plant material.

Town and Association Beaches along the Western Side of the Lake Manual and diver-assisted harvesting or hydro-raking are the most useful approaches to prevent spread of plants into the swimming areas. Benthic barriers might be useful in some limited areas.

Southwest Corner of the Lake
Manual and/or diver-assisted harvesting would be the best approach to cleaning up this area in order to limit damage to native vegetation. However, we do not recommend any action at this time.

South End of Lake (Pelletier Park)
Yearly or biannual diver-assisted harvesting or hydro-raking could be effective methods to prevent spread of plants into the swimming area at Pelletier Park. At this time no action is required, unless diver-assisted harvesting or hydro-raking is being performed elsewhere in the lake. Informal surveys of vegetation spread into this area are recommended.

East Side of Lake
No action is recommended.

Present Plan of Action

Our present focus is on the boat launch, since plants between the boat launch and open water present a problem that may be amenable to action under the present budget. We recommend hydro-raking the area from the boat launch out to clear water, an area of approximately 25 feet by 400 feet. In addition we recommend coordination of the contractor performing the hydro-raking with adjacent property owners along the west shore of the lake, if they choose to have their property raked, to be paid for by the property owners. The town will have paid the one-time set-up fee so costs to property owners would be limited to the time needed to clear particular areas. It would be preferable that docks and rafts not be in the water when the hydro-raking is performed. Therefore, the best time to perform hydro-raking may be in the spring. Commitments (including payments) for areas along the western shore would be made prior to initiation of the work near the boat launch. Additionally, arrangements (transportation of plant waste to a yet to be determined disposal site, Inland Wetlands Agency permit) would have to be made prior to initiation of the work.

We are assuming that the spread of fragments generated by hydro-raking, if any, will not substantially alter the rate of spread of invasive weeds around the lake, because we think the distribution may already be self-limiting.

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