CARING FOR OUR POND
Weed Mitigation
Overview
SPA has been working to eradicate Non-Indigenous Aquatic Species (sometimes also called Non-Native Invasive Aquatic Species) for decades (NIAS). Until the 1960s, lakes and ponds in Massachusetts were mostly populated with indigenous or native aquatic plants. NIAS have been around in New England for some time, but we’ve seen significant propagation of these plants since the late 20th century. NIAS outcompete native species and crowd these out. NIAS grow in the littoral zone of lakes and ponds where sufficient sunlight penetrates to the lake bottom to support photosynthesis. The NIAS typically grow in the shallows down to 10 feet below the surface. Sunlight doesn’t penetrate down much further than 10’ in our pond so there is less NIAS growth, if at all, beyond this depth. The bathymetric map of the pond, below, shows that a large area, from the shoreline to 10’ depth (the area outlined in red), is prime habitat for NIAS plant growth.
A 2000 survey of the pond by Environmental Science Services, Inc (ESS, now ESSGroup) identified plant biovolume area and this is in line with limited growth of NIAS deeper than approximately 10’. Other pre and post treatments of the pond have shown a similar pattern.
NIAS Plants
The primary NIAS plants targeted are variable milfoil, fanwort and curly-leaved pondweed.
Variable Milfoil
Myriophyllum heterophyllum
Fanwort
Cabomba caroliniana
Curly-leaved Pondweed
Potamogeton crispus
A 1987 MassDEP (formerly DEQE) survey of the pond documented variable milfoil as the dominant NIAS in Spectacle Pond. Subsequent surveys in 2000-2005 saw a surge in fanwort and substantial milfoil was also present. After chemical treatments in 2005 milfoil densities subsided and fanwort became dominant. Milfoil was substantially reduced by 2010 and fanwort was dominant with curly-leaved pondweed making inroads. Curly-leaved pondweed became dominant in 2011-2013. There was a resurgence of fanwort between 2014-17 and then a very substantial increase in 2018-2019. When one NIAS is beaten back another NIAS finds its place in the sun and may become dominant. With chemical treatments over time we were able to beat back the milfoil, then fanwort, then curly-leaved pondweed, with the unfortunate regression back to fanwort. 2018-2019 seasons were especially bad for fanwort regrowth due to the unsatisfactory performance of the vendor we selected for treatment. In 2020-2021 we switched back to a tried-and-true vendor and fanwort is coming back under control.
Vendors
SPA has used four vendors over the course of the last three decades to do chemical weeds mitigation work: Lycott, Aquatic Control Technologies (ACT), SOLitude, and All-Habitat. Other vendors have submitted responses to Requests for Proposals (RFPs), but their prices have been typically noncompetitive with the other four vendors. As with most town-funded projects, this work is put out for bids, and SPA must select the lowest bidder unless there is good reason not to. ACT spun off from Lycott some years ago and became their major competitor. Eventually Lycott and ACT were absorbed into SOLitude, now SPA’s primary vendor for this work. SOLitude is a dominant force on the east coast. These vendors have done chemical mitigation work since 2005.
Chemicals
Diquat (Reward) has been the primary chemical used to control milfoil and curly-leaved pondweed. A diquat solution is used for this treatment. Diquat is a contact non-systemic herbicide but does not kill plants down to their roots, so reapplication annually is usually required.
Fluridone (Sonar) is the primary chemical used to control fanwort. Fluridone is absorbed by fanwort and affects its ability to produce carotene, which protects the plant’s chlorophyll from photodegradation. In the absence of carotene, a process known as chlorosis may be observed visually as the plant begins to lose its green color and take on a white or pink shade. Chlorosis begins at the top of the plant and usually extends 8-10” along the plant’s stem when concentrations are most effective. The plant’s structure does not begin to collapse for 45-90 days after treatment. Therefore, treatment effectiveness is best observed in the following season. Fluridone may be applied as pellets or as an aqueous solution for fanwort control. Fluridone “sticky pellets” are applied thru a spreader/broadcaster and sink to the bottom of the pond, often attaching to fanwort plants. Pellets release fluridone slowly ensuring a level of the chemical in close proximity to the targeted plants. Alternatively, when applied as an aqueous fluridone solution, it is recommended to dam up the water body being treated to ensure the chemical is locked in for a period of time, since the solution tends to drift away from treated areas. The aqueous solution of fluridone is often used in areas that don’t see much turnover of the waters surrounding the plants. Fluridone requires a minimum 40-50 days contact time with the fanwort to achieve effective control. Given the high flow rate of the pond, the only way this contact time can be achieved is by performing an initial treatment of the pond, then performing a series of follow-up, “bump up” fluridone applications over the 40-50 day time frame to maintain the require chemical concentration which is on the order of 15-20 ppb. Between chemical applications testing is done to determine if the required level of fluridone is being maintained.
A study was conducted in 2005 to determine if fluridone infiltrated into public and private wells during treatment. The results of the study were that no fluridone was detected in either the Spectacle Pond municipal well or three (3) other private wells. Pictures of the effect of fluridone on fanwort and chlorosis are here:
Treatments
Chemical treatments are usually performed as early as May and sometimes as late as September. Surveys for NIAS are done in the spring to help determine the timing of treatments in the summer. Surveys are also performed during the treatment process and in the autumn to gage the effectiveness of summer treatments. Chemical treatments kill or degrade NIAS these plants remain in the pond and decay. The decay process consumes oxygen and results in a dissolved oxygen problem within the pond. SPA has done water quality studies over the years and will continue to do so. Oxygen depletion can result in fish kills and/or reduction in species present and populations within species.
Funding
Funding for pond cleanup efforts was initially through state grants and town contributions. In the 2000 Town Meeting, Article 6 authorized the construction of a cell tower on Littleton Water Department (LWD) property off Great Road. In 2006, Town Meeting Article 18 directed Spectacle Pond cell tower rental funds to be used by Littleton Clean Lakes Committee (LCLC) for pond clean-up efforts. Most pond improvement or cleanup projects in Littleton are funded through these cell tower fund monies. Currently Bennett’s Brook, Beaver Brook, Long Lake, Lake Matawanakee/Forge Pond, Mill Pond and Spectacle Pond are the focus of LCLC work and funding. A list of LCLC members, Agendas and Minutes from our monthly meetings are here:
https://www.littletonma.org/clean-lakes-committee-clc
The 2000 Spectacle Pond ESS Diagnostic/Feasibility Study for the Management of Aquatic Nuisance Vegetation (mentioned above) was funded by the MA Department of Environmental Management to the tune of $10,000, with matching funds from Littleton and Ayer water departments at $5,000 each. The ESS final report was provided in April 2001. The ESS report considered a number of NIAS mitigation methods and concluded chemical treatment was the best fit for Spectacle Pond. The SPA and LWD, along with ACT, drove the Conservation Committee approval process for this mitigation work and we were able to do our first treatment in 2005. This treatment was so effective that only minor spot treatment was done to reduce milfoil in 2006. Spectacle Pond has been treated chemically from 2005-2021 to the tune of $10,000 to $15,000 typically per year, funded primarily by the LCLC, through the Spectacle Pond cell tower revenues
Looking Towards the Future
SPA explored a new NIAS mitigation method in 2022 with ECO-Harvesting vs chemical treatments of the past. Other ponds in Littleton were also keen to do this but it was decided at the Littleton Clean Lakes Committee (LCLC) that Spectacle Pond would take the point on being the first pond to try this out. With the help of LCLC's cell tower fund, C&D Underwater Maintenance was contracted to do the work.
With ECO-Harvesting, the goal was to pull the weeds by their roots instead of cutting the weeds as do most conventional harvesters. Once the weeds are ECO-Harvested they are transported to a landfill or processing facility. Multi-year treatments are needed for this method to be effective, but SPA has been advised that costs decrease each subsequent year as there should be less biomass to harvest. As the weeds and their biomass do not remain in the pond, there is less oxygen depletion via the decay process. Thus with the use of this new methodology, the pond may have its NIAS mitigated and perhaps help to resolve a persistent dissolved oxygen problem.
ECO-Harvesting was performed from 20-23 June 2022. During this period, approximately 95 cubic yards of slightly-dewatered aquatic weeds weighing between 75-95 tons were harvested and removed from the pond. 19 trailer loads of these spoils, weighing between 4-5 tons each, were transported to Dirt Doctors in Acton for composting. Below is a picture of the spoils dumped off at Dirt Doctors but it's only approximately 1/3 of the total harvested volume as Dirt Doctors had already been composting the other 2/3s prior to this.
In the future, spot chemical treatments may have to complement the ECO-Harvesting efforts. SPA will continue to monitor how this method stands up over time.