2002 Aquatic Plant Survey

Report on Aquatic Plant Survey of Bungay Lake and Management Recommendations

To: Scott Freerkson; Bungay Associates, Inc.

From: Gerald Smith; President/Aquatic Biologist, Aquatic Control Technologies

This report presents the results of an aquatic plant survey performed at Bungay Lake on November 20th, 2002. You were kind enough to spend the afternoon with me to perform this survey and share with me your extensive knowledge of the lake and history of management activities undertaken by the Lake Association.

At the time of our inspection the lake level had been lowered about 2-2.5 feet from what I understand would be its normal, early summer elevation. We inspected the lake from a small boat by travelling around the entire shoreline of the lake (both the main lake and Little Bungay Lake).

Using a “grappling rake” and Aqua-Vu Underwater Camera System, I identified the different types of aquatic plants and produced the attached map showing the major plant groups or assemblages. While several of the plant species had “died-back” significantly from what would normally be seen during the summer, there were still enough remains of these plants for me to see in order to get a good picture of the overall plant community.

Our last similar plant survey had been performed in September 1996 with the plant distribution briefly checked again in August 1996 when our Biologist’s collected water samples for chemical and physical analyses.

The types of plants found recently at Bungay Lake have not changed significantly from these prior surveys. In approximate decreasing order of abundance, I observed the following plants.

wild celery or tapegrass (Vallisneria)
clasping-leaf pondweed (P. perfoliatus or P. richardsonni)
fernleaf or robbins pondweed (P. robbinnsii)
American elodea (Elodea)
coontail (Ceratophyllum)
fanwort (Cabomba)
smartweed (Polygonum)
variable watermilfoil (M. heterophyllum)
white or fragrant waterlily (Nymphaea)
yellow waterlily or spatterdock (Nuphar)
stonewort (Nitella)
View Actual Pictures From Collection Day

I’d say the overall pant growth appeared to be “modestly” more abundant than what I remember from our inspection in 1996. Again, I defer to you people whom have lived on the lake for many years but an overall increase in plant growth is what struck me.

Secondly, we are now seeing more of the invasive/exotic milfoil and fanwort throughout the lake but more so an increase in the fanwort. Neither species is yet widely distributed but there is definitely more fanwort now, throughout the northern portion of the main lake and along the northwest shoreline, than I remember or show on our plant map from 1996.

Never the less, given the invasive characteristics of milfoil and fanwort, I’m surprised these two plants have not spread throughout the lake even more. The fanwort was observed growing to a depth of about 7-8 feet or about 9-10 feet when the lake would be at its normal full level or elevation.

Tapegrass and claspingleaf pondweed were the two most common plants found throughout the main lake. The tapegrass had senesced (died-back) for the winter but the bottom was strewn with the decomposing remains of this plant. Tapegrass is a native plant that provides good habitat for fish and food for different types of wildlife. Rarely do we see it reach densities that are problematic to recreational uses such as at Bungay Lake.

Clasping-leaf pondweed was also common to abundant throughout much of the lake, along with Robbins pondweed. Claspingleaf pondweed will grow in high densities and reach the water surface in depths of about 6-7 feet at Bungay Lake.

Robbins pondweed tends to remain low to the bottom and rarely becomes a nuisance. In fact Robbins pondweed is one of the more desirable plants, since it acts like a “mulch” and helps to out -compete taller plants.

Coontail was also frequent to common throughout the main lake, more so in the northern portion of the lake. Coontail was often mixed -in with growth of elodea, another common and native submersed plant.

In deeper waters, a low growing macro-alga called stonewort (Nitella) formed a thick carpet on the pond bottom. Like Robbins pondweed, rarely is Nitella a problem.

In Little Bungay Lake, submersed fanwort was widely distributed with lesser amounts of variable milfoil. Dense and sizable patches of floating-leaf smartweed still remained. Remnants of white and yellow waterlilies were also observed. Purple loosestrife, another invasive emergent plant, fringed a good portion of the shoreline.

View Plant Distribution Map

Management Recommendations:

We understand the overall goal of the Association is to manage the lake for recreational pursuits (i.e. swimming, fishing and boating) while preserving the wildlife and fisheries habitat.

We also understand that Hydro-Raking is the only organized weed control technique that has been carried out on the lake in recent memory. Last year’s Hydro-Raking program totaled about 40 hrs., and was performed in mid/late May. Raking has generally been performed once every two years, with most participants taking just one hour of time. You mentioned that some participants this year were questioning whether this technique was now as effective as it might have been in prior years. Lowering the lake level during the fall and winter some 2-2.5 feet has been practiced for many years. The lake level is not lowered so much for weed control as it is to allow homeowners to repair walls, rake beach fronts and allows for a lower lake level in the event of heavy fall rains and to mitigate against ice damage in the spring.

Lake Level Drawdown:

Lowering the lake’s water level significantly (say ~6-8 feet) could provide a relatively low cost and effective method to control the fanwort and milfoil throughout the main lake. The channel between Little Bungay and the main lake would need to be dredged and deepened considerably before the Little Lake could be lowered much more than it is currently.

We understand the dam has recently been rebuilt and the new dam would allow you to gravity lower the main lake level by 8 feet or more. Most of the costs associated with drawdowns are typically for permitting and monitoring.

Both plants have root systems (rhizomes) that are normally sensitive to the combined effects of freezing and drying during the fall and winter months. In fact fanwort in particular, is generally found to be one of the most sensitive plants to drawdown. Normally, drying and freezing is required for a sustained period of 6-8 weeks in order to destroy these reproductive structures.

Plant control may not be attained during all years of drawdown, given variations in climatic conditions, such as an early insulating snow-fall, a mild winter or excessive rain, in which case the reproductive structures may not be destroyed.

There is some potential for drawdown tolerant plants to increase after drawdown. Tapegrass and one or more species of pondweed could show some increase post-drawdown but the potential control of milfoil and fanwort may make this a worthwhile approach anyway, in our opinion.

Most of the milfoil and fanwort in the main lake is found in water depths of between 4 and 8 feet, therefore, a drawdown of at least 6 feet and preferably 8 feet is necessary for this to be an effective technique at Bungay Lake.

There are a number of legitimate concerns regarding drawdown that need to be explored before deciding to move ahead with this technique.

First off is determining the time for the lake to refill in the spring, since the lake does not have a terribly large watershed. This can be determined fairly readily by constructing a hydrologic (water) budget for the lake and its watershed, that examines the time and flow rate required to lower the lake along with the time for lake re-fill. Calculations can be performed to for a year given “normal” rainfall and for drought years. Drawdowns typically begin during early October with the lake remaining lowered until early or mid-winter. The final schedule for drawdowns are guided by weather patterns and the projected time to refill the lake by late March, which marks the start of spawning period for certain species of fish.

We strongly recommend that a phased approach be followed for lakes that are being drawn-down for weed control for the first time . This means that if your looking to eventually achieve a maximum drawdown of say eight feet, you develop a plan of drawdown that may span a four year period and perform annual drawdowns in progressive two foot intervals accompanied by monitoring of the lake’s fish and wildlife community, adjacent shallow wells (if any remain) and other environmental parameters.

Where I understand from you that the lake’s maximum depth is only about 15 feet, this lack of deeper water could be an obstacle to deeper drawdowns of say 6 or 8 feet, due to valid concerns regarding potential fish mortality. It would be very helpful if I could look at a bathymetric (depth) map for the lake, if you have one available.

A Feasibility Evaluation of drawdown to address the concerns expressed above and other potential effects ( ie aesthetic impact; potential interference with winter uses of the lake, etc) should be performed if the Association wants to pursue this approach further.

The estimated cost for these investigations should be in the range of $5000-$10,000, providing you have a reasonably accurate map of water depths for the lake. While we do some of this evaluation and design work ourselves, it’s not our forte and we’d recommend you hire a professional engineering/environmental consulting firm. We can recommend a couple of companies to you whom have performed a number of similar assessments for other lakes.

Chemical (Herbicide) Treatment:

Herbicide treatment is the most common approach in MA and across the country to control invasive and nuisance aquatic vegetation. In MA alone, some 150 or more ponds/lakes are chemically treated each year in more than 75 cities and towns. We perform about two-thirds of all chemical treatment work in MA.

The only aquatic herbicide effective on fanwort is Sonar (fluridone). Sonar works best on whole-lake applications, whereas it is highly soluble and tends to dilute out of smaller treatment areas. Within just the past year, the manufacturer of Sonar (SePro Corp.) has developed a new pellet formulation of Sonar which has shown some good results for partial lake applications. Sonar works slowly and requires an approximate 40-50 day “contact time” with the plants for effective uptake. Maintaining this contact time can be difficult in coves with significant water circulation or in lakes that have a rapid flow – through or “flushing rate”.

The weed situation at Bungay Lake is not that severe and does not warrant a whole-lake treatment program with Sonar at an estimated cost in the range of $50,000-$60,000.

Treatment of Little Bungay Lake and the two northern coves in the main lake are warranted to provide some relief from the fanwort and to help retard the further spread of this invasive plant throughout the rest of the lake. Treatment of the far eastern cove in the main lake would also be recommended but it not as critical as these other areas since it is somewhat more isolated from the main body of the lake. If nothing is done to halt the continued spread of fanwort, we predict it will eventually take over the main lake and create a tremendous nuisance.

It makes sense to be pro-active now, while the plant’s distribution is still somewhat limited, the effects of treatment will be less than a whole-lake application and the costs will be less.

The challenge to effective treatment with Sonar at Bungay is the amount of water flow that occurs into Little Bungay and at the head of the main lake where most of the fanwort is found. We would recommend a combined treatment approach using both the liquid and pellet formulations of Sonar. Multiple treatments (one initial treatment and 2-3 booster applications) would likely be required to maintain the required contact period of 40-50 days. The total treatment area is about 35-40 acres and is shown on the attached map. Treatment would commence in late May or June, when the fanwort is actively growing but after the normal higher spring flows have passed.

Prior to treatment, it would be helpful to lower the lake level by about 1-1.5 feet in order to help contain the Sonar in the lake. This lowering would occur only prior to the initial treatment. The culvert between Little Bungay and the main lake could be temporarily sand-bagged to further help contain the chemical in Little Bungay. Sonar’s half-life is about 3 weeks in water, not withstanding the Sonar lost to dilution and outflow.

The timing of the booster applications is guided by collecting and analyzing water samples every 7-10 days post-treatment from the treated areas and having these samples analyzed for residual Sonar concentrations. We ( or the Association) send these samples to SePro overnite mail and they typically have the tests run and the results back to us within 1-2 days.

Based on our extensive experience with prior fanwort treatments in MA, we initially target a dose of 15-25 ppb and try and maintain a minimum concentration of 10 ppb for the 40-50 day period. This dose is well below maximum label rate for Sonar of 150 ppb. We would anticipate good control of the fanwort and also the milfoil. If the milfoil was not completely controlled within the treatment areas, we would spot-treat these areas later in July with Reward (Diquat) herbicide.

Sonar will impact and control most of the other plants within the targeted treatment areas. These non-target plants, however, will rebound over the next 1-2 years while typically the fanwort is controlled for generally 3 years or longer.

The total cost for the Sonar treatment program is approximately $25,000-$30,000 plus an estimated $2,000 to permit the project with both the No. Attleboro and Mansfield Conservation Commissions and MA DEP.

Chemical treatment of tapegrass is generally not very effective. We don’t have any registered herbicide that exhibits “predictably” good control of tapegrass. We could first perform a “pilot or demonstration treatment” of one cove or shoreline area at Bungay Lake with Nautique – a copper based herbicide which some Applicators have reported good results with on tapegrass.

Estimated costs would be in the range of $3,000 plus permitting, if done in combination with the Sonar treatment program or $5,000 if done alone.

Effective treatment of the claspingleaf pondweed, which along with the tapegrass is the most abundant and problematic native plant can be attained with a combination of Reward (Diquat) and Aquathol K (dipotassium endothal) herbicides.

Treatment costs would run about $400/acre, assuming a minimum treatment area of roughly 10 acres. We can discuss with you the priority shoreline and cove areas for this potential treatment.

View Map of Recommended Treatment Areas

Mechanical Cutting/Harvesting:

Mechanical cutting and harvesting is an effective means of controlling native plants like tapegrass and pondweed. Harvesting of milfoil and fanwort must be done very carefully so as to collect all fragments to avoid inadvertent spreading of the plant to other portions of the lake from the fragments that escape collection.

Generally, we do not recommend harvesting in lakes that contain milfoil and fanwort. The commercial Harvesters cut to a maximum depth of between 6 and 7 feet. Typically two cuttings per summer are necessary for adequate plant control. Harvesting is simply an annual maintenance strategy and more lakes are getting away from harvesting rather than adopting this management technique. We believe that either drawdown or herbicides offer a better and more economical approach to managing the nuisance plants at Bungay Lake as opposed to harvesting.

Mechanical Raking:

The residents at Bungay Lake are familiar with Hydro-Raking. Raking has the advantage over harvesting of removing the plants and some of their roots, along with being able to remove rooted plants to a maximum of 12 feet, where necessary. Longer term control is achieved with raking than simply cutting the plants as with harvesting.

Tapegrass is a difficult plant to effectively rake because the plants are not branched and therefore, they often “slip through” the steel tines of the rake. We’ve had the same two operators perform the work at Bungay in recent years. Both of these men have been with us for over 15 years, therefore, any decline in the results (effectiveness) of the raking process now being achieved is not a function of a lesser experienced machine operator.

The pondweed species typically grow from seed and may not be up and established when the raking process occurs in mid/late May. If the Association decides to continue with Hydro-Raking in the future, a July raking may prove to be more effective.

Permitting:

Permitting for any of the management techniques discussed above will be required from the local Conservation Commissions in the two municipalities. Filing of a Notice of Intent (NOI) in accordance with the Wetlands Protection Act is required. We assemble a detailed description of the project, discuss alternatives to the action being proposed and examine the project in-light of the wetland statutory interests.

All lake abutters are notified by certified mail and a public hearing on the project is held by the Commissions. If the Commission approves the project, they typically do so with a set of “conditions” of approval. The Town of North Attleboro is a long-time lake management client of ours and we would not expect a problem in permitting chemical treatment with them. We have no experience with the Mansfield Commission.

The cost for us to assemble and file the NOI and attend a public hearing in each community is about $2,000. You should also budget an additional $1,000 for state/local filing fees, certified mailings and other reimbursable expenses. For chemical treatments we also file what’s called a License to Apply Chemicals with MA DEP, Office of Watershed Management in Worcester. This is a straight forward permit that we typically obtain given 45-60 days lead time.

Allow at least 90 days lead time for the NOI process. For drawdowns, additional state and federal permits may be required. Permitting costs for drawdown are also likely to be more involved and we suggest budgeting $4,000-$5,000 for the two Conservation Commissions and potentially much greater costs if other state and federal permits are required.

In summary, based on our recent observations, we recommend the Lake Association take a more aggressive approach towards the management of vegetation throughout the lake with a need to focus first on the invasive fanwort and milfoil in Little Bungay and the northern coves of the main lake, along with control of native tapegrass and pondweed in localized, high use areas of the main lake.

A Feasibility Assessment of drawdown should be pursued. Partial lake treatment with Sonar herbicide targeting fanwort and milfoil should be considered along with drawdown. Chemical (herbicide) treatment of tapegrass and pondweed can and should proceed in 2003, on a limited scale to evaluate effectiveness and independent of whether drawdown can proceed or not, since these plant species are likely not to be controlled by drawdown.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s