Report on Biological Survey of Bungay Lake and Management Recommendations
by Gerry Smith, President/Aquatic Biologist – Aquatic Control Technology, Inc.
This report presents the findings of an Aquatic Plant Survey and Water Testing performed at Bungay Lake with you on September 12th, 1996. The objectives of the survey were two-fold;- one, to continue the data base of water quality testing performed in recent years and two, to examine the aquatic plant community and reevaluate management options to control nuisance vegetation.
Lake Description and Sampling Approach:
Big Bungay Lake has a surface area of approximately 108 acres as measured from a USGS topographic map. Little Bungay shows a surface area of about 18 acres, although probably 50% or more of Little Bungay is now “emergent wetland”, rather than an open-water pond. Both lakes are quite shallow. You reported a maximum depth for Big Bungay in the range of 15 feet and roughly 3-4 feet for Little Bungay. The watershed or drainage area to the lake is sizable, mostly located in Mansfield and No. Attleborough but also encompassing smaller areas of Plainville and Foxboro to the north. There are an estimated 150-200 homes on the lake with you projecting that roughly 90% are now occupied year-round. All homes are reportedly on cess pools/septic systems as there is no municipal sewage system that serves the lake area. I understand most homes, however, are on town water.
On the day of our inspection, aquatic plants were surveyed from a boat through visual inspection and by dragging a rake or small anchor while proceeding in a counter-clockwise direction around the entire lake shoreline. The plants were identified in the field and dominant plant types keyed to a map of the lake to show distribution (see attached map). Water samples were collected from the same 5 sites that have been sampled in recent years. These were surface “grab” samples, collected approximately 1 foot beneath the surface. The samples were delivered to a state certified laboratory for analyses of bacteria along with certain chemical and physical constituents. A temperature/oxygen profile was taken near the deeper, central portion of the lake, along with collection of a surface sample for microscopic examination of algae.
Results of the Plant Survey:
Overall, I’d characterize the plant community as moderate to locally abundant in specific areas. Little Bungay is now quite shallow and aquatic plants are abundant throughout. There are two invasive and probably exotic (non-native) plants of concern in both lakes, that are not too wide-spread presently but we would expect them to become more problematic as time goes on. These plants are variable watermilfoil (M. heterophyllum) and fanwort or cabomba (C. caroliniana). The fanwort is thought to have been inadvertently introduced to MA waters through the aquarium industry in the south. We find fanwort to be quite invasive, in some cases dominating a lake’s plant community once it’s been introduced. The fanwort was found throughout much of Little Bungay that could be accessed by boat and in the northern cove(s) where Little Bungay enters the Big Lake. It was also found in several other areas in the Big Lake most noticeably the southeast cove. Fanwort is a perennial plant that grows fairly slow in the spring but by mid summer is probably approaching the water surface at depths of 4-5 feet. Where fanwort flowers, it produces a white colored flower that protrudes above the water surface, usually in August or September.
The variable milfoil is not too extensive in either Big or Little Bungay. It did not appear to be vigorously growing and was only locally abundant in a few areas and most noticeably in Little Bungay and again in the northern coves of Big Bungay.
Both lakes also support a good diversity of native plants. Tapegrass or Vallisneria is probably the dominant plant along with clasping leaf pondweed (P. perfoliatus). Both plants are desirable when found in recreational lakes in low to moderate abundance. They provide good cover for fish and fish-food organisms (i.e. invertebrates, small crustaceans, etc.) When found in swimming areas however, they can be problematic. Waterlilies including Nympaea, Nuphar and Brasenia were prevalent in some of the shallow coves. Smartweed or Polygonum, a floating-leafed plant, dominated the vegetation throughout the shallower portions of Little Bungay. Throughout Big Bungay, submersed vegetation was found to a depth of 8-9 feet. Beyond that depth there is insufficient light for plants to grow.
While we no longer have our records of our only previous plant survey dating back to probably 1984/1985, it’s our recollection that neither fanwort or the milfoil were found at that time, at least in any significant abundance. I remember tapegrass as being the dominant plant. It would appear that the fanwort, first became established in Little Bungay and is working its way throughout the Big Lake. Both fanwort and milfoil reproduce and spread primarily through vegetative fragmentation which is important to know for future management decisions (i.e.; weed control and boating) for the lake.
Water Quality Results:
All 5 sampling sites (see attached map) yielded low densities of both fecal and total coliform bacteria, well below the State’s maximum permissible limit of less than 200 for fecal coliform and less than 1,000 for total coliform. The only station that showed any appreciable coliform density was station 1, located on Little Bungay. Stations 2-5 were located on the main lake. Sampling in Big Bungay revealed a pH almost near neutral at 7. 10. Alkalinity which measures the lake’s buffering capacity to resist change in pH was 23 mg/l versus 17mg/l in 1995. Such variations are not thought to be significant. The lake is characterized by generally soft water, with low to moderate susceptibility to long-term acidification. To have sufficient data in order to detect subtle changes from year to year, multiple sampling rounds would be needed throughout the year. This one sampling round provides but a “snap-shot” view of lake quality at one point in time. Turbidity measures the amount of light that passes through the sample. Turbidity is effected by colored and suspended particulates including algae, silt/clay particles, detrital (plant) matter, etc. The turbidity of 1.1 ntu is fairly low and indicative of relatively clear water. The Secchi Disk clarity as measured at station 4 was approximately 6 feet. This is fairly good clarity although particles of blue-green algae could be seen in the water. The state requires a minimum clarity reading of 4 feet for accredited bathing beaches. During mid August 1995, we measured clarity at about 7 feet or not much difference from this year.
Microscopic examination of a surface sample collected at station 4 revealed a moderate density of algae dominated by the “blue-green” genera Coelosphaerium and secondly Microcystis. The overall density of algae throughout the water column was probably not that high, however, these buoyant types of algae tend to skew the results.
Phosphorus and nitrogen are the key nutrients that generally limit plant growth in freshwater systems. The total phosphorus concentration was 0.02 mg/l which is fairly low and desirable. Nitrate nitrogen, which is the inorganic form of nitrogen readily available for plant uptake was less than 0.2 mg/l which is also low. Again we reiterate that multiple sampling rounds and locations are needed to make any conclusive statements regarding average water quality conditions throughout the year.
The temperature/oxygen profile taken at station 4, showed a surface temperature of 22c (72f) and was constant to a depth of about 10 feet. Dissolved oxygen was 8.2 mg/l at the surface and declined slightly to 7.6 at 10 feet. This fairly shallow lake is not expected to stratify thermally and is probably well oxygenated to the bottom throughout most of its area. Summer temperature and oxygen levels are fine for supporting a warm water fishery.
Management Alternatives and Recommendations:
Prudent lake management requires continuous and diligent efforts towards shoreline and watershed protection and maintenance. At Bungay Lake, septic system maintenance is probably the largest contributor of nutrients to the lake which can stimulate floating weed and algae growth. Rooted plants derive most of their nutrition from the nutrient enriched sediments. That’s why watershed management alone will not deal with or solve rooted plant problems. To focus on weed control alone, however, is inappropriate because the weed/algae growth will only worsen over time if the input of nutrients and sediment entering the lake is not curbed. The Lake Association at a minimum needs to aggressively pursue participation in a septic maintenance program for all waterfront property owners. Routine pumping of systems; water conservation ;and care as what goes into the septic system are very important elements of such a plan.
While we understand the lake presently does not presently experience massive algae blooms, the observation of blue-green algae “clumps” suspended in the water during my inspection, suggests the lake may be at a critical point where just a small addition of nutrients may lead to some serious algae problems in the near future.
Aquatic Vegetation Management:
Based on the assemblage and abundance of vegetation observed throughout the lake, vegetation management is appropriate in some areas. We believe the presence of fanwort and milfoil needs to be carefully monitored for future expansion. The only effective method of “controlling” milfoil or fanwort in areas larger than about 0.25 acres is through the application of USEPA/ MA DEP registered aquatic herbicides. The only herbicide effective on both fanwort and milfoil is a herbicide called Sonar (Fluridone). Sonar would be difficult and fairly costly to use at Bungay, because of the continuos water inflow from Little Bungay.
Chemical treatment is not recommended for the main lake. Weighing the importance of the tapegrass and other plants to maintain a balanced aquatic habitat, large-scale treatment with any herbicide is not recommended. In addition, the dominant native plants (pondweed and tapegrass) are quite resistant to those products that are approved for aquatic use. We chemically treat more ponds and lakes throughout MA than any other company but at Bungay Lake we don’t believe chemicals are the most appropriate strategy, other than for dealing with the fanwort or milfoil. Where milfoil and fanwort pose a real threat to the entire lake, such a control program should be funded by the Association and not just the property owners whom live in these areas.
For the continuing maintenance of swim/beach front areas, Hydro-Raking remains the best approach in our opinion. Raking in areas of milfoil or fanwort must be carefully done in order to capture fragments of the plants or not at all. If necessary, we can deploy floating, fragment barriers at an additional cost. It would be best to limit motorboat activity in these areas as well. Residents should be instructed to identify these plants and then informed about minimizing boating activities in such areas and careful mechanized or manual raking of these plants. In areas that have been Hydro-Raked, it will continue to be an annual weed control process although we typically see a reduction in density the following year.
The lowering of some lakes to freeze and control plants during the fall and winter can be an effective and low cost strategy. However, In shallow lake like Bungay, drawdown can have adverse impacts on fish, wildlife, aquatic vegetation, adjacent shallow wells and contiguous wetland areas. Drawdown requires you to drop the body of water 4 to 5 feet for it to be an effective technique for weed control. This would not be practical at Bungay Lake. Scoping out either a drawdown or dredging project for Bungay is well beyond the scope of this survey. Both techniques have some real concerns, however, that need to be thoroughly addressed before deciding to proceed and permits are often required at the local, state and federal level. There are very few, dry -dredging projects of a magnitude the size of Bungay, that are currently proceeding, in view of today’s regulatory constraints.
The use of bottom weed barriers may be an option that some homeowners should consider. We sell and distribute a “fine, meshed screening product” called Aqua-Net. It’s laid over the weeds and controls the weeds through compression and blocking of light, generally within 30 days of installation. It’s fairly costly at $0.65/sq. ft., or $910 plus freight/handling, for a roll measuring 14 ft by 100 ft. It’s intended to control rooted plants in smaller areas and has a useful product life projected at 5-10 years. Installation can be performed by the homeowner. We sell a considerable amount of this product to residents on ponds and lakes where no organized weed control program exists.