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01/24/2022 11:00 PMThe company charged with developing a management plan for Lake Quonnipaug delivered its recommendations at a public meeting last week. The ESS Group, Inc., of Waltham, Massachusetts was requested by the town last year to develop and coordinate a plan to help address the long-term viability and health of the lake’s resources.
The study, which was undertaken this past summer by ESS, was described as “short but focused” and found that overall the water quality at Lake Quonnipaug is quite good, but as with many data sets, there are devils in the details.
Carl Nielsen, project manager and lead scientists for this study, presented the report summary that focused on invasive water plants and chemical levels of the lake.
In the past, the town has treated the lake with herbicides to mitigate invasive plant species, but the company’s report is suggesting that further diligence will be required to maintain an upper hand against several specific species.
Though overall Lake Quonnipaug is “one of the most species rich lakes in Connecticut”, with surveys identifying 44 plant species, two native species, pond weed and water marigold, have not been observed in lake surveys since 2004 and 2015 respectively. According to Nielsen, continuing to promote these types of native species can be a significant factor in the mitigation of invasives.
“The challenge here in managing Lake Quonnipaug is the presence of native species. Water marigold and capillary pond weed are two native species that are actually protected,” said Nielsen. “So, you have to be careful when you are out doing any weed treatments or management of any type, because you want to avoid damage to or impact to any protected species.”
The company conducted testing during wet and dry weather to better understand run off issues that occur during precipitation events. The testing revealed differing results between the large body of the actual lake and the far-smaller inlets, where most of the organic chemical concerns were discovered.
The main body of the lake appears quite healthy by most metrics, according to study, but these various inlets, where runoff is concentrated and the water takes more time to circulate, show higher values of nitrogen, phosphorus, and organic compounds.
ESS stated that water quality results were generally good, but that there are reasons for concern. The company measured oxygen, phosphorus, and nitrogen levels across the lake and determined that in general those levels are under maximum thresholds for quality.
In-lake dissolved oxygen levels were within guidelines according to the report, and “given that it is able to maintain a stocked population of rainbow trout, a species of fish that is particularly sensitive to lower oxygen levels,” oxygen levels are adequate.
According to the report, phosphorus levels within the lake were below 0.01 milligram per liter at both the surface and bottom, which is considered to be below the maximum threshold. Generally, phosphorus values above 0.02 milligram per liter are where problems such as algal blooms begin to materialize, Nielsen said.
When nitrogen concentrations exceed 1.0 milligrams per liter, there is most likely an anthropogenic (man-made) source, according to Nielsen. One of the lake’s inlets exhibited the highest total nitrogen value in the study at 1.12 milligram per liter, indicating that there may be a human-derived source such as a failing septic system, excessive lawn fertilization, or improper pet waste or animal manure management within its drainage area.
ESS said that additional investigation, beyond the scope of its study, would be required to locate the specific source and recommend a solution.
The summary of the ESS water plant management recommendation states:
“Lake Quonnipaug continues to provide shoreline residents and other users of the lake with immense recreational and aesthetic value; however, conditions within the waterbody [have] deteriorated in more recent years due to the infestation of invasive fanwort, milfoils, and curly-leaf pondweed. The prior weed management actions have been very good at preventing these species from spreading further over the past 20 years, but they have not been robust enough to reduce their density and distribution to levels that would allow beneficial native species to dominate the lake. Fanwort, milfoils, and curly-leaf pondweed are still present in the waterbody and thus future management actions will need to be focused on continued vigilance with monitoring and reducing the overall coverage of these species.”
The summary of the water quality management recommendations states:
“Although water quality monitoring is not a management action, per se, given the relationship between water quality and lake biology, it will be an essential component of a successful long-term management plan for Lake Quonnipaug. Monitoring provides continuous data for the purpose of detecting changes in lake conditions that might encourage algae blooms, as well as tracking the effectiveness of any future management practices that may be implemented. ESS recommends that the town implement a water quality monitoring program annually to track in-lake conditions during the summer growing season. Additionally, ESS is recommending monitoring also focus on tracking the impact of stormwater runoff on the bacteria impacting the lake through beach closures. Bacteria (E. coli) samples should be collected following each storm event from any flowing tributaries and storm drains emptying into the lake. Understanding the source with good monitoring [data] will be key to developing solutions that will stop future lake closures.”
The full report is available at the town website www.ci.guilford.ct.us—search “Lake Quonnipaug Management Plan.” The report includes more detailed data and costs associated with any treatments or management plans, and further analysis of plankton levels, boat inspection, and dredging recommendations.