‘Internal loading’ a major concern for Mudge Pond

SHARON — A new report prepared by the Northwest Conservation District found it’s not only recent agricultural runoff that impacts the water quality of Mudge Pond, but pollution from bygone farms of decades ago.

The reason for this is a process called “internal loading,” stated the report, which was prepared by NWCD Natural Resource Specialist Kelsey Sudol and presented to the Board of Selectmen at its August 26 meeting by selectwoman Lynn Kearcher. Drawing from the findings of a February 2025 study (researched in 2024) by environmental consultancy Northeast Aquatic Research, Sudol’s memo declares that “internal loading is the main major water quality concern for Mudge Pond currently.”

Internal loading is the release of harmful particulates that were once entombed in the lake bottom back into the water column. It results from a layer of anoxic or hypoxic — water either entirely or almost entirely devoid of dissolved oxygen – sitting on the lake bottom for longer than usual.

It’s normal for this to happen for a period in New England’s freshwater lakes during the summer when they’re “stratified” (i.e. when warmer, less dense water sits above cooler, denser water). In this state, the layers don’t mix and the deeper water is unable to receive additional oxygen from the well-oxygenated layers above.

Warmer winters, however, can cause this process to begin earlier, especially with a shortened ice season. These extended anoxic periods, which were confirmed by several readings taken during the Northeast Aquatic Research study, allow harmful pollutants that may have been sitting on the lake bottom for decades to reappear and cause damage. Nitrogen and especially phosphorus are two such products of historic agricultural runoff that pose a risk to Mudge Pond.

The NWCD report upholds that “within watersheds that have a long history of agriculture, which Mudge Pond does, this release of historic pollution is common.” There is an urgency to remedying this issue, the report went on, given that “the stressors that are worsening this internal loading, like warmer winters, are not projected to improve.”

The report recommends aeration, a technology which artificially inputs oxygen into deeper water, as the most promising remediation tactic. The suggestion follows the Northeast Aquatic Research study which declared that “the lake is an excellent candidate for artificial aeration.” Northeast Aquatic Research would not suggest a specific method by which to implement the solution, however, until it had completed further research, stating the group would be able to present “state-of-the-art” options to the town by the spring of 2026.

Neither the town nor the Mudge Pond Association — the lake’s newly-formed recreation and protection authority — have stated whether an aeration solution will be pursued, although the Association has indicated a commitment to weigh all possible protective measures.

While the reappearance of old pollutants presents the greatest water quality risk, current runoff also poses a threat. The Northeast Aquatic Research report located a high concentration of nitrogen at certain times of the year near an inlet that enters the lake on its eastern shore, downslope from Low Road. The feeder streams flow through a wetland before reaching the lake at the inlet, which is a cause for concern as wetlands usually act as “biofilters” that remove nutrients from the water, stated Northeast Aquatic Research.

The NWCD offered to conduct a stream-walk to locate the sources of these nutrients that would help develop a “watershed monitoring program.” The group would also help the town educate property owners and farmers within the watershed on erosion control and nutrient runoff management. Such practices have worked before, the NWCD correspondence stated: according to historic reports from 1999, 2000 and 2001, once newly-established best management practices were adopted in area farms in the 1980s and 1990s, Mudge Pond’s water quality drastically improved.

The NWCD also offered to conduct a volunteer event to remove invasive water chestnut, sending out flotillas of kayakers to hand-pull the water weed in a minimally invasive procedure. Earlier in the summer, an effort by the Mudge Pond Association and local consultancy New England Aquatic Services to hand-pull the plant was stymied by a much-greater amount of organic material than anticipated. A bigger team could help, the NWCD recommended in the memo.

The Mudge Pond Association said it is carefully weighing NWCD’s many suggestions, and is working on next steps.