Editor’s note: This article is the second in a series exploring the impacts of climate change on three of Harvard’s key natural resources—and the policies that may be used to improve resiliency. Agriculture is the community’s economic base; Bare Hill Pond is a hub of recreational activity and an indicator of ecological health; forests contribute to climate change mitigation through natural carbon sequestration and storage. Each of these natural pillars faces challenges as a result of a warming climate and changing weather patterns that are especially pronounced in New England. By identifying these challenges and the plans that are already underway to address them, this series aims to provide a local perspective on climate change and its trajectory.
Bare Hill Pond is a hub of year-round community and recreational activity, enjoyed by swimmers, boaters, hikers, and fishermen, and is a source of seasonal employment for Harvard’s student lifeguards. For decades, the town has struggled to keep the water clean and clear of weed growth but, more recently, climate impacts have added an additional layer of concern for those working to keep the pond healthy. Two years of algae, or cyanobacteria, blooms indicate that management techniques that have kept the ecosystem in balance for the past 20 years may no longer be enough to keep the pond healthy and accessible.
The water in Bare Hill Pond has been warming along with the climate (see graph at right). Bruce Leicher, chair of the Bare Hill Pond Watershed Management Committee, said that the surface temperature of the pond hovered near 85 degrees for about six weeks last summer. In previous years it reached the low 80s but for shorter stretches. This warming is the beginning of a cycle that can disrupt the balance of the pond’s ecosystem.
Aquatic life relies on dissolved oxygen in the water to survive—making oxygen levels a common marker of pond health—and colder water holds more dissolved oxygen. As a body of water warms, oxygen is depleted, particularly in deeper areas, and becomes most concentrated toward the surface. Fish that typically reside in deeper water move closer to the surface, but then endure warmer temperatures than they are used to. “I don’t think it’s become life-threatening for the fish, but it affects them,” Leicher said.
In past years oxygen levels in Bare Hill Pond remained high enough to support life down to a depth of 10 feet, according to the 2021 Bare Hill Pond In-Lake Water Quality and Plant Survey. In 2021, that was reduced to 8 feet. Beyond that point, the lake was anoxic, meaning it had no oxygen. Historically, anoxia did not begin until a depth of 12-14 feet, according to the survey.
Anoxia’s visual impact
Anoxia affects the pond in visible ways as well. Leicher said that anoxic conditions trigger the release of phosphorus stored in the pond’s sediment. When this happens, naturally occurring cyanobacteria—photosynthetic aquatic bacteria that produce their own food—grow from dormant spores and rise to the surface, creating algae blooms like those that appeared the past two summers.
Timing of the blooms kept them from having a significant impact on organized activities at the beach but may have been a nuisance to individual users. In 2020, the Board of Health (BOH) issued a no-swimming order in late August, followed by a no-contact order that was not lifted until the end of October. The next year, a no-swimming advisory lasted from Aug. 20 to Oct. 2.
According to the pond’s harbormaster, Bob O’Shea, summer swimming lessons and lifeguarding are typically winding down by that point anyway, so Harvard’s youth avoided missing out on summer activities and employment. The second year, he said, some people chose to swim regardless of the bloom and BOH advisory.
Boating under the no-contact order was still allowed, though the BOH advised boaters to rinse their crafts after use to avoid transferring the toxins to other bodies of water. O’Shea said that he noticed a halt in boating for a while in 2020 before it became clear to people what the safety recommendations were. The second year he said boating continued but at a reduced rate. Holly Hatton, coach for the Bare Hill Rowing Association, said the team was fortunate not to miss much practice as a result of the blooms. O’Shea said people continued to fish during the blooms both years, which was permitted under BOH guidance.
Part of the harm associated with algae blooms comes when they dissipate through bacterial digestion. “When there is too much phosphorus, algal blooms occur,” Leicher wrote in an email to the Press, “and if they bloom more than we have experienced, they cause a crash in the ecosystem when the bloom dies out.” He explained that algae can be consumed by bacteria, which consume and deplete oxygen in the pond, leaving too little for other species such as fish, amphibians, and native shellfish, to survive.
Before 2020, Bare Hill Pond had not suffered an algae bloom in decades. Leicher said that near-yearly drawdowns—a process of gradually reducing the depth of the pond in the winter and restoring it in the spring—beginning in 2003 may have protected against blooms when temperatures were more moderate. The drawdown process reduces phosphorus and bolsters the resiliency of the pond, he said.
The drawdowns have been especially helpful for controlling invasive species, and in doing so, restoring native species. Leicher said that in the past 20 years, the Bare Hill Pond Watershed Management Committee has observed a thriving fish population, multiple species of frogs, water snakes, river otter, beaver, and a variety of plants. He said that bald eagles have returned to the pond, indicating a plentiful food source. “What is happening is that we have helped restore the native habitat, and this allows the native species to return.”
Harvard resident Willie Wickman lives pondside and her family uses the water for boating, waterskiing, paddleboarding, and kayaking. She used to swim as well, but has since given up due to worsening weed and lily pad growth. When the algae blooms occurred, the family was unable to use the pond for over a month. Wickman is concerned that blooms will begin to occur earlier each year, putting the health of the pond in jeopardy. “Five years ago I could paddleboard and observe fish and frogs swimming as I moved through the water in the shallower areas,” she wrote in an email to the Press. “That is not the case anymore.”
Secchi disk transparency—determined by lowering a black-and-white disk into a body of water until it is no longer visible and noting the depth at which it disappears—in July and August of 2021 reached its least favorable transparency levels since the committee began regularly recording the measure in 2004. The August measure put transparency at 3 feet, putting the pond a foot beneath the state water quality threshold for swimming. In May and June of 2021, transparency was around 12 feet, two of the best measures recorded.
Adam Meier, a member of the Harvard Climate Initiative Committee whose professional career intersects climate and public health, lives downstream from the pond. A portion of Bowers Brook, which flows from the pond, runs through his property, and he said that at this time of year he starts seeing “indicator species,” such as caddisfly larvae, crawfish, and freshwater mussels, as well as many others. He said that the biodiversity he observes suggests a healthy aquatic ecosystem and strong shifting food web.
Alexandra Luck (left) and Heather Flokos rake invasive milfoil onto the beach at Bare Hill Pond several summers ago. (Photo by Lisa Aciukewicz)
Still, he is concerned about the health of the pond and the causes of recent changes. “A lot of the impacts that we see on Bare Hill Pond are because of human patterns of environmental interactions [such as land use decisions] that are also, simultaneously, impacting climate change,” he said. Factors such as gas-powered motor boating, landscaping, and poorly constructed waste management systems can all compromise the health of natural spaces, but Meier said they are not inevitable and can be changed. He also pointed to the pond’s past as farmland—which left its sediment nutrient dense—previous management practices of both the pond and surrounding areas, and warming temperatures across the globe.
“The pond is a space where human health and ecosystem health intersect in pronounced ways,” Meier wrote in an email to the Press. “Whether splashing in the shallows, learning to swim, sailing, paddling, fishing, skating, or watching the sunset reflect off the water, the pond can support the health of our community. But we can’t isolate these interactions from the ways we indirectly engage with the pond through other life decisions [such as landscaping and construction].”
The Bare Hill Pond algae blooms of 2020 and 2021 corresponded with two of the region’s warmest summers on record, and temperatures in coming years are expected to continue to trend upward. According to reports from the National Oceanic and Atmospheric Association, average temperatures in the state have risen nearly 3½ degrees since the beginning of the 20th century, and “historically unprecedented warming” is predicted for the 21st century. As a region, the Northeast is warming faster than any other part of the country.
Higher winter temperatures—which the Apple Country Natural Climate Solutions Report projects will increase drastically in coming years—could also reduce the effectiveness of drawdowns in controlling weed growth. According to the 2021 Bare Hill Pond In-Lake Water Quality and Plant Survey, part of what a drawdown does is subject the roots of weeds in newly exposed areas of the pond to freezing sediment. Ideally, days will be consistently below freezing with little to no snow, which insulates the ground and can prevent freezing. Weather was an issue during the 2019 to 2020 drawdown season, when a warmer-than-average January limited the effect on weed growth.
Far from an anomaly
Bare Hill Pond is far from an anomaly in its algae issues and it may be faring better than other bodies of water in the region. The Environmental Protection Agency began mapping algae blooms reported by states in 2015 and its data shows sharp yearly increases that are especially pronounced in the Northeast. These trends may be distorted by discrepancies in state reporting, but reflect what has been reported in Massachusetts. Leicher said that 51 lakes and ponds across the state suffered algae blooms last year, and most started three to four weeks before Harvard’s. This may be a sign that the drawdowns are helping to delay the onset of blooms, even if they are no longer enough to prevent them altogether.
Another difference between Bare Hill Pond and neighboring bodies of water is its stormwater treatment system. A common cause of high phosphorus levels is stormwater runoff. Heavy rain events wash nutrients present on roads and lawns into bodies of water, which can lead to blooms. In the early 2000s Harvard used a Department of Environmental Protection grant to install rain gardens—landscaping features that strategically place wetland species known to retain phosphorus and that act as a filter between producers of urban runoff and bodies of water—that capture the first half inch of rain, which is where phosphorus is most concentrated. Without these, Leicher said Bare Hill Pond would likely also see blooms caused by runoff, but so far the system has protected it from such a fate.
Climate-related changes in storm patterns do not bode well for ponds and lakes that are susceptible to blooms caused by stormwater runoff. According to the 2019 Massachusetts Drought Management Plan, erratic rainfall patterns have become more frequent across New England and annual precipitation is expected to increase due mostly to “extreme precipitation events.” Leicher noted that more time between storms means more phosphorus buildup. “Every time they [lakes and ponds] get a dose, the dose is bigger,” he explained.
An uncertain future
Where the health of the pond is headed is unclear. Leicher said the worst-case scenario would be for blooms to start early in the summer and persist for weeks, limiting recreational use of the pond and threatening its flora and fauna. Meier has similar concerns, referencing recreational closures, continued expansion of invasive plants, and harm to native fish and other species. The town is waiting for an oral report from a consultant based on sediment samples that may help the committee predict and mitigate blooms, but the data, which was expected earlier this year, is not yet available.
“The goal here is to make the pond more resilient, so that it can tolerate these changes in the ecosystem, and maintain as much of the habitat as possible,” said Leicher. He called the drawdown a piece of the resiliency puzzle. “In the last two years, with the temperature so high, it wasn’t enough. But maybe in the future it will be. We’ll see.”
Bare Hill Pond: A brief history
Bare Hill Pond is not a naturally occurring body of water. While a lake did exist in the area, much of what is now the pond was once pasture. In the 1800s a dam was built between the lake and Bowers Brook to power downstream mills. Water levels were stabilized in the 1920s. Its pastoral past means the sediment at the pond’s bottom is especially rich in nutrients, which may further complicate management of its health.
The town has had a tumultuous history caring for the pond, initially struggling with excessive plant growth, then worsening the problem through chemical treatments and cutting that did more damage to native species than invasives. Leicher said the drawdowns have been effective in controlling unwanted plant growth in recent years, but wrote in the Press column Consider This last summer that the pond may have reached a “tipping point” where increasing temperatures and internal phosphorus loading, paired with runoff from lawns and roads, are overwhelming the mitigating effects of the drawdown.
—Lily Robinson
Lily Robinson will graduate this spring from the University of Massachusetts Amherst with a master’s degree in public policy. She has reported for the Press, first as an intern and then as a freelancer, since the summer of 2020.
