Studying Sargent Mountain Pond, Maine's First Lake

Sargent Mountain Pond. Used with permission Catherine Schmitt, Schoodic Institute

Background

Sargent Mountain Pond, located between the summits of Penobscot and Sargent mountains 1,200 feet above sea level, is believed to be the first lake that appeared on the Maine landscape after the last Ice Age some 16,600 years go. According to Dr. Stephen Norton of the University of Maine, given the mountain’s elevation and location near the southern edge of the melting glacier, Sargent Mountain Pond was present for at least 100 years before their Maine lakes appeared. This means that the sediments in the bottom of the lake represent thousands of years; reconstructing this history allows scientists to draw conclusions about the relationship between climate, land cover, and water quality.

Project Status

Sargent Mountain Pond is oligotrophic: clear, nutrient-poor, and naturally acidic. Like other high-elevation lakes, it is especially sensitive to change. The sediment in Sargent Mountain Pond, because of its position high up on the mountain without any streams flowing into it, can be considered an accurate reflection of the small surrounding watershed, in addition to whatever is carried in by rain, snow, and dust, including pollutants like acid rain, lead, and Mercury. Stephen Norton began studying Sargent Mountain Pond in 1983, when he extracted a half-meter core from the lake bottom and found that the pH of the pond was an acidic 4.6, a result of excess sulfate deposited from acid ain. Norton returned to the pond in 2007 to sample a much longer/ deeper core from the lake bottom, not only to look at pH but also climate, land cover, and toxic metals that are deposited from the atmosphere.

Researchers auger through the ice. Photo by Catherine Schmitt, Schoodic Institute; used with permission.

Research Methods

In March 2007, Norton and a group of scientists and students from the University of Maine hiked the icy, steep trail to the pond. They carried the heavy equipment needed for extracting and transporting a five-meter core of the lake bottom. Using the frozen the pond as a level surface, they drilled until they hit bedrock, the bottom—and beginning—of the pond. Sections of the core were wrapped in plastic and foil, placed in a specially prepared box with cushioned walls, and carried back down the mountain and along Route 1A to the University of Maine laboratories, where the core was sliced up and divided among the researchers. The Sargent Mountain Pond project is a multi-proxy study: each scientist examined a different aspect of the core according to their expertise. Anything preserved in lake sediments—a fragment of fossil, a grain of pollen, a band of minerals—can be used to reconstruct the landscape history of Acadia. Each used a different language to tell the pond’s story, but all worked from the same core. Through a shared language of time and place, the very different disciplines found common ground, and together they narrate a history of Maine from a single location

Project Results

The story begins 16,600 years ago, when Sargent Mountain was a nunatak, an island in the ice. The receding glacier had scraped the mountain clean, and meltwater and any rain sent a flush of silt or “rock flour” into the 30-foot depression between Sargent and Penobscot peaks. The rock flour, which Ph.D. student Randall Perry viewed as a layer of dark gray clay at the bottom of the core, contained minerals from the surrounding granite, including feldspar and apatite, a crystallized mineral form of phosphorus, an important nutrient for plants.

Jasmine Saros is a paleolimnologist who looks at microscopic algae called diatoms to infer changes in lake biology over time. Diatoms are single-celled microscopic algae encased in a shell made of hard, glass-like silica; when they die, the shells stay preserved in the bottom of the lake. Like snowflakes, each species has a unique shell design, and each species is indicative of certain water quality conditions. Brought to the newly exposed Sargent Mountain Pond by wind or birds, the early diatoms thrived in an alkaline and productive environment created by the minerals in the rock flour that was flushed into the lake by rain and melting snow.

By analyzing pollen grains in the core, George Jacobson was able to show the gradual emergence of vegetation within and around the pond: 14,900 years ago, while the first diatoms bloomed in the lake, tundra plants like sedges and willows arrived on the mountain. A few thousand years later, scattered spruce trees eventually grew into a mature forest of spruce and jack pine. Runoff into the lake slowed as plants became established over the course of 4,000 years, converting phosphorus into leaves, roots, and soil, as confirmed by soil scientist Ivan Fernandez. With less phosphorus and buffering minerals unavailable, the pond became more acidic.

Working where the lines between biology, geology, climatology, and chemistry blur, the Sargent Mountain Pond research team has provided a glimpse of what happens on a northern landscape when a glacier leaves. Around the world, from Montana to Greenland to the Himalayas to the Andes, mountain glaciers are melting at rates that can be witnessed in a human lifetime. In the short term, the effects are manifested in water quantity and quality; in the long term, changes in the land regulate carbon dioxide in the atmosphere. Results from studies like the one at Acadia can help people anticipate the changes unfolding around them, and know what to expect from the lakes, rivers, and oceans of the place they call home.

Authored by CATHERINE SCHMITT, science communication specialist at the Schoodic Institute at Acadia National Park.

---