Uncovering Adirondack lakes’ hidden histories

By extracting cores from lake bottoms, University at Albany researchers uncover a story of pollution and recovery that spans centuries

By Zachary Matson

At the bottom of an Adirondack lake, the top and most recent layer of dead and decaying plants, algae and all manner of material that has washed in is wet and fluffy. 

As scientists probe just 10 centimeters down, they are examining evidence from the 1980s or 1990s. Go deeper and the sediment becomes more compacted and the years fly by. A full meter of sediment represents about 1,000 years of lake history, enabling scientists to examine the conditions of lakes before modern human activity.

To those with the right know-how and a properly-equipped lab, a lake’s sediment is a time capsule waiting to spill the secrets of past climatic conditions and environmental changes over time. 

Researchers at University at Albany’s Paleoclimatology Lab in recent years used this sediment to document how a small set of Adirondack ponds recovered from intense heavy metals pollution during the era of acid rain.

Sitting in a boat over a lake’s deepest section, they dropped plastic tubes down to the sediment to collect the cores that archive the lake’s history, attempting to peer back in time through centuries and millennia past.  

“When we are in the boat, we don’t know how far back in time we are,” said Aubrey Hillman, a professor at the University at Albany who specializes in studying lake sediments. “We try to get everything we can and figure it out later.”

The field is a unique mix of hard science, challenging field work and the archival research more typical of historians. To help flesh out their chronologies, researchers study first-person accounts of local disturbances like fires and floods, examine fish stocking records, talk to local history buffs and anything else to help understand what has affected a lake’s life history — and what might explain the chemical changes they observe in the sediments.  

Hillman said she likes the finesse of lab work paired with the physicality of the field work. She said it’s hard to beat the satisfaction of eyeing a core on the water. 

“You pull it up and get to see something that potentially no one has ever seen before,” Hillman said.

Charting the effects of human activity

From the earlier baseline, the changes wrought by industry and accelerating human activity are stark. Sky Hooler is a graduate student under Hillman who earlier this summer published a paper examining the lakes’ recovery. Charts in Hooler’s paper recording the presence of heavy metals—chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, cadmium and lead—show dramatic spikes in the 20th century, followed by a fall back to nearly pre-industrial levels. 

The study focused on four Adirondack lakes: Challis Pond near North Hudson; Black Pond at the Paul Smith’s VIC; Rat Pond near Saranac Inn; and Little Hope Pond near Lake Kushaqua. 

In Challis Pond, for example, lead concentrations increased more than 200 times background levels. Those spikes mirror historical coal combustion and leaded gasoline use, peaking around 1980. By 2020, all of the concentrations of heavy metals in Challis had dropped by at least 90% from their highs. The core from Black Pond showed a surge in heavy metals around 1891 associated with a large fire in the watershed, before the much more significant peak of metals connected to industrial activity.   

“Once humans settled the area and started to influence it, we see a drastic increase [in heavy metal concentrations],” Hooler said. “Around 1900 is where we see the shift happen, it’s small at first and then it takes off.” 

While other scientists through a network of monitoring programs have documented the gradual recovery of Adirondack lakes from acidification in the wake of more stringent restrictions on the power plants that induced acid rain, Hillman and Hooler went a step further to document the full trajectory of a lake’s recovery from the heavy metal pollution at the heart of acidification.

The cores from Adirondack lakes aren’t much to look at, at least compared to cores from other lakes around the world. While the Adirondack cores are a consistent dark brown, puddling-like texture throughout, other cores have complex striations, mixes of sand, clay and other sediment types. 

“But the Adirondack cores are the most chemically interesting,” Hillman said. “It’s not until you actually look at the chemistry that you realize how interesting they are.” 

Hillman has talked to leaders of the Study of Climate and Adirondack Lake Ecosystems survey of hundreds of lakes across the park. She hopes to take cores from some of the most intensively studied of the survey lakes after multiple years of continuous data collection. Hillman could then match the sediment record to the data record and help characterize thousands of years of environmental changes. 

Other applications: Charting the rise of toxic algal blooms

Hillman returned to Black Pond earlier this summer with a different graduate student, Sumar Hart, to collect another core for Hooler, this one focused on patterns of algae growth in the lake. 

As officials grapple with the consequences of harmful algal blooms, scientists are racing to understand their impacts and the extent to which they are increasing. By examining concentrations of chlorophyll in the sediments, Hillman and her students hope to document the extent of algal growth over time. 

Using a sturdy inflatable boat, Hillman and Hart paddled to the same spot they collected cores for the heavy metals study in 2022, dropped anchor and went about the precise, though at times makeshift, work of filling a plastic tube with hundreds of years of algae data encased in mud. 

After returning to shore, Hillman and Hart carefully extruded the sediment core, a half centimeter at a time, into plastic bags that were labeled and packaged on ice for the trip back to campus.

Putting the pieces together

Housed inside UAlbany’s new ETEC building, which also includes the school’s emergency preparedness and weather forecasting programs, the paleoclimatology lab enables Hillman and her students to piece together the puzzle of the sediment cores. A machine with a plasma coil as hot as the sun can measure concentrations of 28 elements in the sediment samples, including the heavy metals Hooler investigated. 

Hillman still has to send samples to outside labs to help build their timelines. Picking through the sediment core, the researchers remove organic material like twigs and pieces of charcoal that can be dated. Pop a handful of those known dates into a model, and they can start to align the data on metals and other chemistry in the core to actual dates in time. 

“It’s the most important step,” Hillman said. “You live or die on an age model.”

To pull out chlorophyll concentrations, Hillman took the samples collected at Black Pond and freeze dried them to remove all the water content. After mixing the powdery sediment remains with acetone to help liberate the chlorophyll, Hillman ran the samples through seven different wavelengths of light in a spectrophotometer to generate the proxy for algae activity. 

The small field of paleoclimatologists who study lake sediments—Hillman’s lab co-director studies coral reefs—are working to understand how the current climate is changing and will change by looking into the past. 

“We can understand what did this lake look like when it was warmer, or what did it look like when there was more precipitation?” Hillman said. “It’s not a perfect analog, but it can give us some insight into what the lake will do going into the future.”

Top photo: University at Albany Assistant Professor Aubrey Hillman and Graduate Research Project Assistant Sumar Hart collect lake sediment samples for climate-related research at Black Pond in the Adirondacks on Tuesday, June 3, 2025. Photo by Patrick Dodson, UAlbany