Clean Air Act Helped Reduce Metal Pollution in Adirondack Waters by 90%, Study Finds

University of Albany researchers have presented the first recorded evidence that surface waters in the Adirondack Mountains have made an almost complete recovery — 90 percent — from metal pollution since enactment of the Clean Air Act.

Amended in the decades since it first passed in 1963, the Clean Air Act was one of the United States’ first environmental laws and was intended to lower and control the country’s air pollution.

One of the primary targets of the legislation was Adirondack Park, which had been impacted by decades of acid rain damage to the region’s forests, lakes and fish populations, a press release from the University at Albany (UAlbany) said.

Sky Hooler holds up a sediment core sample collected from Heart Lake in the Adirondack Mountains. University at Albany

“The Adirondacks have been a special place to me since I moved to the region when I was 10 years old. As a kid, I learned about the devastating effects acid rain had on the lakes, rivers and wildlife,” said Skylar Hooler, first author of the study and a doctoral student in the Department of Atmospheric and Environmental Sciences at UAlbany, in the press release. “During my first year of graduate school, I began reviewing the literature and was surprised to find that most recent studies evaluating recovery from metal pollution in the Adirondacks were more than a decade old. I immediately saw an opportunity to revisit this and document how well these ecosystems have recovered since the implementation of the Clean Air Act.”

The researchers analyzed historical data along with newly collected sediment samples and found that metal contamination across four Adirondack ponds had been reduced more than 90 percent over the past five decades.

Hooler’s research partner was Aubrey Hillman, an assistant professor in UAlbany’s Department of Atmospheric Sciences, whose research is focused on using lake sediments — more commonly known as mud — to study past human activities and climate change.

So proud of how hard my PhD student worked on this! And importantly it shows that legislation can WORK.

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— Aubrey Hillman (@mountains-arose.bsky.social) April 9, 2025 at 9:51 AM

Hillman co-leads UAlbany’s Paleoclimate lab, which provided the research team with instruments to collect and analyze lake sediment and coral. The samples offered clues about our planet’s past climate conditions and how they relate to present and future climate trends.

“Collecting a sediment core is like taking a layered history book from the bottom of a lake,” Hooler explained. “Each layer of sediment represents a moment in time. We use specialized coring tools to extract these long, cylindrical records from the lake bed. The goal is to preserve the layers in the exact order they were deposited, so we get an uninterrupted timeline of environmental change that can stretch back thousands of years.”

The team used sediment cores taken from the four ponds to measure concentrations of metals such as lead, zinc and copper across millenia.

The sediment cores offered the researchers a look into pre-industrial baseline conditions, which allowed them to evaluate the extent of pollution, as well as the success of later recovery efforts, such as the Clean Air Act.

“Site selection was strategic,” Hooler said. “First, we had to ensure the lakes were on land we could legally access. Then, we prioritized lakes with similar hydrology and a consistent watershed-to-lake area ratio to allow for better comparisons. Finally, we looked at historical land-use impacts. Some lakes experienced extensive logging, others fire, and some were relatively undisturbed, so we could better understand how these factors influence both contamination and recovery.”

The Clean Air Act was a major factor in pollution reduction, but Hooler feels the recovery of Adirondack surface waters was largely formed by interactions between local watershed processes and lower emissions.

“Many lakes show peak metal deposition between 1970 and 1990, which aligns with the phased implementation of the Clean Air Act and its amendments,” Hooler said. “However, recovery also reflects local factors, like proximity to pollution sources and prevailing wind patterns. So, while the Clean Air Act laid the foundation, the response in each lake depended on its specific environment.”

The findings of the study, “Five decades after the Clean Air Act, legacy metal contaminants in Northeast U.S. surface waters document full recovery for the first time,” were published in the journal Environmental Pollution.