More than 30 years of research in Acadia

Sargent Mountain Pond

More than 30 years of research in Acadia

I have been active in research in Acadia since approximately 1982. I am still publishing the results of the most recent work, which focused on a long sediment core from Sargent Mountain Pond. All of my research has been on the Mount Desert Island portion of the park.

My research has been focused on several aspects:

  • The atmospheric pollution history within the park, with a focus on the last several hundred years;
  • The long-term history of trace metal pollution, particularly mercury and lead, and what controls the pollution levels, both now and in the past;
  • The current chemical climate within the park and the consequences of it in the chemistry of runoff in streams;
  • The role of local weather on the chemistry of surface waters; and
  • What controls the current chemistry of phosphorus in the surface waters of the park, how long these controls are operated, and what influence the processes exert on the mobility of rare earth elements.

Some of my major findings over the course of more than 30 years include:

  • Pollution related to the industrial revolution in the continental United States is measurable in Acadia peat and sediment archives by the late 1800s. Pollution peaked in the 1970–1975 period, and since then has been declining.
  • Mercury and lead pollution have different histories since deglaciation, about 16,700 years ago. Mercury, a naturally occurring metal has been deposited since deglaciation at varying rates; pre-industrial variability is related to variability in the sedimentation rate within lakes, and presence or absence of forests. Forests enhance deposition of mercury from the atmosphere. Virtually all the mercury in Maine is from atmospheric deposition. Conversely, until the industrial revolution, virtually all lead has been derived from the watershed. Variability in rate of accumulation of pre-industrial lead in the sediment is controlled by variation in the sediment accumulation rate. The increase in mercury and lead accumulation rates to peak values (ca. 1975) is approximately 500 percent and 10,000 percent, respectively. Both elements have decreased since 1975; lead the most. Legacy mercury and lead in the watershed soils will continue to be deposited in lakes for many years.
  • The chemical climate of the park is changing as a consequence of changing air pollution. In addition to the reduction in metal pollution, sulfate (the primary culprit in acid rain) has been dramatically declining since at least the mid-1980s and probably by the mid-1970s, because of implementation of the Clean Air Act. Study of the chemistry of the park’s surface waters has been sporadic, both in space and in time, and thus the trajectory of recovery from acid rain is not well described. Recovery from acidification is complicated and will occur over decades.
  • The delivery of sea salt spray from the Atlantic Ocean during storm events causes major depression in the pH — thus, greater acidity — of streams in the park. The most important effect of this pH depression is the mobilization of aluminum from soils and stream sediment — a threat to the health of fish and possibly amphibians. In the last few decades, weather has been characterized by more intense storms that will increase the frequency and possibly severity of pH depressions in streams.
  • Phosphorus is the most limiting nutrient in the surface waters of Acadia. This is in spite of there being abundant phosphorus in the bedrock and soils. We demonstrated that the cause of this impoverishment is the binding of phosphorus by secondary aluminum hydroxide in the soil, as well as in stream and lake sediments. Understanding this role of aluminum in controlling phosphorus availability has its origins, in part, to three studies in the park and a study comparing our results with those from a similar watershed in the Czech Republic. This process of binding phosphorus with aluminum originated after deglaciation as a result of mobilization of aluminum from soil minerals by dissolved organic carbon. The latter results from decay of organic-rich soil produced by forests.
  • Rare earth element mobilization from soils is a function of acidity and is proportional to the amount of dissolved organic carbon, just as for aluminum. This relationship was demonstrated by an analysis of the entire sediment record from Sargent Mountain Pond, with a comparison with a similar lake in the Czech Republic. The chemical behavior of these elements is important to understand because of their use — and disposal — in electronic equipment and batteries.

Acadia National Park, as for all national parks, attempts to minimize anthropogenic disturbances — ranging from visibility to construction of roads and development with associated erosion. One aspect of the park’s environment is that pollution from the atmosphere does not recognize the park’s boundary.

My research has explored natural processes that operate independently of human influence, except for air pollution. The results of the air pollution on the chemical environment, in the absence of physical disturbance, has also been a focus.

The personnel at Acadia National Park are very supportive of science being done and have been extremely helpful in obtaining permits for various activities, and even participate in the activities from time to time. David Manski, who is now retired, was particularly important to our successes.

For some people, just an understanding of history is a pleasant goal. My paleolimnological studies (aided by colleagues) in the park describe the trajectory of the physical and chemical evolution of the surface waters for one lake that is representative of many lakes in the park.

Other people may have an interest in modern processes that determine water quality, in the absence of disturbances in the watershed of lakes. This understanding grows from both the modern chemical studies and the short historical paleolimnological studies.

Air quality in the park has been, and remains, a significant problem. But our studies reveal that air quality has improved measurably in the last few decades, both with respect to sulfate and trace metals, especially mercury and lead. The long-term sediment record helps us understand what background values look like, an important piece of the puzzle, because actual measurements of these contaminants only span the last few decades. We now know that our society has nearly solved the lead problem in natural environments; mercury will follow.

Controls on phosphorus, a major component of biological productivity, are naturally occurring, but they can be overwhelmed by human activity. The aluminum-phosphorus studies have helped to unravel why some lakes are highly productive (algae-rich or eutrophic) and others are unproductive (oligotrophic). The studies lead to better understanding of how resilient lakes are, based on factors that include changing physical climate, sediment chemistry, lake morphometry, and watershed characteristics. They also aid stakeholders in how to best protect lakes.

Lastly, several dozen undergraduate and graduate students, many of them from Maine, cut their scientific teeth on these studies in a remarkably beautiful part of the world. Sometimes while performing field work in the park, I had to convince myself that I was being paid to do it. Data from the studies were commonly exploited by my students not just for theses but for class projects in my graduate-level geochemistry. So the park became part of my classroom.

Stephen Norton is a Distinguished Maine Professor and professor emeritus in the School of Earth and Climate Sciences with a cooperating appointment in the Climate Change Institute

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