Queen's University

What Lies Beneath: PEARL

Many people know the sensation of stepping into a lake and having their feet sink into its floor. But have you ever stopped to consider what is contained in the lake bottom that starts to creep up between your toes? You may be fascinated to know that this sediment contains a microscopic ecological archive that can reveal the impacts of human and natural activity dating back hundreds, even thousands, of years.

It is this sediment, and the many fossils it contains, that members of the Paleoecological Environmental Assessment and Research Lab (PEARL) at Queen’s use to study longterm changes in lake characteristics. Co-directed by Professors John Smol and Brian Cumming, PEARL is a group of about 30 research scientists, post-doctoral fellows, and graduate and undergraduate students. They use innovative paleolimnological and other scientific techniques, such as core sampling and sediment analysis of biological indicators (e.g. fossils), to reconstruct the long-term history of lake systems − ultimately bringing the impacts of human activities on ecosystems and the environment to the surface.

PEARL’s early international recognition grew in part from their scientific work on acid rain in the late 1980s and early 1990s. Key to the acid rain debate was the search for proof that many lakes did not naturally acidify, but instead acidified as a result of industrial activity. A historical record was required to confirm this, but one did not exist – no one kept records of the acidity of the lakes in question in the 1800s (the pH scale was only invented in 1909), so the only way to chronicle acidity was through indirect methods. That is when PEARL entered the scene. Although paleolimnology was still a relatively young and qualitative science at this time, new knowledge in the field allowed PEARL to develop new methods (e.g. refined core-sampling devices, development of new biological indicator groups) that moved paleolimnology into a quantitative and precise science. Their research on acid rain was conclusive − the vast majority of lakes were not naturally acidic and had indeed acidified due to human influence.

What is paleolimnology?

From the Greek paleo (old) + limne (lake) + logos (study), paleolimnology is a scientific discipline concerned with reconstructing the environmental histories of inland lake waters. Using a wide range of approaches, including the study of sediments, erosional features, fossils, and geophysical data obtained from surveys of lake floors, paleolimnologists ascertain how lakes have responded to human impacts and to patterns of global change.

PEARL’s pioneering paleolimnological methods have been adopted by researchers studying lakes around the world, and they have been seamlessly applied to an array of issues, such as eutrophication (excessive lake “nutrition”), fisheries management, calcium decline, contaminant transport to remote locations, and climate change. The results of PEARL’s studies can be surprising and sometimes even controversial. For example, the lab has shown that European settlers were not the first humans to cause major changes to Canadian and US freshwater ecosystems, but that eight centuries ago, prehistoric Inuit whalers dramatically altered High Arctic pond ecosystems through their hunting practices. In another example, they found that potentially toxic metals, like mercury and lead, ingested by Arctic seabirds feeding in the ocean, end up in the sediment of polar ponds and can affect the local ecosystem. More recently, in January 2013, members of the group published a paper in Proceedings of the National Academy of Sciences USA on the long-range impacts of oil sands development in northern Alberta, and the potential long-term effects on northern aquatic ecosystems. This study made headlines around the world the day it was released.

“For almost every environmental issue, you need a historical perspective showing natural versus human impacts,” Smol says. “Using scientific methods we can identify that a problem does indeed exist and we can determine the trajectory of the problem. History is the key that can provide information on how best to deal with today’s issues.”

When asked what inspires the work of PEARL, Smol passionately explains, “We live on a beautiful planet. Why should we give that up when we don’t have to? No one is saying that everything is caused by humans, even climate change, and we know that. But the issue is: how much is caused by humans? And what is the part we can control and change.”

  • [Photo of lake sediment]
    Layers of lake sediment are removed or “sectioned” at intervals (typically 0.5 or 1.0 cm) from a core sample. In a laboratory, contaminants and biological remains are analyzed from select layers to understand lake history and to “reconstruct” environmental change.
  • [Photo of water flea]
    An example of Daphnia, commonly known as the water flea. Daphniids are important grazers of algae and are eaten by fish, waterfowl, and larger invertebrates.
  • [Photo of algal cells]
    Fossil remains such as the tiny algal cells (highly magnified) in the image above are preserved in each layer of sediment and, once analyzed, can tell a history of past environmental change.
  • [Photo of arctic terns]
    Arctic terns (Sterna paradisaea) have the longest yearly migration of any bird species, some covering ~80,000 km annually. Metals and other contaminants accumulated while they feed are ultimately deposited near their nesting sites, sometimes to toxic levels. Sediment cores can be used to track seabird inputs over the long term.
  • [Photo of a whale skeleton]
    This image shows a whale skeleton abandoned by prehistoric Inuit whalers, whose hunting practices dramatically altered High Arctic pond ecosystems eight centuries ago.

Profile by Melinda Knox
(e)Affect Issue 4, Fall 2013