Climate-Ecosystem Threshholds Reached in Temperate, Alpine, & Arctic Lakes

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“The widespread occurrence of these trends is
particularly troubling as they suggest that
climatically-induced ecological thresholds have
already been crossed, even with temperature
increases that are below projected future warming
scenarios for these regions.”
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Queen’s University
Public release date: 16-Dec-2008

Contact: Nancy Dorrance
nancy.dorrance@queensu.ca

Study links ecosystem changes in temperate
lakes to climate warming

Unparalleled warming over the last few decades
has triggered widespread ecosystem changes in
many temperate North American and Western
European lakes, say researchers at Queen’s
University and the Ontario Ministry of the
Environment.


The team reports that striking changes are now
occurring in many temperate lakes similar to
those previously observed in the rapidly warming
Arctic, although typically many decades later.
The Arctic has long been considered a
“bellwether” of what will eventually happen with
warmer conditions farther south.

“Our findings suggest that ecologically important
changes are already under way in temperate
lakes,” says Queen’s Biology research scientist,
Dr. Kathleen Ruhland, from the university’s
Paleoecological Environmental Assessment and
Research Lab (PEARL) and lead author of the study.

The research was recently published in the
international journal Global Change Biology. Also
on the team are Biology professor John Smol,
Canada Research Chair in Environmental Change,
and Andrew Paterson, a research scientist at the
Ontario Ministry of the Environment and an
adjunct professor at Queen’s.

One of the biggest challenges with environmental
studies is the lack of long-term monitoring data,
Dr. Ruhland notes. “We have almost no data on how
lakes have responded to climate change over the
last few decades, and certainly no data on longer
term time scales,” she says. “However, lake
sediments archive an important record of past
ecosystem changes by the fossils preserved in mud
profiles.”

The scientists studied changes over the last few
decades in the species composition of small,
microscopic algae preserved in sediments from
more than 200 lake systems in the northern
hemisphere. These algae dominate the plankton
that float at or near the surface of lakes, and
serve as food for other larger organisms.

Striking ecosystem changes were recorded from a
large suite of lakes from Arctic, alpine and
temperate ecozones in North America and western
Europe. Aquatic ecosystem changes across the
circumpolar Arctic were found to occur in the
late-19th and early 20th centuries. These were
similar to shifts in algal communities,
indicating decreased ice cover and related
changes, over the last few decades in the
temperate lakes.

“As expected, these changes occurred earlier-by
about 100 years-in highly sensitive Arctic
lakes, compared with temperate regions,” says Dr.
Smol, recipient of the 2004 Herzberg Gold Medal
as Canada’s top scientist.

In a detailed study from Whitefish Bay, Lake of
the Woods, located in northwestern Ontario,
strong relationships were found between changes
in the lake algae and long-term changes in air
temperature and ice-out records. The authors
believe that, although the study was focused on
algae preserved in lake sediments, changes to
other parts of the aquatic ecosystem are also
likely (for example algal blooms and deep-water
oxygen levels).

“The widespread occurrence of these trends is
particularly troubling as they suggest that
climatically-induced ecological thresholds have
already been crossed, even with temperature
increases that are below projected future warming
scenarios for these regions,” adds Dr. Paterson.
The authors warn that if the rate and magnitude
of temperature increases continue, it is likely
that new ecological thresholds will be surpassed,
many of which may be unexpected.

“We are entering unchartered territory, the
effects of which can cascade throughout the
entire ecosystem,” concludes Dr. Smol.

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The research was funded by the Natural Sciences
and Engineering Research Council of Canada, and
the Ontario Ministry of the Environment.

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