|
|
BGSU biologists Drs. George Bullerjahn, Scott Rogers and Michael McKay have received a $14,300 grant from the Ohio Lake Erie
Commission's Lake Erie Protection Fund that will allow them, along with collaborators from the University of Tennessee and
Clarkson University, to spend six days conducting a winter assessment of Lake Erie microbiology in February. This will kick
off a three-year study of winter lake production, with the final two years of support coming from a recently announced award
of $108,000 from the Ohio Sea Grant College Program at Ohio State University.
The upcoming trip will be double the length of a 2007 foray during which they discovered widespread algal blooms thriving
in the ice-covered lake. These blooms could be connected to the formation of the lake’s recurrent summer dead zone. The researchers’
goal is to close the knowledge gap between the lake’s winter and summer conditions. They will build upon discoveries made
last February, as they seek answers to the question, “What microbes are in the lake in the dead of winter, and what are they
doing?”
What they learn could help guide policy-makers and environmental scientists manage the lake more effectively.
“We have long known about oxygen loss in the lake’s central basin in the summer months,” said McKay, the Ryan Professor of
Biology. “It is of concern because this oxygen loss ultimately can fuel the proliferation of harmful algal blooms. Phosphates,
mainly from fertilizers, get washed into the lake during spring and summer. When there is enough oxygen present, the phosphates
are bound in the sediments, but under conditions of oxygen depletion, they can be reintroduced into the water column and promote
the growth of harmful algae such as Microcystis. Oxygen loss can also result in loss of habitat to benthic macrofauna, such as mayflies. By extension, this reduces one of
the lake’s food sources for its fish. If persistent, this oxygen loss and resulting bacterial production can also lead to
noxious gas emissions, which most people will notice as a ‘rotten egg’ smell.”
Based on observations made during their February 2007 assessment of Lake Erie, the team of scientists hypothesized that the
oxygen loss in the lake during summer is not solely rooted in activity occurring in the spring and summer months.
“We have been surveying the microbial content of the lake in summer since about 2000, but there had been very few winter studies
done since the 1940s,” McKay said. “On our initial winter trip in February 2007, we coordinated plans through Environment
Canada, a federal agency whose mandate is similar to the Environmental Protection Agency’s, to spend three days on a Canadian
Coast Guard icebreaker that normally escorts ships on Lake Erie in winter. While doing basic winter monitoring, we observed
large, discolored areas under the ice–it looked as if someone had poured vats of coffee on areas of the ice.”
Breaking through the “colored patches” on the ice, the BGSU researchers discovered healthy, robust blooms of algae called
diatoms. Areas both below and within the ice contained high concentrations of algal and bacterial biomass that they termed
CACHEs–Concentrated Algal Community and Heterotrophic Ecosystems.
“We collected samples, brought them back for analysis, measured their photosynthetic rates and compared the winter rates to
the summer rates from our previous summer research,” McKay said. “The maximum photosynthetic rates of the winter algae samples
rivaled that measured in the summer, which means it is possible that the amount of carbon produced in the winter could equal
that produced in the summer.”
During the 2008 expedition, McKay and Bullerjahn will extend their research, enumerating CACHEs, measuring their size and
sampling the algae to measure photosynthetic rates.
“This year, we will start with an aerial survey, flying from Toledo to Buffalo, N.Y., at a height of 500 feet,” Bullerjahn
said. “This will give us a better idea of how abundant and how dense the CACHEs are and will guide the route we then take
with the icebreaker. We’ll employ molecular tools for fine structural analysis of winter versus summer algae. By combining
our knowledge of summer and winter activity in Lake Erie, we hope to be able to develop a more comprehensive carbon budget
for the lake.”
Bullerjahn and McKay were involved with previous studies of Lake Erie that revealed how misleading the term “dead zone” is.
Studies completed from 2002-05 revealed that Lake Erie’s so-called dead zone actually was abundantly populated by microscopic
picoplankton and bacteria. While miniscule in size, their collective mass outweighs any other organism in the lake, making
them an incredibly important link in the lake’s food chain.
Just as these picoplankton and bacteria play a key role in the lake’s ecosystem, so does the algal activity that occurs in
the heart of winter.
“To support the existence of the dead zone in which the bacteria thrive, algal blooms must die, sink to the bottom of the
lake and decay to deplete the lake’s oxygen content,” Bullerjahn said. “We now believe a lot of this activity might have a
wintertime origin. A lot of the algal production that occurs in the spring and summer gets recycled at the water’s surface,
so it never reaches the bottom. Wintertime production is dominated by large, heavy diatom algae that are exported to the bottom
waters with high efficiency. Reduced zooplankton grazing expected during the winter further means that more of the biomass
produced near the surface ends up at the bottom of the lake.
“If we can study the mass of plankton, nutrient geochemistry and plankton productivity in winter, we can develop models that
incorporate situations that impact hypoxia (low oxygen) in summer. Thus, we will be able to predict ecosystem response more
accurately, which will fuel better ecological forecasts and thus better management decisions.”
|
|
