NSF CAREER award:
Resident bacteria may help clean phosphorus from eutrophied lakes
 n recent years, city of Madison residents have
focused new attention on water-quality problems ranging from beach closings
to unsightly, odoriferous blue-green algae blooms caused by an overload
of phosphorus within area lakes. In reality, those problems began in
the city more than a century ago. They originated in an era when “wastewater
treatment” meant dumping largely untreated sewage back into the
lakes, says Assistant Professor Katherine
McMahon. “Phosphorus is something that, once it gets
into the lakes, it’s very hard to get out,” she says.
Recipient of a prestigious $400,000 National Science
Foundation CAREER award, which provides funding to early-career faculty
for creative projects that effectively integrate research and education,
McMahon will use her expertise in wastewater engineering and in biological
systems to study the bacterial community in dissimilar eutrophied lakes—two
in Madison and one in China—to learn more about how those bacteria
affect phosphorus cycling in the lakes.
In eutrophied lakes, or those contaminated with excess
nutrients, phosphorus generally is trapped in the sediments at the bottom.
In spring, the lake “turns over” and the phosphorus becomes
a major ingredient in that giant, oxygen-rich mixing bowl. It’s
a recipe for an algae bloom.
In summer, cooler water far below the lake surface
traps phosphorus on the lake bottom, where McMahon’s previous
research suggests that bacterial communities release it in a biological
process similar to that which is responsible for enhanced biological
phosphorus removal, or EBPR, a method often used during wastewater treatment.
In fact, McMahon will use new tools in molecular
biology and recent research advances that apply to EBPR processes to
help her develop hypotheses about how phosphorus is released into the
water column by bacteria during the summer, and taken up during the
spring and fall.
Traditionally, limnologists who study lake phosphorus
group bacteria into a single “black box,” says McMahon.
Conversely, she seeks to identify specific bacterial populations present
within eutrophic lakes, learn how those populations respond to changing
lake conditions, and learn how they work as a community to cycle phosphorus.
For three years, she will collect weekly bacteria
samples in multiple locations from Madison Lakes Mendota and Wingra
during ice-off seasons and monthly samples when the lakes are frozen.
Likewise, her collaborator, Guang Gao of the
Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,
will sample Lake Taihu, a large, shallow lake in Jiangsu Province, China,
that supplies drinking water to 40 million people in Shanghai and surrounding
cities. “We are looking at the relationship between what types
of bacteria are present and the availability of phosphorus in the water,”
says McMahon.
She and her students also will incubate water samples
in the laboratory. In one experiment, they will add radioactive phosphorus
that will help them track which bacteria are responsible for phosphorus
recycling. Ultimately, McMahon hopes her research will contribute to
a future solution to excess phosphorus in any lake. “Eutrophication
of fresh-water lakes is a problem everywhere in the developed world,
and in many developing countries as well,” she says.
Working with graduate students
Ashley Shade and Ryan Netwon, UW-Madison
Center for Biology Education Outreach Program Director Robert
Bohanan, and staff in the UW-Madison Center for the Integration
of Research, Teaching and Learning, McMahon will expand her current
middle-school outreach activities, which include activities that inspire
students to think like environmental engineers, to include inquiry-based
activities based on phosphorus-driven eutrophication. In addition, she
will develop a three-week summer workshop on microbes and water quality
for underrepresented high school students who participate in the UW-Madison
Pre-college
Enrichment Opportunity Program for Learning Excellence (PEOPLE) program.
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