U.S. Water News Online
MADISON, Wis. -- Farmers' routine application of chemical
fertilizers and manure to the land poses a far greater environmental
problem to freshwater lakes than previously thought, potentially
polluting the water for hundreds of years, according to new research.
Phosphorus in those substances has built up in the soil and will
slowly end up in many lakes, where the nutrients lead to plant and
algae growth. The environmental problem, known as eutrophication, can
turn pristine lakes into smelly, weed-filled swamps with lots of dead
In a paper published in the Proceedings of the National Academy of
Sciences, a University of Wisconsin-Madison expert blames the buildup
largely on industrial agriculture's excessive use of fertilizer and
manure since the 1940s.
The concentration could cause the eutrophication of lakes for
centuries as the treated soil slowly washes into lakes and streams,
writes Stephen Carpenter, a professor of zoology and a leading expert
on freshwater lakes. The problem leads to fish kills and the growth
of toxic algae that can make lakes unsuitable for swimming.
"A very small percentage of the phosphorus moves into the lake
each year and that small amount is sufficient to cause a great deal
of water pollution," Carpenter said.
Paul Zimmerman, executive director of governmental relations for
the Wisconsin Farm Bureau Federation, said he hadn't seen the report,
but he defended farmers, saying they've improved soil conservation
over the last two decades to make sure more dirt remains in place.
Dams have made lakes more stagnant, exacerbating pollution, he said.
"You can't blame all eutrophication on agriculture," Zimmerman
said. "Each year we're getting better and better. The eutrophication
of lakes didn't happen overnight and it's not going to be solved
The study concludes that major changes in soil management are
needed to reverse the trend. It may add urgency to government efforts
to stop phosphorus from fouling up lakes and streams.
Carpenter studied Lake Mendota, an urban lake in the Madison area
that is a popular recreation and fishing spot, as a model for all
freshwater lakes in rich farming areas. He said the lake's water
quality has declined in recent decades, which will continue if left
Carpenter said machines called manure digesters should be used to
convert phosphorus into a sludge that can be put in landfills or
transferred to phosphorus-deficient areas. He also said buffer strips
should be developed to protect waterways from runoff and new
technologies found to remove phosphorus from soil.
"If we don't do something," Carpenter said, "the water quality
will get considerably worse, the lake will smell bad, there will be
algae blooms all summer long, and more and more of those blooms will
be the toxic kind."
Zimmerman said few farmers can afford manure digesters, which can
run about $1 million apiece. Most in Wisconsin are found only on
farms with 1,000 or more cows. "It's way too expensive," Zimmerman
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