Climate change is expected
to increase the frequency of intense spring rain storms in the Great Lakes
region throughout this century and will likely add to the number of harmful
algal blooms and “dead zones” in Lake Erie, unless additional
conservation actions are taken, according to a University of Michigan aquatic
ecologist.
Climate models suggest that
the number of intense spring rain storms in the region could double by the end
of the century, contributing to an overall 30 to 40% increase in spring
precipitation, says Donald Scavia, director of the U-M’s Graham Sustainability
Institute.
That increase, combined
with the greater availability of phosphorous due to current agricultural
practices in the Midwest, means that increased amounts of the nutrient will be
scoured from farmlands and run into rivers that feed Lake Erie, fueling algae
blooms and low-oxygen zones known as dead zones.
“Climate change is
likely to make reducing phosphorous loads even more difficult in the future
than it is now, which will likely lead to even more toxic algae blooms and
larger dead zones unless more conservation is undertaken,” says Scavia,
who will present his latest findings on the topic at Great Lakes Week events in
Cleveland.
“Current agricultural
practices and climate are conspiring to increase the phosphorous loads that
make their way into Lake Erie,” says Scavia, a professor at the U-M School
of Natural Resources and Environment.
The agricultural practices
that contribute to increased availability of phosphorous from fertilizer
include no-till farming, a method of planting crops without plowing. The
technique reduces soil erosion but also leaves “high concentrations of
phosphorous in the upper surface soil, and these intense storms appear to be
flushing it out,” Scavia says.
The widespread adoption of
no-till farming and other agricultural techniques since the mid-1990s have had
some positive effects but appear to have also increased the availability of the
type of phosphorous, known as soluble reactive phosphorous, that promotes algae
blooms, Scavia says.
Since the mid-1990s,
intense spring rain storms have also become more common in the Great Lakes
region, especially in southeast Michigan and northwest Ohio, the regions that
provide runoff into Lake Erie, Scavia says.
Current agricultural best
management practices—such as planting buffer strips around cropland, protecting
wetlands and using less fertilizer—applied at the current scales are likely
“not going to be sufficient to reduce the phosphorous loads to the levels
we need to prevent the blooms and to get rid of the dead zones,” Scavia
says.
In the late 1960s, 1970s,
and early 1980s, control strategies focused on reducing phosphorous from
specific sources, such as waste-treatment plants. Reductions from those
so-called point sources led to major gains in Great Lakes health, including a
drop in the frequency and extent of harmful algae blooms and dead zones.
Some of those gains have
been reversed since the mid-1990s. The increased availability of soluble
reactive phosphorous and a surge in extreme rainfall events in the region have
contributed to a resurgence of both harmful algal blooms and dead zones in Lake
Erie, Scavia says.
Algae blooms can foul
harbors, clog boat motors, reduce fish populations, and can sometimes be toxic
to humans. Dead zones are low-oxygen regions where most aquatic organisms
cannot survive.
Source: University of Michigan
