Urban dead seas—road deicers, fertilizers and the dynamics of urban lakes
by Olga Bonfiglio
College of Arts and Sciences Staff Writer
As if climate change weren’t enough to worry about, what goes on below the
surface of our lakes threatens fresh water for ourselves and the plants and animals
who live it.
Dr. Carla Koretsky, dean of the Lee Honors College, donned her geosciences
professor hat on February 9 to present her research on the dynamics of
contaminants residing in three local lakes at the college’s “Our Blue Marble” Lyceum
series held every Wednesday at noon.
Koretsky’s research team of geosciences graduate and undergraduate students
collected data on the effects of algal blooms in Asylum Lake (20 hectares) and
Woods Lake (10 hectares) in Kalamazoo and rural Brewster Lake (5 hectares) in
Barry County over the past five or six years.
What they found was excess nutrient loading of phosphorus and nitrogen ending up
in the lakes with possible sources including sewage, detergents, agricultural run-off
(fertilizers and animal manure) and residential run-off (fallen leaves, animal
excrement, car washing residue).
We used to think that “Dissolution was the solution to pollution,” said Koretsky, who
pointed out that this strategy no longer works. For example, a study presented at
the Honors College by James Clift of the Michigan Environmental Council suggests
that: “Half of Michigan is on septic tanks and about 40 percent of them are in
failure.”
The result of nutrient loading is that algal blooms grow, the resulting organic matter
in the lakes degrades and oxygen is reduced such that fish may die and habitat may
be lost. Termed “eutrophication,” this is a major global problem in fresh and salt
water, and it has created what we now call “dead zones.”
The Gulf of Mexico is the site of one of the largest dead zones in the world; it lies at
the base of Louisiana and is the size of New Jersey (5,052 square miles). The
Kalamazoo River was featured in Life magazine in the 1950s because periodic
massive fish kills occurred due to hypoxia (lack of oxygen) caused by pollutants
from the paper industries. In the 1960s, Lake Erie was declared dead, mostly due to
the effects of excess nutrient loading and sewage input. It recovered in the 1970s,
but 20 years later algal blooms began appearing again.
Koretsky showed a March 2012 satellite picture of algal blooms in Lake Erie to
illustrate the enormous scale of the problem. This same phenomenon is occurring in
the three lakes Koretsky’s team studied.
“Local residents talked about how Woods Lake was a pristine, crystal clear lake
before the algal blooms started in the 1970s or 1980s,” said Koretsky.
The data gathered in the three lakes took place all year round and included
measurements of temperature, oxygen, and other dissolved solutes in the water.
What Koretsky found was that, as expected in eutrophic lakes in summertime, the
three lakes became colder, had less oxygen and contained more dissolved iron and
manganese and ammonia in the deeper waters all due to excessive nutrient inputs.
All of these conditions are bad for fish and other aquatic organisms that require
oxygenated water to survive.
“Although there are some remediation strategies available, preventing nutrient
loading in the first place is the best strategy,” she said. “This can be done by limiting
runoff from lawns, agricultural areas and making sure that septic systems are not
leaking, as well as by using fertilizers and detergents that do not contain
phosphorous.”
Road salt is another problem.
“Go eight meters down into Asylum or Woods Lakes and you can taste salty water,”
said Koretsky. “Salt levels are much lower in Brewster Lake probably because it is a
rural lake and not surrounded by deiced roads.”
When salt is put on the roads, it melts the ice and the salt dissolves and goes where
the water goes—into groundwater, rivers and lakes, said Koretsky.
Also, lakes in Michigan are typically dimitic, which means their waters turn over
from top to bottom in spring and fall, mixing the whole lake. This turn over
phenomenon is caused by wind mixing that can occur because of changes in water
temperature, which change the water density.
With higher amounts of road salt seeping into the lakes, this mixing is slowed down
or halted entirely because the salt increases the density of the bottom waters. This
can produce so-called “urban dead seas,” said Koretsky, in which bottom waters
permanently lack oxygen. Woods Lake appears to have stopped mixing altogether
due to road salt input, and Asylum Lake has an especially sluggish turnover.
Moreover, salt is difficult to remove from water. The salt mines under Detroit are
accumulations from ancient seas that covered the region. Consequently, there are no
good options for remediation except to use less road salt.
Increasing levels of sodium chloride have been introduced into surface waters since
at least the 1940s when widespread use of road salt began. Because many more
roads have been built, many more miles are covered with salt and many more lakes
and streams are probably being affected by salt.
The United States produces 50 million tons of salt per year, of which 66 percent is
used for road salt. China is now the Number One producer. However, many cities are
looking to cut the use of road salt because it is so expensive.
“The Flint water crisis was ultimately caused by road salt,” said Koretsky. “The salt
made the water corrosive, which leached lead from pipes through which the water
flowed. Corrosion controls should have been put into place because of the high salt
levels, but they were not.”
The combination of nutrient loading due to algal blooms and heavy use of road salt
presents a significant problem for all our lakes and streams. There is much that can be
done to reduce the use of excess nutrient and road salt if we can change the old
paradigm “dilution is the solution to pollution.”