June 2022 - 13

Wetlands built next to farmlands, like this one at the Franklin Research and
Demonstration Farm in Lexington, Illinois, can dramatically reduce the amount of
excess nutrients reaching aquatic environments. Photo: Tim Lindenbaum/Alliance of
Crop, Soil and Environmental Science Societies
Mallard ducks are among the many wildlife species that benefit
from wetlands constructed along the edges of farmland that reduce
nutrient runoff. Wetlands can protect local drinking water supplies and
reduce nutrients reaching freshwater and marine systems. Photo: Tim
Lindenbaum/Alliance of Crop, Soil and Environmental Science Societies
DAMAGE
CONTROL
Small wetlands can have big impacts
By Adityarup " Rup " Chakravorty
Wetlands built next to farms can
dramatically reduce excess nutrients
reaching vital waterways, according to
a study.
Crops need nutrients like nitrogen
and phosphorus to grow and thrive.
However, excess nutrients from farms
can wash into streams and rivers, and
even make their way to oceans. The
surplus of nutrients can cause major
damage to aquatic ecosystems. Small
wetlands, however, can significantly
help reduce or prevent damage.
In a new study, researchers show
that wetlands built next to farmlands
can dramatically reduce the amount
of excess nutrients reaching aquatic
environments, according to a release
from the Alliance of Crop, Soil and
Environmental Science Societies.
The study was recently published in
the Journal of Environmental Quality,
a publication of the American Society
of Agronomy, Crop Science Society of
America and Soil Science Society of
America.
" Even very small wetlands can
be effective, " Maria Lemke, lead
researcher of the study at The Nature
Conservancy, said in the release.
The study was conducted over 12
years on a 272-acre farm in McLean
County in central Illinois. Many
farms in this part of the U.S. use
tile drainage systems - a network of
interconnected underground pipes
that drain water from the farms.
" Our findings show that constructed
wetlands can be very effective at
reducing excess nitrogen losses from
agricultural tile systems, " said Lemke.
" We also show that these wetlands
can capture dissolved phosphorus
efficiently. "
Lemke and colleagues showed that
wetlands with as small as 3% of the
tiled area draining into them can be
effective. These wetlands catch excess
nutrients draining from surrounding
farmlands and results in fewer
nutrients ending up in streams and
rivers, and ultimately, the ocean.
Nitrogen and phosphorus are vital
nutrients for all life and are part
of the essential building blocks of
life, including DNA and proteins.
But when too much nitrogen and
phosphorus make it into aquatic
systems, they can fuel massive
growth of organisms such as algae or
cyanobacteria that ultimately reduce
much of the oxygen in marine systems.
That can force other organisms - like
fish or shrimp - to move away or even
die, creating " dead zones. "
" Our findings show that
constructed wetlands
can be very effective at
reducing excess nitrogen
losses from agricultural
tile systems "
− Maria Lemke,
The Nature Conservancy
Nutrient losses to the environment
can originate from many sources. In
the Midwest, excess nutrients drain
into the Mississippi River system.
These nutrients travel through the
river system and eventually end up in
the Gulf of Mexico, which is the site of
the world's second-largest dead zone.
Constructed wetlands can be a
useful conservation practice that
mitigates nutrient export from farms
to aquatic ecosystems. Nitrogen runoff
that enters wetlands comes in the
One of three wetland cells connected in a series that was monitored at the inlet
and outlet tiles to measure nutrients and water moving into each system from
underground agricultural tiles. Photo: Krista Kirkham/Alliance of Crop, Soil and
Environmental Science Societies
form of dissolved compounds called
nitrates. Microbes in wetlands can
use these dissolved nitrates as energy
sources.
The microbes convert the nitrates
into harmless nitrogen gas, which
is released into the atmosphere.
Conversion from dissolved nitrate to
nitrogen gas results in less nitrogen
exiting the wetlands into aquatic
ecosystems. " Wetlands provide the
perfect habitats for microbes to
perform this process, " Lemke said.
Phosphorus removal from farm
drainage is a more complex process.
Soil chemistry and clay content play
important roles in removing dissolved
phosphorus. " It's important to analyze
soils at potential wetland sites to
characterize their long-term retention
capacity for phosphorus, " he said.
Even the smallest wetlands reduced
nitrogen loss from farm tiles by
15% to 38%. As drainage water
moved through a series of connected
wetlands, nitrogen loss increased up
to 57%.
Removal of phosphorus was even
more effective. Between 53% to 81%
of dissolved phosphorus in farm tile
drainage water was removed by the
smallest of the constructed wetlands.
" These wetlands provide a vital
service by filtering out pollutants and
excess nutrients, " Lemke said. " This
protects local drinking water supplies
and reduces nutrients reaching
freshwater and marine systems. "
Along with capturing excess nutrients
from farm tile drainage, small wetlands
also produce other benefits. They
provide habitat for aquatic plants
and animals, including resident and
migratory ducks, herons, otters, turtles,
frogs, muskrats and dragonflies.
" It is incredible to stand on the edge
of a corn field and hear a cacophony of
chorus frogs or watch a flock of bluewinged
teals take off from a nearby
constructed wetland, " Lemke said.
Lemke and colleagues are currently
exploring the effects of combining
winter cover crops with constructed
wetlands. The idea is combining
in-field practices with edge-of-field
wetlands could further decrease the
wetland sizes needed for desired
nutrient reductions, said Lemke.
Collectively, the American Society
of Agronomy, Soil Science Society
of America and the Crop Science
Society of America, which participated
in the study, represent more than
12,000 individual members around
the world. Members are researchers
and professionals in the areas of
growing the world's food supply
while protecting the environment.
Together, the organizations work
toward solutions to advance scientific
knowledge in agronomy, crop science
and soil science. VGN
VGN | JUNE 2022 | 13
June 2022

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