Researchers try to grasp how wetland
plants purify water
a clown twisting a balloon into a poodle, humans mold
resources into substances that suit our needs. The countryside
is dotted with fill-in-the-blank processing plants that
make, among other things, our food fit to eat and our
water fit to drink.
Water treatment facilities spend billions
of dollars every year trying to bring contaminated water
within the drinking standards set by the Environmental Protection
Agency. Peter Jaffé, professor of civil and environmental
engineering, is studying ways to help Mother Nature do the
processing for us.
by Frank Wojciechowski
Professor Peter Jaffé researches
the impact that trace metals have on wetland biology.
Studying trace metals
Professor Jaffé is studying trace
metals such as chromium and arsenic in wetlands and how plantlife
affects the related biogeochemical cycles.
Wetland surface waters are a combination
of precipitation, road runoff, agricultural runoff, industrial
waste, and other waters—all of which are served up
in an unsavory cocktail of contaminants from their sources.
Vegetation in these wetlands can reduce
the toxicity of surface waters, and different plants have
different purification abilities.
Professor Jaffé and his group are
studying a variety of flora and their effects on trace metals.
This research could help scientists and planners “design” wetlands
to process local waters and serve other purposes as well.
“The gist is, we’re not
biologists or geologists,” Professor Jaffé said, “but
we want to understand these processes in a quantitative manner
sufficiently enough to design a wetland. That’s the long-term
Professor Jaffé has recently focused
on chromium in these wetland surface waters.
According to the Agency for Toxic Substances
and Disease Registry, chromium is released into surface waters
primarily by electroplating, leather tanning, and textile
Chromium is generally found in three common
stable valence states, chromium (O), (III), and (VI).
Chromium (VI) is water soluble and considered
to be about 1,000 times more toxic than chromium (III). It
may be a human carcinogen, although there is not enough evidence
to definitively prove it.
In wetland sediments, chromium (VI) reacts
with organic materials in the soil and is reduced to chromium
(III). The aim is to pull as much chromium (VI) out of the
water and into the sediments as possible. Professor Jaffé is
trying to discover which plants will do that job best. He
is studying two common, hardy wetland plants: cattails and
In the lab, his researchers created microcosms
of various, typical wetland sediments with controls, cattails,
The first piece of the puzzle was to see
just how much chromium (VI) was in the microcosm soils. This
showed that the microcosms planted with cattails had much
less chromium (VI) in the pore water of the sediments than
did the phragmites.
by Peter Jaffé
Cattail was grown in a laboratory-created
wetland microcosm to study its ability to purify
Not so simple
On this information alone, one might conclude
that the cattails were reducing more chromium (VI) than were
the phragmites. Yet the issue is not quite that simple.
“It’s a complex interplay,
and just by looking at a single, simple measurement we can’t
understand what is really happening,” Professor
Jaffé said. “So that’s
why a combination of experiments and numerical modeling are
done to tease out what is going on.”
The experiments also study another key
element in the ability of these plants to immobilize chromium—their
rate of evapotranspiration. Evapotranspiration is the loss
of water from plant leaves.
“We’re looking at contaminated
water moving slowly through a swamp,” Professor Jaffé said. “If
a plant is losing a lot of water through evapotranspiration,
it will need more water to replace it. So that plant will
suck more freestanding water down into the sediments, and
we want as much in the sediments as possible, where the chromium
will be reduced and therefore not enter surface waters.”
After this experiment, it became clear
that the phragmites reeds evapotranspired more than twice
the amount of water than the cattails.
After factoring this in, Professor Jaffé believes
that phragmites reeds are capable of reducing more chromium
(VI) every day than cattails.
Phragmites, however, is an invasive species
that can take over wetlands. Some ecologists would be wary
of any wetland design strategy that pushed for the planting
of this species.
One of the species that was driven out
by the pushy phragmites is spartina, a native species from
the Meadowlands area. Professor Jaffé and his group
are now doing microcosm studies on spartina, to see how well
it reduces chromium (VI).
“The question is ‘Does it
make sense to replant spartina if we want to immobilize metals’?” Professor
He recently applied for a grant from the
National Science Foundation to do another wetland research
project to study the role of detention ponds in processing
nitrogen in urban wetlands.
Research applicable to local wetlands
of Professor Jaffé’s research has been used
to educate the public and policy-makers about the integral
role wetlands play in the health of watersheds. The project
is run by the Stony Brook Millstone Watershed Association
(SBMWA) and is supported by a grant from the Environmental
Protection Agency, under their grant program Science
to Achieve Results (STAR).
Professor Jaffé has assisted SBMWA
in compiling a survey that tested citizens’ and public
officials’ knowledge of, interest in, and opinion of
wetlands. His findings about the dynamics of trace metals
in wetland sediments contributed to the survey.
Survey questions examined knowledge about
how to identify wetlands, wetlands’ abilities to treat
contaminated water, wetlands’ ability to protect against
flooding, and the protection of wetlands by state regulations.
Questions also examined opinions about
developing or preserving local wetlands, the perceived benefits
of wetland preservation, and the amount of trust citizens
can place in various entities entrusted with the protection
of the wetlands. For more information about the SBMWA, see www.thewatershed.org.
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