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ANNE THOMPSON: Baltimore, Maryland's Inner Harbor is known
for its crab cakes, tall ships, and the beautiful Chesapeake
Bay, a 64,000 square mile watershed that is a critical
habitat for wildlife. But the Bay is facing an environmental
crisis, partly due to pollutants in the form of nitrates that
come from such things as power plant combustion, lawn
fertilizers, automobiles, and even road salt.
Nitrate, or nitrogen, is a nutrient that causes the growth
of algae in the water. When the algae die, their decomposition
depletes oxygen levels in the water, creating "dead zones"
that are killing fish and crabs in the Bay.
CLAIRE WELTY: We are trying to clean up the Chesapeake Bay, and
we are determining the quantity of nitrogen going into the
Chesapeake Bay and we would like to reduce that, because it's a
problem in the bay.
THOMPSON: Claire Welty is a hydrologist at the University of
Maryland-Baltimore County. She is leading a study funded by the
National Science Foundation that is mapping Baltimore's urban
streams in order to understand how nitrates from city streets,
parking lots, and backyards are making their way into
the Chesapeake Bay.
WELTY: Anything that's deposited on the land eventually gets into
the stream to affect the water quality.
THOMPSON: To gather data on how an urban stream differs from a
natural stream, especially in the processing of nitrate,
Welty's team has installed dozens of sensors in the urban
streams of Baltimore and its surrounding communities.
WELTY: We're measuring dissolved oxygen. We're measuring water
temperature. Nitrate is a concern because of
the Chesapeake Bay.
THOMPSON: Streams have natural ways of processing nitrates,
which can be affected by the rate of flow of water in the
stream. If the water in a stream travels too fast, less time is
available for nitrates to be processed. Less time means less
removal, sending more of the nitrates downstream.
WELTY: In urban systems, the velocity of water is high,
meaning that the flow rate is high. The high flow rate is what
is causing the degradation of streams in terms of erosion.
THOMPSON: The natural processing of nitrates begins when runoff
travels into the stream and across something called the
riparian zone, or the banks of the stream. Urban encroachment
and the clearing of vegetation can erode the riparian zone,
which causes runoff to flow into the stream more quickly.
WELTY: Typically what municipalities try to do is
protect the riparian zone and, and keep it planted to
help keep streams healthy.
THOMPSON: Once runoff enters a stream, water seeps into the
streambed, also known as the hyporheic zone. In this zone,
naturally occurring bacteria enable chemical reactions that
remove nitrates from the water. If the stream flows in a
concrete channel or a pipe, as many urban streams do, then no
hyporheic exchange can occur and more of the nitrates
are delivered downstream.
WELTY: It is a very biologically and chemically active area. So,
it's a very important zone ecologically.
THOMPSON: Understanding this close relationship between
runoff and water travel times is crucial for scientists working
to improve water quality. It is also important to know how a
stream functions in an urban environment and to determine how
it has changed from its natural condition, and what can be done
to restore it.
WELTY: What we're hoping is that our system is similar enough to
other urban areas in the same kind of climates that some of
our results are directly applicable. So, the methods we
come up with to quantify these urban water components, should
be directly transferrable to other Northeastern cities.
THOMPSON: By gaining a better understanding of how Baltimore's
urban streams work, Welty is not only hoping to revive the
Chesapeake Bay, but to also ensure water quality for a
more sustainable future.
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