Baltimore, Maryland is a major city situated on the Chesapeake Bay- a sprawling 64,000 square mile watershed. Currently, the Chesapeake is facing an environmental crisis due to pollutants. Scientist Claire Welty of the University of Maryland-Baltimore County is monitoring the travel times of pollutants in the urban streams in and around Baltimore. Through her research, she hopes to gain an understanding of the urban water cycle, and how municipalities can better prevent pollutants from contaminating the greater watershed. "Sustainability: Water" is produced in partnership with the National Science Foundation.
Sustainability- Water - Baltimore's Urban Streams
ANNE THOMPSON, reporting:
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 (University of Maryland-Baltimore County): 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 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.
Mr. Trash Wheel is a googly-eyed, trash-skimming water wheel. He is installed at the bottom of Jones Falls watershed, which empties into the Baltimore Harbor.
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