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Research

Paddling Against the Current on Stream Restoration

Study Shows Environmental Benefits Higher Where Residents Less Willing to Pay

By Kimbra Cutlip

Three illustrations of streams

Stream restoration projects can reduce nutrient pollution flowing downstream, but often require trees to be cut down near the banks (below)—a step that can make local homeowners feel their neighborhood is losing natural amenities.

Illustrations by iStock; photo by Tom Doody

Stream restorations filter pollutants out of local waterways and improve the health of the Chesapeake Bay, but there’s a mismatch between where such work would do the most good and where the most public support for it lies, according to a new study of Baltimore-area neighborhoods by a University of Maryland environmental economist and an interdisciplinary team of colleagues.

Stream restoration projects in less densely populated and generally wealthier parts of the study area would create a greater environmental effect downstream than they would in denser, generally less wealthy urban areas—even though urbanite homeowners are more open to taking on taxes and fees related to stream restoration, according to the study published today in the journal Environmental Research Letters. The study should help inform decision makers charged with improving water quality, who often must balance community support with environmental impacts.

“We see this strong urban-to-rural gradient where in urban areas there’s a higher economic potential as far as community support to pay for stream restoration, but less ecological potential to reduce nutrient pollution, and vice versa,” said David Newburn, an associate professor in the Department of Agricultural and Resource Economics at UMD and co-author of the study. “The overall trend is that there’s often a trade-off for environmental and economic benefits from stream restoration projects, and it’s hard to find the win-win locations.”

Stream

Stream restoration projects vary greatly with the local environment, but they are all designed to improve the ability of a stream to absorb and process nutrient pollutants and prevent them from flowing downstream, where nitrogen-rich material ranging from fertilizer to animal waste to fallen vegetation can help spur problems such as huge algae blooms in the Chesapeake Bay. Such projects are central to improving water quality in watersheds around the world, but they can also change the local landscape in ways homeowners may not like—sometimes replacing trees with open areas along stream banks.

Newburn and his colleagues wanted to understand the complex relationship between the environmental benefits of stream restoration and the perceived value to homeowners who frequently pay for them through taxes and fees. To do so, they leveraged long-term sampling data from the Baltimore Ecosystem Study, which has been measuring streamflow and nutrient load (a measure of ecological health of a waterway) since 1998 across fully forested, agricultural and highly developed watersheds alike. Using modern ecosystem modeling techniques, they estimated how much of the nitrogen would be removed by different stream restoration designs in a variety of settings.

They focused on small, headwater streams within the Baltimore region spanning urban, suburban and exurban neighborhoods (defined as neighborhoods outside of city septic systems that are dominated by single-family homes on one- to five-acre lots). Newburn and his colleagues developed hydrologic models that showed stream restoration had the most nitrogen reduction in the less densely populated exurban areas, where small streams predominantly have low flows. Streams lined by grassy buffers had the highest nutrient reduction compared to tree-lined streams.

The researchers suggest that low water flow in these areas allowed the streams to process nutrients in the water, and grassy buffers allowed more sunlight to reach the water than did tree-covered stream banks. Sunlight is important because it helps the algae in streams to remove nitrogen from the water more effectively.

The projects that had the least nitrogen pollution reduction were in the most densely populated, urban areas of Baltimore city. In these neighborhoods, runoff from impervious surfaces like rooftops and parking lots leads to local flooding during rainstorms, and the torrents of swift-moving water do not allow streams time to remove a substantial portion of the nutrient pollution.

Next, the researchers used homeowner survey data to analyze willingness to pay for different stream restoration designs and mapped their results throughout the study region.

Homeowners often enjoy trees’ aesthetic benefits, and removing them from less-dense areas equates to removing the value of this amenity from the neighborhood. But in closely populated urban areas, where streams were more likely to be surrounded by man-made infrastructure, the addition of grassy meadows or trees during restoration provides green-space amenities that are often lacking, particularly in lower-income urban neighborhoods.

Newburn said that the added green space in urban areas has social benefits beyond water quality improvement that may be factored into the environmental and socio-economic analysis for decision makers. He also suggested that future research focus on additional benefits of restoration projects such as reducing urban heat islands and restoring habitats.

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