ON A CHILLY MIDMORNING IN WEST BALTIMORE, Christopher Redwood and I ponder an empty 32-ounce beer can that an anonymous passerby had lobbed into a small park. Once a vacant lot, the park is located near Redwood's house on West Lombard Street in the historic Hollins Market neighborhood, and he has worked on a project to beautify it. "What can you do?" Redwood says, a verbal shrug tinged with the stubborn optimism of an advocate for community-based greening in hardscrabble West Baltimore.

Maybe it's just one cast-off beer can, but it testifies to a chronic problem: once you convert a weedy, vacant lot into an urban oasis, someone has to keep it free of litter.

Hollins Market is one of 12 neighborhoods (plus Carroll Park) that make up Watershed 263, a densely urbanized area of the city where stormwater is channeled through a common drainage system. Each heavy rain flushes fine sediment and a film of pollutants from the roadway into the storm drains gurgling below. These eventually empty into Baltimore Harbor and into the Chesapeake Bay beyond.

On the map, Watershed 263 stretches from Presstman Street in the Sandtown-Winchester neighborhood in the north to Russell Street in the Carroll-Camden Industrial Area in the south. Below the ground, water quietly flows downslope toward the harbor through Baltimore's vast masonry and concrete "gray infrastructure."

This system of drains and pipes has entirely replaced the surface streams that once drained old West Baltimore. The watershed's 930 acres include 355 stormwater drains and 43 miles of pipes. At its southernmost edge on Russell Street, the network pinches to a single 25-foot-wide stonework mouth, named Pipe 263, which disgorges its contents into the brackish backwater where the Middle Branch of the Patapsco River empties into the harbor. Those contents include trash, oil, heavy metals, and lots of nitrogen and phosphorus, whose reduction is central to the cleanup of the Bay.

Starting in 2004, Watershed 263 was the target of an experiment to see if urban greening strategies like planting trees, converting vacant lots into parks, and landscaping formerly paved-over schoolyards could improve both water quality and quality of life for the residents. In addition to soaking up stormwater and removing pollutants, the parks and plantings provide places to walk and socialize. Researchers wanted to find evidence — still hard to come by — for those subtle social benefits, which buried drains and pipes cannot offer.

The network of storm drains and buried pipes in Watershed 263 discharges stormwater runoff from all or part of 12 neighborhoods, plus Carroll Park, in West Baltimore. The runoff, bearing sediment and a mix of pollutants, drains into Baltimore Harbor at the southernmost end of the watershed and into the Chesapeake Bay beyond. Map, adapted by Sandy Rogers using a base map from the City of Baltimore Department of Planning

Greening isn't always cheaper or even as effective as gray infrastructure, but demonstrating that it transforms neighborhoods could lead to changes in how cities manage their stormwater. "We need to be able to provide advice about how to spend public money to make these environments better for people where they live, and at the same time achieve those stormwater goals for which the city government is accountable," says Morgan Grove, a social scientist with the U.S. Forest Service who worked on the Watershed 263 project.

In 2002, Bill Stack, then-chief of stormwater pollution control for the Baltimore Department of Public Works (DPW), looked at Watershed 263 and saw an opportunity where others may have seen only urban blight: the area was peppered with some 2,000 empty lots, left behind after burned-out or decrepit buildings were torn down. "There was a tremendous number of vacant properties that would lend themselves to greening," he recalls.

To start, greening the lots would allow water to soak more slowly into the soil rather than pouring into storm drains. Watershed 263 is heavily paved — about 75 percent of its surface area is impervious to water. That means the stormwater flowing over all those streets, sidewalks, roofs, and parking lots carries pollutants into the Bay.

Stack also knew about a program in Boston that had stripped the asphalt from city schoolyards and replaced it with trees and gardens. Why couldn't the paved-over playgrounds in West Baltimore also be removed to create new porous surfaces to intercept stormwater runoff?

The most critical piece of the project was already in place: the Parks and People Foundation of Baltimore, a nonprofit that promotes community-based green projects and environmental education and already had deep roots in West Baltimore. "I talked to Parks and People and they said, great, sign us up," Stack says.

In 2004, project workers started greening the neighborhood. They turned vacant lots into parks. They planted trees along the streets. They installed specially engineered plantings, or "green infrastructure," such as curb "bump-outs" filled with native plants. These extend a few feet into the street, allowing them to capture and soak up street-level runoff before it can gush, unfiltered and at full force, into the storm drains.

Stack also teamed up with scientists to design a study to find out if the newly greened surfaces do more than just clean stormwater. Would people living near them feel better about their neighborhoods and want to stay? Would others feel good enough about the improved neighborhoods to buy one of the scores of unoccupied row houses in Watershed 263, thus helping to revitalize the community?

The evidence that greening fuels social change has often been limited to subjective opinions and impressions. The Watershed 263 project tried to go beyond anecdotes and collect hard data about the project's benefits on the neighborhood level. "That's a huge big deal," says Peter Groffman, a hydrologist with the Cary Institute of Ecosystem Studies in New York state who assisted in the water quality research on Watershed 263. Nationally, there have been relatively few scientific studies of how community greening affects how people think, feel, and behave.

DPW workers and project scientists began climbing down manholes to draw water samples from stormwater pipes once or twice a week to measure pollutants. They also set instruments in place to monitor flow during storms. Monitoring would continue from 2004 to 2011.

The scientists wanted to find out if they could link the new green projects to improvements in water quality. To test their hypothesis, they measured and compared water quality and storm flow in two smaller areas of Watershed 263's sprawling 930-acre footprint. Each of these so-called subwatersheds drained only 37 acres (about ten city blocks each), but together they could provide a snapshot of water-quality changes across the larger watershed. It was like studying drainage from an entire high-rise apartment building by tapping into drainpipes from only two of its floors.

A variety of community-managed greening efforts are underway in West Baltimore. In the Penrose-Fayette Street Outreach neighborhood, summer camp participants from Positive Youth Expressions, Inc. Educational Institute helped tend a community garden at the corner of Pulaski and Vine Streets. In 2015, a coalition of community groups won city funding to beautify additional locations in the area. Photograph, Timothy Bridges

The manhole for one subwatershed was on Baltimore Street; the other, north of Baltimore Street, was on Lanvale Street. There had been a lot of greening in the Baltimore Street sample area, but none in the Lanvale Street subwatershed. If greenscaping had any effect on water quality, it should show up at Baltimore Street but not at Lanvale Street.

In 2013, scientists with the project reported their results in the journal Frontiers in Ecology and the Environment. They summarized the greenscaping that workers had carried out across Watershed 263 during the study period from 2004 to 2009: 1,000 trees planted, more than 200 lots greened, and four acres of schoolyard asphalt ripped up and replaced by trees, gardens, and grass. The project also installed 12 new pieces of green infrastructure to soak up rainwater runoff — the curb bump-outs, for example.

Did all this improvement have an effect on water quality? The preliminary answer is yes, though the details were unclear. In the Baltimore Street subwatershed, nitrogen and phosphorus declined by 50 percent. (The Lanvale Street area showed no such change.) However, the amount of greening completed by 2009 in the Baltimore Street area could not account for all of the improvement in water quality observed there. "There was a significant decline in nutrients," says Guy Hager, a recently retired senior greenscaper with Parks and People who was deeply involved in the Watershed 263 project. "The problem is that the decline was so large nobody believes it was just from our projects. That part is still up in the air."

Other causes might have contributed — like street sweeping, which removes surface pollutants before they can wash into the storm drains. Another possibility was that the city had repaired or rerouted a sewer line in the Baltimore Street sample area, preventing sewage from trickling into the stormwater network. (Sewer and stormwater pipes share the city's subterranean spaces, and cross-contamination happens.) But the team was unable to pin the decline in pollutants on either street sweeping or sewerage repairs. The evidence that greening helped to reduce surges of rainwater into the system during storms was also inconclusive.

What the team could be sure of was that greening had changed the landscape in Watershed 263's neighborhoods. But did the new parks, trees, and rain gardens have a measurable impact on people's behavior and attitudes? If so, that could be a real selling point for people who advocate for a bigger role for trees, parks, and plantings in Baltimore's stormwater management strategy.

To assess the social effects of the Watershed 263 project, the team drew on data from community surveys by scientists with the Baltimore Ecosystem Study (BES), a long-term, city-wide research project that began in 1998. The BES had surveyed approximately 3,000 Baltimore residents by phone in 2003 and 2006, including 100 people within the boundaries of Watershed 263.

Fresh produce grows year-round inside plastic-covered greenhouses located on the 1800 block of Lorman Street in West Baltimore. Operated by Strength to Love II, a grass-roots community organization, the one-and-a-half-acre farm provides produce for farmers markets and restaurants as well as jobs to help men transition out of correctional facilities. In the future, Baltimore’s Growing Green Initiative hopes to foster more urban agriculture like this. Photograph, Wendall Holmes, Strength to Love II

Their survey showed that people in Watershed 263 were more likely to engage in outdoor recreation, such as walking and bicycling, compared with those in other areas of Baltimore. People said they were satisfied with their neighborhoods and were more likely to stay than to move out. What is more, a study conducted at elementary and middle schools in Watershed 263 indicated that students' understanding of environmental science concepts improved after schoolyard asphalt was replaced by a garden "reading circle."

These kinds of social benefits persist today as neighborhood groups continue to push for greening in Watershed 263. But with the benefits have also come concerns from some residents about certain aspects of these projects.

Maintenance, for example, is a continuing challenge because open spaces like parks can be magnets for trash. "The greening is beautiful," says Romina Campbell, who lives just over the western border of Watershed 263. "Personally I love it, but when they get those grants, they need to ask for more money for upkeep."

Stack, now with the nonprofit Center for Watershed Protection in Ellicott City, recalls that during the project, some residents "didn't understand why the money spent on planting green space couldn't be used to address more immediate needs, say creating jobs or addressing crime and drugs."

Leaders can help to address such concerns by talking to residents in neighborhoods targeted for greening, door to door or at public meetings, says Inez Robb, who has represented the Sandtown-Winchester neighborhood on the Watershed 263 Stakeholder Community Council. "If you put in a curb bump-out with this green stuff and nobody knows what it is, who put it there, and what it's for," Robb says, "then nobody cares."

Watershed 263's experiment also left an impression beyond West Baltimore, according to Mark Cameron, a city planner with Baltimore DPW. He says that the Watershed 263 project "provided multiple lessons learned regarding green infrastructure and community greening in Baltimore." In addition to the educational benefits and community engagement, partnerships between citizens and organizations like Parks and People make it possible to launch new greening projects in Baltimore neighborhoods using outside funding from nonprofits and federal and state agencies.

But, says Cameron, the project also highlighted some of the challenges that would-be urban greenscapers face, like managing costs, avoiding conflicts with city utility infrastructure, and winning neighborhood acceptance of greening projects.

The lessons learned may come in handy as Baltimore pursues its city-wide Growing Green Initiative, managed by the city's Office of Sustainability. Its goal is to turn city-owned vacant land into green space that delivers a variety of benefits. Some of these efforts will reduce stormwater runoff, but the city also wants to nurture other drivers of sustainability like urban agriculture.

Knowing the benefits of greening also matters as the DPW strives to meet part of its federal stormwater requirements. Out of the roughly $21.3 million that the Baltimore Department of Public Works spent in 2015 on stormwater-related activities, about $2 million went to watershed restoration construction projects, and among them were many greening and green infrastructure improvements. Most of DPW's stormwater-related expenditures went to other priorities like maintaining the city's stormwater plumbing system.

Although green infrastructure makes up a relatively small percentage of the city's stormwater management, Cameron says it plays an important and beneficial role. Street sweeping helps keep pollutants out of the Bay, but it doesn't offer the social or economic benefits that greening does. "That's why we looked at it as a suite of options," Cameron says. "We can't just do one thing. We need to do a number of different practices."

Today, the greening of Watershed 263 continues. Christopher Redwood and other members of a coalition of three neighborhood associations in Watershed 263 are still working to beautify the small park back in his Hollins Market neighborhood. In 2014, the project, called "Lots of Art," won a city-sponsored Growing Green Design competition that provided $13,010 to green the corner lot at West Lombard.

The park includes a small wooden deck for performances or just a barbecue. It's a place to read a book, have a relaxing sit-down, or chat with neighbors — or so the builders hope. Grass-roots action is nothing new for Redwood. "In the family I come from, we see problems but don't just complain about it," he says. "We go out and do things."

Parks and People also continues to help community groups to remove asphalt and plant trees in other parts of the city. Christina Bradley, the group's director of capital improvements, says, "If it can work in West Baltimore, it can work anywhere."