Impacts of urban green infrastructure on attentional functioning: insights from an fMRI study.

Multiple studies using various measures, technologies, and participant groups have found that exposure to urban green infrastructure can help alleviate the daily attentional fatigue that human experience. Although we have made significant progress in understanding the effects of exposure to urban green infrastructure on attention restoration, two important gaps in our knowledge remain. First, we do not fully understand the neural processes underlying attention restoration that exposure to urban green infrastructure elicits. Second, we are largely unaware of how typical patterns of urban green infrastructure, such as combinations of trees and bioswales, affect recovery from attentional fatigue. This knowledge is crucial to guide the design and management of urban landscapes that effectively facilitate attention restoration. To address these gaps in our knowledge, we conducted a controlled experiment in which 43 participants were randomly assigned to one of three video treatment categories: no green infrastructure (No GI), trees, or trees and bioswales. We assessed attentional functioning using functional Magnetic Resonance Imaging (fMRI) and the Sustained Attention Response Task (SART). Participants exposed to urban settings with trees exhibited improved top-down attentional functioning, as evidenced by both fMRI and SART results. Those exposed to urban settings with trees and bioswales demonstrated some attention-restorative neural activity, but without significant improvements in SART performance. Conversely, participants exposed to videos of urban environments without green infrastructure displayed increased neural vigilance, suggesting a lack of attention restoration, accompanied by reduced SART performance. These consistent findings offer empirical support for the Attention Restoration Theory, highlighting the effectiveness of tree exposure in enhancing attentional functioning. Future research should investigate the potential impact of bioswales on attention restoration.

Lifestyle and language barriers influence community engagement with green infrastructure.

Few studies have focused on value structures, experiences, and cultural diversity as it relates to bioswale planning and implementation. We used 'Point of Opportunity Interactions' to understand previously undocumented views of the Cantonese-speaking immigrant community regarding bioswale design and use for stormwater management in Portland, Oregon, USA. Approximately half of participants were not aware of bioswale function. Maintenance costs and aesthetics were noted concerns, but parking and safety were not. Lack of outreach materials in the Chinese language(s), evening and weekend work schedules, and lack of clarity about maintenance responsibility were among barriers to public participation. Overall, lack of trust for the city and city officials was apparent, and hindered outreach and engagement. Emphasis on informality and place-based data collection near bioswales as neutral outdoors spaces, and proximate to participant residences, facilitated communication with this 'hard-to-reach' population and revealed information that would have gone unknown using traditional outreach strategies.

Observations of the seasonal buildup and washout of salts in urban bioswale soil.

The objective of this study was to quantify the seasonal risk of salt damage to bioswale plants, soil, microbes, and downstream waterbodies. To do so, we measured sodium, chloride, and electrical conductivity levels at seven bioswales located in the Bronx, New York City, over 42 storm events during a three-year monitoring period. The bioswale with the greatest salt contamination (median 206 mg/L chloride) had a unique inlet design without any possibility of inlet bypass. The most severe effects at all sites were found during the winter season, as infiltrate concentrations frequently (40% of winter samples) exceeded 1000 mg/L chloride, a level lethal to aquatic plants and invertebrates, and electrical conductivity exceeded 1500 µS cm-1 (50% of winter samples), a level that may displace bound metals from bioswale soils and into the subsurface. However, low levels of permanent salt contamination may be expected all year, as concentrations frequently (87% of all samples) exceeded the United States Environmental Protection Agency drinking water standard of 20 mg/L sodium. A regression of chloride washout over the year yielded concentrations greater than those damaging to soil structure and soil microbes (90 mg/L) until August 20th, and above those damaging to roadside vegetation (30 mg/L) for the entire year. Today, the vast majority of bioswales in cold climates are built with salt-tolerant vegetation, but prior to this study, it was unclear to what degree this was, in fact, necessary. Our findings confirm salt-tolerant vegetation to be optimal, as winter de-icing salts are not sufficiently flushed from soils by the spring growing season. Our findings also demonstrate how bioswale inlet design and site location can influence soil contamination.

Studying the effect of bioswales on nutrient pollution in urban combined sewer systems.

The objective of this study was to evaluate the impact of bioswales on nutrient pollution in an urban combined sewershed. This evaluation was based on two criteria: the ability of bioswales to (1) remove nutrient pollution from stormwater runoff directly and (2) decrease sewer overflow volumes, which indirectly reduces total sewershed nutrient pollution during a storm event. Bioswales' direct nutrient removal was determined by analyzing nitrogen and phosphorus levels in water samples at seven bioswales located in the Bronx, New York City (NYC) over 42 storm events, while a bioswale's indirect nutrient removal through combined sewer overflow reduction was estimated by quantifying water retention at one of the bioswales. The study results indicated that: 1) the bioswale retained about 40% of stormwater conveyed to it from a drainage area 231 times its size, 2) bioswales leach nutrients into the subsurface, and 3) nitrogen leaching from bioswales varied seasonally, while phosphorus leaching decreased steadily over the study period. Although the studied bioswales leached a median 1.3 kg nitrogen per year into the subsurface, they provided an aggregate decrease in watershed nutrient pollution, from 7.7 to 6 kg nitrogen per year, due to their reduction of combined sewer overflow via stormwater retention.