2017 ASHS Annual Conference

Many cities around the world are expanding the number of green infrastructure systems installed adjacent to impervious surfaces. These systems capture stormwater runoff and thus prevent it from contributing to combined sewer overflows, which are a major threat to water quality in streams and rivers near urban areas. For example, Philadelphia’s ‘Green City, Clean Waters’ initiative has prompted the Pennsylvania Department of Transportation (PennDOT) to integrate numerous raingardens and bioswales into their plans for the renovation of Interstate 95 (I-95) over the next 25 years. I-95 is the main north/south highway in the eastern U.S. and runs along the edge of Philadelphia, paralleling the Delaware River. However, it is unclear how tolerant plants will be of the unique stressors inherent in these bioswales, which will be capturing runoff from the busiest highway in the U.S. To be successful, plantings will need to be resilient to periodic inundation by water high in heavy metals and salts, extended periods of dry weather, elevated temperatures, and other stressors. We investigated the first-year survival and health of plants in the first set of bioswales constructed by PennDOT along the I-95 renewal in 2016. We inventoried five basins (totaling 0.28 ha), in which the planting design indicated that 7343 plants from 55 species were installed in 2015. We visually scored plants on a 4 level scale (dead, and three levels of health/size). First-year mortality rates ranged from 0-96%, with Geranium maculatum L. and Actaea ramosa (DC.) Wormsk. ex Prantl 'Hillside Black Beauty' [formerly Cimicifuga ramosa] experiencing the greatest mortality (77% and 96%, respectively). In some species, such as Calamagrostis ×acutiflora (Schrad.) DC. 'Karl Foerster', Viburnum trilobum Marshall, Mondarda didyma L. and Cornus sericea L., variation in phenology and/or growth was observed between individuals of the same species that were planted in close proximity to each other (<0.5m in some instances), but that likely experienced different hydrological regimes. Typically, lower health and poorer survival occurred in plants with lower elevations. To better understand their stress responses to these varying growing conditions, a subset of the species are currently being investigating for leaf-level physiological responses (primarily transpiration, photosynthesis, and chlorophyll fluorescence). The soil and plant tissues are also being analyzed to determine concentrations of salts and heavy metal contaminants. By better elucidating plant responses to the many stressors of urban bioswales, the performance of the green infrastructure installations can be maximized.