2018 ASHS Annual Conference

Plants are critical components of the sustainable stormwater management systems, as they provide both ecosystem services and aesthetic value. However, plant health and survival can be compromised by the extreme hydrological conditions that characterize stormwater systems, as well as by the salts and contaminants present in stormwater. We determined how the health of nine plant species varied as a function of exposure to stormwater in large bioswales that capture runoff from a section of Interstate 95 in Philadelphia. We evaluated canopy size, leaf areas, and leaf-level physiology in 72 plants (eight per species) after two years of growth; individuals within each species were selected such that they spanned a wide range of micro-topographic positions. For the majority of species (Asclepias incarnata, Calamagrostis × acutiflora, Hemerocallis, Iris sibirica, and Monarda didyma), canopy volumes became progressively smaller as plants were positioned lower in the basins. Two additional species (Cornus sericea and Viburnum trilobum) had reduced canopy sizes at both low and high topographic positions. However, leaf-level physiological rates exhibited a very different pattern. In most species, gas exchange rates were reduced at higher topographic positions, while several additional species had maximal physiological rates in the middle of the elevation range. Although the growth of most species was strongly reduced when plants grew in wetter soils, our results suggest that neither photosynthetic capacity nor heavy metal toxicity limit growth at the corresponding elevations. Instead, our results are consistent with limitation by high salinity in spring or the high carbon requirements for growth in anoxic soil conditions. Our results also suggest that plants experienced water limitation at higher elevations, though this was far less severe than were the effects of growth at low elevation.