Mazer, Greg. 1998. Environmental limitations to vegetation establishment and growth in vegetated stormwater biofiliters. M.S.
Limitations to vegetation establishment and abundance in biofiltration swales (also called bioswales or biofilters), which are vegetated stormwater facilities intended to improve runoff water quality, were studied through field monitoring and greenhouse experimentation. The relative degree to which various environmental factors influence vegetation and organic litter abundance was investigated in eight bioswales, including three that were retrofitted with new soil and grass. A nested 2x2 factorial greenhouse experiment tested the response of four turfgrass species commonly seeded in bioswales to three inundation regimes plus a control. In the greenhouse experiment and in the field, extended periods of inundation significantly suppressed plant germination and growth. Field monitoring further revealed that bioswale vegetation and organic litter biomass is best predicted by inundation duration during the driest time of year (summer). Flow velocity and hydraulic loading during storm events were generally too large to permit sedimentation of silt and clay particles and their associated pollutants regardless of vegetation and organic litter abundance. Thus, herbaceous vegetation abundance may not provide good indication of bioswale treatment performance, which appears to be much lower than is anticipated for the typical bioswale.