Divergent Vegetation Growth Patterns Relative to Bioinfiltration Unit Size and Plant Placement: Fid-Bau Portal

Divergent Vegetation Growth Patterns Relative to Bioinfiltration Unit Size and Plant Placement

Brown, Robert A. / O’Connor, Thomas P. / Borst, Michael

In 2009, the U.S. EPA constructed six experimental bioinfiltration units (BUs) at the Edison Environmental Center in Edison, New Jersey. They were designed as two sets of three BUs with drainage area to surface area ratios of $5.5 ∶ 1$ , $11 ∶ 1$ , and $22 ∶ 1$ . The intent was to determine the effects of area on side-by-side systems that received equivalent inflow. A 0.86-m deep media layer containing 97% sand was installed over 0.10 m of gravel and sandy underlying soils. Water content reflectometers (WCRs) and thermistors were installed 0.38 m into the media and 0.25 m into the underlying in situ soil near the front and rear of each bioinfiltration unit to monitor stormwater infiltrating through the media and into the underlying soil. Infiltration monitored at these sites with the WCRs was not in accordance with the simplified conceptual model of uniform infiltration across the surface; rather, infiltration was concentrated near the inlet. After the third growing season, plant basal area and height were measured for the shrubs. The shrubs planted include Myrica pensylvanica (northern bayberry), Vaccinium corymbosum (northern highbush blueberry), and Ilex verticillata (winterberry holly). The plant layout allowed for evaluation of different plant growth rates with distance from the inlet. The WCR measurements, meteorological observations, and plant size measurements demonstrated that the bayberry bushes closest to the inlet correlated with larger growth patterns than the bushes farther from the inlet primarily because the closer bushes received substantially more runoff due to the rapid infiltration near the inlet; also, bayberries were larger in the smaller surface area bioinfiltration units which had deeper water depth in the media profile. Runoff provides a source of water and nutrients, and both are essential for plant growth. Proximity to the runoff inlet significantly affected bayberry and winterberry growth, and the shading provided by the bayberry benefited both the blueberry and winterberry growth. Future bioinfiltration design should consider plant placement and species selection relative to the proximity of the runoff source. Oversized bioinfiltration units increase the likelihood that vegetation planted farthest from the runoff source will experience water-deficit stress which could limit growth, cause mortality, or necessitate additional maintenance (i.e., irrigation and fertilization).