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Divergent Vegetation Growth Patterns Relative to Bioinfiltration Unit Size and Plant Placement
Citation:
Brown, R., T. OConnor, AND Mike Borst. Divergent Vegetation Growth Patterns Relative to Bioinfiltration Unit Size and Plant Placement. Journal of Sustainable Water in the Built Environment. American Society of Civil Engineers (ASCE), New York, NY, 1(3):04015001, (2015).
Impact/Purpose:
Experimental bioinfiltration units at the Edison Environmental Center in Edison, New Jersey, were designed as two sets of three bioinfiltration units with drainage area to surface area ratios of 5.5:1, 11:1, and 22:1. Water content reflectometers (WCRs) and thermistors were installed 0.38 m into the media and 0.25 m into the underlying 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 did not follow the 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 plant layout allowed for evaluation of different plant growth rates with distance from the inlet. The WCR measurements, climatic observations, and plant size measurements demonstrated that the shrubs farthest from the inlet were smaller than those closer to the inlet because they received a lack of runoff that hindered growth. Runoff provides a source of both water and nutrients, and both are essential for plant 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., irrigate, fertilize).
Description:
In 2009, the U.S. Environmental Protection Agency constructed six experimental bioinfiltration units at the Edison Environmental Center in Edison, New Jersey. They were designed as two sets of three bioinfiltration units 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 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 did not follow the 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, climatic observations, and plant size measurements demonstrated that the bayberry farthest from the inlet were smaller than those closer to the inlet because they received a lack of runoff that hindered growth. Runoff provides a source of both 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., irrigate, fertilize).
