A Decade of Bioretention Research
Bioretention systems are intermittently inundated 'subsurface flow wetlands' designed to drain within a few days; they support vegetation that can tolerate waterlogged media and drought. This ecotechnology has been extensively incorporated into the urban landscape to treat stormwater runoff, BUT do we really know enough about their long term sustainability and performance efficiency? Over the past decade researchers at Griffith University have focussed on evaluating the effectiveness of using different soil media and plant species to maximise nutrient removal. The performance efficiency of ten different media types including amendments for enhanced phosphorus adsorption, and ten different plant species have been investigated. Total Phosphorus removal was highest (94-99%) in sand media amended with Water Treatment Residuals, followed by 'brickies loam' (92%), then sand amended with Red Mud or Krasnozems (86-89%) and lowest in sand-gravel 44%. Total Nitrogen removal was highest in the loam (78%) but relatively poor in other media types (around 50%). Of the herbaceous plants the grasses Pennisetum alopecuroides and Vetiver -Chrysopogon zizanioides, and the sedge Carex appressa had the highest growth rates and biomass yield (12-18gP/m2/y and 51- 64gN/m2/y). The woody species Callistemon pachyphyllus and Melaleuca quinquenervia had the highest carbon sequestration (1000g C/m2/y). Thus, various sandy loam media can be used to enhance long term effective phosphorus removal, and plants can be used for carbon credits.
8th International Water Sensitive Urban Design Conference 2013