Abstract
While the use of bioretention for stormwater management is widespread, data about the impacts of plants and microorganisms on long-term treatment efficacy remain region-specific. To help address this knowledge gap for the Pacific Northwest region of the United States, we installed twelve under-drained bioretention mesocosms built to Washington State Department of Ecology stormwater management standards in an urban watershed in Seattle, WA that included a busy portion of Interstate 5. Six mesocosms were planted with Pacific ninebark (Physocarpus capitatus) and six were inoculated with the wine cap mushroom (Stropharia rugoso-annulata) resulting in four replicated factorial treatments. Because region-specific studies must be mindful of the prevailing regulatory framework, all mesocosms used the Washington State Department of Ecology design standard soil: a blend of 60% sand and 40% compost by volume, despite the known leaching problems with high compost volume fraction soils. Five water quality sampling events over 15 months of continuous stormwater loading were analyzed for dozens of water quality parameters. Multiple linear regression analyses of treatment differences over the 400-day loading period illustrate that incorporating fungi into the wood mulch slowed the release of total and ortho-phosphorus from the bioretention soil; however net export of phosphorus from this compost rich media continued through 400 days of loading for all treatments. Multivariate ordination methods illustrate that time and temperature dramatically affect performance of this media, but the impact of planting and fungal inoculation had marginal detectible effects on overall water quality during the study timeframe. These results demonstrate that future studies of this media blend must plan for at least one year of nutrient and metal leaching before the time-dependent heterogenous variance introduced by these exports will no longer pose an obstacle to analysis of other performance changing factors. The results highlight important physical and chemical considerations for this media blend, and the opportunity for continued research on the use of fungal inoculated mulch application as a new ecological engineering tool for reducing phosphorus leaching from soils.
Highlights
The many deleterious effects of urban stormwater runoff on US surface waters have been extensively described for over a decade [1]
To ascertain the relative contributions of sand and compost to the metals content of the bioretention soil mix (BSM), representative samples of each media component were analyzed in triplicate for a suite of total and dissolved metals (Table 1)
This study set out to test fungal and plant mediated effects on stormwater chemistry in replicated bioretention systems operating under field conditions for an extended period of time
Summary
The many deleterious effects of urban stormwater runoff on US surface waters have been extensively described for over a decade [1]. While bioretention has demonstrated unequivocal improvements in stormwater management when compared with historical “grey infrastructure”. Questions about how to implement it most effectively have been under investigation for over a decade and remains an area of active research [2,3]. The ambiguity about how to best implement bioretention is evident in the debate around bioretention soil composition and the search for improved formulations [4,5]. Bioretention soil as a global stormwater BMP is far from a universally consistent formulation. All bioretention soils are intended to provide high infiltration rates, water holding capacity, specific surface area, and cation exchange
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
