Abstract
Abstract Bioretention systems maintain the natural water cycle and help to mitigate climatic extremes impact on urban areas by retarding, storing, and evaporating stormwater runoff. Although bioretention systems have been operated for more than 25 years, systematic investigations on the hydrological functionality and pollutant retention performance of older systems are rare. We employed laboratory and field experiments to investigate three long-term operated bioretention systems in Germany with the following objectives: (i) physico-chemical substrate characterisation; (ii) an event-based influent and effluent trace metal concentration monitoring covering 22 months and (iii) the calculation of metal retention rates. Regarding the pollution status, we found significantly increased trace metal contents in the soil substrate mainly as a function of the drainage area type and the inflow regime. Nonetheless, all measured metal seepage concentrations fall below the German legislative trigger values. Our current findings demonstrate no risk of groundwater degradation even for old bioretention systems suggesting bioretention as a powerful and sustainable tool for stormwater management. Further research requires the handling of soil substrates modified by stormwater infiltration showing enhanced trace metal contents and a certain amount of technogenic sediments.
Highlights
Urban areas will continuously grow in future due to the growing world population, even further enforced by the rural exodus (Wong et al 2006; Liu et al 2014)
This study aims to investigate and describe the pollution status in soil water and soil matrix of three different long-term operated (.20 years) bioretention systems to assess the risk of heavy metal leaching
This study seeks to improve our understanding of the behaviour of bioretention systems with increasing operation time regarding heavy metal transfer processes
Summary
Urban areas will continuously grow in future due to the growing world population, even further enforced by the rural exodus (Wong et al 2006; Liu et al 2014). Urban stormwater drains by central sewer systems, which discharge directly into surface water bodies during high flow (LeFevre et al 2015). Such conventional overflow systems were developed in the past to rapidly drain urban areas in order to prevent flooding on the one hand and to reduce the runoff volume to be treated in the treatment plant to not exceed its capacity on the other hand. The basic principle of all so-called blue-green infrastructures is to capture and infiltrate runoff water of the surrounding sealed area into soil media, in which containing pollutants are potentially filtered (Ahiablame et al 2012). Blue-green infrastructures maintain the natural water cycle and are referred to as low impact developments (LIDs) or best management practice (BMP) (Winogradoff & Coffman 2002)
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