Rain gardens, a type of green infrastructure (GI), have been recognized for mitigating flooding and improving water quality from minor storms by trapping stormwater pollutants. Yet, the capability of ...these systems to retain microplastics (MPs) from stormwater, especially in size <125 μm, remains inadequately understood. This study investigated the spatial and temporal distributions of MPs in three rain gardens located in Newark, New Jersey, USA. The rain gardens have been in operation for ∼7 years and located in different land uses: low-density residential (Site 1), commercial (Site 2), and high-density residential (Site 3). The sediment samples were collected during May 2022, August 2022, and February 2023 at various soil depths and horizontal distances of rain gardens. The MPs were quantified and characterized using Fourier transform infrared (FTIR) spectrometer and a Raman microscope. The overall mean concentration varied between sampling sites, with 469 ± 89.8 pkg−1 in Site 1, 604 ± 91.4 pkg−1 in Site 2, and 997 ± 64.3 pkg−1 in Site 3, with Polypropylene as the dominant polymer, followed by nylon and polyethylene. In the vertical direction, larger MPs (250 μm–5 mm) were effectively retained within the top 5 cm and their concentration declined exponentially with the increasing depths. Small-sized MPs (1–250 μm) were prevalent at deeper depths (≥ 10 cm), and no MPs were found below 15 cm. In the horizontal direction, the highest MP concentration was observed near the stormwater inlet, and the concentration decreased away from the inlet. Over the nine-month period, a notable increase in concentration was observed at all sites. These findings contribute valuable knowledge towards developing effective measures for retaining MPs from stormwater and monitoring GIs in urban environments.
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•The MP accumulation decreases with depth in the bioretention media.•The larger-sized MPs (250 μm–5 mm) are primarily retained in the top 5 cm.•The MPs in rain gardens reached down to 15 cm.•In the horizontal direction, MPs are highest near the inlet of rain gardens.
Rain gardens are widely used for low impact development (LID) or as a nature-based solution (NbS). They help to reduce runoff, mitigate hot temperatures, create habitats for plants and insects, and ...beautify landscapes. Rain gardens are increasingly being established in urban areas. In Taiwan, the Ministry of Environment (MoE) initiated a rain garden project in Taipei city in 2018, and 15 rain gardens have since been constructed in different cities. These Taiwanese-style rain gardens contain an underground storage tank to collect the filtrated rainwater, which can be used for irrigation. Moreover, the 15 rain gardens are equipped with sensors to monitor temperature, rainfall, and underground water levels. The monitoring data were transmitted with Internet of Things (IoT) technology, enabling the capture and export of real-time values. The water retention, temperature mitigation, water quality, and ecological indices of the rain gardens were quantified using field data. The results from the young rain gardens (1–3 years) showed that nearly 100 % of the rainfall was retained onsite and did not flow out from the rain gardens; however, if the stored water was not used and the tanks were full, the rainwater from subsequent storms could not be stored, and the tanks overflowed. The surface temperatures of the rain garden and nearby impermeable pavement differed by an average of 2–4 °C. This difference exceeded 20 °C in summer at noon. The water in the underground storage tanks had very low levels of SS and BOD, with averages of 1.6 mg/L and 5.6 mg/L, respectively. However, the E. coli concentrations were high, and the average was 6283 CFU/100 mL; therefore, washing or drinking water is not recommended. The ecological indices, i.e., the Shannon and Simpson indices, demonstrated the good flora status of the rain gardens after one year. Although the weather differed by city, the performance of the rain gardens in terms of water retention, temperature mitigation, rainwater harvesting, and providing biological habitats was consistent. However, maintenance influences rain garden performance. If the stored water is not frequently used, the stored volume is reduced, and the stored water quality degrades.
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•The Taiwanese-style rain gardens with underground tanks and IoT monitoring systems.•They showed nearly 100 % water conservation and 2-4 °C temperature mitigation.•The harvested rainwater was of good quality except E.coli concentration was high.•Frequent use of stored rainwater is to increase water retention and water quality.
Green infrastructure installations such as rain gardens and bioswales are increasingly regarded as viable tools to mitigate stormwater runoff at the parcel level. The use of adaptive management to ...implement and monitor green infrastructure projects as experimental attempts to manage stormwater has not been adequately explored as a way to optimize green infrastructure performance or increase social and political acceptance. Efforts to improve stormwater management through green infrastructure suffer from the complexity of overlapping jurisdictional boundaries, as well as interacting social and political forces that dictate the flow, consumption, conservation and disposal of urban wastewater flows. Within this urban milieu, adaptive management—rigorous experimentation applied as policy—can inform new wastewater management techniques such as the implementation of green infrastructure projects. In this article, we present a narrative of scientists and practitioners working together to apply an adaptive management approach to green infrastructure implementation for stormwater management in Cleveland, Ohio. In Cleveland, contextual legal requirements and environmental factors created an opportunity for government researchers, stormwater managers and community organizers to engage in the development of two distinct sets of rain gardens, each borne of unique social, economic and environmental processes. In this article we analyze social and political barriers to applying adaptive management as a framework for implementing green infrastructure experiments as policy. We conclude with a series of lessons learned and a reflection on the prospects for adaptive management to facilitate green infrastructure implementation for improved stormwater management.
•Stormwater governance is difficult due to inherent complexity and high uncertainty.•Adaptive management can address ecological, economic and social stormwater issues.•Adaptive management can increase learning to improve stormwater governance.•Adaptive management to implement green infrastructure for stormwater management.•Governance networks can create space for green infrastructure in urban sewersheds.
•Over 7–8 years of operation metal concentrations have not increased significantly.•Cd, Pb and Cu unlikely to exceed soil quality standards within the biofilter life.•Zn concentrations were often ...high and exceeded local prescribed waste guidelines.
Short term studies have found that stormwater biofiltration systems, also known as bioretention systems or raingardens, are very effective in reducing heavy metal concentrations. However, their long-term treatment performance, as well as the spatial and temporal accumulation of metals within these systems remain uncertain. This paper reports on a large scale field study that assessed the changes over time of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) levels in biofilters varying in age, design, and catchment characteristics. The survey incorporated 29 biofilters in 2006/7 and 49 biofilters, in 2014/15, located in three major Australian cities (Melbourne, Brisbane, and Sydney). Noting that these results are influenced by having just one industrial site with 25 filters measured at that site Catchment characteristics were significantly correlated with metal accumulation rates. Biofilters in catchments with current or past industrial activities had elevated heavy metal concentrations in the filter media. Zinc concentrations in the surface 0–100 mm exceed both soil quality and ecological guidelines. In contrast, heavy metal concentrations in residential catchments are unlikely to (ever) reach levels that exceed soil quality guidelines for human health, although zinc concentrations approach ecological guideline criteria.
•Spatial determinants of residential intention to adopt GSI varied among practices.•Household and neighborhood problems predicted intention to adopt infiltration trenches.•Intention to adopt ...diversion of roof runoff show association with broader green actions and norms.•Residing in a town with stormwater permitting may influence one’s intention to adopt rain gardens.
Improved stormwater management for the protection of water resources requires bottom-up stewardship from landowners, including adoption of Green Stormwater Infrastructure (GSI). We use a statewide survey of Vermont paired with a cross-scale and spatial analysis to evaluate the influence of interacting spatial, social, and physical factors on residential intention to adopt GSI across a complex social-ecological landscape. Specifically, we focus on how three GSI practices, (“rain garden (bio retention),” “infiltration trenches,” and “actively divert roof runoff to a rain barrel/lawn/garden instead of the street/sewer”) vary with barriers to adoption, and household attributes across stormwater contexts from the household to watershed scale. Private landowners, who may be motivated more by on-site and neighborhood stormwater problems, may gravitate toward practices like infiltration trenches compared with practices (e.g., rain gardens) perceived to serve stormwater function over larger areas. Diversion of roof runoff was found to be more likely to be a part of a larger assembly of green behaviors. Improved stormwater management outcomes at the watershed, town, neighborhood, and household levels depend on adaptive approaches and adjusting strategies along the rural-urban gradient, across the bio-physical landscape, and according to varying norms and institutional arrangements.
The implications of climate change and changing precipitation patterns need to be investigated to evaluate mitigation measures for source water protection. Potential solutions need first to be ...evaluated under present climate conditions to determine their utility as climate change adaptation strategies. An urban drainage network receiving both stormwater and wastewater was studied to evaluate potential solutions to reduce the impact of combined sewer overflows (CSOs) in a drinking water source. A detailed hydraulic model was applied to the drainage basin to model the implementation of best management practices at a drainage basin scale. The model was calibrated and validated with field data of CSO flows for seven events from a survey conducted in 2009 and 2010. Rain gardens were evaluated for their reduction of volumes of water entering the drainage network and of CSOs. Scenarios with different levels of implementation were considered and evaluated. Of the total impervious area within the basin directly connected to the sewer system, a maximum of 21% could be alternately directed towards rain gardens. The runoff reductions for the entire catchment ranged from 12.7% to 19.4% depending on the event considered. The maximum discharged volume reduction ranged from 13% to 62% and the maximum peak flow rate reduction ranged from 7% to 56%. Of concern is that in-sewer sediment resuspension is an important process to consider with regard to the efficacy of best management practices aimed at reducing extreme loads and concentrations. Rain gardens were less effective for large events, which are of greater importance for drinking water sources. These practices could increase peak instantaneous loads as a result of greater in-sewer resuspension during large events. Multiple interventions would be required to achieve the objectives of reducing the number, total volumes and peak contaminant loads of overflows upstream of drinking water intakes.
•A model simulating combined sewer overflow (CSO) characteristics was used.•The implementation of rain gardens was modeled and evaluated for 7 rainfall events.•Rain gardens can reduce the volume of runoff and volume of CSOs.•Reduction of CSO volumes was small for large rainfall events.•Stormwater management objectives may run counter to source water protection.
Green infrastructure (GI) has been touted as a more economically, socially, and environmentally sustainable option for urban stormwater management than more traditional gray infrastructure solutions. ...There are many types of GI, however, and there has been limited comparison of sustainability between types. This study examines the benefits and detriments of current GI designs (rain gardens, green roofs, porous pavements, and tree plantings) using emergy analysis, an environmental accounting system that evaluates the direct and indirect energy inputs used in the production of goods or services. Results of the analysis revealed inherent differences between the four GI typologies examined and identified system inputs that dominate emergy flows, and thus sustainability outcomes. Porous pavements performed the worst when evaluated using standard emergy-based environmental sustainability indices and the best when using economic indices. Indices calculated for green roofs and tree plantings indicated that these types of green infrastructure might inherently be more environmentally sustainable. Emergy inputs of stone and soil were dominant inputs for all systems, as was the emergy cost of disposal of excavated materials. Porous asphalt was a high emergy input for the porous pavement projects examined. Labor and equipment inputs were high for most projects, but were overshadowed by stone and soil inputs. These dominant emergy inputs show areas where efficiency of designs could be improved by practices such as recycling excavated sediments or utilizing construction materials that are less emergy intensive. In addition, the results of this study show that not all GI projects are created equally. Urban planners and other decision makers can use this information to improve standard design and implementation practices for GI projects.
•Porous pavements performed relatively poorly in emergy-based measures of sustainability.•Emergy inputs of purchased stone and soil dominated emergy flows.•Design impacted emergy sustainability of projects within each type of green infrastructure.
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