Sustainable urban drainage systems (SuDS) or nature-based solutions (NBSs) are widely implemented to collect, store and infiltrate stormwater. The buildup of pollutants is expected in NBSs, and Dutch guidelines advise monitoring the topsoil of bio-swales every 5 years. In the Netherlands, almost every municipality has implemented bio-swales. Some municipalities have over 300 bio-swales, and monitoring all their NBSs is challenging due to cost and capacity. In this study, 20 locations where bio-swales with ages ranging between 10 and 20 years old were selected for a field investigation to answer the following question: is the soil quality of bio-swales after 10 years still acceptable? Portable XRF instruments were used to detect potential toxic elements (PTEs) for in situ measurements. The results showed that for copper (Cu), zinc (Zn) and lead (Pb), 30%, 40% and 25% of the locations show values above the threshold and 5%, 20% and 0% above the intervention threshold, meaning immediate action should be taken. The results are of importance for stakeholders in (inter)national cities that implement, maintain, and monitor NBS. Knowledge of stormwater and soil quality related to long-term health risks from NBS enables urban planners to implement the mostappropriate stormwater management strategies. With these research results, the Dutch guidelines for design, construction, and maintenance can be updated, and stakeholders are reminded that the monitoring of green infrastructure should be planned and executed every 5 years.
Stormwater runoff can contain high amounts of Potential Toxic Elements (PTE) as heavy metals. PTE can have negative and direct impact on the quality of surface waters and groundwater. The European Water Framework Directive (WFD) demands enhanced protection of the aquatic environment. As a consequence, the WFD requires municipalities and water authorities to address the emissions from drainage systems adequately and to take action when these emissions affect the quality of receiving waters together with mitigating the quantity challenges in a changing climate (floodings and drought). NBS is the most widely used method for storing stormwater and infiltrating in the Netherlands. However, there is still too little knowledge about the long-term functioning of the soil of these facilities. The research results are of great importance for all stakeholders in (inter)national cities that are involved in climate adaptation. Applying Nature-Based Solutions (NBS), Sustainable Urban Drainage Systems (SuDS) or Water Sensitive Urban Design (WSUD) are known to improve the water quality in the urban water cycle. The efficiency of NBS, such as the capability of bio swales to trap PTE, highly depends on the dimensions of the facility and on its implementation in the field [Woods Ballard, B et al, 2015]. For the determination of the removal efficiency of NBS information about stormwater quality and characteristics is essential. Acquiring the following information is strongly advised [Boogaard et al. 2014]:1. stormwater quality levels (method: stormwater quality database);2. location of NBS (method: mapping NBS in international database);3. behaviour of pollutants (method: cost effective mapping pollutants in the field). Stormwater quality contains pollutants as heavy metal in higher concentrations than water quality standards dictate. Over 500 locations with bio swales are mapped in the Netherlands which is a fraction of stormwater infiltration locations implemented in 20 years’ time. Monitoring of all these NBS would acquire high capacity and budget from the Dutch resources. This quick scan XRF mapping methodology of topsoil will indicate if the topsoil is polluted and whether the concentrations exceed national or international standards. This was only the case in one of the youngest pilots in Utrecht indicating that there are multiple factors other than age (traffic intensity, use of materials, storage volume, maintenance, run off quality, etc.). Several locations show unacceptable levels, above the national thresholds for pollutants where further research on the prediction of these levels in relation to multiple factors will be the subject of future research.The results of study are shared in 2 national workshops and valued as of great importance for all stakeholders in (inter)national cities that are involved in implementation of NBS for climate adaptation. The Dutch research results will be used to update (inter-)national guidelines for design, construction and maintenance of infiltration facilities this year. Stormwater managers are strongly advised to use this quick scan method within the first 10 years after implementation of swales to map possible pollution of the top soil and prevent pollution to spread to the groundwater in urban areas.
Online knowledge-sharing platforms could potentially contribute to an accelerated climate adaptation by promoting more green and blue spaces in urban areas. The implementation of small-scale nature-based solutions (NBS) such as bio(swales), green roofs, and green walls requires the involvement and enthusiasm of multiple stakeholders. This paper discusses how online citizen science platforms can stimulate stakeholder engagement and promote NBS, which is illustrated with the case of ClimateScan. Three main concerns related to online platforms are addressed: the period of relevance of the platform, the lack of knowledge about the inclusiveness and characteristics of the contributors, and the ability of sustaining a well-functioning community with limited resources. ClimateScan has adopted a “bottom–up” approach in which users have much freedom to create and update content. Within six years, this has resulted in an illustrated map with over 5000 NBS projects around the globe and an average of more than 100 visitors a day. However, points of concern are identified regarding the data quality and the aspect of community-building. Although the numbers of users are rising, only a few users have remained involved. Learning from these remaining top users and their motivations, we draw general lessons and make suggestions for stimulating long-term engagement on online knowledge-sharing platforms
