Implementing stormwater green infrastructure in shallow groundwater areas presents major challenges that could restrict widespread adoption of swales in such areas. These limitations are driven by concerns about reduced swale infiltration capacity, which negatively impacts the effectiveness of green measures in managing runoff volumes. This study evaluates the spatial and temporal distribution of infiltration rates in a 30-m grass swale section using a Modified Philip-Dune infiltrometer and full-scale infiltration testing. Groundwater levels were continuously monitored by three piezometers adjacent to the grass swale to assess the impact of unsaturated zone depth on the swale infiltration capacity. Results showed that infiltration rates varied widely from 13 mm/h at the swale bottom to 98 mm/h on the right slope and highlighted the potential overestimation of swale capacity when relying only on point measurements of infiltration. Results from a full-scale infiltration test revealed an overall swale infiltration rate of only 4 mm/h, which is below the values recommended in the literature for swale applicability. A 52 % decrease in infiltration rates was observed between 2022 and 2024. Experimental results indicated that the grass swale had the capacity to recover its storage and managed a subsequent rainfall event within 15 h of the full draw-down. While the findings did not show a strong correlation between swale infiltration rates and the depth of the unsaturated zone, the results underscore the need to balance the soil permeability and groundwater protection for effective stormwater management.

A curtained stormwater storage and treatment facility was constructed in Lake Storsjön (Sweden) to treat urban stormwater runoff discharges. Over two and a half years, sediments were sampled four times across four facility zones (from inlet to outlet) in two depths to inform facility operation and polluted sediment management. Sediments were analysed for particle size distribution, metals, polycyclic aromatic hydrocarbons, and organic matter content to assess the spatial distribution of deposited sediment characteristics. Finer sediments (<0.016 mm) prevailed near the outlet, with a higher presence of fine particles in the deeper layer (10–20 cm). Substantial variations in chemical concentrations were observed, differing by up to three orders of magnitude. Higher concentrations were consistently found in the inlet zone and deeper layers (10–20 cm depth) throughout the sampling program. Combined horizontal and vertical distributions of sediment characteristics indicated a predominance of historical deposits in the sediments collected. Frequent exceedances of Predicted No-Effect Concentrations of chemicals, particularly in the inlet zone, highlighted potential risks to the aquatic environment that would result from dredging activities. This underscores the importance of considering broad mitigation strategies, including the capping of contaminated sediment, to control the environmental impacts of contaminated sediments on the lake ecosystem.

To assess the reliability of green stormwater infrastructure (GSI), including grass swales, it is required to characterize the frequency of system failures. This involves identifying the conditions when the system operates in failure mode, potentially causing downstream flooding. The study utilized three 23-year meteorological time series from three Swedish locations, characterized by frontal, convective, or orographic rainfall events. These time series served as inputs for the simulation of runoff flows using the SWMM model, representing the physical characteristics of a grass swale (GS) located in Luleå, Sweden. Results showed a trend of reduced overflow occurrences and flood risks at higher ksat values of 25 and 31 mm/h. Exceedance curves indicated that ksat values of 2 or 4 mm/h resulted in the swale operating in failure mode 100% of the time. A minimum ksat of 31 mm/h was required to achieve acceptable operation for more than 50% of the time in Gothenburg and Luleå. Östersund was the only location where the studied GS did not operate in failure mode under a high ksat of 31 mm/h. Local climate – especially rainfall distribution and frequency – sets performance thresholds and underscores the need to integrate technical performance with flood risk management in GSI design.

Reduction of runoff flow peaks and volumes is one of the performance objectives of grass swales in the context of Green Stormwater Infrastructure (GSI). Towards this end, a study of the feasibility of using a retrofitted swale outlet control weir (SOCW) to reduce runoff volume and peak flow, by enhancing swale runoff storage and infiltration into swale soils, was conducted in Luleå, Northern Sweden. Experimental field work consisted of 43 irrigation-driven runoff experiments, mimicking rainfall events with return periods between 1- to 50-years, with a constant intensity and duration of 30 min, in a 30-m long grass swale section. Experimental results confirmed that, under the tested conditions, swales with the retrofitted outflow control, reduced runoff volumes and peak flows. Such reductions ranged from 32 percentage points (for 2-year) to 1 and 4 percentage points (for 50-year return period) for runoff volumes and peak flows, respectively. Outcomes of scenarios with outflow controls clearly indicated a decreasing performance with increasing flow rates (and irrigation event return periods). Furthermore, the retrofitted swale controlled the outflow release during less frequent 20 to 50-year events, which would contribute to reducing flood risks in downstream urban areas.

A literature search on traffic related metals in polluted urban snow revealed a significant volume of references representing a substantive knowledge base. The frequently studied metals in urban snow included Zn, Cu, Pb, Cd and Ni. However, comparing metal concentrations across studies proves to be a complex effort due to the variations in site-specific factors among studies, such as traffic intensity, pavement conditions, hydrometeorological conditions, and research method aspects, such as sampling equipment and frequency, and laboratory analytical methods. The literature review indicated that among the commonly studied metals, Zn and Cu indicated potential environmental concerns, and that there was a lack of data on the occurrence and accumulation in snow of antimony (Sb), tungsten (W), and platinum group elements (PGEs). To partly mitigate this knowledge gap, a field study of these elements was carried out by sampling urban roadside snow at six locations with various land use and traffic intensities, focusing on accumulation of these elements in snowbanks along roadways. The results indicated that traffic related activities are the sources of PGEs, W and Sb in roadside snowbanks, as the concentrations of these metals increased with increasing traffic intensity. The mean concentrations of the studied metals followed this descending order: W (0.4 (Reporting limit-RL)–987 μg/l) > Sb (0.1 RL–33.2 μg/l) > Pd (0.02 (RL)–0.506 μg/l) > Rh (0.02 (RL)–0.053 μg/l). In laboratory melted snow, both W and Sb were mostly in the particulate-bound phase, with <25 % in the dissolved phase. For sites with metal concentrations above the detection limit, the regression analysis indicated linear trends in unit area deposition rates of W with time (snow age), described by R2 = 0.94.

Winter road salt applications are increasing chloride concentrations in many freshwater ecosystems. This trend is alarming, giv­en chloride’s potential to impair aquatic ecosystems. Short- and long-term exposure to salt could affect ecosystem metabolism and nutrient cycles. Here, we examine connections between chloride concentrations, water quality conditions, benthic respi­ration, and sediment-water nutrient flux throughout a large (722 km2) lake and its catchment. Aquatic locations experiencing high concentrations of chloride are indicators of anthropogenic activities and are often associated with additional pollutants. We used sediment core flow-through incubations under ambient and enriched chloride concentrations to determine the effects of road salt on benthic respiration and nutrient fluxes in stream, stormwater pond, and lake sites. Salt (as sodium chloride) ad­ditions caused a significant overall increase in benthic respiration. Acute exposure to road salt caused the strongest increase in benthic respiration when water was warm and at sites that had low (< 50 mg Cl-/L) or high (> 400 mg Cl-/L) ambient chloride concentrations or when water was cold and sites had intermediate (100-400 mg Cl-/L) ambient chloride concentrations. Nitrate flux responded less uniformly to salt additions. Depending on waterbody type and season, ambient nitrate flux into the sediment was similar, increased, or decreased post-chloride addition. Dissolved phosphorus flux was not significantly impacted by salt additions. Across lake and stream sites, our results supported the hypothesis that chloride causes increased respiration while nutrient cycles were weakly and inconsistently altered under experimental pulse road salt additions.

El uso de sal de carreteras en invierno para el deshielo está aumentando las concentraciones de cloruro en muchos ecosis-temas de agua dulce. Esta tendencia es alarmante, dado el potencial del cloruro para dañar los ecosistemas acuáticos. Laexposición a corto y largo plazo a la sal podría afectar el metabolismo del ecosistema y los ciclos de nutrientes. En este estudio,examinamos las conexiones entre las concentraciones de cloruro, la calidad del agua, la respiración béntónica y el flujo denutrientes entre el agua y el sedimento en un gran lago (722 km2) y su cuenca. Los sistemas acuáticos que experimentan altasconcentraciones de cloruro son indicadores de actividades antropogénicas y, a menudo, se asocian con contaminantes adicio-nales. Utilizamos incubaciones de sedimento con flujo continuo, en condiciones ambientales y con enriquecimiento de cloruropara determinar los efectos de la sal de carreteras en la respiración bentónica y los flujos de nutrientes, en un arroyo, una pozade aguas pluviales y en el lago. Las adiciones de sal (como cloruro de sodio) causaron un aumento general significativo en la respiración bentónica. La exposición aguda a la sal causó el aumento más fuerte en la respiración bentónica cuando el aguaestaba tibia y en los cuando tenían concentraciones de cloruro ambiental bajas (< 50 mg Cl-/L) o altas (> 400 mg Cl- /L); ocuando el agua estaba fría y tenían concentraciones de cloruro ambiental intermedias (100-400 mg Cl-/L). El flujo de nitratorespondió de manera menos uniforme a las adiciones de sal. Según el tipo de cuerpo de agua y el período del año, el flujo denitrato ambiental hacia el sedimento fue similar, aumentó o disminuyó después de la adición de cloruro. El flujo de fósforo di-suelto no se vio afectado significativamente por las adiciones de sal. En el lago y en el arroyo, nuestros resultados respaldaronla hipótesis de que el cloruro provoca una mayor respiración, mientras que los ciclos de nutrientes se alteraron de maneradébil e inconsistente bajo las adiciones experimentales de sal de carreteras.

Urban areas play a key role in the production of microplastics (MPs) and their entry into water bodies. This article reviews the literature on the sources, transport, and control of MPs in urban environments with the aim of clarifying the mechanisms underlying these processes. Major MP sources include atmospheric deposition, micro-litter, and tire and road wear particles (TRWPs). MPs deposited from the atmosphere are mostly fibers and may be particularly important in catchments without traffic. Littering and attrition of textiles and plastic products is another important MP source. However, the quantities of MPs originating from this source may be hard to estimate. TRWPs are a significant source of MPs in urban areas and are arguably the best quantified source. The mobilization of MPs in urban catchments is poorly understood but it appears that dry unconsolidated sediments and MP deposits are most readily mobilized. Sequestration of MPs occurs in green areas and is poorly understood. Consequently, some authors consider green/pervious parts of urban catchments to be MP sinks. Field studies have shown that appreciable MP removal occurs in stormwater quality control facilities. Street cleaning and snow removal also remove MPs (particularly TRWPs), but the efficacy of these measures is unknown. Among stormwater management facilities, biofiltration/retention units seem to remove MPs more effectively than facilities relying on stormwater settling. However, knowledge of MP removal in stormwater facilities remains incomplete. Finally, although 13 research papers reported MP concentrations in stormwater, the total number of field samples examined in these studies was only 189. Moreover, the results of these studies are not necessarily comparable because they are based on relatively small numbers of samples and differ widely in terms of their objectives, sites, analytical methods, size fractions, examined polymers, and even terminology. This area of research can thus be considered “data-poor” and offers great opportunities for further research in many areas.

Building surface materials, exposed to wash-off by rainwater or snowmelt, are recognised as one of the significant urban diffuse pollution sources contributing to the impairment of stormwater quality. The pollution conveyed by roof runoff originates from two potential sources, migration of surface material constituents, or wash-off of pollutants deposited on the surface by atmospheric deposition. This study investigated the releases of metals and several groups of contaminants of emerging concern: alkylphenols, alkylphenol ethoxylates, and phthalates, from commercially available materials, which are commonly used on buildings and structure surfaces in the urban environment. The materials tested included the following: metal sheets of stainless steel, copper, zinc, galvanised steel, corten steel, corrugated and coated steel, coated zinc; and bitumen-based roofing felt and shingles, as well as polyvinyl chloride (PVC) from two manufacturers. The stainless steel was considered a control material serving to estimate pollutant contributions deposited on the pilot panels from the surrounding environment. Moreover, this study presents novel data on roof snowmelt induced runoff quality, not reported in the previous literature. The experimental setup consisted of 2-m2 rectangular panels mounted in triplicates of each material and placed in an open-air setting on the campus of Luleå University of Technology, Sweden. Runoff leaving the gently sloping material panels was collected during 11 rain and three snowmelt driven runoff events occurring over a five-year period. The results showed that, in general, the micropollutant concentrations and loads were lower in snowmelt than rain induced runoff, and no decreasing trend was detected in the releases of phthalates or metals during the study period. Moreover, on a yearly basis, copper sheets were estimated to release 0.6 g/m2 Cu to runoff, zinc and galvanised sheets 1.3 and 0.7 g/m2 Zn, respectively, and, PVC sheets were estimated to release up to 78 mg/m2 of diisononyl phthalate (DINP).