Green roofs have emerged as effective stormwater management systems, but understanding the contribution of their various components to hydrological performance is crucial for optimizing their design and implementation. More empirically measured data on the hydrological function of green roof vegetation is needed, especially under realistic low-maintenance, non-irrigated scenarios. Further, targeted, evidence-based plant selection based on ecological theories may improve green roof hydrological performance. Previous research has suggested that, in contrast to monocultures, mixtures of species with complementary traits could optimize provisioning of various ecosystem services. Thus, species mixtures based on their adaptive life strategy using the CSR theory (Competitor, Stress tolerator, and Ruderal) were hypothesized to have better hydrological performance than a Sedum monoculture or bare substrate under natural conditions over multiple seasons. To test this hypothesis, the runoff from thirty 2 m2 green roof modules was measured. The retention and detention performance of different green roof treatments were evaluated for 84 precipitation events of varying rain depth and intensity during snow-free periods. Differences in retention as well as detention between the vegetation treatments varied, but generally increased with increasing rain event volume and the Stress-tolerant treatment generally performed better than bare substrate. On a mean event basis, the mixture of stress-tolerator species demonstrated a 74 % retention rate, while the Bare substrate retained 72 % of the rainfalls. Overall, the green roofs, including bare substrate and vegetated treatments, effectively retained >50 % of the cumulative precipitation depth. In line with previous studies, the Sedum monoculture generally showed worse hydrological performance than other non-succulent vegetation mixtures, despite its relatively high cover and survival. The vegetated treatment with the highest species richness and diversity in life strategies (Mix) did not provide the best vegetation cover, or hydrological performance. Instead, the Stress-tolerant treatment, characterized by the high survival rate of a single graminoid species, consistently demonstrated superior event-based stormwater retention and peak attenuation capabilities.

Pollutant loads in urban runoff from anthropogenic sources contribute to degradation of downstream waters. Cities are turning toward green infrastructure to manage urban stormwater. Bioretention is popular as green infrastructure and is commonly installed to remove runoff pollutants. A significant proportion of pollutants in urban runoff are particulates or particulate-bound and are effectively removed in bioretention cells. Pollutants accumulate in concentrated areas of the bioretention (e.g., forebays, inlets, surficial filter layers), which require maintenance to restore effective treatment and to increase the operational lifespan. Particles trapped in forebays risk diminished effectiveness of the pretreatment, which may eventually lead to filter clogging and leaching of toxic pollutants. Studies have examined pollutant accumulation and distribution in bioretention filter media, but less is known about processes in bioretention forebays. In this study, 28 bioretention forebays were examined in urban areas of Ohio and Michigan (United States) as well as Stockholm and Malmö (Sweden) to investigate the occurrence and accumulation of metals (i.e., Cd, Cr, Cu, Ni, Pb, and Zn) and 38 analytes of organic micropollutants [OMPs, i.e., alkylphenols, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and phthalates]. Investigated metals were present in all 28 samples, except Cd detected in 27 samples. Of 38 OMP analytes, 31 were detected in at least one sample. PAHs and PCBs were the most frequently detected pollutants found at all examined sites. In general, high concentrations of pollutants were detected in all forebay sediments. Cu, Ni, Zn, PAHs with high molecular weight, and PCBs were detected at concentrations above US and Swedish soil quality guidelines. It was concluded that forebays regularly need to be excavated to maintain their function, and excavated sediments must be handled safely during maintenance work and disposal.

Per- and polyfluoroalkyl substances (PFAS) are extensively used in urban environments and are, thus, found in urban stormwater. However, the relevance of stormwater as a pathway for PFAS to urban streams is largely unknown. This study evaluated the impact of urban stormwater runoff on PFAS concentrations and spatial distribution in three urban streams affected by stormwater discharges from separate sewer systems. River water was sampled during dry (DW) and wet weather (WW) upstream, immediately downstream, and further downstream of three urbanized areas with separate sewer systems and with and without point sources (i.e. waste water treatment plant, airports). Water samples were analyzed for 34 targeted PFAS compounds and sediment samples for 35 targeted PFAS and 30 PFAS compounds using a total oxidizable precursor assay. The sum of the quantified PFAS concentrations ranged from the reporting limit (RL) to 84.7 ng/L during DW and increased as the streams were affected by WW discharges (0.87 to 102.3 ng/L). The highest PFAS concentrations were found downstream of urban areas and/or point sources (i.e. airports) during WW, indicating a clear contribution from stormwater discharges. A consistent PFAS contribution from the WWTP was observed under both DW and WW conditions. During WW events, concentrations of perfluorooctanesulfonic acid (PFOS) and total PFAS (PFOA equivalents) exceeded the annual average environmental quality standards, which are an established limit of 0.65 ng/L for PFOS and a proposed limit of 4.4 ng/L for total PFAS. Notably, except for the legacy PFAS, PFOS and perfluorooctanoic acid (PFOA), the most frequently quantified PFAS during DW were short-chain. For WW, long-chain perfluorocarboxylic acids (PFCAs) and a precursor, 6:2 Fluorotelomer sulfonic acid (6:2 FTS), were more frequently quantified, suggesting stormwater is a source of these longer-chain and particle-associated PFAS. The detection of unregulated fluorotelomer sulfonates (FTSs) such as 6:2 and 8:2 FTS during WW suggests a need for regulatory action, as these compounds can degrade into more stable PFAS. In sediment, higher concentrations, and a greater variety of PFAS were found at sites with known point sources i.e. airports. Long-chain PFCAs (C7–C13), perfluoroalkyl sulfonates (PFSAs) (C6), and precursors (i.e. N-Ethyl perfluorooctane sulfonamidoacetic acid), were more prevalent in sediments than in the water. Notably, PFOS concentrations in sediment exceeded the lowest Predicted No-Effect Concentration (PNEC) across sites, posing a potential long-term environmental risk, though current PNECs for other PFAS may underestimate such risks. The findings of the study highlight urban stormwater as a source of PFAS to urban streams indicating the need to minimize PFAS sources in the urban environment and to effectively treat stormwater to protect receiving water bodies.

Urbant dagvatten kan innehålla per- och polyfluoralkylämnen (PFAS). Den nuvarande kunskapen omförekomst och transport av PFAS i reningsanläggningar för urbant dagvatten är fortfarande mycketbegränsad. Den här studien utvärderar förekomst, ackumulering och fördelning av 35 PFAS och derasprekursorer i filtermaterial och försedimenteringssteg i tjugo biofilteranläggningar som varit i drift längreän 7 år. C5-14,16 perfluoralkylkarboxylsyror (PFCA), C4,8,10 perfluoralkansulfonsyror (PFSA), metylperfluoroktansulfonamidättiksyra (MeFOSAA, en känd PFSA-prekursor) och okända C6-8 PFCAprekursorer var de vanligast förekommande ackumulerade föreningarna. PFAS och deras prekursoreråterfanns i alla djup i liknande förekomster och koncentrationer. Trots att halterna var något högre i detövre filterlagret och minskande med djup var dessa skillnader i regel inte statistiskt signifikanta. Det fannsingen tydlig skillnad mellan fördelningen av kort- och långkedjiga PFAS, trots att långkedjiga ämnen(PFSAs>C5 och PFCAs>C7) förväntades ha mindre mobilitet på grund av deras högre hydrofobicitet. Deövre 5 cm av biofiltren innehöll ofta de högsta föroreningsnivåerna av PFAS och okända prekursorer,men de fanns också djupare ner i filtret. I motsats till exempelvis metaller och PAHer, räcker det sannolikt inte att endast byta ut det översta filterlagret och/eller sediment på toppen av filtret för att avlägsnamer komplexa och mobila föroreningar som PFAS.

Biocides are incorporated into building surface materials to protect them against algae and fungi growth. When such treated surfaces are exposed to precipitation, they may release these biocides, contaminating receiving water bodies. To regulate the use of biocidal products in line with the European Biocidal Products Regulation it is crucial to identify the precise origin of this type of pollutant. In this study, the leaching of a wide range of biocides and chemical elements from 15 materials was investigated through a laboratory scale experiment. The experimental setup was based on the standard method, SIS-CEN/TS 16637-2:2015. The materials tested included bitumen roofing felt and shingles, impregnated wood, as well as paints intended for concrete, wood, and metal surfaces. Each material was tested in duplicates. All materials were tested at a liquid volume to surface area ratio (L/A) of 22.5 L/m2. Sampling was carried out at three intervals: 6 h, 18 h, and 5 days with the leachant being renewed after each leaching step. The results were that diuron was the most commonly detected biocide from the materials tested. The largest number of biocides, including diuron and its degradation products 1-(3.4-dichlorophenyl) urea (DCPU) and diuron desdimethyl (DCPMU), terbutryn, carbendazim and monuron, were detected in the wood paints. Diuron was detected in all three types of wood paint with a mean areal release ratio of 64.6, 25800, and 5710 μg/m2 for the respective paints. Copper was detected in all leachates from impregnated wood, with mean concentrations of 687, 648, 1450, and 279 μg/L from the four tested wood types, respectively. Some of the biocides released were not reported on the data sheets of the tested materials, indicating a need to investigate broader than only based on the information provided by the manufacturers. Future use of biocides in building surface materials may change due to regulations, phase outs and introduction of new biocides, indicating that source identifications is a continuing effort.

Blue green infrastructure (BGI), in recent decades, have been increasingly recognized as robust stormwater control measures to reduce urbanflooding, promote infiltration, and restore a catchment’s flow to its pre-development stage. However, studies comparing the hydrologicalbenefits of BGI alternatives at catchment scale are often limited to single catchment or single/few BGI options scaled over a catchment.This study designed a set of BGI alternatives as a combination of different BGI facilities in terms of the following: (a) spatial distributionscale (end-of-pipe vs. decentralized) and (b) naturalness scale (less engineered vs. more engineered), in three different urban catchmentsrepresenting an inner city, a residential suburb, and a new urban housing. In addition, their hydrological performances were compared.A 10-year return period design rain and a continuous rain series of 11 years were modelled for each BGI alternative using the computermodel stormwater management model (SWMM). It was observed that in most catchments, decentralized alternatives (both engineeredand natural) showed better potential to reduce the magnitude and frequency of flooding than centralized measures. Similarly, the testeddecentralized natural, less engineered alternatives showed higher potential to increase infiltration than the decentralized engineered alternativesin all three catchments. Meanwhile, infiltration-based BGI alternatives showed similar potential to mimic pre-development flow as otherdecentralized BGI alternatives.

Stormwater is recognised as a vector for microplastics (MPs), including tyre wear particles (TWPs) from land-based sources to receivingwaterbodies. Before reaching the waterbodies, the stormwater may be treated. In this study, sediments from six treatment facilities (fiveretention ponds and a subsurface sedimentation tank) were analysed to understand MP occurrence, concentrations, sizes, polymer typesand distribution between inlet and outlet. The concentrations of MPs showed large variations between and within different facilities withMP concentrations of 1,440–72,209 items/kg (analysed by μFTIR) corresponding to 120–2,950 μg/kg and TWP concentrations from ,DL upto 69,300 μg/kg (analysed by pyrolysis–GC–MS), with significantly higher concentrations at the inlet compared to the outlet. Polypropylene(PP) was the predominant MP type in terms of number in all samples. TWPs were dominant by mass in most (nine) samples. The relativelylow density of PP polymers implies that density might not be the sole factor influencing particle settlement behaviour. Small particlesoccurred more frequently than large ones; around 70% of the particles detected in the samples were 100 μm or smaller. In summary, thisstudy highlights the occurrence of MPs, including TWPs, in stormwater facilities and demonstrates variations in concentrations dependingon sites and locations within the facility.

This study involved a survey of Swedish water utilities to evaluate their pipe-network data-collection objectives, usage, storage, and exchange routines. Factors impacting data integration (and the associated benefits) were also identified. Results showed that current data storage and exchange routines can be augmented to support commonly identified objectives and data utilisation needs, especially in larger water utilities. Levels of awareness of the opportunities for and benefits gained through asset management processes and data integration varied between utilities. Further research on the benefits of data integration in pipe network asset management is required to develop an evidence base on benefits accrued in practice, especially considering metadata, the diversity of legacy systems still in operation, costs and policy use.