Traffic-related metals in urban snow cover: A review of the literature data and the feasibility of filling gaps by field data collection.

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.

Releases of micropollutants from building surface materials into rainwater and snowmelt induced runoff.

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).

Toxicity of sediments in eight urban stormwater management ponds: bioassessment by oligochaete community metrics used in the sediment quality triad.

Implemented for decades as part of the 'best management practices (BMPs)' for controlling urban runoff impacts on receiving waters, stormwater management ponds (SMPs) have been increasingly viewed as potential habitats for urban wildlife. However, since SMPs are subject to a lot of environmental constraints, research toward assessing their ecological quality and their actual benefits as habitats for biota is needed. In this study, the sediment toxicity of eight SMPs located in Southern Ontario, Canada was assessed using the sediment quality triad (SQT) approach. Sediment samples were collected for chemical, ecotoxicological and biological analyses. An oligochaete-based index approach (Oligochaete Index of Lake Bioindication and percentage of pollution-sensitive species) was used as the biological endpoint and integrated into a weight-of-evidence approach to assessing the general sediment quality of the ponds. Our results showed that (i) heavy metals in the sediment and (ii) chloride concentrations in the sediment interstitial water caused detrimental effects on the ecological quality of the sediments in the ponds studied. The oligochaete indices applied in this study showed value as biological endpoints to be integrated into the SQT and used for setting up sediment ecological quality goals.

Microplastics in urban catchments: Review of sources, pathways, and entry into stormwater.

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.

Green infrastructure drainage of a commercial plaza without directly connected impervious areas: a case study.

A paired-catchment study of two adjacent commercial areas in northern Sweden, one with Green Infrastructure (GI) storm drainage and the other with a conventional storm sewer system, served to evaluate the hydrological performance of both drainage systems and demonstrate advantages of GI. The GI catchment avoided directly connected impervious areas by diverting runoff from a parking lot to a cascade of three infiltration features, a fractured rock strip draining onto a sloping infiltration area, followed by a collector swale. Both catchments were monitored over 4 years by measuring rainfall, runoff and, in the vicinity of the swale, soil water content and groundwater levels. For frequent storms, the median GI efficiencies in reducing runoff volumes and peak flows, and extending peak flow lags, were 96, 99 and 60%, respectively, compared to conventional drainage. The storm rainfall depth, initial soil water content, increases in intra-event soil water storage and groundwater levels had statistically significant effects on either runoff volume or peak flow reductions. No effects were found for storm rainfall intensity and duration, antecedent dry days, and initial groundwater levels. The study demonstrated that GI drainage can be successfully applied even in the challenging environment of a subarctic climate.

Microplastics (MPs) in urban roadside snowbanks: Quantities, size fractions and dynamics of release.

The microplastics (MP) pollution has been receiving high attention in recent years, because of the massive amounts of plastics it contributes to the environment. Tyre wear and road wear particles (TWP and RWPs) were identified as major sources of MPs, but the observed data on these particles in urban snow deposits and snowmelt is scarce. To contribute to remediation of this situation, a study designed to quantify TWPs and RWPs in urban roadside snowbanks, and assess the MP occurrence in three size fractions, was conducted in the Luleå and Umeå municipalities in Northern Sweden. TWPs and RWPs were determined in three size fractions: 50-100 µm, 100-300 µm, and ≥300 µm, and their release from melting snow was investigated in the laboratory under controlled conditions. Among the MPs identified in snow and the associated snowmelt samples, a majority consisted of both types of particles (T&RWPs) with an average of 20,000 ± 48,000 number/L, whereas other MPs (fibres, fragments, flakes, and films of plastic) were much less plentiful with an average concentration of 24 ± 16 number/L. The largest proportion of T&RWPs was detected in the size fraction 50-100 µm (around 80%), and the smallest proportion was in the fraction ≥300 µm (about 2%). Of the T&RWPs, about 85% were black bitumen particles (RWPs), composed of bitumen, mineral material and polymer modifiers, and 15% were tyre wear particles (TWPs) composed of rubber. The laboratory snow melting experiments demonstrated that urban snow stored MPs, which were eventually released during snowmelt. The ultimate fate of released MPs would depend on snowmelt drainage; it may either drain away from the road pavement and infiltrate into the ground, or enter the road gutter and be conveyed to storm sewers discharging to the receiving waters.

Exploiting urban roadside snowbanks as passive samplers of organic micropollutants and metals generated by traffic.

Stormwater and snowmelt runoff is known to contribute to the deterioration of quality of urban surface waters. Vehicular traffic is recognised as a major source of a wide range of pollutants to urban runoff, including conventional pollutants, such as suspended solids and metals, and those referred to as 'contaminants of emerging concern'. The aim of this study was to investigate the contribution of selected metal(loid)s (Cd, Cr, Cu, Ni, Pb, Pd, Sb, W, Zn), polycyclic aromatic hydrocarbons (PAHs), nonylphenols, octylphenols and -ethoxylates, phthalates and bisphenol A (BPA) from vehicular traffic by sampling urban roadside snow at eight sites, with varying traffic intensities, and one control site without direct impacts of traffic. Our results confirmed that vehicles and traffic-related activities were the sources of octylphenols, BPA and phthalates as well as the metal(loid)s Sb and W, infrequently reported in previous studies. Among metal(loid)s, Cu, Zn and W occurred in the highest concentrations (up to 1.2 mg/L Cu, 2.4 mg/L Zn and 1.9 mg/L W), while PAHs and phthalates occurred in the highest concentrations among the trace organic pollutants (up to 540 µg/L phthalate diisononyl phthalate). Among the phthalates, di-(2-ethylhexyl)phthalate had the highest frequency of detection (43% of the roadside samples). While BPA and octylphenols had relatively high frequencies of detection (50% for BPA and 81% for octylphenols), they were present in comparatively low concentrations (up to 0.2 µg/L BPA and 1.1 µg/L octylphenols). The control site displayed generally low concentrations of the pollutants studied, indicating that atmospheric deposition was not a significant source of the pollutants found in the roadside snow. Several of the pollutants in the roadside snow exceeded the applicable surface water and stormwater effluent guideline values. Thus, the transport of these pollutants with runoff posed risk of causing adverse effects in the receiving surface waters.

Comparison of three explorative methods for identifying building surface materials contributing pollutants to stormwater.

Runoff from building and structure surfaces may contribute to the pollution of urban stormwater and, thereby, to the degradation of the receiving water quality. Various micropollutants have been found in surface runoff from buildings in the urban environment, including metals and organic micropollutants. Effective methods for identification of such pollutants and their sources are the prerequisites for the development of control measures. In this paper, three different methods for the identification of building surface materials acting as sources of metals (Cd, Cr, Cu, Ni, Pb and Zn), nonylphenols and phthalates are presented: (i) screening of the material composition, (ii) laboratory leaching experiments with synthetic rainwater, and (iii) open-air pilot testing of material panels exposed to actual rainfall and runoff. These three methods cover a wide span of experimental aspects, including, e.g., size of material samples, resource demands, and control of influential factors. Nine materials commonly used on building and structure surfaces in the urban environment were tested: metal sheets of zinc, copper, galvanised steel, coated corrugated steel and stainless steel; and, four different roofing membranes of bitumen as well as polyvinyl chloride (PVC). The experimental results indicated that all three methods were meritorious in providing some information contributing to the identification of pollutant sources. The screening of material composition for targeted pollutants is relatively quick and inexpensive, but may fail to identify minor sources of pollutants, or may identify the substances present in the material, but not released in contact with water. Laboratory leaching was generally effective in identifying sources of substances present in surface runoff, but was unsuitable for estimating the magnitude of actual concentrations in building runoff. Open-air pilot studies of material samples (exposed area = 2 m2) were thought to provide the results corresponding well to concentrations in runoff from actual building surfaces, but required relatively large financial and labour resources. Thus, the choice of the method for pollutant identification should be based on study objectives, and some benefits may be achieved using more than one method in an integrated manner; e.g., composition screening and lab or open-air leaching of targeted materials.

Metal enrichment of soils in three urban drainage grass swales used for seasonal snow storage.

Enrichment of soils in three urban drainage swales by metals associated with traffic sources was investigated in a cool temperate climate with seasonal snow. Such swales differed from those not exposed to snow by receiving additional pollutant loads from winter road maintenance involving applications of salt and grit, use of studded tires, and storage and melting of polluted snow cleared from trafficked areas into swales. Among the swales studied, swale L2 in the downtown was the oldest (built around 1960), drained runoff from a road with the highest traffic intensity, and exhibited the highest mean concentrations of most of the metals studied (Pb, Cu, Zn, Cr, Cd, Ni, Co, V, Ti, and W). In the case of Pb, this exceedance was about an order of magnitude: 71 mg/kg DW in L2, compared to about ~8 mg/kg DW in L1 and L3, both built in 1979. Among the metals originating from local geology, barium (Ba) was found in the swales and the grit material at high concentrations of ~650 mg/kg DW and 700-1000 mg/kg DW, respectively. Such concentrations exceeded the Swedish EPA guideline limits of 300 mg/kg DW for less sensitive soil use. The sequential extraction analysis of samples from swale L2 indicated that Ba was mostly in the immobile residual fraction (90%). The absence of clear decline in metal concentrations with distance from the trafficked surfaces suggested that stored snow was another source of metals partly balancing spatial distribution of metals in swale soils.

Enhancing stormwater sediment settling at detention pond inlets by a bottom grid structure (BGS).

Stormwater sediments of various sizes and densities are recognised as one of the most important stormwater quality parameters that can be conventionally controlled by settling in detention ponds. The bottom grid structure (BGS) is an innovative concept proposed in this study to enhance removal of stormwater sediments entering ponds and reduce sediment resuspension. This concept was studied in a hydraulic scale model with the objective of elucidating the effects of the BGS geometry on stormwater sediment trapping. Towards this end, the BGS cell size and depth, and the cell cross-wall angle were varied for a range of flow rates, and the sediment trapping efficiency was measured in the model. The main value of the observed sediment trapping efficiencies, in the range from 13 to 55%, was a comparative assessment of various BGS designs. In general, larger cells (footprint 10 × 10 cm) were more effective than the smaller cells (5 × 5 cm), the cell depth exerted small influence on sediment trapping, and the cells with inclined cross-walls proved more effective in sediment trapping than the vertical cross-walls. However, the BGS with inclined cross-walls would be harder to maintain. Future studies should address an optimal cell design and testing in an actual stormwater pond.

The pollution conveyed by urban runoff: A review of sources.

Urban stormwater and snowmelt pollution contributes significantly to the deterioration of surface waters quality in many locations. Consequently, the sources of such pollution have been studied for the past 50 years, with the vehicular transportation sector and the atmospheric deposition identified early as the major pollution sources. In search for mitigation of this pollution, source controls, besides other measures, were recognised as effective pollution mitigation tools, whose successful implementation requires a good knowledge of pollution sources. Even though great research efforts have been exerted to document specific sources of urban runoff pollution, or specific groups of pollutants present in urban runoff, a comprehensive overview of all known contributing sources is still missing. This review contributes to closing this gap by compiling findings of previous research and critically synthesizing the current knowledge of various stormwater pollution sources. As the emphasis is placed on the sources, the related issues of implications for urban surface water quality and possible source controls for individual sources are touched upon just briefly, where required. The review showed that the atmospheric deposition, vehicular transportation-related activities and metallic building envelopes continue to be among the major pollution sources, which have been studied in a far greater detail than other sources. Furthermore, it was noted that because of the rapid advances in clean manufacturing and pollution control technologies, a large part of the body of data on stormwater quality available in the literature should be considered as historical data, which may no longer describe well the current conditions. Progressing historical data obsolescence, combined with continuing releases of new materials and chemicals, and, in some cases of new substances of potential concern, into the environment, suggests that the identification of important stormwater runoff/snowmelt pollution sources, and the associated pollutants, has been and will remain to be a work in progress.

Building surface materials as sources of micropollutants in building runoff: A pilot study.

Control of diffuse pollution is critical for achieving good surface water quality status. In this context, pollutant contributions from building materials have received increased attention in recent decades. This study examined the releases of metals, nonylphenols and phthalates from ten common building surface materials (installed in triplicates) into rainwater runoff from six rain events. The highest releases of metals were from copper and zinc sheets (average concentrations of 3090 µg/L Cu and 7770 µg/L Zn respectively), while other metal materials, e.g., Corten weathering steel, exhibited lower releases. PVC roofing released high concentrations of nonylphenols and phthalates (average concentrations of up to 26 µg/L nonylphenols and 455 µg/L Diisononyl phthalate, DINP) which have not been investigated in the earlier studies. Pollutant releases varied between events, likely because of weather conditions and rainfall characteristics. Study findings should be valuable for environmentally responsible applications of the existing building materials and the development of new ones, as well as the investigations and risk assessment of specific pollutants in stormwater.

Processes improving urban stormwater quality in grass swales and filter strips: A review of research findings.

Increasing interest in urban drainage green infrastructure brings attention to grass swales and filter strips (GS&GFS) and their role in stormwater management. While the understanding of the hydrology and hydraulics of these stormwater control measures is adequate for current needs, there are knowledge gaps in understanding the water quality processes in GS&GFS and such a finding motivated preparation of the review paper that follows. The review revealed that most of the empirical studies of GS&GFS flow quality focused on the removal of pollutants associated with road runoff, and particularly solids, with relatively few studies addressing nutrients, traffic associated hydrocarbons, oxygen demanding substances, chloride, and faecal indicator bacteria. The reported results suffer from limitations caused by experimental conditions often representing a steady flow used to irrigate GS&GFS and generate runoff, non-submerged flows, no lateral inflows along swale side slopes, constant dosing of solids, emphasis on larger-than-typical solids, incomplete descriptions of experimental conditions, and limited attention to experimental uncertainties. Besides settling, other treatment processes, like adsorption/desorption, plant uptake, chemical precipitation and microbial degradation are often acknowledged, but without attempting to quantify their effects on flow quality. The modelling of GS&GFS flow quality would be beneficial for an improved understanding of green urban drainage infrastructure, but currently it is infeasible without a better knowledge of stormwater quality processes in GS&GFS facilities.

An exploratory study of the effects of stormwater pipeline materials on transported stormwater quality.

Implications of three sewer pipe materials (concrete, galvanized corrugated steel, and polyvinyl chloride (PVC)) for stormwater quality were explored in laboratory experiments, in which three types of stormwater, SW1-SW3, were circulated in 0.5 m long sewer pipe sections. SW1 and SW2 represented synthetic rainwater, without and with fine street sediment added (CTSS = 150 mg/L), respectively, and SW3 was actual stormwater with the same sediment addition as SW2. Following 20-min runs, with an equivalent distance of 500 m travelled by water particles, a number of statistically significant changes in the stormwater chemistry were observed: (i) pH of all the simulated stormwaters increased in the concrete pipe (from 7.0-7.3 to 8.1-9.3), (ii) turbidity decreased in two stormwaters with sediments (SW2 and SW3) in concrete and galvanized corrugated steel pipes (by 50 and 85%, respectively), (iii) the type of stormwater affected the observed copper (Cu) concentrations, with Cudiss concentrations as high as 25.3 µg/L noted in SW3 passing through the PVC pipe, and (iv) zinc (Zn) concentrations sharply increased (Zntot = 759-1,406 µg/L, Zndiss = 670-1,400 µg/L) due to Zn elution from the galvanized steel pipe by all three stormwaters. Such levels exceeded the applicable environmental guidelines.

Contribution of coarse particles from road surfaces to dissolved and particle-bound heavy metal loads in runoff: A laboratory leaching study with synthetic stormwater.

Laboratory leaching experiments were performed to study the potential of coarse street sediments (i.e. >250µm) to release dissolved and particulate-bound heavy metals (i.e. Cd, Cr, Cu, Ni, Pb and Zn) during rainfall/runoff. Towards this end, street sediments were sampled by vacuuming at seven sites in five Swedish cities and the collected sediments were characterized with respect to their physical and chemical properties. In the laboratory, the sediments were combined with synthetic rainwater and subject to agitation by a shaker mimicking particle motion during transport by runoff from street surfaces. As a result of such action, coarse street sediments were found to release significant amounts of heavy metals, which were predominantly (up to 99%) in the particulate bound phase. Thus, in dry weather, coarse street sediments functioned as collectors of fine particles with attached heavy metals, but in wet weather, metal burdens were released by rainfall/runoff processes. The magnitude of such releases depended on the site characteristics (i.e. street cleaning and traffic intensity), particle properties (i.e. organic matter content), and runoff characteristics (pH, and the duration of, and energy input into, sediment/water agitation). The study findings suggest that street cleaning, which preferentially removes coarser sediments, may produce additional environmental benefits by also removing fine contaminated particles attached to coarser materials.

Source-Based Modeling Of Urban Stormwater Quality Response to the Selected Scenarios Combining Future Changes in Climate and Socio-Economic Factors.

The assessment of future trends in urban stormwater quality should be most helpful for ensuring the effectiveness of the existing stormwater quality infrastructure in the future and mitigating the associated impacts on receiving waters. Combined effects of expected changes in climate and socio-economic factors on stormwater quality were examined in two urban test catchments by applying a source-based computer model (WinSLAMM) for TSS and three heavy metals (copper, lead, and zinc) for various future scenarios. Generally, both catchments showed similar responses to the future scenarios and pollutant loads were generally more sensitive to changes in socio-economic factors (i.e., increasing traffic intensities, growth and intensification of the individual land-uses) than in the climate. Specifically, for the selected Intermediate socio-economic scenario and two climate change scenarios (RSP = 2.6 and 8.5), the TSS loads from both catchments increased by about 10 % on average, but when applying the Intermediate climate change scenario (RCP = 4.5) for two SSPs, the Sustainability and Security scenarios (SSP1 and SSP3), the TSS loads increased on average by 70 %. Furthermore, it was observed that well-designed and maintained stormwater treatment facilities targeting local pollution hotspots exhibited the potential to significantly improve stormwater quality, however, at potentially high costs. In fact, it was possible to reduce pollutant loads from both catchments under the future Sustainability scenario (on average, e.g., TSS were reduced by 20 %), compared to the current conditions. The methodology developed in this study was found useful for planning climate change adaptation strategies in the context of local conditions.

Contamination of stormwater by wastewater: a review of detection methods.

Even in separate sewer systems, wastewater may find its way into the receiving waters through stormwater sewers. The main reasons for this are cross-connections, illicit connections, overflows and leakages through broken sewers. Such discharges may affect receiving water quality and increase risks to public health and aquatic organisms. Detecting wastewater contamination and locating its points of ingress into storm sewer systems can be a challenging task, which should be addressed using proper methods and indicator parameters. A number of detection methods have already been proposed in this area, yet there is a lack of a general overview of such methods. This literature review summarizes and evaluates the methods used for detecting wastewater in stormwater, including those recently developed. The advantages, weaknesses and limitations of individual methods are discussed. It is concluded that while no single method can as yet produce results in a precise, fast and inexpensive way, the use of human waste specific chemical and microbiological markers, and their innovative sampling, offer the way forward. Guidance for selecting the most effective combinations of detection methods, under specific conditions, is also provided.

Measuring solids concentrations in urban stormwater and snowmelt: a new operational procedure.

A comparative study of five methods measuring suspended sediment or solid concentrations in water-sediment mixtures indicated that, depending on the method used, broadly varying results can be obtained. For water-sediment mixtures containing sand size particles, the standard TSS method produced negatively biased results, accounting for 0 to 90% of the present solids; the negative bias directly depended on the magnitude of the sand fraction in the water-sediment mixture. The main reason for the differences between the TSS and the rest of the methods laid in the handling of samples; in the former methods, whole samples were analysed, whereas the TSS analysis was performed on sub-samples withdrawn from the water sample, the withdrawal process tending to exclude large particles. The methods using whole water-solid samples, rather than aliquots withdrawn from such samples, produced accurate estimates of solid concentrations, with a fairly good precision. Two whole-sample methods were studied in detail, a slightly modified standard SSC-B method and the newly proposed operational procedure referred to as the Multiple Filter Procedure (MFP), using three filters arranged in a series with decreasing pore sizes (25, 1.6 and 0.45 µm). Both methods assessed accurately concentrations of solids in a broad range of concentrations (200-8000 mg L(-1)) and particle sizes (0.063-4.0 mm). The newly introduced MFP was in good agreement with the SSC procedure, the differences between the two procedures not exceeding the standard bias defined for the SSC-B method. The precision of both SSC and MFP was generally better than ±10%. Consequently, these methods should be used when the total mass of transported solids is of interest.

Simulating future trends in urban stormwater quality for changing climate, urban land use and environmental controls.

The effects of climatic changes, progressing urbanization and improved environmental controls on the simulated urban stormwater quality in a northern Sweden community were studied. Future scenarios accounting for those changes were developed and their effects simulated with the Storm Water Management Model (SWMM). It was observed that the simulated stormwater quality was highly sensitive to the scenarios, mimicking progressing urbanization with varying catchment imperviousness and area. Thus, land use change was identified as one of the most influential factors and in some scenarios, urban growth caused changes in runoff quantity and quality exceeding those caused by a changing climate. Adaptation measures, including the reduction of directly connected impervious surfaces (DCIS) through the integration of more green spaces into the urban landscape, or disconnection of DCIS were effective in reducing runoff volume and pollutant loads. Furthermore, pollutant source control measures, including material substitution, were effective in reducing pollutant loads and significantly improving stormwater quality.

Thermal stratification patterns in urban ponds and their relationships with vertical nutrient gradients.

Ponds that collect and process stormwater have become a prominent feature of urban landscapes, especially in areas recently converted to residential land use in North America. Given their increasing number and their tight hydrological connection to residential catchments, these small aquatic ecosystems could play an important role in urban biogeochemistry. However, some physicochemical aspects of urban ponds remain poorly studied. Here we assessed the frequency and strength of water column stratification, using measurements of vertical water temperature profiles at high spatial and temporal frequency, in 10 shallow urban stormwater management ponds in southern Ontario, Canada. Many of the ponds were well stratified during much of the summer of 2010 as indicated by relatively high estimates of thermal resistance to mixing (RTRM) indices. Patterns of stratification reflected local weather conditions but also varied among ponds depending on their morphometric characteristics such as maximum water depth and surface area to perimeter ratio. We found greater vertical nutrient gradients and more phosphorus accumulation in bottom waters in ponds with strong and persistent stratification, which likely results from limited particle resuspension and more dissolved phosphorus (P) release from sediments. However, subsequent mixing events in the fall diminished vertical P gradients and possibly accelerated internal loading from the sediment-water interface. Our results demonstrate that stormwater ponds can experience unexpectedly long and strong thermal stratification despite their small size and shallow water depth. Strong thermal stratification and episodic mixing in ponds likely alter the quantity and timing of internal nutrient loading, and hence affect water quality and aquatic communities in downstream receiving waters.