Stormwater ponds (SWPs) are becoming increasingly important due to the negative impacts on flood mitigation and water quality control that results from rapid urbanization. These ponds are not only designed to control the discharge of large precipitation and snow melt events, but also to mitigate the water quality of the retained stormwater. Consequently, improper design and maintenance may lead to hypoxic conditions in SWPs, which result in poor water quality and generation of noxious gases. Riverside South Stormwater Pond II (RSPII) in Ottawa periodically experiences low dissolved oxygen (DO) concentrations and subsequently hypoxic conditions at depth in the pond, especially during summer days with less precipitation and winter ice covered periods. Hydrogen sulfide gas (H2S) has been generated and released into the ambient atmosphere during these periods of lesser water quality. Hence, there is a need to understand how DO spatial distribution and seasonal change trigger and affect H2S production. The conventional shallow design criteria of SWPs likely cause these systems to be susceptible to wind conditions. Very few research has demonstrated the correlation between wind-driven hydraulic performance and detained stormwater quality. Hence an understanding of pond-scale mixing generated by wind-induced flow and the subsequent correlation to DO concentrations and stratification in SWPs are important to understanding the water quality and performance of these systems, especially in a wind-induced flow dominated SWPs. The overall research objective is to develop a comprehensive understanding of hypoxic conditions of SWPs and to investigate the impact of wind induced hydraulics on DO seasonal characteristics and the subsequent production of H2S. RSPII was shown to experience lower DO and longer hypoxic conditions than an adjacent reference pond (RSPI) at both non-ice covered and ice covered months. In addition, hypoxia was shown to be initiated at the outlet of RSPII where the depth of the pond was a maximum. Interestingly, chlorophyll-α blooms were observed during ice covered conditions in the study, with synurids, tabellaria, and asterionella being identified as the dominant species. A bottom-mount acoustic Doppler current profiler (aDcp) was used to collect small wind-generated currents in RSPII. The three-dimensional current and DO model produced by MIKE 3 (DHI software) suggests a conclusive result of pond scale mixing produced by wind-driven flow as well as countercurrents near the bed opposite to wind direction. A wind dominated circulation was shown to be generated even with moderate wind speed, and with a higher wind condition pond-scale complete DO mixing was created. The MIKE 3 simulation further provided a comprehensive understanding of the correlation between wind-induced hydraulics and DO concentrations distribution in a shallow stormwater pond. Therefore, this research demonstrates that wind is an essential hydraulic driver in shallow ponds, which also likely affects water quality by initiating pond mixing.

Integrating green or blue space into cities can provide environmental and public health benefits which maximize urban sustainability. One type of green/blue infrastructure that has been understudied is urban stormwater ponds, which are used to manage stormwater runoff. Their performance is typically only evaluated in terms of hydrological functions, with little focus on their capacity to provide ancillary benefits to communities. In this exploratory study, an online survey was distributed to six neighbourhoods in the City of Ottawa, ON to gain insight into the social value of urban stormwater ponds. The results revealed that despite some disadvantages, most respondents visited their neighbourhood stormwater ponds regularly and largely appreciated the cultural ecosystem services provided by these ponds, such as opportunities for experiencing nature, especially wildlife, and outdoor recreation. These findings can be used to improve the multifunctionality of stormwater ponds and optimize both environmental and social sustainability outcomes.

Mikroplast, här definierat som plastobjekt mindre än 5 mm, befaras kunna göra stor skada på vattenlevande djur. Fram tills idag har studier av mikroplastreduktion främst utförts i kommunala avloppsreningsverk där mycket av plasten avskiljs. De stora spillvattenflödena gör ändå reningsverken till betydande utsläppspunkter av mikroplast till sjöar och hav. Information har hittills till stor del saknats om mikroplastförekomst i dagvatten, vilket ofta släpps ut orenat och i större volymer än spillvatten. Förekomst av mikroplast >20 µm (>0,02 mm) har undersökts för tre tätorters dagvatten samt för två avloppsreningsverks utloppsvatten. Avskiljning av mikroplast har undersökts för två spillvattenvåtmarker och två dagvattendammar. Båda anläggningstyper är relativt billiga och effektiva när det gäller reduktion av tungmetaller och övergödande näringsämnen. Örsundsbro våtmark och våtmark Alhagen tar båda emot behandlat spillvatten från kommunala avloppsreningsverk. I våtmark Alhagen finns även ett inlopp för dagvatten från Nynäshamn. Till dagvattenanläggningen Korsängens vattenpark leds en stor del av Enköpings dagvatten, medan Tibbledammen tar emot det dagvatten som kommer från Kungsängen i Upplands-Bro kommun. Vatten från anläggningarnas inlopp och utlopp, samt från två punkter inuti våtmark Alhagen har pumpats genom 20 µm-filter och 300 µm-filter. Provtagningen har kompletterats med insamling av mindre vattenvolymer som har filtrerats på laboratorium. Kvantifiering av mikroplast har gjorts med hjälp av stereomikroskop och vanligt förekommande objekts material har undersökts genom FTIR-spektroskopi. I våtmark Alhagens inkommande spillvatten var mikroplastkoncentrationen 4 objekt/liter, vilket liknar de koncentrationer andra svenska studier uppmätt i behandlat spillvatten. I inkommande vatten till Örsundsbro våtmark var koncentrationen över 950 objekt/liter, långt över vad andra svenska studier uppmätt i helt obehandlat spillvatten. I dagvatteninloppen var mikroplastinnehållet 5,4–10 objekt/liter, vilket indikerar på att mikroplatsutsläpp via dagvatten kan befaras vara minst lika stora som via spillvatten. I alla anläggningars inkommande vatten, förutom i våtmark Alhagens dagvatteninlopp, uppmättes höga koncentrationer av rödfärgade partiklar. Partiklarna kan vara av plast eller av annat okänt material och är till utseendet relativt lika de som andra studier påträffat i svenska kustvatten. Svarta partiklar påträffades i alla inflöden och ofta i mer än 100 gånger högre halter än de för mikroplast och röda partiklar, förutom i våtmark Alhagens spillvatteninlopp där de röda partiklarna var något fler. Partiklarna tros kunna vara däck- och vägrester eller förbränningspartiklar. Alla anläggningar visade på en tydlig avskiljning, ofta 90-100 %, för mikroplast, svarta och röda partiklar >20 µm. Till följd av resultatet samt anläggningarnas variation i ålder, storlek och utformning bör dagvattendammar och anlagda våtmarker generellt kunna förväntas fungera som effektiva barriärer mot spridning av mikroplast, svarta partiklar och röda partiklar. / Microplastics (MPs), here defined as plastic objects smaller than 5 mm, are suspected to cause great harm to fish when released into lakes and oceans. Studies of MP retention have until recently mainly been done for sewage treatment plants (STPs), where much of the plastics are shown to be retained in the sludge. However, due to large water flows in STPs, they can be seen as significant points for the spreading of MPs to recipient waters. Today there isn’t much information to be found about MP contents in stormwater. Stormwater is often released untreated and depending on climate it can be released in greater volumes than sewage water from urban areas. The occurrence of MPs >20 µm (>0.02 mm) has been studied in two STP effluents, and in stormwater from three urban catchments. The retention of MPs has been studied for two stormwater ponds, and for two free water surface wetlands constructed for tertiary treatment of sewage. Wetland Alhagen and Örsundsbro wetland both receive the effluents of secondary STPs. In wetland Alhagen there is also a stormwater inlet from the town of Nynäshamn. To the stormwater pond Korsängens vattenpark, stormwater is lead from the town of Enköping, while the stormwater pond Tibbledammen receives stormwater from Kungsängen in Upplands-Bro municipality. Influents and effluents from the facilities, as well as water from two points within wetland Alhagen was pumped through 20 µm and 300 µm filters. In addition, water from every sampling point was collected in minor volumes for later filtration carried out in a laboratory. Quantification was done with microscopy and a number of objects were analyzed with FTIR spectroscopy for material determination. In wetland Alhagen, the sewage inlet contained 4 MPs/liter, which is similar to results for STP effluents in other Swedish studies. In Örsundsbro wetland, the incoming water contained more than 950 MPs/liter, far greater than what other studies have shown for untreated sewage. The MP concentrations in the three stormwater inlets were between 5.4-10 MPs/liter. This indicates that untreated stormwater could be seen as a pathway for MPs at least as big as treated sewage. In almost all inlets, characteristic red particles were found in great numbers and in sizes of 20-300 µm. Analysis of some of the red particles indicated that they contained plastic while others were of unknown materials. The particles had a similar appearance to red particles commonly found in Swedish coastal waters. Black particles, a kind of microscopic particles that may originate in tyre wear (i.e. MPs) or combustion, was also found in large quantities. Except for in the main influents of wetland Alhagen, where the number of red particles was slightly higher, the black particles were always found in far greater numbers than both regular MPs and red particles (often >100x greater). The retention of MPs, black particles and red particles >20 µm was high in all the facilities, often around 90-100 percent. Based on these results and the variation of size, design and year of construction, stormwater ponds and constructed free water surface wetlands can be seen as effective barriers against the spreading of MPs.

Urban runoff is generated by precipitation of rain and snowmelt on impervious surfaces.  The increasing demand of urbanization causes contaminants to accumulate on roads,  roofs and pathways. In turn, as runoff wash off these surfaces, contaminants such as heavy metals, particles and organic pollutants end up in the stormwater. Urban stormwater ponds improve water quality of runoff by facilitating contaminants in form of particles. To preserve the function of a stormwater pond accumulated sediment must periodically be removed.Therefore, upland disposal alternatives should be evaluated. This study examined stormwater sediment and outlet stormwater quality in seven and four ponds respectively in the vicinity of Halmstad. 7 heavy metals and 24 organic contaminants were analysed in both sediments and stormwater. Results showed metal and organic contaminant concentrations in stormwater pond discharge and sediment exceeding concentrations reported in guideline values. From the analysed heavy metals, Zn and Pb was considered the most critical contaminants. Heavier organic compounds were more frequently quantified than lighter ones, where 42 % of the analysed organic contaminants were quantified in at least one sample. Variability between inlets and outlets, between ponds and between sampling occasions was observed. The observed variability suggests that the contamination level is influenced by catchment area characteristics and activities. Significant correlation from Spearman’s rank correlation was found between the individual heavy metals (Cu, Cr, Ni, Pb and Zn), which suggest they originate from similar sources

Urbanization involves the conversion of natural areas to impervious surfaces, which can lead to an increase in the frequency and severity of flood events in cities. To mitigate flood risk, stormwater ponds are constructed to manage urban runoff. Stormwater ponds can also be colonized by wildlife, but their suitability as habitat is disputed due to potential toxicological risks. This study assessed the suitability of stormwater ponds as habitat for the bioindicators Odonata (dragonflies and damselflies) and determined environmental factors that impact their community structure. Odonata (adults, nymphs and exuviae) were sampled at 41 stormwater ponds and 10 natural reference ponds across the National Capital Region of Canada, with a subset of ponds sampled over four years (2015-2018). Plant communities, water quality and surrounding land cover were analyzed at each pond to determine their impacts on Odonata community structure. Overall, stormwater ponds had lower Odonata abundance and a greater variation in species richness and community structure compared to natural ponds but had comparable dragonfly reproduction rates. Plants were the most significant driver of Odonata communities, as stormwater ponds with a high richness of native wetland plants had higher Odonata abundance and community structures similar to natural ponds. Water quality was the second most important driver of Odonata communities with dragonflies showing greater sensitivity to urban contaminants than damselflies. While stormwater ponds had higher concentrations of trace elements than natural ponds (e.g. Ni, V, As), concentrations were generally below toxic levels for all elements except copper and chloride, the latter likely an input from winter road salting. Surrounding land cover was the least important factor affecting Odonata communities. In conclusion, this research demonstrated the importance of local-scale factors related to plants and water quality in sustaining Odonata communities and specifies recommendations for stormwater pond design and maintenance that enhance urban biodiversity.