Investigating drivers of microplastic pollution in urban settings

As one of the emerging contaminants and the major by-products of plastic materials, microplastics (MPs) have recently been stated as being remarkable contaminants of different environmental matrices including soils, sediments, groundwater, and surface water. Stormwater and flowing surface water are important carriers of MPs to downstream surface water bodies such as ponds and lakes, yet, little work has been done to develop models for predicting MP loads in these systems. One common approach in contaminant load modeling is to couple a hydrological model with relationships relating the contaminant concentration or load to explanatory variables such as water discharge, typically the most important variable controlling concentrations and loads, and variables representing other drivers of contaminant loading such as land use and climate variables. In this work, our goal is therefore to assemble a database of MP load and/or concentration and discharge measurements in different flowing surface water systems as well as potential explanatory variables such as catchment land use and climate conditions to examine the dependencies of MP loading on these explanatory variables. We searched the Scopus and Web of Science databases and found 64 articles focusing on quantifying MP loads or concentrations in different surface water systems and extracted or calculated the relevant data for the database. The main focus of this work is urban settings, or their shear impact on microplastic production in larger areas of mixed land cover types. Despite inconsistencies in the definition of MPs as well as in sampling, extraction, and analytical methods, the results indicated a significant relationship between impervious land cover and MP loading within urban catchments (polynomial R2 = 0.75), where each hectare of imperviousness corresponds up to 7% of increase in MP concentration. MP loads were, unsurprisingly, highly positively correlated with flow (R2 of up to 0.86), which is the basis for the relationship between MP concentration and climatic factors. We also found that there is a high positive correlation between total suspended solid (TSS) concentrations and MP concentrations, and therefore also between their respective loads, which has been reported by others before and indicates that TSS loads can be used to estimate MP loads in the absence of sufficient data. The relative importance of discharge, land use and climate variables as drivers of MP loading has not yet been investigated, and our assembled database will enable the prediction of MP loads in stormwater, streams and rivers at the watershed scale using the explanatory relationships derived from our analysis

URBAN PHOSPHORUS SPECIATION AND EXPORT LOADS: A PAIRED SEWERSHED FIELD AND MODELING STUDY

In this study, annual and seasonal loads of phosphorus (P) exported from two neighbouring urban sewersheds (AJE and AJW) discharging into Lake Ontario were estimated. The following different chemical pools of P were considered: total P (TP), particulate P (PP), and dissolved P (DP), that in turn were divided in their respective reactive (R) and unreactive (U) fractions. The AJW sewershed is more residential while AJE is dominated by commercial and industrial land cover. A load-flow regression model coupled to the Stormwater Management Model (PCSWMM) was calibrated against measured flow and P speciation data and used to derive seasonal export concentrations (ECs) for the two sewersheds. The annual P loads from the sewersheds were significantly different (AJE: 0.61±0.05 kg/ha/year; AJW: 0.39±0.07 kg/ha/year). Relative to AJE, the TP loads from the more vegetated AJW were enriched in both total DP (TDP) and reactive DP (DRP). Overall, the TP loads were dominated by PP (83-91% of TP), with slightly higher PP contributions for AJE. Our chemical extraction results further simplied that close to half (38-47%) of the PP loads were comprised of reactive P forms. The large contribution of PRP to the TP loads indicates that DRP alone may not provide a reliable measure of the potentially bioavailable P exported from urban areas to downstream aquatic environments.This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF)

A GIS-Based LID Framework for Sustainable Urban Runoff Management

Low Impact Development (LID) is one of the most popular sustainable techniques for runoff reduction in urban areas. LID mimics nature by retaining or detaining the runoff at the source. Examples of LID include bioretention cells, green roofs, and porous pavements. While the primary purpose of LID is runoff reduction, several lateral benefits (environmental and socioeconomic) are accrued from LID. Even though many studies have shown the effectiveness of LID on runoff reduction, investigation around many other aspects of LID has remained limited. Out of all these aspects, there is a significant lack of a systematic decision-making model to rank LID solutions (suggest where to implement LID and what type of LID to use) to maximize the LID benefits. The objective of this dissertation is to develop an innovative simplified geospatial model (referred to as LID-Solution Evaluation and Ranking ApproacH (SERAH)) to rank the LID solutions. SERAH develops a Hydrological-Hydraulic Index (HHI) and integrates it into a Multi Criteria Decision Making (MCDM) model considering the key criteria contributing to the ranking LID solutions. In this research, the application and effectiveness of SERAH and its corresponding indices were examined under various case scenarios and case studies (e.g., City of Toronto as the study site). Also, SERAH was validated against physical models such as HEC-HMS and PCSWMM. Further, the HHI was used for modelling climate change and urbanization scenarios for three Canadian metropolitans (Toronto, Montreal, and Vancouver). The results of this study show that, unlike the traditional methods which use stormwater modeling for ranking LID solutions, SERAH effectively ranks LID solutions using geospatial analysis. SERAH and its corresponding indices are universally applicable since they have been deductively developed and like many similar methods are not induced and custom-built around a sample dataset. The results of this research lend themselves to the strategic planning of multifunctional sustainable infrastructures (LID); give a holistic insight about current and future demands for LID; integrate multiple disciplines (socioeconomic, environmental, geography, and hydrology) to find comprehensive sustainable solutions; and suggest a future need for similar multidisciplinary research by highlighting the gaps and limitations

The Effect of Climate Change and Urbanization on the Demand for Low Impact Development for Three Canadian Cities

Climate change and urbanization are increasing the intensity and frequency of floods in urban areas. Low Impact Development (LID) is a technique which attenuates runoff and manages urban flooding. However, the impact of climate change and urbanization on the demand or need for LID in cities for both current and future conditions is not known. The primary goal of this research was to evaluate the demand for LID under different climate change and urban growth scenarios based on a physical-based geospatial framework called the hydrological-hydraulic index (HHI). To do this, 12 scenarios considering four climate change and three urbanization conditions were developed. The HHI for three cities in Canada (Toronto, Montreal, and Vancouver) were estimated, evaluated, and compared for these scenarios. The results show that both urbanization and climate change increase the demand for LID. The contribution of climate change and urbanization on LID demand, measured using HHI, varies for each city: in Toronto and Montreal, high rainfall intensity and low permeability mean that climate change is dominant, whereas, in Vancouver, both climate change and urbanization have a similar impact on LID demand. Toronto and Montreal also have a higher overall demand for LID and the rate of increase in demand is higher over the study period. The results of this study provide us with a comprehensive understanding of the effect of climate and urbanization on the demand for LID, which can be used for flood management, urban planning, and sustainable development of cities

Carbon Budget of an Urban Stormwater Pond: Importance of Riparian Vegetation

Stormwater ponds (SWPs) within urban areas are rapidly growing as a runoff and nutrient control measure and act as reactive zones for carbon and nutrient cycling. While SWPs are known to emit significant amounts of carbon dioxide (CO2) and methane (CH4) while also sequestering organic and inorganic carbon. Understanding the net effect of urban SWPs on carbon cycling is therefore far from straightforward. Here, we present the carbon budget of a SWP in the greater metropolitan area of Toronto, Canada to evaluate whether the SWP acts a net source or sink of CO2. The budget calculations included the dissolved and particulate carbon fluxes at the inflow and outflow points of the pond, plus the particulate carbon burial fluxes associated with the sediments accumulating in the pond. The CO2 flux required to close the carbon budget was compared with the CO2 efflux from the pond water column. According to the carbon budget, the SWP sequesters about 29×103 moles of CO2 per year. The water chemistry data, however, imply that the SWP emits around 55×10^3 moles of CO2 annually. This contrasting result, therefore, indicates a missing carbon influx into the pond, which we identify as organic carbon (OC) produced through photosynthetic CO2 fixation by the riparian vegetation. Part of this OC is eroded into the pond, and its subsequent mineralization generates the missing CO2. We estimate that around 71×10^3 moles of riparian OC must be mineralized to CO2 to balance the SWP’s carbon budget. Altogether, when including the riparian vegetation, the SWP system acts as a net CO2 sink, although it emits CO2. Furthermore, the emitted CO2 is primarily contributed by the mineralization of OC from the riparian vegetation, rather than catchment-exported OC. Our work highlights the importance of considering OC production by the vegetation closely surrounding SWPs and the transfer of this OC into the pond and its subsequent mineralization. Our results also caution against only relying on floating flux chamber measurements when assessing the overall effect of SWPs on pond-atmosphere CO2 exchanges.This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF