Nitrogen Loadings in Stormwater and Snowmelt from Cold-region Urban Catchments in 1991 – 2018 and Prediction for Year 2050
Creators: Zhang, Xiaoyu
Publisher: name: University of Alberta Library
Year: 2022

<p>Urban stormwater and snowmelt runoff has become a primary source of pollution in receiving water bodies (e.g., rivers, lakes and oceans), causing eutrophication, harmful algae blooms and hypoxia and many other environmental issues. It is therefore imperative to study pollutant loadings from urban surface runoff, examine their spatiotemporal variabilities and predict future loadings to improve the stormwater/snowmelt management for federal, provincial and municipal governments. This thesis focused on nitrogen loadings, and was written in paper-based format that includes two parts: Part I “Nitrogen Loadings in Stormwater and Snowmelt from a Major, Cold Region, North American City in the Past 30 years”; and Part II “Predicting Stormwater Nitrogen Loadings from an Urban Catchment in Cold-region in Year 2050”. Part I and Part II explored nitrogen loadings in the past and predicted loadings in the future, respectively. <br>
Long-term monitoring on pollutant loadings in urban surface runoff is scarce in the literature. In Part I of the thesis, nitrogen loadings were examined in storm/snowmelt runoff from four urban catchments of a major North America city (Edmonton, Canada) located in cold-region in the past almost 30 years (1991 to 2018), with a focus on both spatial and temporal variabilities. The TN loading exhibited a pronounced inter-annual variability, with an increasing trend from 1991 to 2011 due to the increases of annual precipitation, and a decreasing trend afterwards as a result of discharging stormwater into creeks. The ratios of monthly loadings in wet season (April – October) to dry season (November – March) for TN, TON and NOx-N were 2.26, 2.77 and 2.93, respectively, whereas the ratio was 1.17 for the NH4-N loading. The maximum monthly fluctuation appeared in March/April and July due to the high frequency of snowmelt and storm events, respectively. Event mean concentrations (EMCs) of TN in snowmelt was slightly higher than in storm runoffs from 2007 to 2018. We further used Mann-Kendall test, Pettitt test and Rescaled Range Analysis to detect the abrupt change time. The results showed that climatic condition, catchment characteristics and urban drainage infrastructure had substantial impacts to the loading variability. Moreover, we compared the EMCs and loadings with those reported worldwide. <br>
Modeling and predicting stormwater nitrogen loadings in urban catchments of cold regions have been much less reported. In Part II of the thesis, a build-up and wash-off model was developed in MIKE Urban to assess the impacts of climate change and urban densification on stormwater nitrogen loadings (TN, TKN, NOx-N and NH4-N) of an urban catchment (the 30th Ave Catchment in Edmonton) in Canada. The model was calibrated and validated against the observed loadings and event mean concentrations (EMCs) in 2010 - 2016. Based on the model, important factors for the nitrogen loadings were found as rainfall intensity and duration and antecedent dry days. The model also showed that first flush effect was clear for storm events, with 32.1 - 59.8% of the nitrogen loadings transported by the first 30% of runoff volume. Based on projections of future precipitation and population, the model predicted that the loading of TN, TKN, NOx-N and NH4-N in 2050 will increase by 33.7%, 39.4%, 27.1%, and 31.1% for months from May to September, compared to those of 2010 - 2016.<br>
Finally, general conclusions and future directions were provided at the end of this thesis based on the above two (Part I and II) studies.</p>