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• Stormwater nitrogen loads from a cold-region urban catchment were examined. • A build-up and wash-off model coupled with a climate change model was conducted. • Correlations among loads, rainfall, land use, and population were analyzed. • Nitrogen loads were predicted to increase in 2050 under three RCPs. Urban stormwater is a primary source of pollution for receiving water, but there is a shortage of studies on pollutant loads from urban catchments in cold regions. In this study, we coupled a build-up and wash-off model (in Mike Urban) with a climate change model to assess the impacts of climate change and urban densification on stormwater nitrogen loads (TN, TKN, NO x -N, and TAN) in an urban catchment in Canada. We calibrated and validated the Mike Urban model against observed event mean concentrations and nitrogen loads from 2010 to 2016. Results show that the nitrogen loads were mainly governed by rainfall intensity, rainfall duration, and antecedent dry days. Future precipitation data were downscaled using the Global Climate Models (GCMs), and three different Representative Concentration Pathways (RCP 2.5, RCP 4.5, and RCP 8.5) were used. Modeling results show that the TN, TKN, NO x -N, and TAN loads in 2050 will increase by 28.5 - 45.2% from May to September under RCP 2.5 compared to those from 2010 to 2016, by 34.6 - 49.9% under RCP 4.5, and by 39.4 - 53.5% under RCP 8.5. The increase of our projected TN load (from 1.33 to 2.93 kg·N/ha) is similar or slightly higher than the limited studies in other urban catchments. This study provides a reference for predicting stormwater nitrogen loads in urban catchments in cold regions. [ABSTRACT FROM AUTHOR]

The nitrogen stable isotopic signature (δN) of sediment is a powerful tool to understand eutrophication history, but its interpretation remains a challenge. In a large-scale comparative approach, we identified the most important drivers influencing surface sediments δN of 65 lakes from two regions of Canada using proxies that reflect watershed nitrogen (N) sources, internal lake microbial cycling and productivity. Across regions, we found that water column total nitrogen (TN), %N in the sediments and lake morphometric variables were the best predictors of sedimentary δN, explaining 66 % of its variation. Significant relationships were also found between sediment δN and human-derived N load ( $$ R_{{{\text{adj}} .}}^{2} $$ = 0.23, p < 0.001), the latter being a strong predictor of TN ( $$ R_{{{\text{adj}} .}}^{2} $$ = 0.68, p < 0.001). Despite a relatively strong overall relationship, variation partitioning revealed an interesting difference in the dominant variable that influenced regional δN. Alberta lake sedimentary δN signature was dominated by human derived N load. In contrast, internal processing appeared to be more important in Quebec lakes, where sediment δN was best explained by %N in the sediments and lake volume. Overall, our findings support the use of δN in paleolimnological investigations to reconstruct changing N sources to lakes but also highlight that regions may have distinctive drivers. Interpretations of sediment δN are likely to be strongest when multiple lines of evidence are employed and when placed in a regional context. [ABSTRACT FROM AUTHOR]