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Stream channel burial drastically alters watershed flowpaths by routing surface waters underground and increasing the potential for interactions between stream water and urban infrastructure such as storm and sanitary sewers. While numerous studies have investigated storm event solute loads from urban watersheds, the influences of stream channel burial and sewer overflows are often overlooked. This study uses grab samples and natural abundance stable isotope tracers to quantify the event dynamics of solute concentration-discharge relationships as well as cumulative loads in a buried urban stream. Our results demonstrate that different solutes, as well as different sources of the same solute (atmospheric NO₃⁻and sewer-derived NO₃⁻differentiated by the Δ¹⁷O tracer), are delivered via separate watershed flowpaths and thus have different timings within the event and contrasting relationships to flow. This inter-event variability reveals dynamics that result from temporal and spatial heterogeneity in infiltration, exfiltration, and pipe overflows. These results can help guide system-wide infrastructure maintenance as cities seek to meet challenges in sustaining and improving water quality as infrastructural systems age. 

Although human reshaping of the nitrogen (N) cycle is well established, contributions of individual N sources to riverine and coastal eutrophication are less certain. Urban N fluxes are potentially substantial, particularly from sewer overflows. Results from four longitudinal surveys in rivers in and around the city of Pittsburgh, Pennsylvania, were used to characterize N chemistry and isotopic composition and were compared with LOADEST‐model‐derived total N (TN) flux budgets from three urban areas along the Ohio River (Pittsburgh, Pennsylvania; Cincinnati, Ohio; and Louisville, Kentucky). Triple nitrate isotopes reveal that riverine nitrate in the Pittsburgh region is dominated by wastewater inputs despite high atmospheric deposition rates. Our budget estimates demonstrate that the magnitude of urban N yields is comparable to yields reported for agricultural watersheds and that these high urban N yields cannot consist of permitted, point‐source discharges alone. Our results reveal that nonpoint sources in urban systems represent an important but overlooked source of TN to overall riverine budgets.