Dissolved Organic Carbon Dynamics During the Snowmelt Period in a Small Urban Watershed

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O'Riley, Jaclyn L.
carbon; CDOM; DOC; modeling; snowmelt; SWAT; Biogeochemistry; Environmental Sciences
thesis / dissertation description
Riverine transport of dissolved organic carbon (DOC) from land to sea is an important linkage in the global carbon cycle. In many seasonally snow-covered watersheds, the brief snowmelt period dominates the annual hydrograph, and more than half of annual DOC flux can occur during this time. The "flushing hypothesis" suggests that DOC accumulates underneath snow during the winter, and is then rapidly flushed into streams during spring when meltwaters move through the soil. Due to traditionally sparse sampling during the snowmelt period there is a lack of understanding of what controls DOC dynamics during this time. High-temporal resolution sampling of 31 sites was undertaken in the Neponset River watershed during the March, 2011 snowmelt. Most sites had their highest concentrations before the peak in the hydrograph, and samples on the rising limb of the hydrograph were higher than those on the falling limb, suggesting that DOC flushing did occur, however higher-frequency sampling is necessary. A SWAT model was developed for the Neponset River watershed to estimate discharge at ungauged sample sites, which was then used to explore DOC:discharge relationships and calculate DOC flux estimates for 2008-2011. Flux patterns suggest that winters with persistent snowcover and a single melt result in annual DOC flux being spread evenly throughout the year, while winters with intermittent snowcover and spring precipitation falling as rain result in a disproportionately large spring DOC flux. While this is opposite of patterns seen in northern Arctic latitudes, it points towards the importance of the "quality" of a winter in determining DOC concentration and export.