Snowpack enhanced dissolved organic carbon export during a variety of hydrologic of events in an agricultural landscape, Midwestern USA

This study investigates the dynamics of riverine DOC concentrations during a series of stream discharge events (3–10 days) following rainstorms of different intensity and duration. We examined six events, when high-frequency (hourly) water samples for DOC (n = 321) were collected in spring (n = 166) and autumn (n = 155). Results identified three distinct water-mediated processes during stream discharges events that linked DOC source supply from agricultural land surfaces with sinks in a receiving river. These were as follows: 1) snowpack drives significant high DOC concentrations in base-flow during spring, 2) abundant organic matter in topsoil from crop residues determines a rapid DOC loading profile in the first flush, and 3) very large hydro-climatic events in snow-melting season over agricultural watersheds could increase the riverine DOC flux by 2.3 folds. These results revealed that ca. 76.5% of annual DOC was exported during a handful of storm-discharge events (78.9% for spring and 74.2% from autumn) over agricultural landscapes. Given the significant amount of riverine DOC exported from agricultural landscapes during severe weather events, our results suggest that changes in climate promote larger precipitation events that would likely enhance the export of terrestrial DOC to receiving water bodies. The study presents a semi-analytical model that is able to extrapolate the riverine DOC dynamics during storm discharge events of varying duration and intensity (R² up to 0.9).