Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artiWcially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC speciWc UV absorbance (SUVA) and Xuorescence index (FI) were monitored at 2-4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation Xushing dynamics indicates that DOC is mainly exported via overland Xow/macropore Xow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil proWle at baseXow, to DOC originating from surWcial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artiWcially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high Xow periods in order to understand the fate of DOC in streams.

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