Event controlled DOC export from forested watersheds

We performed a meta-data analysis to investigate the importance of event based fluxes to DOC export from forested watersheds. A total of 30 small eastern United States forested watersheds with no wetland component, with a total of 5,176 DOC and accompanying discharge measurements were used in this analysis. There is a clear increase in DOC concentration during hydrologic events (storms and snow melt) that follows a power relationship. We estimate that 86% of DOC is exported during events. The majority (70%) of this event based DOC flux occurs during the rising hydrograph and during large events. Events with a discharge greater than 1.38 cm day(-1) make up only 4.8% of the annual hydrograph, yet are responsible for 57% of annual DOC flux. The relationship between event discharge and both DOC concentration and flux is also regulated by temperature and antecedent conditions, with a larger response in both fluxes and concentrations to events during warmer periods and periods where the preceding discharge was low. The temperature relationship also shows seasonality indicating a potential link to the size or reactivity of watershed OM pools. The 86% of DOC lost during events represents a conservative estimate of the amount of allochthonous forested DOC transported laterally to streams. Future research on watershed cycling of DOC should take into account the importance of events in regulating the transport of DOC to downstream ecosystems, determine the relative importance of abiotic versus biotic processes for the temperature regulation of event-associated DOC fluxes, and elucidate the interactions between processes that respond to climate on event versus longer time scales.