Storm pulses and varying sources of hydrologic carbon export from a mountainous watershed

SummaryAlthough soil erosion and leaching can transfer a substantial portion of the annual terrestrial carbon (C) increment to aquatic systems, little is known about rapid changes in the amount and characteristics of soil organic C exported from mountainous watersheds during storm events. To trace short-term changes in sources and characteristics of soil organic C exported during storm events, we investigated storm-induced changes in concentrations of particulate and dissolved organic C (POC and DOC) and the stable isotope composition of suspended sediment (SS) in a mountainous, mixed land-use watershed in northern South Korea. Biweekly stream sampling in a headwater forest stream and a watershed outlet receiving agricultural runoff showed that concentrations of SS and POC were higher in the watershed outlet. In both the forest stream and outlet, POC concentrations were lower than DOC concentrations during baseflow, but increased rapidly with rising discharge during intense storms, resulting in higher peak POC concentrations than peak DOC concentrations. When δ13C and δ15N were compared between SS and potential source soils during three storm events, SS δ13C and δ15N in the forest stream were similar to forest floor δ13C and δ15N. SS δ13C and δ15N in the watershed outlet reflected the contribution from forest and cropland mineral soils during peak flow, with sand-size SS displaying increasing δ13C and δ15N with rising rainfall intensity. The results suggest that storm pulses of POC can be a transient, but dominant pathway of hydrologic C export overwhelming DOC export and that POC sources and characteristics can rapidly change corresponding to varying rainfall intensity.

► Storm pulses of C export represent soil C losses from mountainous watersheds.
► Storm pulses of POC can be a dominant pathway of C export overwhelming DOC export.
► POC sources can rapidly change with varying rainfall intensity during storms.
► Coupled soil and sediment stable isotope measurements are useful in tracing C export.