Response of dissolved and particulate organic carbon and nitrogen in runoff to monsoon storm events in two watersheds of different tree species composition

Abstract

<p><strong>Abstract.</strong> Heavy storm events may increase the amount of organic matter in runoff from forested watersheds as well as the relation of dissolved to particulate organic matter. Little is known about the behaviour of dissolved and particulate organic N and its relations to C. This study evaluated the effects of monsoon storm events on the runoff fluxes and on the quality of dissolved (< 0.45 µm) and particulate (0.7 µm to 1 mm) organic carbon and nitrogen (DOC, DON, POC, PON) in a mixed coniferous/deciduous (mixed watershed) and a deciduous forested watershed (deciduous watershed) in South Korea. During storm events, DOC concentrations in runoff increased with discharge, while DON concentrations were stable. DOC, DON and NO<sub>3</sub>-N fluxes in runoff increased linearly with discharge, whereas nonlinear responses of POC and PON fluxes were observed. The cumulative C and N fluxes in runoff were in the order; DOC > POC and NO<sub>3</sub>-N > DON > PON. The cumulative DOC fluxes in runoff during the 2 months study period were much larger at the deciduous watershed (16 kg C ha<sup>−1</sup>) than at the mixed watershed (7 kg C ha<sup>−1</sup>), while the cumulative NO<sub>3</sub>-N fluxes were higher at the mixed watershed (5.2 kg N ha<sup>−1</sup>) than at the deciduous watershed (2.9 kg N ha<sup>−1</sup>). Cumulative fluxes of POC and PON were similar at both watersheds. Quality parameters of organic matter in soils and runoff suggested that the contribution of near surface flow to runoff was larger at the deciduous than at the mixed watershed. Our results demonstrate different responses of dissolved C and N in runoff to storm events as a combined effect of tree species composition and watershed-specific flowpaths.</p>