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. This study evaluated the effects of monsoon storm events on the runoff fluxes and on the composition 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 remained almost constant. DOC, DON and NO₃–N fluxes in runoff increased linearly with discharge pointing to changing flow paths from deeper to upper soil layers at high discharge, whereas nonlinear responses of POC and PON fluxes were observed likely due to the origin of particulate matter from the erosion of mineral soil along the stream benches. The integrated C and N fluxes in runoff over the 2-month study period were in the order of DOC > POC and NO₃–N > DON > PON. The integrated DOC fluxes in runoff during the study period were much larger at the deciduous watershed (16 kg C ha⁻¹) than at the mixed watershed (7 kg C ha⁻¹), while the integrated NO₃–N fluxes were higher at the mixed watershed (5.2 kg N ha⁻¹) than at the deciduous watershed (2.9 kg N ha⁻¹). The latter suggests a larger N uptake by deciduous trees. Integrated fluxes of POC and PON were similar at both watersheds. The composition of organic matter in soils and runoff indicates 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 particulate and dissolved C and N in runoff to storm events as a combined effect of tree species composition and watershed specific flow paths.

In the last decade, the South Korean government has implemented an unprecedented series of plans and policy actions to promote sustainable development, including the National Strategy for Green Growth. Some of these initiatives were direct responses to the evolving challenges in the water sector, and put forest hydrological services into perspective. To a certain extent, water was managed within a wider environmental context through the combination of forest and water management. However, the efforts to enhance forest hydrological services did not correspond to the immense potential of forests for the achievement of sustainable water management. We present a comprehensive and current view of the major challenges and opportunities related to forest hydrological services in South Korea. We identify key forest hydrological services in view of the major biophysical, environmental, and economic challenges in the water sector. We propose guidelines for the enhancement of forest hydrological services and for a better inclusion of these services in South Korea’s sustainable development strategy. An increased contribution of forests to the provision of high-quality water in sufficient, regulated amounts, and to the preservation of a safe environment in regards to natural hazards is imperative for the long-term development of South Korea.