How landslide-triggering rainfall conditions vary with geology is unclear. The effects of three different geological conditions (gneiss, GN; granite, GR; sedimentary rock, SR) on variations in intensity–duration (I-D) conditions and rainfall characteristics responsible for initiating shallow landslides were examined using data from 476 landslides in South Korea from 1963 to 2018 and detailed statistical analyses. Results from quantile regression and one-way analysis of variance analyses clearly showed that impermeable SR slopes result in smaller critical rainfall than permeable GN and GR slopes do, indicating a relatively high occurrence exceedance probability and susceptibility to landslides in SR slope. These findings suggest that geological conditions, particularly the relatively high susceptibility of SR slopes, should be considered when establishing rainfall information-based landslide warning criteria for South Korea. Our findings can contribute to the assessment of landslide susceptibility and probability based on geological conditions; however, they should be further investigated through in situ observations.

In order to determine the suitability of reusing the sediment deposited in the upper part of the dam as soil for growing forest products, a total of eight treatment plots were formed by mixing cultivated soil, compost, and biochar with the sediment in a volume ratio. Generally, the soil fertility of SS100 was relatively lower than that of CS, with Av. P₂O₅ being only 22%. SS70 and SS50 increased soil physicochemical properties including OM, exchangeable cations, CEC, and BS by 1.1–2.9 times more than SS100, thus, A. scaber Thunb. treated in SS70 and SS50 showed increased photosynthetic parameters including A, V_cmax, J_max, and the growth characteristics, especially in the aboveground part, were 20% and 31% higher than the SS100, respectively. Furthermore, A. scaber in CS, SS50, Bc10, and Comp had higher PI_abs, DFI_abs, and SFI_abs while maintaining lower V_K/V_J after 10 days of drought stress, Comp and Bc10, in particular, had a high Y(NPQ) and a low Y(NO). Bc5 and Bc10, revealed no discernible differences in soil physicochemical properties, nonetheless, A. scaber in Bc10 demonstrated relatively high drought tolerance. Overall, CS, SS50, and Comp had relatively well-balanced plant growth, and drought tolerance was found to be higher in CS, Comp, SS50, and Bc10, which is thought to have higher water-holding capacity and soil fertility. As a result, if appropriate treatment methods are established, such as mixing sediment soil with cultivated soil at a one-to-one ratio or adding compost, increase the public value of forests by promoting activities such as watershed conservation, soil runoff prevention, and reducing the financial burden associated with sustainable forestry management and SS50 is recommended as the most cost-effective method.

Identifying potential sources of suspended sediment (SS) in headwater catchments is crucial for water quality management. To differentiate these potential SS sources, we investigated the distribution of two fallout radionuclides (FRNs), ¹³⁷Cs and ²¹⁰Pb_ex, using gamma spectrometry along with soil organic matter (SOM) analysis in a headwater catchment with five potential SS sources: cultivated land, non-harvested forest floor, eroded hillslope, harvested forest floor, and stream bank. The ¹³⁷Cs and ²¹⁰Pb_ex concentrations and the SOM content were considerably higher in the harvested forest floor materials than in the other four potential SS source materials. FRN concentrations revealed distinct properties according to the type of potential SS sources. Specifically, the combination of FRNs (with the effect of SOM content removed) associated with the mineral fraction and SOM showed distinguishable differences among the potential SS sources, except for no difference between cultivated land and eroded hillslope. Therefore, SOM and FRNs, or their combination, can be effective indices to differentiate or trace potential SS sources on various land use/land cover types within a catchment. Further field tests will allow the tracing techniques that bind FRNs with SOM to contribute to understanding SS transport from non-point sources within a catchment.