Evaluating the impact of land use on soil organic carbon spatial distribution by SWAT-C model – a case study of the Wu River Basin, Taiwan

Land use is a primary driver of the spatial distribution of soil organic carbon (SOC) and significantly influences the terrestrial carbon cycle. This study used the SWAT-C model to simulate the export of SOC, dissolved organic carbon (DOC), and particulate organic carbon (POC) in the Wu River Basin, analyzing the effects of land use on SOC spatial distribution. Model calibration with 2012–2017 total organic carbon (TOC) data achieved Nash-Sutcliffe efficiency values above 0.7, confirming reliability. The simulated results showed an average annual TOC export of 17.3 kgC/ha, with DOC and POC contributing 10.38 kgC/ha and 6.9 kgC/ha, respectively. Bare land had the highest POC export (66.7 kgC/ha), followed by dry cropland (32.3 kgC/ha), while urban areas and coniferous forests exhibited the highest DOC exports (15.1 and 12.4 kgC/ha, respectively). SOC storage was highest in rice field (313 tonC/ha) and lowest in bare land (175 tonC/ha). Sub-watersheds dominated by bare land and dry cropland recorded TOC exports exceeding 21 kgC/ha, marking them as future SOC export hotspots. These findings highlight the significant influence of land use on SOC distribution and provide a scientific basis for ecosystem service preservation, and sustainable watershed management.

Key words: Soil organic carbon, SOC storage, SWAT-C model, land use, Taiwan