Field-Based Soil Organic Carbon Stock Assessment and RothC-Based Scenario Modelling in a Mountain Micro-Catchment, Eastern Türkiye

Abstract

Soil organic carbon (SOC) stocks are strongly influenced by land use, vegetation condition and climate, particularly in heterogeneous mountain catchments. This study quantified SOC stocks and simulated long-term SOC dynamics in the Çapakçur micro-catchment, eastern Türkiye, by integrating field assessment, geostatistical prediction, uncertainty analysis, inverse RothC calibration and scenario modelling. A total of 428 soil samples were collected from the 0–30 cm layer across forest, degraded forest, and pasture areas. SOC stocks were calculated from SOC concentration, bulk density and soil depth, and spatially predicted using ordinary kriging of log-transformed SOC stocks. RothC was calibrated for each land-use class to estimate the annual carbon inputs required to maintain observed SOC stocks, followed by 50-year restoration and climate-sensitivity simulations. SOC stocks ranged from 7.69 to 247.68 Mg C ha−1, averaging 55.52 Mg C ha−1. Forest had the highest mean SOC stock (78.5 Mg C ha−1), followed by pasture (55.9) and degraded forest (50.2 Mg C ha−1). Required annual carbon inputs were 5.17, 4.58 and 3.29 Mg C ha−1 yr−1, respectively. Increasing degraded forest carbon inputs to forest-equivalent levels increased SOC by 14.76 Mg C ha−1 over 50 years, equivalent to 37.77 Gg C or 138.49 Gg CO2eq at the catchment scale. A stronger restoration scenario increased this potential to 63.77 Gg C. Warming caused SOC losses, with +2 °C reducing catchment SOC by 56.78 Gg C. These findings demonstrate the potential of degraded forest restoration for SOC sequestration while highlighting the vulnerability of long-term SOC gains to climate warming.