Comparing Estimation Methods for Soil Organic Carbon Storage in Small Karst Watersheds

In order to accurately estimate soil organic carbon storage (SOCS), 2,755 soil profiles and 23,536 soil samples were acquired by grid method, followed by a study on the SOCS, soil bulk density (SBD), gravel content (GC), and distribution characteristics of rock coverage (RC) in a small karst watershed (SKC). Then on the basis of soil profile summation, an investigation was done on the applicability of RC/GC-based soil type method, land utilization type method, and aspect method to the estimation of SOCS in SKC at different depths. As shown by the results, the average soil organic carbon content (SOC) in the soil samples ranged from 5.25 to 24.87 g.kg(-1), and decreased with the soil depth increasing; the average SBD ranged from 1.17 to 1.41 g.cm(-3), which first increased with the soil depth increasing and then tended to be steady; the average GC ranged from 0 to 20.15%, which decreased gradually with the soil depth increasing and finally to zero; the RC ranged from 0 to 86.32% at different sample points. RC and GC greatly affected the estimation of SOCS, so after correction based on RC and GC, the soil type method was adopted for estimation, concluding that SOCS at depths of 0-20 cm, 0-30 cm, and 0-100 cm was 341.82x10(6) kg, 449.29x10(6) kg, and 738.351x10(6) kg, respectively; RC and GC affected white sandy soil the most, as shown by the following SOCS estimated by the land utilization type method: 319.56x10(6) kg, 416.04x10(6) kg, and 607.02x10(6) kg, respectively, at depths of 0-20 cm, 0-30 cm, and 0-100 cm; RC and GC affected wasteland the most, as shown by the following SOCS estimated by the aspect method: 318.64x10(6) kg, 411.63x10(6) kg, and 628.46x10(6) kg, respectively, at depths of 0-20 cm, 0-30 cm, and 0-100 cm; RC and GC affected the SOCS in the south slope the most; in terms of catchment scale, the "vertical stratification + horizontal classification" pattern was expanded to the "land utilization type method" and "aspect method." For estimating the SOCS in topsoil, the aspect method achieved the best result, while the land utilization type method achieved the best result at a depth of 100 cm.