A cost-efficient method to assess carbon stocks in tropical peat soil

Abstract. Estimation of belowground carbon stocks in tropical wetland forests requires funding for laboratory analyses and suitable facilities, which are often lacking in developing nations where most tropical wetlands are found. It is therefore beneficial to develop simple analytical tools to assist belowground carbon estimation where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (kgC m⁻³; C_d) as a function of bulk density (gC cm⁻³; B_d), which can be used to rapidly estimate belowground carbon storage using B_d measurements only. Predicted carbon densities and stocks are compared with those obtained from direct carbon analysis for ten peat swamp forest stands in three national parks of Indonesia. Analysis of soil carbon density and bulk density from the literature indicated a strong linear relationship (C_d = B_d × 495.14 + 5.41, R² = 0.93, n = 151) for soils with organic C content > 40%. As organic C content decreases, the relationship between C_d and B_d becomes less predictable as soil texture becomes an important determinant of C_d. The equation predicted belowground C stocks to within 0.92% to 9.57% of observed values. Average bulk density of collected peat samples was 0.127 g cm⁻³, which is in the upper range of previous reports for Southeast Asian peatlands. When original data were included, the revised equation C_d = B_d × 468.76 + 5.82, with R² = 0.95 and n = 712, was slightly below the lower 95% confidence interval of the original equation, and tended to decrease C_d estimates. We recommend this last equation for a rapid estimation of soil C stocks for well-developed peat soils where C content > 40%.