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Estimation of soil carbon stocks in tropical wetlands requires costly 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 yet robust analytical tools to assess soil carbon stocks where financial and technical limitations are common. Here we use published and original data to describe soil carbon density (gC cm-3; Cd) as a function of bulk density (g dry soil cm-3; Bd), which can be used to estimate belowground carbon storage using Bd 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 (Cd = Bd x 0.49 + 4.61, R² = 0.96, n = 94) for soils with an organic C content >40 %. As organic C content decreases, the relationship between Cd and Bd becomes less predictable as soil texture becomes an important determinant of Cd. The equation predicted soil C stocks to within 0.39% to 7.20% of observed values. When original data were included in the analysis, the revised equation: Cd = Bd x 0.48 + 4.28, R² = 0.96, n = 678 was well within the 95% confidence intervals of the original equation, and tended to decrease Cd estimates slightly. We recommend this last equation for a rapid estimation of soil C stocks for well developed peat soils where C content >40 %. [ABSTRACT FROM AUTHOR]

Degradation of tropical peats is a global concern due to large Carbon emission and loss of biodiversity. The degradation of tropical peats usually starts when the government clears closed peat forests into open and drained peatlands for agricultural uses. Tropical peats have high values of Water Contents (WC), Organic Matters (OM) and Total Organic Carbon (TOC), and low values of Total Nitrogen (TN) and Total Sulphur (TS). Dry Bulk Density (DBD) is commonly less than 0.1 g cm-3. Decline of concentration values of OM (<90%) and TOC (<40%) indicate peat degradation. In disturbed peats, TN concentration tends to decrease and the concentration of TS slightly increases. Changes in OM, TOC, TN and TS are potentially important indicators for assessing peat degradation in the tropics. [ABSTRACT FROM AUTHOR]

There are limited data for greenhouse gas (GHG) emissions from smallholder agricultural systems in tropical peatlands, with data for non-CO 2 emissions from human-influenced tropical peatlands particularly scarce. The aim of this study was to quantify soil CH 4 and N 2 O fluxes from smallholder agricultural systems on tropical peatlands in Southeast Asia and assess their environmental controls. The study was carried out in four regions in Malaysia and Indonesia. CH 4 and N 2 O fluxes and environmental parameters were measured in cropland, oil palm plantation, tree plantation and forest. Annual CH 4 emissions (in kg CH 4 ha -1  year -1 ) were: 70.7 ± 29.5, 2.1 ± 1.2, 2.1 ± 0.6 and 6.2 ± 1.9 at the forest, tree plantation, oil palm and cropland land-use classes, respectively. Annual N 2 O emissions (in kg N 2 O ha -1  year -1 ) were: 6.5 ± 2.8, 3.2 ± 1.2, 21.9 ± 11.4 and 33.6 ± 7.3 in the same order as above, respectively. Annual CH 4 emissions were strongly determined by water table depth (WTD) and increased exponentially when annual WTD was above -25 cm. In contrast, annual N 2 O emissions were strongly correlated with mean total dissolved nitrogen (TDN) in soil water, following a sigmoidal relationship, up to an apparent threshold of 10 mg N L -1 beyond which TDN seemingly ceased to be limiting for N 2 O production. The new emissions data for CH 4 and N 2 O presented here should help to develop more robust country level 'emission factors' for the quantification of national GHG inventory reporting. The impact of TDN on N 2 O emissions suggests that soil nutrient status strongly impacts emissions, and therefore, policies which reduce N-fertilisation inputs might contribute to emissions mitigation from agricultural peat landscapes. However, the most important policy intervention for reducing emissions is one that reduces the conversion of peat swamp forest to agriculture on peatlands in the first place., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)