A natural tropical freshwater wetland is a better climate change mitigation option through soil organic carbon storage compared to a rice paddy wetland

Abstract

The high productivity together with hypoxic conditions in sediments enables wetlands to accumulate large amounts of soil organic carbon (SOC). However, natural tropical freshwater wetlands are increasingly being converted into other land uses, mainly rice cultivation. In this study, we investigated the impact of conversion of a natural tropical freshwater wetland into a rice paddy wetland on SOC, by determining SOC content, density and storage potential in the natural section (under different vegetation communities dominated by Cyperus papyrus [Papyrus], Typha latifolia [Typha] and Phragmites mauritianus [Phragmites]) and in the converted section (under rice cultivation). The SOC contents (g kg−1) and densities (kg m−2) of the 3 vegetation communities (Papyrus; 123.7 ± 2.6 [SE] and 7.22 ± 0.11, Typha; 85.3 ± 1.1 and 6.71 ± 0.12, and Phragmites; 78.2 ± 3.4 and 6.20 ± 0.06, respectively) of the natural section of the wetland were significantly higher (p < 0.05) than those (39.7 ± 0.7 and 3.90 ± 0.06, respectively) of the converted section. Similarly, for the entire sampled soil depth (0–50 cm), SOC storage potentials (Mg ha−1) of Papyrus (361.18 ± 5.53), Typha (335.31 ± 6.18) and Phragmites (310.17 ± 3.16) significantly exceeded (p < 0.05) that obtained in the converted section by nearly 46%, 42% and 38%, respectively. Soil physico-chemical characteristics: bulk density, salinity, pH and temperature, showed comparably significant correlations (p < 0.05) with SOC in both the natural and converted sections of the wetland. We strongly believe that exploration of alternative options for increasing rice production outside wetlands is paramount if natural tropical freshwater wetlands are to remain important ecosystems in climate change mitigation.