Temporal stability of soil organic carbon in grazing lands of Eastern Australia

ABSTRACT Sequestering soil organic carbon (SOC) has been identified as a critical tool to mitigate anthropogenic climate change. Therefore, the response of SOC to climate variability needs to be quantified to achieve carbon sequestration over decadal to centennial scales. This study assesses the temporal variability of SOC for a grazed catchment in Australia that has been exposed to periods of drought and flood over the last 100 years. The analysis utilises field-measured SOC data obtained 2006–2018, along with modelled SOC data derived from a linear regression model and BIOS2 model outputs (1908–2015). Catchment SOC did not vary significantly, with mean values of 3.40% (2006), 3.21% (2014) and 3.10% (2018), despite the catchment experiencing extreme drying and wetting events during the sampling period. This stability was further supported by the long-term modelling, which showed a mean SOC of 3.68% and coefficient of variance of 0.16%. SOC was believed to be buffered against short term fluctuations in climate that persist for less than the SOC turnover times (i.e., multi-decadal). This indicates that temporal changes in SOC reflects only long-term climate variability. Current SOC and sequestered SOC are therefore unlikely to become a carbon sink in the short-term due to climate variability.