Soil Organic Carbon Stability at the Large Catchment and Centennial Scales: Field and Modelled Insights

Mr Abraham Gibson1, Dr Greg Hancock1, Dr  Vanessa Haverd2, Dr Danielle  Verdon-Kidd1

1The University Of Newcastle, Australia, Callagahan, Australia, 2CSIRO Oceans and Atmosphere, Canberra, Australia

Soil Organic Carbon (SOC) represents the largest terrestrial store within the carbon cycle at 1550 Gt. SOC fluxes and quantification within global climate models is generally poor and adds uncertainty due to the large amount of carbon it accounts for. The ability to constrain the estimates of the response of such a large amount of carbon to global changes is pertinent to projections of the future global carbon budget. High resolution, continental-scale modelling and field methods are ways to better constrain this uncertainty. This study presents findings on SOC stability for a large (585 km²), agricultural catchment in eastern Australia over the past 115 years using the BIOS2 model recently developed by CSIRO to study the carbon and water cycles in the Australian landscape. Independent field observations (not previously used in the validation of BIOS2) from 2004 and 2014 were compared with modelled outputs for the study catchment, with coefficients of determination ranging from 0.14 to 0.30. The spatial variation of the modelled inputs was also compared with the field observations to determine the sensitivity of the model to topographically influenced climatic variations. The field observations from 2005 to 2015 captured SOC dynamics during and post a significant drought event and were found to be stable. This finding was supported by the modelled outputs which also showed SOC stability from 1900-2015, during multiple dry and wet periods. Spatially, SOC was shown to vary with elevation both within the field and modelled data in response to increased rainfall. Collectively, these results indicate that SOC is resistant to climatic variations under consistent land use at the large catchment scale within a temperate agricultural region. Therefore, SOC flux under land use change may present greater uncertainty to quantify for projected carbon budgets rather than the influence of climate in stable areas.

Biography: Abraham is a current PhD candidate at the University of Newcastle, Australia. Currently, he is researching the interactions between climate change and changes in soil organic carbon, with a special focus on what these changes might look like in a drying world. His work builds on  research out of Dr. Greg Hancock’s research group looking at SOM dynamics on a variety of scales and the interactions between land use and erosion with SOM. Abraham’s other research areas include; drought, soil quality, soil erosion and catchment management issues.

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