Miss Christina Asanopoulos1,2, Dr Lynne Macdonald2,1, Dr Jeff Baldock2,1, A/Prof Timothy Cavagnaro1
1University Of Adelaide, Glen Osmond, Australia, 2CSIRO, Glen Osmond, Australia
Blue carbon ecosystems such as mangrove forests, tidal marshes and seagrass meadows account for almost 50% of total soil carbon stores, globally. Their exceptionally high carbon burial rates are attributed to the retention of organic matter by extensive root systems that encourage deposition and prevent erosion of rich organic material. High carbon burial rates coupled with slow decomposition of the soil organic matter (SOM) results in long term carbon storage. However, the chemical nature of blue carbon through the soil profile and its potential vulnerability to decomposition, particularly with changes in environmental conditions, is largely unknown. The objective of this study was to investigate the relationship between chemical structure of the SOM in the blue carbon environment and its age. Specifically, we characterised the chemical structure of the soil organic carbon (SOC) in mangrove soils through the depth profile with solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Samples were collected from an undisturbed temperate mangrove forest in South Australia to a depth of 1 m. All samples were analysed for elemental carbon content and aged by 210Pb and 14C (radiocarbon) dating methods prior to being selected for 13C NMR. Samples were selected to reflect a continuum in age based on short term (210Pb) and long-term (14C) dating data. The relationship between age and chemistry was then assessed using a partial least squares regression (PLSR) analysis. Radiocarbon age tends to increase with depth and is assumed to reflect the mean residence time of the SOM and in turn its stability. Characterising the chemical structure of SOM through the depth profile will contribute to a better understanding of carbon cycling and long-term stability of SOC in the blue carbon environment. An in-depth analysis of the chemical structure of the blue carbon SOM and the PLSR analysis will be discussed.