Saltmarshes gain organic carbon (OC) through in-situ (autochthonous) production by vegetation and benthic microalgae, and the accumulation of marine and terrestrial material during tidal inundation (allochthonous). Scotland’s saltmarshes are estimated to accumulate 16 kt CO₂ equivalent annually, approximately 0.04 percent of Scotland’s national greenhouse gas emissions in 2020. A key blue carbon challenge is to empirically understand, under current and predicted warmer conditions, the sources of OC accreted into and respired from saltmarshes. This can help determine the proportion of the total OC pool which could represent carbon savings under management intervention scenarios. Alongside 13C and 15N isotopes, radiocarbon (14C) analysis/dating can be used to determine the sources of saltmarsh surficial soil OC. We collected soil cores and surficial sediment samples from three contrasting Scottish saltmarshes and analysed them for 14C to gain an understanding of the age and sources of the autochthonous and allochthonous organic matter (OM) accumulating. We also aerobically incubated sub-samples of the soil in temperature-controlled experiments at 11 degrees C and 20 degrees C. The evolved CO2 was collected on molecular sieve traps and analysed for 14C content/age. Our results will facilitate comparison of the age of the bulk OM and the respired CO2 to the thermogravimetrically measured reactivity of the OM, contributing to a growing evidence base for emissions from saltmarshes, and the sources of OC accreting in their soils, which is vital for understanding how they cycle carbon.

Primary Presenter: Alex Houston, University of St Andrews (ah383@st-andrews.ac.uk)

Authors:

William Austin, University of St Andrews  (wena@st-andrews.ac.uk)

Mark Garnett, Scottish Universities Environmental Research Centre  (mark.garnett@glasgow.ac.uk)