Variability of Plant and Surface Soil Carbon Concentration Among Saltmarsh Habitats in Ireland

Saltmarshes are disproportionally efficient at sequestering C into their substrates and thus help to mitigate climate change but are declining globally because of human pressures. Accurately assessing their C storage capacity to inform coastal management is important, but variability among saltmarsh vegetation types is rarely investigated explicitly. Using field surveys across 15 Irish saltmarshes, we characterised C concentration variability among plant assemblages, in above- and below-ground plant parts, surface soil (upper 10 cm; indicative of the accumulation rate of particular vegetation communities, as opposed to the full depth profile aggregated throughout the different successional stages) and their three combined pools. We also assessed if environmental data can improve C models. We found between 2- and 17-fold variability in C concentration among the vegetation classes. Increasing the resolution of vegetation classification usually improved our C models. C concentration in most pools increased with elevation and decreased with the proportion of sand in the soil, whereas soil salinity was not influential. Biological and environmental variables alone were sufficient to predict above-ground plant C and soil C, respectively, but for below-ground plant C their combination was best. Not accounting for any vegetation heterogeneity within and among saltmarshes can introduce error in C inventories.

Automated summary

Saltmarshes play a crucial role in mitigating climate change by efficiently sequestering carbon, but they are declining globally due to human pressures. This study investigated the variability in carbon concentration among saltmarsh vegetation types and assessed the impact of environmental factors on carbon models. The findings highlight the importance of considering vegetation heterogeneity in carbon inventories and emphasize the need to improve the resolution of vegetation classification to enhance the accuracy of carbon models.