Volumetric contributions to coastal wetlands accretion and elevation change

Coastal wetlands are among the most valuable ecosystems on the earth but are under threat by the rising sea level. A central requirement of understanding coastal wetlands vulnerabilities is to convert the sediments (mineral and organic) mass to volume, and hence the elevation gain. Here, we used a network of Surface Elevation Table-Marker Horizon (SET-MH) stations deployed in SE Australia as a benchmark against the wetland surface accretion. We measured the mangrove and saltmarsh accretion of inorganic, organic and living root material in fluvial and marine sand geomorphic settings. We found living root material to be the dominant contributor to accretion above feldspar marker horizons over our observation years (20 - 21 years). Higher rates of accretion were associated with higher proportional root contributions in saltmarsh, and higher proportional organic matter contributions in mangroves. This difference may be attributed to the difference in hydroperiod between mangroves and saltmarsh, which results in different sediments inputs and organic preservation. Despite several limitations, this study supports the view that marsh accretion associated with higher sea-level rise rates is primarily driven by plant biogenic feedback and demonstrates the potential of combining quantitative estimates of root development with the SET-MH method.