USING SURFACE ELEVATION TABLES TO MONITOR TIDAL WETLAND RESPONSE TO CLIMATE CHANGE IN CALIFORNIA

Tidal marshes reside in the low-lying areas of the coastal zone and are dynamic ecosystems influenced by both ocean and terrestrial processes. They are directly impacted by climate change through sea level rise and extreme weather events. Many of the marshes in California are public lands adjacent to urban environments. They support multiple wildlife species and provide benefits to humans including flood protection and carbon sequestration. Identifying climate change impacts and early indicators of vulnerability are important when managing marshes in a changing world. Tidal marshes build elevations by below- and aboveground organic and mineral soil processes. Marsh elevation and accretion data can be used to determine if marshes are keeping pace with sea-level rise and how they are impacted by extreme weather events. Using a network of over 50 deep rod surface elevation tables with paired feldspar marker horizon plots, we tracked elevation and accretion trends across 16 marshes in California, USA. All sites had overall positive gains across years that included severe drought conditions and extreme rain events. Marsh elevation relative to tidal datum (z*) was the key predictor for elevation and accretion rates, with higher change rates at lower z* sites. High temperature days were a key predictor for elevation, accretion, and shallow subsidence rates in select regions. Central and Southern California marshes were keeping pace or out-pacing sea-level rise, while none of the Humboldt Bay marshes were keeping pace. Marsh surface elevation data can inform management intervention and be a leading indicator for sea-level rise vulnerability. Long term monitoring across geomorphic settings can help inform management and anticipate marsh change in the face of a changing climate.