How tidal freshwater forested wetland response to salinization affects carbon balance and soil surface elevation
Results/Conclusions . Along both salinity gradients, aboveground forest productivity from wood and litterfall decreased while aboveground herbaceous and belowground fine root production increased as forested wetlands transitioned to high oligohaline marsh. Site-specific variation in contemporary (< 3 years) C sedimentation was large, but suggested greater C sedimentation in high oligohaline marshes compared to TFFW. Decomposition of root biomass was greater in high oligohaline marsh and TFFW with prevailing freshwater (<0.5 ppt) conditions, but lower in salt-impacted forest. When decomposition was modelled assuming different deliveries of salinity (drought, pulsed, sea-level rise induced), we found different fates of root material that differentially influence surface elevation maintenance. Soil CO2 losses tended to be lowest from salt-impacted forests due to altered hydrology and decreased belowground productivity, while CH4 fluxes were static. Along one river (Waccamaw), surface elevation increased in both TFFW and moderately salt-impacted forests, decreased in heavily salt-impacted forests, and increased in the high oligohaline marsh. Long-term C accumulation in soils (decades) were sometimes opposite to the contemporary C sedimentation patterns, with significantly less C sequestration in high oligohaline marsh. Acute pulses of salinity versus long-term persistence of salinity differentially alter the C balance along transects requiring separate treatment in models.