Coastal salt marsh restoration drives element composition of soils toward its original state by recovering soil organic matter

Large areas of coastal wetlands have been restored recently throughout the world; it is important to know if restoration practice recovers original levels of biogeochemical functioning in coastal wetlands. We did samplings in five sites in the Liaohe River Delta, China. Each site had three salt marsh types: natural, restored, and degraded. We measured the concentrations of 43 elements and environmental variables including soil organic matter, soil electrical conductivity, soil pH, soil salinity, and soil water content. Concentrations of 39 elements differed significantly between salt marsh types. The values of the concentrations of 39 elements in the restored salt marshes were all in between those of natural and degraded salt marshes. Soil organic matter and the relative abundance of most elements including nutrients and metals increased simultaneously during restoration. Redundancy analysis indicated that soil organic matter explained 72.1% of the total variation in element composition. Our findings indicated that the recovery of soil biogeochemical functioning in salt marshes was driven by the accumulation of soil organic matter during restoration. It may take a very long time for the soil composition and biogeochemistry to reach the original levels prior to disturbance.