Effects of Ecological Restoration on Trophic Dynamics in Estuarine Wetlands

Ecological restoration actions to improve hydrologic conditions, including the construction of levees and freshwater release have been widely used to restore wetlands degraded by excessive soil salinity in coastal areas. However, the construction of levees for impoundments blocks the connectivity between the restored wetlands and the sea. In addition, freshwater inputs also altered some physical and chemical properties of the water bodies. In this study, stable isotopic compositions of primary producers and the shared consumers were analyzed to evaluate the impacts of these hydrologic changes on the function of the restored wetland ecosystems. After freshwater inputs, due to the change in salinity, the vegetation of the restored wetlands was replaced by the freshwater wetland vegetation. Although significant differences in the composition of basal sources existed, carbon stable isotope analyses indicated that there were no significant changes in source contribution between natural and restored wetlands for the shared consumers, with Suspended POM/ submersed aquatic vegetation being identified as contributing more carbon sources to consumers than emergent macrophytes/sediments. The construction of the impoundments eliminated the natural hydrological connection between the restored wetlands and the ocean, leading to the oligotrophic conditions in restored wetlands. For shared consumers, the δ15N values and trophic level positions in the restored wetlands became significantly lower than that in the natural wetlands.