Does the element composition of soils of restored wetlands resemble natural wetlands?

Abstract

The main goal of this study was to assess if wetland restoration changes soil biogeochemistry, here measured as organic matter content (OM) and element concentrations of the soils, back to its original state. We selected nine sampling sites in the Sanjiang Plain, China, that had two or three of the wetland types ‘undisturbed/natural’, ‘restored’, and ‘paddy field’ close to each other. The paddy fields were originally established on natural wetlands, and the original wetland soils would therefore have been similar. We analyzed the soils for element composition, OM, as well as electrical conductivity (EC) and pH. Distinct differences between undisturbed wetlands, restored wetlands and paddy fields existed in terms of element composition, OM, and EC, with most values for restored wetlands in-between those of undisturbed wetlands and paddy fields. Ordination analysis of the element concentrations by RDA identified that OM explained most variance (23.9% of 34.4% of total). OM correlated positively with N and S, negatively with most metals. Disturbance of wetland soils by agricultural activities most likely depleted OM of the soils, which in turn altered the concentrations of most elements. Restoration, even if only a few years ago, recovered the OM and changed the element contents in the direction of a natural condition to some extent. This information is important for restoration of wetlands, because to be successful, not only hydrology and biodiversity need to be restored but also the soil composition and biogeochemistry. It further can be used for assessment of success of wetland restoration.