Wetlands are unique ecosystems delivering important ecosystem services to society. Due to extensive drainage only a minor fraction of the original wetland areas still remains in e.g. Europe. During the last decades, wetland restoration has become a prioritized environmental protection action in many European countries. Also the Swedish government has defined wetland restoration as major national undertaking, with numerous authorities and landowners actively involved. The major objectives behind wetland restoration are increased biodiversity, increased carbon sequestration, increased groundwater storage and improved surface water quality. However, wetland restoration also causes fundamental changes in biogeochemical properties and may result in undesired impacts and potential environmental threats. In addition, a century or more of drained conditions has drastically changed the soil properties in relation to natural wetlands and this is likely to profoundly influence the potential for various biogeochemical processes. This renders the impact of restoration on biogeochemical processes difficult to predict. Methane is the second most important green-house gas after carbon dioxide. Another process of grave concern is mercury (Hg) methylation. The overall aim of the project is to identify properties of rewetted wetlands that are critical for methane dynamics (including both production and consumption) and for the transformation of inorganic Hg to elemental gaseous Hg and the toxic MeHg molecule. We will the compare these properties and the associated biogeochemical pathways relative adjacent undisturbed natural wetlands. Understanding these biological systems will be fundamental for developing strategies to minimize emissions of the greenhouse gas methane and concentrations of methyl mercury in ground and surface waters of our landscape following wetland restoration.