Effects of riparian wetland restoration and grazing on CH4 and CO2 exchange more than a decade after rewetting

Abstract

Introduction: Riparian wetlands provide several important ecosystem services, including carbon sequestration. Drained and degraded wetlands act as carbon sources, but rewetting might result in elevated methane (CH4) emissions and does not always reestablish a carbon sink. Objectives: This study examines the impacts of riparian wetland restoration and disturbance regime (grazing vs. no grazing) on CH4 and CO2 exchanges in wetlands 12–17 years post-restoration. Methods: Greenhouse gas fluxes were measured using a static chamber at monthly intervals over a year to assess the effects of disturbance regime, groundwater level, and soil temperature on CH4 and CO2 exchange. Results: Our results show no significant differences in CH4 emissions between restored and near-natural sites. We demonstrate that grazed sites, both near-natural and restored, are net carbon sinks, while ungrazed sites are carbon sources. However, we did not capture the production from shrubs and trees which were abundant at near-natural ungrazed sites and would be expected to act as carbon sinks. Conclusion: Our results suggest that ecosystem functioning with respect to carbon cycling was reestablished post-restoration, but that ecosystem function of the restored areas was contingent on the prevalent disturbance regime.