Eddy Covariance Measurements of CO2 and CH4 with a view to Optimizing Carbon Capture in Wetland Restoration

The artificial isolation of floodplain wetlands from inundation has been one of the most widespread causes of ecological decline across the globe. Wetlands are biodiversity hotspots in the landscape, and their isolation from floodwaters and, on the coast, flood tide inundation has led to the degradation of ecological services including reductions in fisheries production, waterbird habitat, and habitat refugia. Scientific and policy interest has recently turned to the value of coastal wetlands for carbon sequestration (“Blue Carbon”). These coastal mangrove and saltmarsh restorations are now at the forefront of developments for ecosystem-based climate change mitigation and adaptation. International policy developments relating to climate change mitigation have fuelled interest in the measurement of wetland carbon sequestration. The 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands (Wetlands Supplement), provides a framework for the incorporation of wetland carbon sequestration in national carbon accounts. This is particularly relevant where the carbon sequestration occurs as a result of a government activity, such as the restoration of the wetland. Currently, the benefits of wetland restoration to carbon sequestration are not captured in the national carbon accounts, even though the UNFCCC policy framework allows for this. In view of this, we have developed a study for broad-scale accounting of carbon benefits resulting form wetland restoration. The Tomago wetland located near Newcastle, NSW, Australia is undergoing rehabilitation restoring tidal inundation to a previously leveed floodplain. It is hypothesised that the restoration of tidal inundation would convert a methane source into a sink as a consequence of soil salinization. Here a Before-After-Control-Impact experimental design has been applied to measure the impact of tidal reinstatement on wetland floodplain accretion and gas flux. Prior to tidal reinstatement, we have installed eddy covariance towers (CO2 and CH4), surface elevation tables, and continuous water level and water quality loggers. Hydrodynamic modelling identified the sites within the wetland predicted to remain disconnected from tidal flow. Concurrent with the micrometeorological energy balance and gas flux measurements environmental variables such as soil water salinity, inundation regime, and soil microbial communities were undertaken. This comprehensive set of data facilitates the predictive power to explain variation in greenhouse gas flux. At Tomago before flooding studies were carried out 4 months prior to tidal reinstatement, November 2015, and post reinstatement monitoring which is still underway. Results to date show an increase in methane emissions and CO2 uptake post flooding. These results are presented in the context of assessing carbon budgets (carbon inputs and fluxes) associated with this large-scale coastal and inland wetland restoration project.