Greenhouse Gas Balance in a Restored and Natural Wetland

Abstract:

The greenhouse gas balance of natural and restored wetlands is an important consideration when assessing ecosystem services, structure and function and restoration success of wetlands. Fast methane (CH₄) gas analyzers such as the LI7700 are now enabling continuous ecosystem scale (eddy flux) measurements and assessment in conjunction with CO₂ measurements. Here, we have set up two locations, one in a natural and one in a restored tidal salt marsh in the Meadowlands of New Jersey (MNJ) USA, in order to compare ecosystem level methane and carbon dioxide fluxes. Continuous methane fluxes were measured at the ecosystem level over three growing seasons at the restored site and two growing seasons at the natural wetland site concomitant to carbon dioxide fluxes. Methane and carbon dioxide emissions were highly variable in space and time over the three years of investigation (2012-2014). The temporal dynamics of methane and carbon dioxide fluxes in each of the sites suggest small-scale site-specific controls on methane emissions, but ubiquitous, non-specific controls on carbon dioxide uptake and release. Methane emissions increased at the restored site from 2012 to 2013, despite no corresponding increases in carbon dioxide uptake. In contrast, methane emission decreased at the natural wetlands site over the same time with concomitant increase in carbon dioxide uptake (more negative net ecosystem exchange). In 2014, the trend continued at the natural and the restored wetland sites with decreasing methane emission and increasing CO₂ uptake. The influence of temperature and phenology on the observed patterns will be discussed.