Wetlands and carbon revisited

This paper summarizes 19 papers published in a special issue of Ecological Engineering under the general banner of wetlands and carbon. Many of the papers were presented at a special session at EcoSummit 2016 in Montpellier, France in August-September 2016. The papers are in four general categories: estimating greenhouse gas fluxes with eddy covariance; methane and other greenhouse gas emissions from wetlands; carbon sequestration by wetlands; and organic carbon decomposition in wetlands. Overall, we found that further development and wider use of eddy covariance measuring stations could help clarify long-term annual budgets of CO2 and CH4 in wetlands and, while CH4 fluxes in some coastal wetlands such as mangroves can be negligible, some inland wetlands can be significant sources of CH4 where hydroperiods are the major determinants of the emission rates. The papers here demonstrated a variety of parameters determining dynamics of methane fluxes and carbon sequestration in different wetlands and lead us to suggest that more attention should be paid to detailed analysis of the impact of environmental and management factors on carbon budgets in wetlands. Carbon sequestration is almost always estimated by soil dating methods such as with 137Cs and 210Pb isotopes and results continue to show order of magnitude differences among systems but sometimes among laboratories. This is due to the inexact nature of estimating soil dates over relatively short (∼50 year) time horizons. The idea of capping landfills, which are enormous methane sources, with wetlands which could then turn them into carbon sinks is worth investigating further but the design of these systems is still in its infancy. Organic carbon decomposition in wetlands has been investigated extensively for decades and more recently on the biogeochemical processes. 'Enzymic latches” such as phenol oxidase, which can break down phenolics and therefore speed up decomposition, may be key controllers of organic matter decomposition in waterlogged and submerged soils in wetlands. The best approach for balancing greenhouse gases and carbon sequestration remains an enigma, but the papers in this special issue take us one step closer to providing clarity.