Contribution of natural and drained wetland systems to carbon stocks, CO2, N2O, and CH4 fluxes: an Australian perspective

Abstract

Greenhouse gas (GHG) flux from wetland systems, both in their natural state and following drainage, has not been well accounted for in the carbon accounting process. We review GHG production from both natural and drained wetlands, and estimate the likely GHG emissions from these systems in Australia. Only a small number of studies have quantified GHG emissions from undisturbed Australian wetland environments. Consequently, in order to estimate GHG flux for Australia, it was necessary to collate data collected overseas from similar climatic zones. Using this approach, it appears that undisturbed, vegetated wetlands in Australia are likely to be net GHG sinks, with the greatest rates of sequestration occurring in mangrove ecosystems (–2669 g CO2-e/m2.year) where biomass production is high but CH4 emissions are limited by salinity. The uncertainty surrounding these values is high, however, due to (a) the low number of measurements from Australia, (b) the low number of measurements for CO2 flux, and (c) the low number of studies where all GHGs have been measured concurrently. It was estimated that the drainage of melaleuca and mangrove forest wetlands in Australia would turn them from carbon sinks into carbon sources, and that in the first 50 years since drainage, this has increased global warming potential by 1149 Tg CO2-e or 23 Tg CO2-e/year. This is significant given that GHG emissions due to land-use change in 2007 totalled 77.1 Tg CO2-e. However, data surrounding the area of wetlands drained, carbon stocks in drained wetlands, and the effect of drainage on CH4 and N2O flux are limited, making the uncertainty surrounding these estimates high. Further study is clearly required if Australia wishes to accurately incorporate wetland systems into national carbon and greenhouse gas accounting budgets.