Emissions from wetlands

Longer ice-core records show that methane concentrations have varied on a variety of time scales over the past 220 000 years (Fig. 18-15) Qouzel et al, 1993 Brook et al, 1996). Wetlands in tropical (30° S to 30° N) and boreal (50° N to 70° N) regions are the dominant natural methane source. As a result, ice-core records for preanthropogenic times have been interpreted as records of changes in methane emissions from wetlands. Studies of modem wetlands indicate that methane emissions are positively correlated with temperature, precipitation, and net ecosystem productivity (Schlesinger, 1996). 

Whiting GJ, Chanton JP. Primary production control of methane emission from wetlands. Nature. 1993 364 794-795. 

Bachelet D, Neue HU. 1993. Methane emissions from wetland rice areas of Asia. Chemosphere 26 219-237. 

Cao MK, Gregson K, Marshall S. 1998. Global methane emission from wetlands and its sensitivity to climate change. Atmospheric Environment 32 3293-3299. 

Conrad R. 1993. Mechanisms controlling methane emission from wetland rice fields. In Oremland R, ed. Biogeochemistry of Global Change. Radiatively Active Gases. New York Chapman HaU, 317-355. 

Bartlett, K. B., and R. C. Harriss. 1993- Review and assessment of methane emissions from wetlands. Chemosphere 26 261-320. 

A variety of process-based models of methane emission from wetlands have been published, ranging from very complex models requiring a large number of measured input parameters to straightforward special-purpose models involving correlations between measured parameters. These models have been developed to understand controls on CH4 fluxes from a range of environments, as well as to scale fluxes and soil consumption to global scales. 

Rising atmospheric CO2 will influence CH4 emissions from wetlands even in the absence of... 

Methane is the most abundant hydrocarbon in the atmosphere. Table 2.9 summarizes the global sources of CH4, which are estimated at 535 Tg(CH4) yr (range 410 to 660) (IPCC, 1995). Of the estimated global annual emissions, 160 Tg(CH4) yr is attributed to natural sources, with the most prominent contribution being emissions from wetlands. Of the estimated 375 Tg(CH4) yr from anthropogenic sources, 100 Tg(CH4) yr comes from fossil fuel combustion, and the remainder from biospheric sources. Methane is removed from the atmosphere through reaction with hydroxyl radicals (OH) in the troposphere, estimated at 445 Tg(CH4) yr, and by reaction in the stratosphere, estimated at 40 Tg(CH4) yr. Microbial uptake in soils contributes an estimated 30 Tg(CH4) yr removal rate. The im-... 

Methane and carbon dioxide produced in soils are transported into the atmosphere by diffusion and mass flow via two pathways (1) the aerenchyma tissues of plant roots and stems and (2) flux from soil to the overlying water column (Figure 5.61). Gas exchange in plants is discussed in detail in Chapter 7. Carbon dioxide is highly soluble and undergoes various chemical reactions, and it may be difficult to estimate flux accurately without considering aU associated reactions. Because of the potency (on molecule-to-molecule basis, methane absorbs 25 times as much infrared radiation as carbon dioxide) of methane as greenhouse gas, we will focus our discussion on methane emissions from wetlands. 

As a result of these uncertainties, the acmal contribution of wetlands to the atmospheric methane budget is even more poorly known than the factor-of-two that is usually quoted (Cicerone and Oremland, 1988). Another important consideration is that the areal extent of various types of wetlands worldwide is only known to a factor of two (Aselmann and Crutzen, 1989 Fung et al, 1991 Chapman, 1977). Bartlett et al. (1989) have discussed the large variations of methane fluxes measured from adjacent but diverse wetlands (Everglades) and the related problems of estimating a global wetland flux. Thus, the uncertainty in methane emissions from wetlands may vary by a factor of two or three. 

Bartlett K. B. and Harriss R. C. (1992) Review and assessment of methane emissions from wetlands. In Atmospheric Methane Sources, Sinks and Role in Global Change (eds. M. Khalil and M. Shearer), Shearer proceedings of NATO workshop, October 1991, pp. 261-320. Pergamon Press, New York. 

Moore T. R., Heyes A. and Roulet N. T. (1994) Methane emissions from wetlands, southern Hudson Bay lowland. J.Geophys. Res. 99D, 1455-1467. 

---