Wetlands, atmospheric

Sources of tliis information include site descriptions mid data from the preliminary assessment (PA), site inspection (SI), and remedial investigation (RI) reports. Other sources include local soil sur eys, wetland maps, aerial photographs, and reports by the National Oceanograpliic and Atmospheric Association (NOAA) and tlie U.S. Geological Sur ey (USGS). One cmi also consult with appropriate tecluiical e.xperts (e.g., hydrogeologists, air modelers) as needed to cluuacterize tlie site. 

Controlling methane release from wetland, rice paddies and gaseous emissions from animals is more problematic. The release from rice paddies and wet lands is slow, intermittent and takes place over a wide geographic area, and thus very difficult to control. Gaseous emissions from agricultural animals contribute to atmospheric accumulation of methane due to fermentative digestion that produces methane in... 

Dead vegetation also afreets the global carbon cycle. Dead organic matter decomposes, releasing carbon dioxide to the atmosphere. Rates of decomposition vary with material, location, and climate. Non-woody organic matter decomposes rapidly woody organic matter slowly. Decomposition tends to occur faster at the soil surface than below. Decomposition is relatively fast in warm moist climates. In cold climates and in wetlands, decomposition is so slow that there is a net increase of stored carbon in the soil and organic soils called, "histosols, are formed. 

Sensitive sites would include sites that are receiving high inputs of atmospheric Hg deposition and sites with aquatic ecosystems where top end predators have high levels of Hg. We also recommend that urban sites with elevated atmospheric Hg deposition and forest sites with shallow hydrologic flowpaths, wetlands, and unproductive aquatic ecosystems should strongly be considered as candidate sites. 

The saturated soils that occur during wetland, or lowland, rice cultivation give rise to a set of physical, chemical, and biological properties that are quite different from upland soils. Rice is the only major row crop produced under flooded-soil conditions and the absence of air-filled pores along with reduced soil-atmosphere interactions result in an almost entirely different set of processes than those occurring in upland cropping systems. 

Air bubbles in the ice corroborated the increased wetness in other areas. The amount of methane in the bubbles indicates that this gas was entering the atmosphere 50 percent faster during the warming than it had earlier. The methane probably entered the atmosphere as wetlands flooded in the tropics and ice and snow thawed in the north. 

Nitrogen occurs in several oxidation states under Earth-surface conditions, from - -V to —III, and its fixation from and loss to the atmosphere depend on transformations between these states. Because wetlands are the main reducing system... 

The water column and soil surface are often the main sites of biological nitrogen fixation in wetland systems (Buresh et al., 1980 Roger 1996). Biological nitrogen fixation is the process by which atmospheric N2 is reduced to NH4+ and the... 

Snbmerged soils are important sinks for atmospheric snlfnr (Howarth et al 1992). Snlfate washed into wetlands or deposited from the atmosphere is largely rednced to snlflde by sulfate-reducing bacteria. Subseqnent precipitation with metals, especially as FeS, results in more or less permanent removal of the S from the global S cycle. 

Little snlfnr is re-emitted from wetlands into the atmosphere. Table 8.7 gives estimates of global emissions of volatile sulfur compounds from different sources. Total emissions are in the range 98 to 120 Tg (S) year 75 % is anthropogenic, mainly from fossil fnel combustion in the northern hemisphere. The main natural sources are the oceans and volcanoes. Wetlands and soils contribnte less than 3 % of the total emission. 

Aselmann 1, Crutzen PJ. 1989. Global distribution of natural fresh-water wetlands and rice paddies their net primary productivity, seasonality and possible methane emissions. Journal of Atmospheric Chemistry 8 307-358. 

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