A Review of Wetland Remote Sensing <s> Trace Gases from Wetland <s> Rates of emissions of the biogenic sulfur (S) gases carbonyl sulfide (COS), methyl mercaptan (MSH), dimethyl sulfide (DMS), and carbon disulfide (CS2) were measured in a variety of marine and freshwater wetland habitats in the Florida Everglades during a short duration period in October using dynamic chambers, cryotrapping techniques, and gas chromatography. The most rapid emissions of >500 nmol m−2 h−1 occurred in red mangrove-dominated sites that were adjacent to open seawater and contained numerous crab burrows. Poorly drained red mangrove sites exhibited lower fluxes of ∼60 nmol m−2 h−1 which were similar to fluxes from the black mangrove areas which dominated the marine-influenced wetland sites in the Everglades. DMS was the dominant organo-S gas emitted especially in the freshwater areas. Spectral data from a scene from the Landsat thematic mapper were used to map habitats in the Everglades. Six vegetation categories were delineated using geographical information system software and S gas emissions were extrapolated for the entire Everglades National Park. The black mangrove-dominated areas accounted for the largest portion of S gas emissions to the area. The large area extent of the saw grass communities (42%) accounted for ∼24% of the total S emissions. <s> BIB001 </s> A Review of Wetland Remote Sensing <s> Trace Gases from Wetland <s> The source strength of atmospheric trace gases from natural ecosystems must be quantified in order to assess the effect of such inputs on the background tropospheric chemistry. A static chamber technique and a gas exchange technique were used to determine the emissions of nitrous oxide from five sites within the Hudson Bay Lowland, as part of the Northern Wetland Study. Two mechanisms, one diffusive and the other episodic, were found likely to be responsible for the emissions of nitrous oxide. The annual diffusive flux ranged from -3.8 mg(N20)/m 2 in a treed bog to 7.9 mg(N20)/m 2 in an open fen. The addition of the episodic flux, increased this range to -2.1 mg(N20)/m 2 and 18.5 mg(N20)/m 2 respectively. These episodic emissions occurred in from 2.5 % to 16.7 % of the samples during the late summer peak emission period. Since the gas exchange rate could not detect the episodic emissions, it was found to be a poor method for water emission rate determination within the wetland. LANDSAT-Thermatic Mapper (TM) imagery was used to scale the emissions, from the chamber level to an integrated average over the entire Hudson Bay Lowland. The total emission rate of N20 from the Hudson Bay Lowland, was determined to be 1.2 Gg(N20)/year, of which 80% was attributed to episodic emissions. <s> BIB002 </s> A Review of Wetland Remote Sensing <s> Trace Gases from Wetland <s> Based on point measurements of methane flux from wetlands in the boreal and subarctic regions, northern wetlands are a major source of atmospheric methane. However, measurements have not been carried out in large continuous peatlands such as the the Hudson Bay Lowland (HBL) (320,000 km2) and the Western Siberian lowland (540,000 km2), which together account for over 30% of-the wetlands north of 40°N. To determine the role the Hudson Bay Lowland as a source of atmospheric methane, fluxes were measured by enclosures throughout the 1990 snow-free period in all the major wetland types and also by an aircraft in July. Two detailed survey areas were investigated: one (≈900km2) was in the high subarctic region of the northern lowland and the second area (≈4,800 km2) straddled the Low Subarctic and High Boreal regions of the southern lowland. The fluxes were integrated over the study period to produce annual methane emissions for each wetland type. The fluxes were then weighted by the area of 16 different habitats for the southern area and 5 habitats for the northern area, as determined from Landsat thematic mapper to yield an annual habitat-weighted emission. On a per unit area basis, 1.31±0.11 and 2.79±0.39 g CH4 m−2 yr−1 were emitted from the southern and northern survey areas, respectively. The extrapolated enclosure estimates for a 3-week period in July were compared to within 10% of the flux derived by airborne eddy correlation measurements made during the same period. The aircraft mean flux of 10±9 mg CH4 m−2 d−1 was not statistically different from the extrapolated mean flux of 20±16 mg CH4 m−2 d−1. The annual habitat-weighted emission for the entire HBL using six wetland classes is estimated as 0.538±0.187 Tg CH4 yr−1 (range of extreme cases is 0.057 to 2.112 Tg CH4 yr−1). This value is much lower than expected, based on previous emission estimates from northern wetlands. <s> BIB003 </s> A Review of Wetland Remote Sensing <s> Trace Gases from Wetland <s> [1] We used field measurements of methane (CH4) flux from upland and wetland soils in the Northern Study Area (NSA) of BOREAS (BOReal Ecosystem-Atmosphere Study), near Thompson, Manitoba, during the summers of 1994 and 1996 to estimate the overall CH4 emission from a 1350 km2 landscape. June–September 1994 and 1996 were both drier and warmer than normal, but summer 1996 received 68 mm more precipitation than 1994, a 40% increase, and had a mean daily air temperature 0.6°C warmer than 1994. Upland soils consumed CH4 at rates from 0 to 1.0 mg m−2 d−1, with small spatial and temporal variations between years, and a weak dependence on soil temperature. In contrast, wetlands emitted CH4 at seasonal average rates ranging from 10 to 350 mg CH4 m−2 d−1, with high spatial and temporal variability, and increased an average of 60% during the wetter and warmer 1996. We used Landsat imagery, supervised classification, and ground truthing to scale point CH4 fluxes ( 1000 km2). We performed a sensitivity analysis for error terms in both areal coverage and CH4 flux, showing that the small areas of high CH4 emission (e.g., small ponds, graminoid fens, and permafrost collapse margins) contribute the largest uncertainty in both flux measurements and mapping. Although wetlands cover less than 30% of the landscape, areally extrapolated CH4 flux for the NSA increased by 61% from 10 to16 mg CH4 m−2 d−1 between years, entirely attributed to the increase in wetland CH4 emission. We conclude that CH4 fluxes will tend to be underestimated in areas where much of the landscape is covered by wetlands. This is due to the large spatial and temporal variability encountered in chamber-based measurements of wetland CH4 fluxes, strong sensitivity of wetland CH4 emission to small changes in climate, and because most remote sensing images do not adequately identify small areas of high CH4 flux. <s> BIB004 </s> A Review of Wetland Remote Sensing <s> Trace Gases from Wetland <s> The Sanjiang Plain located in Northeastern China is one of the major rice producing regions in the country. However, differing from the majority rice regions in South- ern China, the Sanjinag Plain possesses a much cooler cli- mate. Could the rice paddies in this domain be an important source of global methane? To answer this question, methane (CH4) emissions from the region were calculated by inte- grating remote sensing mapping with a process-based bio- geochemistry model, Denitrification and Decomposition or DNDC. To quantify regional CH4 emissions from the plain, the model was first tested against a two-year dataset of CH 4 fluxes measured at a typical rice field within the domain. A sensitivity test was conducted to find out the most sen- sitive factors affecting CH4 emissions in the region. Based on the understanding gained from the validation and sensi- tivity tests, a geographic information system (GIS) database was constructed to hold the spatially differentiated input in- formation to drive DNDC for its regional simulations. The GIS database included a rice map derived from the Landsat TM images acquired in 2006, which provided crucial infor- mation about the spatial distribution of the rice fields within the domain of 10.93 million ha. The modeled results showed that the total 1.44 million ha of rice paddies in the plain emit- ted 0.48-0.58 Tg CH4-C in 2006 with spatially differentiated annual emission rates ranging between 38.6-943.9 kg CH4- C ha 1 , which are comparable with that observed in Southern China. The modeled data indicated that the high SOC con- tents, long crop season and high rice biomass enhanced CH4 production in the cool paddies. The modeled results proved that the northern wetland agroecosystems could make impor- tant contributions to global greenhouse gas inventory. <s> BIB005
Greenhouse gases (GHGs) have become a hot topic in recent years because of global warming. The concentration of CH 4 , which is the second most important GHG following CO 2 , has doubled over the past 200 years BIB002 , with a recent increase rate of~1% BIB004 . In total, 15% of the global warming has been thought to be contributed by CH 4 BIB004 . Many researchers pay attention to the CH 4 fluxes from wetlands, which are considered to be the largest natural source of CH 4 BIB003 . Chamber-based trace gas flux measurements were commonly used to monitor trace gases from soil which results just on behalf of the characteristic of points (usually within 1 m 2 ). Sometimes people are more concerned about the trace gas flux on a large area. It is challenging to extrapolate the trace gas fluxes from a quadrat scale to landscape or regional scale. Many studies used chambers or enclosures to measure trace gas fluxes for each land cover type and used Landsat data to classify the land cover types of the study region. They determined trace gas flux on a regional scale using the sum of the trace gas fluxes of each land cover type BIB003 BIB002 BIB001 BIB004 BIB005  .