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Symposium 1. Global Wetlands and Greenhouse Gases
Sponsor: INTECOL
Co-Chairs:
Dr. Donald D. Adams
Professor of Environmental Sciences
Center for Earth and Environmental Science
State University of New York
Plattsburgh, NY
USA 12901
Phone: (518) 564-2028
Fax: (518) 564-3152
E-mail: donald.adams@plattsburgh.edu
and
Dr. Bernhard Wehrli
Limnological Research Center, EAWAG/ETH
Kastanienbaum
Switzerland CH-6047
Overview of Symposium:
The symposium has invited papers on the theme of greenhouse gas cycling processes and site specific studies of gas production and consumption, bubble transport, and diffuse gas flux across the sediment-atmosphere interfaces of fresh water and saline wetlands. Greenhouse gas cycling in both natural and constructed wetland systems would also be considered. Studies of greenhouse gases in wetlands from countries normally receiving little attention in the literature are particularly invited.
First Session
Bruce R. Forsberg, Instituto Nacional de Pesquisas da Amazonia, INPA-CPEC, Manaus, Amazonas, Brazil; A. Rosenqvist, Joint Resarch Centre of the European Commission, Space Applications Institute, Ispra, Italy; T.P. Pimentel, Instituto Nacional de Pesquisas da Amazonia, INPA-CPEC, Manaus, Amazonas, Brazil; and J. E. Richey, School of Oceanography, University of Washington, Seattle, Washington, USA - Modeling of flooding patterns and methane emissions in the Jau River floodplain (Central Amazon) using JERS-1 imagery.
We present here an analysis of spatio-temporal patterns of flooding and methane emission on the Jau River floodplain (Central Amazon). The Jau is a black water river with extensive lateral floodplains covered with seasonally inundated forest. Twenty JERS-1 images of a scene covering 1,030 km2 in the central Jau basin, acquired at 44 day intervals during 3 years, were used to characterize the local flooding pattern. Methane emissions, estimated regularly along a flooding gradient in the same scene, were used to characterize flux variations. Flooded area in the scene varied as a function of river stage height. Methane emissions varied as a function of the ten day average change in stage height. Using these relationships, methane emissions from the scene were estimated to vary from 1,377 to 2,488 mtonsC /y, averaging 2,021 mtonsC/y. Annual emission from the entire Jau basin (17,000 km2) in 1996, estimated from 9 JERS-1 mosaics, was 16,500 mtonsC/y.
A. Miyata and Y. Harazono,National Institute for Agro-Environment Sciences, Tsukuba, Ibaraki, Japan; and J. Kim, Department of Atmospheric Sciences, Yonsei University, Seoul, Korea - Micrometeorological measurements of carbon dioxide and methane exchanges at a Kushiro mire, Japan.
To quantify CO-2 and CH4 exchanges at mid-latitude wetlands under conditions of a boreal rainy climate, and to make evaluate the factors controlling the exchanges of these gases, CO2 and CH4 fluxes were measured, using a micrometeorological technique, at the Kushiro Mire, Hokkaido, Japan, during midsummer. Measurements were conducted at two sites: a flooded fen dominated by sedges, reeds and buckbeans, and a bog covered with sphagnum and sparse sedges. An eddy covariance method was employed to measure CO2 flux, while CH4 flux was measured by the gradient method. Variations in the daily amount of CO2 absorption at the fen were caused principally by changes in solar radiation and temperature-dependent plant respiration, whereas smaller CO2 absorption at the bog (about a quarter to a third as much as the fen) was attributable to photosynthesis by smaller plants. The CH4 flux at the fen showed a distinct diurnal variation with a midday peak, while diurnal variations at the bog were smaller. The daily amounts of CH4 emissions from the bog were two thirds as much as from the fen. Year-to-year variations in the daily CH4 emission from the fen, and lower emissions from the bog, were caused mainly by the difference in the daytime emission levels, which were controlled by plant-mediated transport as well as CH4 production and consumption in the soil.
Reinoud Segers and P. A. Leffelaar, Department of Theroretical Production Ecology, Wageningen Agricultural University, Wageningen, The Netherlands - Wetland methane fluxes: upscaling from kinetics via a single root and a soil layer to the plot.
In order to increase the basic understanding of wetland methane fluxes, theories of microbial and chemical conversions were linked to the plot scale by modeling with stepwise upscaling. At the kinetic scale we considered aerobic respiration, C-mineralization, methane production and oxidation, and electron acceptor reduction and re-oxidation. At the single root scale the kinetic model was extended with diffusion around a gas-transporting root. Bubble formation was modeled with simultaneous liquid-gas equilibria for all gases and bubble export as a function of bubble volume. The model was successfully simplified by assuming quasi steady-state for oxygen and by spatially averaging other compounds. At the soil layer scale the methane dynamics were calculated with a set of single root systems with different sizes. Averaging over single root systems had some effect on methane production and transport, but little on fluxes. At the plot scale, water dynamics were calculated using Richards' equation and vertical transport of the compounds with diffusion and mass flow. Simulated methane fluxes were of the same order of magnitude as measured fluxes. They were sensitive to several uncertain parameters, indicating that predictive process modeling of methane fluxes are still difficult to develop. Heterogeneities within a soil layer appear less important than heterogeneities between soil layers.
Klaus Butterbach-Bahl, Fraunhofer Inst. Atmos. Environment, Garmisch-Partenkirchen, Germany with C. Li, University of New Hampshire, Durham, New Hampshire, USA and X. Zheng, Institute of Atmosheric Physics, Chinese Academy of Sciences, Bejing, P.R. China - Biogeochemical modeling of C- and N-trace gas emissions from managed and natural wetland ecosystems.
Wetlands are a major source of atmospheric CH4; also N2O, if such soils are drained (e.g. rice paddies between growing seasons). Estimates of the contribution of wetlands to the global budgets of CH4 and N2O gases are primarily based on simple upscaling approaches. The complex nature of processes involved in the emissions of trace gases from wetlands and the large ecological amplitude of such ecosystems suggests that this approach may not be sufficient to estimate emissions with high precision. To overcome this problem, a biogeochemical model "DNDC" was improved by including mechanisms of CH4 production, oxidation, transport and diffusion. To describe trace gas production/consumption by oxidative/reductive processes in soils, a kinetic scheme was adopted to predict the soil oxygen profile and aeration status in submerged soils. Methane production vs. oxidation rates were calculated based on the aeration status and concentrations of substrates. In addition, sub-models for plant growth were developed, such as photosynthesis, biomass production and plant-mediated exchange of gases between the pedosphere and atmosphere. Validation for rice paddies in China, Italy and the United States showed that simulations of CH4 and N2O fluxes were consistent with observed fluxes. Sensitivity tests revealed that CH4 fluxes from rice paddies were mainly controlled by SOC, soil texture, root biomass and water management. We emphasize that biogeochemical models are a useful tool for inventory studies and may allow us to better predict the impacts of changes in land-use or climate on trace gas exchanges between wetlands and the atmosphere.
Jonathan J. Cole and M.L. Pace, Insitute for Ecosystem Studies, Millbrook, New York, USA, and S.R. Carpenter and J.F. Kitchell, Center for Limnology, University of Wisconsin, Madison, Wisconsin, USA - Does the food web control greenhouse gas flux in wetland ponds? Results from whole lake manipulations.
We measured whole-system gross primary production (GPP), respiration (R) and carbon dioxide gas flux over a six-year period in a series of wetland ponds in which the food webs were manipulated and nutrients were added. In the absence of manipulation these lakes had GPP/R ratios consistently <1 with R exceeding GPP by a factor of about 2. Likewise, net ecosystem production (NEP = GPP - R) was consistently negative, and carbon dioxide flux was consistently from the lake to the atmosphere. Nutrient enrichment, in the absence of strong planktivory, increased both GPP and R but resulted in little change to GPP/R, NEP, or carbon dioxide gas flux. When planktivorous fish dominated the food web large zooplankton were rare, nutrient enrichment resulted in large increases in GPP, the GPP/R ratio, NEP became positive and the flux carbon dioxide reversed direction, i.e., entered the ponds from the atmosphere. Thus, the food web mediates net gas flux in these ecosystems.
Mark E. Hines, K.N. Duddleston, R.B. Reich, Department of Biological Sciences, University of Anchorage, Anchorage, Alaska, USA and R.P. Kiene, Department of Marine Sciences, University of South Alabama, Mobile, Alabama, USA - Low molecular weight organic compounds are not consumed in northern wetlands: Implications for methane formation.
Typical methanogenic decomposition pathways include near terminal carbon intermediates that turn over rapidly with small pool sizes. Here we report that these intermediates are not utilized in many northern wetlands due to the lack of consumption by methanogenic bacteria. Incubations of peat samples from wetlands in New Hampshire and Alaska were compared to sediment samples from lakes and creeks. Sphagnum-dominated wetlands did not consume acetate or any of the C-1 compounds when the natural pH was below 4.6 or the temperature was below 15oC. In some instances, we were unable to detect any turnover using 14C substrates. Higher pH wetlands in Alaska did not consume these compounds either. However, temperate minerotrophic fens and freshwater sediments readily consumed all compounds tested. The lack of consumption of intermediates occurred only when methanogenesis was the terminal process. Acetate levels decreased in the presence of oxygen. Acetate accumulated all season despite the occurrence of rapid methane production. Methanogenesis in these wetlands is restricted primarily to hydrogen metabolism. Under methanogenic conditions, acetate production represents a terminal process and is a sink for a significant portion of metabolized C. The ultimate fate of this acetate is aerobic oxidation to CO2. C destined for methane is bypassed to CO2 via oxygen respiration, and does not contribute to atmospheric methane. Global warming may reverse this trend by enhancing the methanogenic degradation of acetate.
Second Session
Matthias Drösler, Vegetation Ecology, Technical University of Munich, Freising, Germany; T. Kamp, Institute of Soil Ecology, Munich, Germany; and J. Pfadenhauer, Vegetation Ecology, Technical University of Munich, Freising, Germany - Relationship of C-balance with GWP-balance: an evaluation tool for trace gas fluxes of of wetland ecosystems.
Wetlands function as sinks for and sources of the GHGs CO2, CH4 and N2O. In view of the climatic relevance of the GHG-fluxes from wetlands, it is important to focus on both the C-balance as well as on the GWP-balance. The relationship between them is distinctive of the specific wetland ecosystems and provides a useful evaluation-tool for the climatic relevance of the site. Necessary input data are simultaneous measurements of the three GHGs. For that purpose a new transparent chamber technique, equipped with a cooling system, was developed. In a weekly measurement program the GHG-fluxes were sampled on 36 plots in natural, degraded and restored bog-stands in pre-alpine southern German mires. The samples were analyzed by gas chromatography and IRGA. In general, the natural sites show a significantly positive C-balance and 'negative cooling to slightly positive heating' GWP-balance. The restored sites show more variation in the C-balance from positive to negative but still do not reach a negative GWP-balance. The degraded sites act with wide variation as C-releaser (negative C-balance) and climate heater (positive GWP-balance). This scheme is differentiated due to the specific vegetation cover.
Haruo Tsuruta, National Institute Agro-Environmet Sciences, Tsukunda, Japan; M. Yoh and T. Akagi, Tokyo University Agriculture and Technology, Fuchu, Tokyo, Japan; and T.K. Inubushi, Chiba, University, Matsudo-shi, Matsudo, Japan - Emission of methane, carbon dioxide, and nitrous oxide from Ozegahara Wetlands during an intensive three-year field program.
An intensive three-year (1995-1997) biogeochemical cycling study was conducted to study the emission of greenhouse gases (CH4, CO2, and N2O), and associated soil and groundwater chemistry, C and N isotope ratios, and soil microbiology in the Ozegahara Wetlands, a typical bog type of wetland environment in Japan. The wetland is located 1400 m above sea level in a national park 150 km north of Tokyo. CH4 flux showed a clear seasonal variation with a late summer/early autumn maximum, correlating with that of the soil temperature in the sub-surface soil layer (10-30 cm). On the other hand, the CO2 and N2O showed maximum fluxes in mid-summer, correlating with the surface soil temperature (0-10 cm). The vertical distribution of CH4 in soil gas (0-50 cm) showed a maximum concentration at ca. 20 cm. The CH4 flux was highest in the area of a kermis-schlenke complex where the representative vegetation was sphagnum. The spatial variation of CH4 emissions exhibited a negative correlation with that of CO2. N2O emissions were observed only from sloping soils where the surface was dry and CH4 flux was zero or negative (uptake). These facts strongly suggest that the major factors controlling emission of the GHGs are different for each of the gases. By using anti-correlation relationships between the methane emission rate and the maximum height of the vegetation divided by the depth of groundwater table, emission factors and annual CH4 emission rates were estimated for the Ozegahara wetlands.
Peter Casper, Institute for Freshwater Ecology and Inland Fisheries, Department of Limnology, Stechhlin, Germany; A.L.S. Furtado, Institute of Biology, Ecology Department, Federal University, Rio de Janeiro, Brazil; and D.D. Adams, Center Earth and Environmental Sciences, State University of New York, Plattsburgh, New York, USA - Methane in an acidic bog: influence of peat in the catchment on the biogeochemistry of methane.
The acidic bog Grosse Fuchskuhle in northeastern Germany, 90 km north of Berlin, was divided by plastic curtains into four different compartments. Two of these compartments were influenced by the surrounding peat. In these two compartments the pH remained low at ca. 4.5, while it increased to 6.5 in the other two compartments. The sediment anaerobic processes changed rapidly after this artificial separation. This resulted in the layer of most active methane production moving upwards to the surface from a sediment depth of more than 20 cm. The concentration profiles of CH4, as a function of depth, were then characterized by higher gas concentrations in the surface layers. Migration of the active zone of methanogenesis resulting in conditions of oversaturation near the sediment-water interface, thus producing bubbles which were observed in late summer. Using molecular-biological techniques of in-situ hybridization, the main groups of methanogens were analyzed.
Alla Nozhevnikova, O. Kotsyurbenko and M. Simankova, Russia Institute of Microbiology, Moscow, Russia - Microbial methanogenesis in polar Ural tundra wetlands.
Permafrost tundra wetlands of the Euro-Asian continent occupy a large surface area and represent an important source of atmospheric methane. Degradation of organic matter, with production of methane, occurs at temperatures that do not exceed 15oC. Psychrophilic microbial methanogenesis was investigated with samples from the polar Ural tundra wetlands (68 oN, 65 oE). Methanogenesis from tundra soil organic matter occurred in a temperature range of 5-28 oC and were most active at 5-6o C. Anaerobic microbial populations of tundra wetlands fermented different organic compounds added as substrates, with the formation of H2, volatile fatty acids (mainly acetate and butyrate) and alcohols (mainly ethanol and methanol) at all temperatures tested. Acetate appeared as an intermediate when methane was produced from H2/CO2, formate, methanol and carbon dioxide. Acetogenic bacteria played an important role in low temperature environments. A new psychrophilic acetogen Acetobacterium tundricum was isolated from tundra wetland soil. Acetate was the main methane precursor at low temperatures. The highest rate of methane production from acetate was observed at 15oC. A new coccoid methanogenic bacterium was isolated.
Donald D. Adams, Center Earth and Environmental Sciences, State University of New York, Plattsburgh, New York, USA; Irma Vila, Dept. Ciencias Ecologicas, Universidad de Chile, Santiago,. Chile; Eduardo Cortez, Comisión Chinena de Energía Nuclear, La Reina, Santiago, Chile; Aldo Aguilera, Insituto de Química, Univ. Ausral de Chile, Vadevia, Chile; Francisco Squeo, Dept. Biologica, Universidad de La Serena, La Serena, Chile; and Carlos Salazar, Direccion General de Aguas, Ministerio de Obras Poeblicas, Santiago, Chile - Chilean altiplanic wetlands - ecology and environmental conditions related to fluxes of greenhouse gases at three high elevation (>3,700 m) Andean sites.
Three wetlands at high elevation sites in the arid and semi-arid zones of the Chilean Andes were sampled for greenhouse gas (GHGs = CH4, CO2 and N2O) emissions three times during the 1997-98 period. Plans are to sample again in 2000. The wetlands are: 1) shores near Lago Chungara at 4500 m (18o 15' S., 69o 10' W.), 2) Salar de Huasco at 3900 m (20o 17' S., 68o 53' W.) and 3) Salar de Ascotan at 3700 m (21.5o S. lat., 67' W. long.). Wetland vegetation at these sites consist of Oxychloe andina, Distichia muscoides and Calamagrostis rigescens. Other species are Myriophyllum aquaticum, Azolla filiculoides, Werneria spp., Hypsela reniformis and Gentiana postrata. Gases were collected from clear and darkened static flux boxes, placed in evacuated vacutainers, and measured by FID-GC (CH4), including methanizer (CO2), and by ECD (N2O). The fluxes of GHGs at these wetland sites will be described along with their environmental ecology.
Vincent Gauci and N.B. Dise, Department of Earth Sciences, The Open University, Milton Keynes, United Kingdom - Acid rain links to methane emissions from wetlands.
Models of methane emission from freshwater wetlands largely assume that alternate electron acceptors have been removed from the anaerobic system. While this is generally the case there has, until recently, been little examination of the effects on methane emissions of alternate electron acceptors that may be introduced to these systems as a result of acid rain. In theory such introduced species as sulfate stimulate microbial competition between sulfate reducers and methanogens over limiting substrates. We present a review of work that has taken place to examine such interactions and highlight findings from a recent 20 month experiment where plots in a Scottish peatland were manipulated with low protracted deposition of sulfate (25 to 100 kg of sulfate-S per year). Methane fluxes were measured using a static chamber /GC FID technique. Results show that methane emissions can be strongly suppressed by sulfate deposition (40-50%) at acid rain levels. The extent of the suppression is dependent on temperature and hydrology rather than on sulfate dose size (within the experimental dose range).
Muneoki Yoh, Tokyo University of Agriculture and Technology, Tokyo, Japan; H. Tsuruta, National Insitute of Agro-Environmental Sciences, Ibaraki, Japan; and H. Terai, Insititute Hyrdospheric-Atmospoheric Sciences, University of Nagoya, Nagoya, Japan - Anaerobic nitrogen fixation as a partner of methanogenesis in peatlands.
Little knowledge is available about anaerobic nitrogen fixation and its implication for methanogenesis in wetlands, even though a number of studies have indicated that nitrogen fixation is widespread and could be an important source for the N economy of these ecosystems. In the wetlands we studied, the presence of nitrogen fixation in anaerobic peat habitats was evidenced in several ways: 1) a significant decrease in the N2/Ar ratio in peat interstitial air and peat 'bubbles' versus atmospheric values (83.6), suggesting a gaseous N2 removal in poorly ventilated milieus; 2) an increase in delta 15N of N2 with increasing apparent N2 consumption; and 3) high acetylene reducing activities under completely deoxygenated conditions (which were almost 10-fold larger than the activities under aerobic condition within the 0-50 cm depth interval). Measurements of interstitial water chemistry revealed quite low inorganic N (at 1 µM or below) except at sites under the influence of water inflows. This showed an extreme N-oligotrophy, thus encouraging nitrogen fixation. In two wetlands of different types, apparent N2 consumption was strongly correlated with CH4 bubbles. Anaerobic habitats rich in organic substrates may allow for both methanogenesis and anaerobic nitrogen fixation, suggesting a forgotten counter-flux of atmospheric N2 associated with CH4 emissions from peatland ecosystems.
Xunhua Zheng, M. Wang and Y. Wang, LAPC, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, P.R. China - CH4, N2O and NO emissions from a rice-based ecosystem.
A simultaneously measurement of CH4, N2O and NO emissions from a rice-wheat rotation agricultural ecosystem, which is a widely adopted crop system under subtropical climates in China, was undertaken continuously for more than one year. The effects of water regime, chemical fertilization, organic manure incorporation, temperature and soil moisture were also investigated during this study. Mitigation options obtained from the experimental results will be recommended. One major purpose of the case study was to provide field measured data for verification and validation of gas emission models, which are required in preparation for GHG inventory estimates. Some examples of model validation will be proposed and discussed in this paper as well as the experimental methods and procedures.
Bernhard Wehrli, J. Friedrich, C. Dinkel, K. Nyundu, E. Sahan and K. Zepp, Swiss Federal Institutes of Environmental Science and Technology (EAWAG) and Technology (ETH), Limnological Research Center, Kastanienbaum, Switzerland - Methanogenic activity in anaerobic sediments of the Danube delta.
The Danube delta is one of the largest wetlands in Europe with a total area of 5800 km2. A complex of channels and shallow lakes drains its extensive reed beds. In our study we have addressed the question how benthic methane fluxes and methanogenic activities in the sediment change between inflow and outflow of three different delta lakes (Lakes Rosu, Uzlina and Matita). We have used an autonomous benthic lander and dialysis pore water sampler to quantify methane release across the sediment-water interface. The spatial distribution of anaerobic activity in the sediments has been quantified by in-situ hybridization with 16SrRNA-targeted probes. The density of the archaeal community was determined in sediment cores with the probe Arch915. These counts were compared with those for Eubacteria (Eub338) and total cell counts after DAPI staining. Competition with sulfate reducers can be estimated from the analysis of the delta subgroup of Proteobacteria with the probe SRB385. Lake Uzlina, which receives river water directly from the Danube, showed larger methane fluxes of 24 mmol /m2/day compared to 2.4 in Lake Matita, which receives water from reed beds and other lakes. Benthic methane fluxes increased significantly between July and September.
Thomas Kamp, GSF Institute of Soil Ecology, Neuherberg, Germany with U. Wild, Department of of Vegetation Ecology, Technical University of Munich, Freising, Germany and J. C. Munch, GSF Institute of Soil Ecology, Neuherberg, Germany - Gas fluxes and global warming.
Investigations on nutrient cycling, plant physiology, water balance and others were carried out on a restoration project in the Danube valley in southern Germany. One aspect of the project was measurements on trace gas fluxes of both restored wetland and drained permanent grassland. Trace gas measurements (CO2, N2O, CH4) were undertaken to get an idea of the global warming potential (GWP) of the differently managed plots. Results show, that high emissions of N2O occurred from the drained permanent grassland (7.2 kg N2O /ha /a). On the other hand, highest flux rates of CH4 from differently flooded plots (with and without plants, high and low water level; 10 to 70 kg CH4 /ha /a) were noticed. Calculating CO2 equivalents from N2O and CH4 flux rates, the drained permanent grassland showed a higher GWP (2300 kg CO2 equivalents /ha /a) in contrary to the restored wetland plots (620 to 1600 kg CO2 equivalents /ha /a). Up to now, we have not taken into account the decomposition and mineralisation of the drained plot on the one hand and the plant biomass used as renewable raw material from the flooded plots on the other hand. The present investigations show that the restoration of formerly drained peatland can reduce the atmospherical load with trace gases.
Patrick Megonigal, George Mason University, Fairfax, Virginia, USA; and A. Marsh and B. Drake, Smithsonian Environmental Research Centre, Edgewater, Maryland, USA - Rising CO2 and long-term carbon storage in terrestrial ecosystems: an empirical carbon budget.
Our goal was to determine the fate of ~7 kg C /m2 of excess carbon dioxide (CO2) assimilated over a 12-year period by a salt marsh exposed to elevated atmospheric CO2. We identified three potential carbon sinks: soil carbon stocks, winter ecosystem respiration, and hydrologic export. Winter whole-system respiration rates were not affected by the CO2 treatment. Plots dominated by a C3 sedge, Scirpus olneyi, and exposed to elevated atmospheric CO2 showed a consistent increase in dissolved inorganic carbon of 6 to 27% compared to ambient levels of CO2. The differences were not significant, probably a result of the small sample size (n=5). Nonetheless, the trend is evident that hydrologic export may account for 15% of the excess carbon in the elevated chambers. Elevated CO2 had no affect on dissolved inorganic carbon in plots dominated by a C4 grass, Spartina patens, or dissolved organic carbon in either community. We are currently analyzing soil samples for C content, the only pool that represents a long-term carbon sink for carbon sequestration in this ecosystem.
Third Session
Vladimir Samarkin, Institute, for Physical-Chemical an Biological Problems of Soil Science, Russian Academy of Sciences, Pushchino, Russia; D. Wagner, Institute of Soil Science, Hamburg University, Hamburg, Germany; and E-M. Pfeiffer, Alfred Wegener Insitute for Polar and Marine, Research, Bremerhaven, Germany - Methane biogeochemistry and microbial processes in Siberian tundra wetlands.
Tundra wetlands are an important natural methane source. Methane production, consumption and emissions were studied in distinct areas of polygonal tundra in northern Siberia using static chambers along with incubation and radiotracer techniques. Methane flux was much higher from wet polygon soils with Carex and Eriophorum than from inter-polygonal moist soils with Sphagnum. The mean summer flux from the area was about 50 mg CH4 /m2/day. Microbial methane generation from carbon dioxide plus hydrogen and from acetate was detected throughout the unfrozen layer of wet soils at low (both positive and near zero) temperatures. Methane oxidation was most effective in the near surface layers associated with Sphagnum, where bacteria consumed most of the methane produced in the underlying soils. In soils covered by Carex about one third of the generated methane was oxidized. Climate warming may result in an increase in the thickness and lifetime of an unfrozen tundra soil layer where there are active microbial processes occurring.
Pertti Martikainen, J. Alm*, H. Nykanen*, S. Saarnio, M. Maljanen, J. Heikkinen and J. Silvola, Department of Environmental Sciences, University of Kuopio, Kuopio, Finland [*Department of Biology, University of Joensuu, Joensuu, Finland] - Dynamics of greenhouse gases in natural and disturbed northern peatlands.
Carbon balances for different peatlands and microsites within specific peatlands can vary greatly and is highly dependent on weather conditions. Although natural peatlands act as carbon sinks in normal wet years, they might loose carbon in years with hot and dry summers. Decomposition of organic matter takes place also in the winter, and constitutes 10-30% of the annual gas release. Our results show that the carbon balance for northern peatlands is very sensitive to climatic factors. Hydrology is even more crucial for carbon gas (CO2 and CH4) dynamics than is the temperature. The relationship between photosynthesis and methane release is greatly modified by water table and vegetation type. The focus of our studies has been on the dynamics of CH4, N2O and NO on peatlands drained for forestry. These have a general value in predicting the possible changes in gas dynamics for peatlands with lowered water tables during changing climate. In addition to altered carbon dynamics, the lowering of the water table is followed by an increase in emissions of nitrogen oxides, but only in fertile sites. The agricultural use of organic soils causes the most dramatic changes in the gas dynamics. Examples for the annual balance of CO2, CH4 and N2O for organic agricultural soils growing grass or barley will be shown.
Tomoko Nakano, Department of Geography, Tokyo Metroploitan University, Hachioji, Japan; G. Inoue, Center for Global Environment Research, Insitute for Environmental Studies, Tsukuba, Japan; M. Sorokin, Aernet Team, GSFA, National Aernautics and Space Adminstration, USA; and S. Maksyutov, Center for Global Environment Research, Insitute for Environmental Studies, Tsukuba, Japan - Automatic measurement of methane and carbon dioxide fluxes at West Siberian wetlands in 1997.
Methane emissions from summer to autumn were investigated in a west Siberian wetland (57o 51 'N, 83o 05 'E) during 1997. These observations were conducted continuously using an automatic flux measurement system with a semi-conductor detector. The flux measurements were made at six points including five vegetation components. The largest flux, obtained at a Carex site, was 21.1 mg CH4 /m2 /hr. Emission in August from the study area (250 m x 175 m) was estimated as 475 kg CH4 (10.9 mg CH4 /m2 /hr). The Carex zone exhibited the largest contribution to the CH4 emission for the entire area. The relationship between net methane flux and environmental factors will be discussed based on the observed data. At both Carex and Sphagnum sites, a significant linear correlation between CH4 flux and soil temperatures was obtained. The flux was also highly correlated with the rates of respiration and photosynthesis of plants at the Carex sites. We expect the photosynthesis rate to be a good indicator for estimating broad scale CH4 emissions, because the former can be evaluated by remote sensing data from satellites or airplanes.
Rob G. Striegl, K.P. Wickland, M.A. Mast and D.W. Chow, U.S. Geological Survey, Denver, Colorado, USA - Annual exchange of carbon gases at a mountain wetland.
Field measurements and modeled estimates of carbon dioxide and methane exchange were used to determine the carbon balance of a subalpine wetland at 3200 m in the Rocky Mountain National Park, Colorado. Carbon gas fluxes were measured using light and dark chambers during snow free periods and gas concentration gradients in the snow during winter. Fluxes were simulated using empirically and theoretically based models and hourly sediment temperature and solar radiation data. Carbon dioxide and methane fluxes were continuous, even through several meters of snow in the winter, and they were highly seasonal. Methane emissions increased ten-fold shortly after snowmelt in June, then gradually declined back to winter emission rates by November. Respiration and photosynthesis peaks followed the methane emission peak, within about a month after snow melt, then they both declined. Respiration plus methane emission averaged 31.5 mole C /m2 /yr, having a CO2:CH4 ratio of 10:1. Measured and modeled photosynthetic uptake of atmospheric CO2 averaged ~20 mole C /m 2 /yr, resulting in a loss of ~11.5 mole C /m 2 /yr from this high altitude wetland for the 1996-98 period.
G.T. Klaver and J. Baker, Netherlands Institute of Applied Geoscience, Utrecht, The Netherlands; N. Panin, S. Radan, and A.Gianciu, GeoEcoMar, Bucharest, Romania; and N. Berlinski, IBSS, Odessa, Ukraine - Fluxes and in situ measurements of greenhouse gasses in the Danube Delta.
The Danube Delta is the second largest delta in Europe covering 5,800km2 of lakes, marshes and channels. Sampling for greenhouse gases used the principle of circulated equilibrated water/air through a multi-gas monitor, with a photo-acoustic infrared detector. Land gas fluxes employed the static chamber system with the same monitor. The response time for a single sequential measurement of CO2, N2O and CH4 was about 100 sec. Detection limits were 3ppmv for CO2, 0.05ppmv for N2O and 0.1ppmv for CH4. The main branches in the Danube Delta showed a general decrease in N2O and CH4 and an increase in CO2 in the direction of water flow. In contrast, small branches with dewatered marsh areas and lakes showed a continuous increase in CH4 and CO2 until they entered the main branch. Lakes in the northern part of the Delta contained the highest concentrations of greenhouse gases. Comparisons of channels and Delta lakes showed that the lakes were the more important producers of CH4 while channels had higher concentrations of CO2 and N2O.
Elaine Matthews and E.B. Walter, Columbia University Center for Climate Systems Research, New York, New York, USA; and V. Gauci, Department of Earth Sciences, The Open University, Edinburgh Research Station, Midlothian, United Kingdom - Wetlands and the global methane cycle: Current role and future outlook.
Although wetlands occupy only about 4% of the earth's ice-free land surface, they are the world's largest methane (CH4) source and the only surface feature likely to be strongly dominated by climate. Processes governing current global CH4 emissions from wetlands are relatively well understood, but the sensitivity of wetlands and their CH4 emissions to climate variability and change remains the largest uncertainty in the global CH4 cycle and could strongly influence predictions of future climate. Furthermore, recent research suggests that chemical impacts on wetlands, in the form of low-dose sulfate deposition, may result in substantial reductions in future methane emissions. Therefore, understanding large- and small-scale climate-sensitive processes prevailing in the world's wetlands is crucial to predicting physical and biogeochemical responses of wetlands to interannual and longer-term climate variations. This presentation will provide an overview of current understanding concerning the role of wetlands in the global methane cycle, state-of-the-art modeling of methane emissions and wetland dynamics, and likely scenarios of methane emissions and of wetland dynamics over the next half century.
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