Chair: Roland Bobbink (r.bobbink@bio.uu.nl)
P. Frenzel, I. Arth, P. Claus and M. Kruger - Linking nitrogen and carbon cycles: methane oxidation and nitrification in the rhizophere of wetland plants.
The rhizosphere of wetland plants forms an oxygenated microhabitat in an otherwise reduced bulk soil. Biogeochemical reactions like the O2 dependent oxidation of CH4 or NH4+ take place at this interface. We used rice as a model plant and combined results from microcosms and from a field site in Italy. We applied microelectrode and rate measurements with inhibitor studies and 13C signatures to analyse the interactions between N- and C-cycling. NH4+ is the dominating N-species in wetland soils but it is taken up very effectively by plants resulting in a strong nitrogen limitation of both NH4+ and CH4 oxidizing bacteria. The latter bacteria showed the potential to take over a significant part of NH4+ oxidation and might even out compete nitrifying bacteria for NH4+. Denitrification was closely coupled to nitrification and repressed, too. The addition of fertilizers transiently relieved this inhibition resulting in an increase of both denitrification and, unexpectedly, of CH4 oxidation. This stimulation is in sharp contrast to published evidence from upland soils where NH4+ was found to be an inhibitor of CH4 oxidation. Natural wetlands and rice fields are major sources of the greenhouse gas methane. Until now it was expected that increasing nitrogen deposition and intensified N-fertilization might inhibit CH4 oxidation resulting in an increased CH4 emission. However, at least in rice agriculture the reverse may be true.
R.L. Miller (romiller@usgs.gov), L.L. Hastings and R. Fujii - Carbon cycling in an experimental wetland project to mitigate subsidence of organic soils in the Sacramento-San Joaquin Delta, California.
In a study examining the use of permanent shallow flooding to mitigate subsidence of organic soils in the Sacramento-San Joaquin Delta, California, carbon (C) inputs (plant biomass) and C outputs (litter loss and gaseous C emissions) were compared in two wetland treatments on Twitchell Island. Plant colonization in wetlands with depths of 25 and 55 centimeters was monitored using permanent transects. Biomass harvests and turnover measurements of the dominant emergent macrophytes (cattail, or Typha spp. and tule, Scirpus acutus) were used to estimate annual fixed C inputs into the marsh systems on an areal basis. Losses of new plant litter were assessed with litter-bag trials, and gaseous emissions of carbon -- carbon dioxide (CO2) and methane (CH4) -- from the wetlands were measured using closed chamber techniques.
Net C inputs into the 25-cm deep treatment were greater than into the 55-cm-deep treatment because a larger amount of the 25-cm-deep treatment area was colonized by emergent vegetation and plant density within these stands tended to be greater. Loss of new litter was similar between the treatments. Gaseous C emissions were higher in the 25-cm-deep treatment for both CH4 and CO2. Thus, while the 25-cm-deep treatment had higher C inputs than the 55-cm-deep treatment, it also exhibited higher gaseous C losses. This can be the result of a greater amount of plant respiration and degradation of the greater plant C inputs in the 25-cm-deep treatment.
R. Bobbink (r.bobbink@bio.uu.nl) and H. de Caluwe - Emission of greenhouse gases from peaty fen soils: effects of water table and nitrate.
Methane and nitrous gas emissions from wetlands significantly contribute to the increase of greenhouse gases in the atmosphere. These emissions can be seriously influenced by both changes in hydrology or increased nitrogen inputs. An experiment was done to investigate the effects of water tables and nitrate enrichment on the emissions of methane and nitrous gas from intact acidic fen meadow soil cores. After a two-week acclimation period the cores were installed at ca. 20 oC with two water tables, respectively 10 cm and 1 cm below soil surface (n=10). After 10 weeks half of the cores were repeatedly treated with nitrate during 2 months. After a lag phase methane emissions were observed from the soil cores with both water tables, but the emissions from the cores with a high water table were significantly higher than from cores with a low water table. No emissions of nitrous oxide were found in this period, probable because only ammonium was present in the soil pore water. After nitrate additions hardly any effects upon methane emissions were observed, whereas nitrous emissions strongly increased in both water table treatments. It became obvious that small differences in water table or enhanced nitrate input strongly control the greenhouse gas emissions of these fen soils.
M.J. Kessler, M.G. Kalnins and G.J. Whiting - Carbon dioxide and methane soil emissions in eight Chamaecyparis thyoides wetland sites in southeastern USA.
Chamaecyparis thyoides natural forested wetland systems are thought to be a source and sink of methane and carbon dioxide, respectively. This study evaluated the amount of soil carbon dioxide emission and methane flux within a chronosequence of natural and regenerating sites in southeastern United States over a twelve-month period. Soil emission sampling plots were established to allow repeat gas sampling throughout the analysis period. Carbon dioxide emission rates showed definite seasonality in all sites, with peak emission rates (800mg CO2 /m2 /h) occurring in late summer (August). Emission rates were positively connected with temperature, which may be related to root and microbial activity. Carbon dioxide emissions significantly decreased following two precipitation events which elevated the water table above the soil surface (September).
Methane emissions were expected to follow a similar seasonality, with zero emission or oxidation in winter months and peak emission in late summer. However, methane emissions were linked more closely to hydrology. Peak methane emissions (2.4mg CH4 /m2 /h) were found following site inundation. Sites that were not inundated during growing season, and sites with a history of effective ditching, did not show any significant methane emissions. Persistent alteration of natural hydrology caused by site draining may greatly affect the natural functions of Chamaecyparis thyoides wetland soils.
X. Zheng, M. Wang and Y. Wang - CH4, N2 0, N0 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.
P. Bodelier, P. Roslev, Ta. Henckel and P. Frenzel - Evaluation of fertilizer effects on methane emission from rice paddies: the role of methane-oxidizing bacteria.
Among wetlands, rice paddies are the most important source of atmospheric methane accounting for 10-20% of the global annual emission of this greenhouse gas to the atmosphere. As an increase of rice production by 60% is the most appropriate way to sustain the estimated increase of the human population during the next three decades intensified global fertiliser application will be necessary. However, it is expected that an increase of the commonly used ammonium-based fertilisers will enhance methane emission from rice agriculture. Approximately 10-30% of the methane produced by methanogens in rice paddies is consumed by methane-oxidising bacteria (MOB) associated to the roots of rice; these bacteria are generally thought to be inhibited by ammonium-based fertilisers. In this study we tested the effect of urea and ammonium-diphosphate amendments to laboratory microcosms planted with rice and with a physical separation between root- and bulk soil compartment. The effects on the MOB were assessed using a combination of potential activity measurements, MPN counts, 14C-PLFA fingerprinting and molecular biology techniques (DGGE). The combined results showed a clear stimulation of growth and activity of MOB following fertiliser application. Type I MOB appeared to proliferate to a higher degree than type II MOB following fertiliser application. The results of this study will make necessary a re-evaluation of the link between fertiliser use and methane emission, with effects on global warming studies.
P.M. Van Bodegom (peter.vanbodegom@staff.tpe.wau.nl), J. Goudriaan, P.A. Leffelaar and A.J.M. Stams - Mechanistic modeling of methane emissions from rice paddies.
A principal reason for the large uncertainties in global methane emission estimates result from the large spatial and temporal variability in methane emissions. This large variability is the result of complex interactions between underlying processes; methane production, oxidation and transport. This variation is only partly explained by correlations with environmental variables.
A series of models was developed to understand and predict methane emissions from rice paddies. A fully mechanistic model was developed to describe the competition between microorganisms for acetate and hydrogen during the reduction sequence in rice paddies. A mechanistic model on the competition for oxygen in the rice rhizosphere was developed and a model on gas transport through a rice paddy based on a set of diffusion equations was developed. The information on these processes was simplified in a process-based field scale model that predicts methane emissions. This model needs only a few input parameters so that it can be used to estimate regional emissions with a Geographical Information System.
In this study we compared the characteristics of the process-based field scale model with the mechanistic process information. Although the field scale model included some important simplifications, the major process information could be captured. Part of the variation with a season was missed, but total seasonal methane emissions were comparable. This shows that the simplified model is appropriate to use at regional scales.
H. Terai, S. Shidara, K. Ohta and D.D. Adams - Methane and hydrogen fluxes and distribution of nitrogen cycling bacteria in Kushiro wetland, Hokkaido, Japan.
Wetlands are a major natural source for atmospheric methane, which is one of the important greenhouse gases. In this study we compared methane and hydrogen fluxes, and bacterial populations concerned with nitrogen-cycling bacteria, to evaluate the importance of the microbial processes related to methane emissions. Three different vegetative sites (low moor, high moor and alder moor) in a Kushiro wetland, Hokkaido, Japan, were compared. Methane and hydrogen fluxes were measured with static chambers consisting of plastic cylinders (50 cm dia., 80 cm height). After enclosing the vegetation, chamber air gas concentrations were monitored with a semi-conductor detector gas chromatograph. Viable bacterial populations were also estimated with a plate count method (aerobic heterotroph) or MPN method (nitrifier, denitrifier and free-living nitrogen fixer) by inoculating wetland soils into culture media at a field station. The highest methane flux (11-28 mg CH4 /m2 /h) was observed in the low moor, while the high moor had the lowest flux (4-12 mg CH4 /m2 /h). Nitrifier and denitrifier populations were abundant in low moor soils and were lacking in the high moor, whereas free-living nitrogen fixers were abundant in the high moor but not detected in the low moor. Emission of hydrogen from low moor sites was observed while uptake occurred at the high moor. These results suggest that the nutritional conditions between the different types of wetland vegetation might be important in controlling the microbial processes associated with methane production and hydrogen flux.
M.B. Jones (mike.jones@tcd.ie) - Plant mediated transport of methane in papyrus (Cyperus papyrus).
Information on methane emissions from natural tropical wetlands is extremely sparse. In Africa, the sedge Cyperus papyrus (papyrus) forms the dominant emergent vegetation of many permanently flooded wetlands but little is known about this plant's role in methane emissions from these swamps. Furthermore, the contribution of plant mediated transport to total methane emissions from papyrus has not been quantified. Because of the size of papyrus plants, in situ measurements are very difficult. Consequently, plant mediated emissions of methane have been measured using plants growing in tanks in a greenhouse. Perspex cylinders, 5.4 cm in diameter and 100 cm long, were placed over individual culms and sealed to form a closed cuvette. Methane accumulation over several hours was measured by sampling gas from the cuvette and determining methane concentration. Results suggest that younger culms are the main route for plant mediated transport but this form of emission is only about 20% of the total from papyrus swamps.
M. Glagolev, V. Lebedev, O. Glagoleva, V. Erohin, P. Olenev and A. Nozhevnikova - Plant-mediated methane transport in West Siberian bog.
Methane fluxes through plants were monitored in Big Vasyuganskoe Bog, Tomsk Region, west Siberia, during the summer of 1998-1999, using micro-chamber methods. The intensity of methane fluxes differed from species to species and also was dependent on the season. The results obtained in the experiments with individual plants correlated with the data observed at the sampling areas where the same species dominated. Methane oxidation was estimated by stable isotope analysis of methane. Maximum oxidation and minimum methane emission were observed with soils under Eriophorum vaginatum and Menyanthes trifoliata vegetation. Minimum oxidation and maximum methane emission were observed with Carex rostrata and Equisetum palustre. An increase in methane emission was observed at the end of the summer. Up to 60% of total methane emission was plant-mediated transport.
O. Kotsyurbenko and A. Nozhevnikova - Microbial methanogenesis in acidic Taiga bog.
Siberian acid bogs represent one of the main global sources of atmospheric methane. Anaerobic microbial processes were studied in samples from the west Siberian Lowlands, the world's largest wetland (south taiga region, 57 oN, 82 oE). Experiments were performed at different temperatures (1-30 oC) and pH (4.3, 5.0 and 6.2). The highest rates of methanogenesis from bog soil organic matter (peat) was observed at 20 oC and pH 5.0. The Q10 was 3.2 in the temperature range 1-30 oC. High rates of glucose metabolism occurred at all temperatures at a pH of 4.3, resulting in production of H2, CO2, CH4, acetate and butyrate. At a pH of 4.3, methanol and H2/CO2 were the main precursors of methanogenesis at low temperatures (1-10 --oC). Results obtained during this study indicated the existence of acidophilic bacteria in these peat systems. Mesophilic enrichment of acidophilic methanogens was obtained on the medium, with very low mineralization, using H2/CO2 as a substrate.
S.H. Cho and K.H. Cho (khcho@inha.ac.kr) - Environmental factors affecting methane production from the littoral sediments in a reservoir.
Methane emission from wetland sediments makes an important contribution to the enhanced greenhouse effect. Methane production rate from sediment slurries incubated at thirty degrees centigrade showed a considerable range from 0 to 0.19 nmol /g /hr at 21 sampling sites in the littoral zone of the Reservoir Paltangho. Vegetation types dominated with Phragmites australis, Typha angustifolia, and Zizania latifolia had no significant effect on methane production rate in the littoral zone. Cation exchange capacity, particle size, organic matter, Fe2+, and total nitrogen in sediments were significantly correlated with each other. Methane production rates were positively correlated with organic matter, Fe2+, acetate, total nitrogen, and cation exchange capacity of sediments and negatively correlated with redox potential and pH. Acetate, an important source of organic substrate for methanogenesis, was interrelated with particle size, cation exchange capacity, and total nitrogen in sediments. As a result of stepwise multiple regression, organic matter, clay, and redox potential of sediment could explain the spatial variation of methane production in the littoral zone of a reservoir.
