Μg CH4 Research Articles

Effect of rice cultivar on CH4 production potential of rice soil and CH4 emission in a pot experiment

Methane production potential (MPP) of rice soil, defined here as the mean value of methane production rate (MP-R) of rice soil over a given period in which the substrate for methanogenesis is presumably depleted, significantly affects CH4 emission to the atmosphere. To expand our understanding of how MPP was affected in soils grown with different rice cultivars (Yanxuan, 72031 and 9516) and its consequence on CH4 emission, the changing pattern of MP-R was elucidated in the present study. On an entire rice growing scale, the MPP of planted soil was significantly higher than that of unplanted soil, and the MPP of 72031 rice soil was 9.42 µg CH4 kg (d.w.s) −1 h−1, significantly lower than Yanxuan (18.2 µg CH4 kg (d.w.s) −1 h−1) and 9516 rice soils (17.7 µg CH4 kg (d.w.s) −1 h−1). Yanxuan and 9516 soils had a similar MP-R changing pattern, which was distinct from 72031 soil. On a temporal scale of the representative rice growing stages (i.e. early tillering, late tillering, panicle initiation, ripening and harvesting stages), the MPP of rice soils varied widely among rice cultivars, and MPP coincided well with CH4 emission regardless of rice cultivars. No clear pattern was observed in soil redox potential (soil E h ), or in above-ground biomass of rice cultivars to MPP and CH4 emission.

Moisture Controls on Trace Gas Fluxes in Semiarid Riparian Soils

Variability in seasonal soil moisture (SM) and temperature (T) can alter ecosystem/atmosphere exchange of the trace gases carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). This study reports the impact of year‐round SM status on trace gas fluxes in three semiarid vegetation zones, mesquite (30 g organic C kg−1 soil), open/forb (6 g organic C kg−1 soil), and sacaton (18 g organic C kg−1 soil) from July 2002–September 2003 in southeastern Arizona. Carbon dioxide and N2O emissions were highly dependent on available SM and T. During the heavy rains of the 2002 monsoon (238 mm total rainfall), large differences in soil C content did not correlate with variations in CO2 production, as efflux averaged 235.6 ± 39.5 mg CO2 m−2 h−1 over all sites. In 2003, limited monsoon rain (95 mm total rainfall) reduced CO2 emissions by 19% (mesquite), 40% (open), and 30% (sacaton), compared with 2002. Nitrous oxide emissions averaged 21.1 ± 13.4 (mesquite), 2.1 ± 4.4 (open), and 3.9 ± 5.2 μg N2O m−2 h−1 (sacaton) during the 2002 monsoon. Limited monsoon 2003 rainfall reduced N2O emissions by 47% in the mesquite, but N2O production increased in the open (55%) and sacaton (5%) sites. Following a dry winter and spring 2002 (15 mm total rainfall), premonsoon CH4 consumption at all sites was close to zero, but following monsoon moisture input, the CH4 sink averaged 26.1 ± 6.3 μg CH4 m−2 h−1 through April 2003. Laboratory incubations showed potentials for CH4 oxidation from 0 to 45 cm, suggesting that as the soil surface dried, CH4 oxidation activity shifted downward in the sandy soils. Predicted climate change shifts in annual precipitation from one dominated by summer monsoon rainfall to one with higher winter precipitation may reduce soil CO2 and N2O emissions while promoting CH4 oxidation rates in semiarid riparian soils of the Southwest, potentially acting as a negative feedback for future global warming.

Methane Oxidation in Forest, Successional, and No‐till Agricultural Ecosystems

Methane oxidation in well‐aerated soils is a significant global sink for atmospheric methane. We examined the effects of soil disturbance (simulated tillage) and N‐fertilizer additions on methane oxidation in old‐growth forest, mid‐successional, and no‐till maize ecosystems in southwest Michigan, USA. We found highest oxidation rates in forest sites (about 30 μg CH4–C m−2 h−1 on average), with average rates in successional and agricultural sites about 75 and 12% of this, respectively. In the forest and successional sites a one‐time N‐fertilizer addition (100 kg NH4NO3–N ha−1) significantly suppressed oxidation for the several weeks that inorganic N pools were elevated. There was no effect of fertilizer addition in the agricultural site, where available N was already high and oxidation rates low. Soil disturbance by itself had no detectable effect on fluxes in any of the sites. Results confirm the overriding importance of elevated N for suppressing CH4 oxidation in managed and unmanaged ecosystems, and suggest further that recovery of CH4 suppression following agriculture is related to slow‐changing soil properties such as soil organic matter composition or microbial community structure.

Emission of N 2O, N 2, CH 4, and CO 2 from constructed wetlands for wastewater treatment and from riparian buffer zones

We measured nitrous oxide (N 2O), dinitrogen (N 2), methane (CH 4), and carbon dioxide (CO 2) fluxes in horizontal and vertical flow constructed wetlands (CW) and in a riparian alder stand in southern Estonia using the closed chamber method in the period from October 2001 to November 2003. The replicates’ average values of N 2O, N 2, CH 4 and CO 2 fluxes from the riparian gray alder stand varied from −0.4 to 58 μg N 2O-N m −2 h −1, 0.02–17.4 mg N 2-N m −2 h −1, 0.1–265 μg CH 4-C m −2 h −1 and 55–61 mg CO 2-C m −2 h −1, respectively. In horizontal subsurface flow (HSSF) beds of CWs, the average N 2 emission varied from 0.17 to 130 and from 0.33 to 119 mg N 2-N m −2 h −1 in the vertical subsurface flow (VSSF) beds. The average N 2O-N emission from the microsites above the inflow pipes of the HSSF CWs was 6.4–31 μg N 2O-N m −2 h −1, whereas the outflow microsites emitted 2.4–8 μg N 2O-N m −2 h −1. In VSSF beds, the same value was 35.6–44.7 μg N 2O-N m −2 h −1. The average CH 4 emission from the inflow and outflow microsites in the HSSF CWs differed significantly, ranging from 640 to 9715 and from 30 to 770 μg CH 4-C m −2 h −1, respectively. The average CO 2 emission was somewhat higher in VSSF beds (140–291 mg CO 2-C m −2 h −1) and at the inflow microsites of HSSF beds (61–140 mg CO 2-C m −2 h −1). The global warming potential (GWP) from N 2O and CH 4 was comparatively high in both types of CWs (4.8 ± 9.8 and 6.8 ± 16.2 t CO 2 eq ha −1 a −1 in the HSSF CW 6.5 ± 13.0 and 5.3 ± 24.7 t CO 2 eq ha −1 a −1 in the hybrid CW, respectively). The GWP of the riparian alder forest from both N 2O and CH 4 was relatively low (0.4 ± 1.0 and 0.1 ± 0.30 t CO 2 eq ha −1 a −1, respectively), whereas the CO 2-C flux was remarkable (3.5 ± 3.7 t ha −1 a −1). The global influence of CWs is not significant. Even if all global domestic wastewater were treated by wetlands, their share of the trace gas emission budget would be less than 1%.

Plant species effects on methane emissions from freshwater marshes

Abstract Wetland plants not only stimulate CH 4 emissions from wetlands to the atmosphere by providing the gas conduit and releasing organic compounds through root exudation and debris to increase CH 4 production, but also reduce CH 4 emissions by delivering O 2 into the underground to accentuate CH 4 oxidation in the rhizosphere. The capacity of the plants Carex lasiocarpa , Carex meyeriana and Deyeuxia angustifolia to transport CH 4 from freshwater marshes in Sanjiang plain, China to the atmosphere was measured. Their integrated effects on dissolved porewater CH 4 concentration and CH 4 emission were studied by clipping plants just above the water surface. The amount and fraction of CH 4 emissions via intact plants C. lasiocarpa , C. meyeriana and D. angustifolia was 16.0, 20.8 and 8.0 μg CH 4 stem −1 h −1 , and 73–82%, 75–86% and 28–31%, respectively, indicating that when CH 4 is released by the diffusive rather than pressurized transport through the aerenchyma system, cyperaceous plants have a significantly higher gas transport capacity than gramineous plants. After plants were clipped 3 cm above the water surface, CH 4 emissions and CH 4 concentrations in the C. lasiocarpa marsh with a standing water depth of ∼20 cm increased significantly; only slight increases were measured in the C. meyeriana marsh with a standing water layer of ∼15 cm. The redox potentials ( E h ) in the vertical profiles of both marshes were further lowered after plants were clipped. These results suggest that apart from being a conduit for gas transport, C. lasiocarpa made a greater contribution to CH 4 oxidation than CH 4 production, whereas C. meyeriana made nearly the same contribution to CH 4 oxidation as to CH 4 production. In contrast, a decrease in dissolved porewater CH 4 concentration and a very limited increase in CH 4 emission in the D. angustifolia marsh with a standing water depth of ∼5 cm indicated that D. angustifolia might make a greater contribution to CH 4 production than to CH 4 oxidation. Thereafter, as the standing water depth and the capacity of plants to transport CH 4 from wetlands increased, plant integrated effect of stimulating CH 4 production by releasing root exudates and debris minus accentuating CH 4 oxidation by excreting O 2 from roots not only decreased but also varied from increasing CH 4 concentration for D. angustifolia to reducing CH 4 concentration for C. lasiocarpa . The higher CH 4 emission in the C. lasiocarpa marsh than in the D. angustifolia marsh was due to the high CH 4 transport capacity of C. lasiocarpa rather than the stimulating effect of C. lasiocarpa on CH 4 production. This finding suggests that when models are used for estimation of CH 4 emissions from natural wetlands, difference in plant species effect on CH 4 production and oxidation should be involved in.

Fluxes of methane and carbon dioxide from soil under forest, grazing land, irrigated rice and rainfed field crops in a watershed of Nepal

Field evolution of CH4 and CO2 from soils under four dominant land uses in the Mardi watershed, western Nepal, were monitored at 15-day intervals for 1 year using closed chamber techniques. The CH4 oxidation rate (mean±SE, μg CH4 m−2 h−1) in the forest (22.8±6) was significantly higher than under grazing land (14±2) and an upland rainfed maize and millet system (Bari) (2.6±0.9). Irrigated rice fields (Khet) showed an oxidation rate of 6±0.8 μg CH4 m−2 h−1 in the dry season (December–May) but emitted a mean rate of 131 μg CH4 m−2 h−1 in the rainy season and autumn (June–October). The evolution of CO2 ranged from 10 mg CO2 m−2 h−1 in the Bari in January to 1,610 mg CO2 m−2 h−1 in the forest in July. Higher evolution of CO2 (mean±SE, mg CO2 m−2 h−1) was observed in the Bari (399±39) and forest (357±36) compared to Khet (246±25) and grazing (206±20) lands. The annual emission of CO2 evolution varied from 86.6 to 1,836 g CO2 m−2 year−1. The activation energy for CH4 and CO2 varied between 16–283 and 80–117 kJ mol−1, respectively. The estimated temperature coefficient for CO2 emission varied from 2.5 to 5.0. Temperature explained 46–51% of the variation in CO2 evolution, whereas it explained only 4–36% of the variation in CH4 evolution.

Anaerobic microbial metabolism in hyporheic sediment of a gravel bar in a small lowland stream

Distribution of dissolved oxygen, nitrate, sulphate, carbon dioxide and dissolved organic carbon (DOC), acetate and lactate was studied in the stream and interstitial water along the subsurface flowpath in the hyporheic zone of a small lowland stream. Sediments were found to act as a source of nitrous oxide and methane. Interstitial methane concentrations were significantly much higher in comparison to those from surface water, and were significantly lower in the relatively well oxygenated downwelling zone than in the rather anoxic upwelling zone. The interstitial concentrations of O2, NO3−1 and SO4−2 showed significant decline along the subsurface flowpath, while concentrations of CO2, N2O, DOC, acetate and lactate remained unchanged. In addition to field measurements, ex situ incubation of sediments was carried out in the laboratory. Maximal methane production was found in the incubation assay using acetate (mean value 380 µg CH4 kg DW−1 d−1). Mean value of the denitrification potential was 1.1 mg N2O kg DW−1 d−1. Nitrous oxide production potential reached 71–100% of denitrification potential. Our results demonstrate that respiration of oxygen, nitrate, sulphate and methanogenesis may coexist within the hyporheic zone and that anaerobic metabolism is an important pathway in organic carbon cycling in the Sitka stream sediments. Copyright © 2005 John Wiley & Sons, Ltd.

Methane concentration and emission as affected by methane transport capacity of plants in freshwater marsh

To elucidate effect of the CH4 transport capacity of plants on CH4 production and CH4 emission, we measured CH4 emission and the CH4 transport capacity of plants as well as CH4 and dissolved organic carbon (DOC) concentrations in porewater and redox potential in the freshwater marsh vegetated with Carex lasiocarpa, Carex meyeriana and Deyeuxia angustifolia. Although only 31% of CH4 emitted was released via Deyeuxia angustifolia into the atmosphere compared to 72–86% via Carex plants and the CH4 transport capacity of per stem of Deyeuxia angustifolia was only 8.0 μg CH4 stem−1 h−1 being equal to half for Carex plants, the flux of CH4 emission from the Deyeuxia angustifolia marsh was just lower by 17–28% than those from the Carex marshes as the standing water depth decreased significantly from 15–20 to 5 cm, indicating that despite the poor CH4 transport capability of Deyeuxia angustifolia partly reduced CH4 emission via plants, however CH4 emission was not greatly reduced as expected. This is because although the poor gas transport capability of Deyeuxia angustifolia lowered CH4 emission to some extent, however it also decreased the input of O2 into the rhizosphere via plants; the latter not only reduced CH4 oxidation in the rhizosphere and/or rhizome but also lowered redox potential in the vertical profile resulting in an increase in CH4 production potential and CH4 concentration especially at 5 cm depth, which in turn facilitated CH4 emission through diffusion in the Deyeuxia angustifolia marsh. This study suggests that the sharp decrease in the CH4 transport capacity of plants did not necessary result in an expected lowering of CH4 emission in the freshwater marsh.

Cultivation, nitrogen fertilization, and set‐aside effects on methane uptake in a drained marsh soil in Northeast China

AbstractTo evaluate the effect of cultivation, nitrogen fertilizer, and set aside on CH4 uptake after drained marshland was converted into agricultural fields, CH4 fluxes and CH4 concentrations in soil gas were in situ measured in a drained marsh soil, a set‐aside cultivated soil, and cultivated soils in Sanjiang Plain of Northeast China in August 2001. Over the measuring period, the highest CH4 uptake rate was 120.7±6.2 μg CH4 m−2 h−1 in the drained marsh soil and the lowest was 29.5±4.9 μg CH4 m−2 h−1 in the set‐aside cultivated soil, showing that there was no significant recovery of CH4 uptake ability 5 years after cultivation activity was stopped. CH4 uptake rates were significantly less in the cultivated soils than in the drained marsh soil by 30.1–74.6%, which resulted mainly from cultivation and partly from nitrogen addition. A significantly negative correlation between CH4 flux and bulk density in the cultivated soils tilled by machine suggests that cultivation reduced CH4 uptake through compaction, because of the enhanced diffusion resistance for CH4 and O2. Nitrogen fertilization slowly reduced but persistently affected CH4 uptake even after long‐term application of nitrogen.

Trace gas emissions from soil of the central highlands of Mexico as affected by natural vegetation: a laboratory study

In the central highlands of Mexico, mesquite (Prosopis laevigata) and huisache (Acacia schaffneri), N2-fixing trees or shrubs, dominate the vegetation and are currently used in a reforestation program to prevent erosion. We investigated how natural vegetation or cultivation of soil affected oxidation of CH4, and production of N2O. Soil was sampled under the canopy of mesquite (MES treatment) and huisache trees (HUI treatment), outside their canopy (OUT treatment) and from fields cultivated with maize (ARA treatment) at three different sites while production of CO2, and dynamics of CH4, N2O and inorganic N (NH4+, and NO3−) were monitored in an aerobic incubation. The production of CO2 was 2.3 times higher and significantly greater in the OUT treatment, 3.0 times higher in the MES treatment and 4.0 times higher in the HUI treatment compared to the ARA treatment. There was no significant difference in oxidation of CH4 between the treatments, which ranged from 0.019 μg CH4–C kg−1 day−1 for the HUI treatment to 0.033 CH4–C kg−1 day−1 for the MES treatment. The production of N2O was 30 μg N2O–N kg−1 day−1 in the MES treatment and >8 times higher compared to the other treatments. The average concentration of NO3− was 2 times higher and significantly greater in the MES treatment than in the HUI treatment, 3 times greater than in the OUT treatment and 10 times greater than in the ARA treatment. It was found that cultivation of soil decreased soil organic matter content, C and N mineralization, but not oxidation of CH4 or production of N2O.

Labile carbon and methane uptake as affected by tillage intensity in a Mollisol

Methane (CH 4) oxidation potential of soils decreases with cultivation, but limited information is available regarding the restoration of that capacity with implementation of reduced tillage practices. A study was conducted to assess the impact of tillage intensity on CH 4 oxidation and several C-cycling indices including total and active microbial biomass C (t-MBC, a-MBC), mineralizable C (C min) and N (N min), and aggregate-protected C. Intact cores and disturbed soil samples (0–5 and 5–15 cm) were collected from a corn ( Zea mays L.)–soybean ( Glycine max L. Merr.) rotation under moldboard-plow (MP), chisel-plow (CP) and no-till (NT) for 8 years. An adjacent pasture (<25 years) and secondary growth forest (>60 years) soils were also sampled as references. At all sites, soil was a Kokomo silty clay loam (mesic Typic Argiaquolls). Significant tillage effects on t-MBC and protected C were found in the 0–5 cm depth. Protected C, a measure of C retained within macro-aggregates and defined as the difference in C min (CO 2 evolved in a 56 days incubation) between intact and sieved (<2 mm) soil samples, amounted to 516, 162 and 121 mg C kg −1 soil in the 0–5 cm layer of the forest, pasture and NT soils, respectively. Protected C was negligible in the CP and MP soils. Methane uptake rate (μg CH 4-C kg −1 soil per day, under ambient CH 4) was higher in forest (2.70) than in pasture (1.22) and cropland (0.61) soils. No significant tillage effect on CH 4 oxidation rate was detected (MP: 0.82; CP: 0.41; NT: 0.61). These results underscore the slow recovery of the CH 4 uptake capacity of soils and suggest that, to have an impact, tillage reduction may need to be implemented for several decades.

Roles of moss species and habitat in methane consumption potential in a northern peatland

Abstract In northern peatlands with water tables at or near the surface, the Sphagnum moss layer is potentially the only aerobic region where CH4 oxidation can occur. We hypothesized that mosses with varying physiologies would create different conditions for methane-oxidizing bacteria and, in turn, affect rates of CH4 consumption. We measured in-vitro CH4 consumption potential of Sphagnum magellanicum and Sphagnum capillifoliun taken from the same habitat and S. magellanicum and Sphagnum majus across habitats to compare and contrast species and environmental effects. In certain cases, S. capillifolium consumed CH4 more rapidly than S. magellanicum taken from identical habitats, although the greatest difference in consumption rates between species was only 29 μg CH4 g−1 dry moss d−1, compared to a maximum difference of 126 and 415 μg CH4 g−1 dry moss d−1 in S. magellanicum and S. majus sampled from different habitats. In most cases, CH4 was consumed most rapidly in the lower, non-photosynthetic portions of...

Methane consumption in a frequently nitrogen‐fertilized and limed spruce forest soil after clear‐cutting

Abstract. The effects of especially frequent nitrogen (N) additions (from 1959 to 1986, totalling 860 kg N ha−1) and liming (in 1958 and 1980, totalling 6000 kg CaCO3 ha−1) on CH4 uptake by a boreal forest soil were studied in a stand of Norway spruce. Except for a forested reference plot, the stand was clear‐cut in January 1993 and the following year one‐half of each clear‐cut plot was prepared by mounding. Fluxes of CH4 were measured with static chambers in the autumn before clear‐cutting and during the following four summers. The average CH4 uptake during 1993–96 in the forested reference plot was 82 μg CH4 m−2 h−1(ranging from 10 to 147 units). In the first summer after clear‐cutting, the cleared plot showed 42% lower CH4 uptake rate than the forested reference plot, but thereafter the difference became less pronounced. The short‐term decrease in CH4 consumption after clear‐cutting was associated with increases in soil NH4+ and NO3−concentrations. Mounding tended at first to stimulate CH4 uptake but later to inhibit it. Neither liming nor N‐fertilization had significant effects on CH4 consumption. Our results suggest that over the long term, in N‐limited upland boreal forest soils, N addition does not decrease CH4 uptake by the soil.

Effect of nitrogen deposition on CH4 uptake in forest soils in Hokkaido, Japan

It has been well documented by short-term artificial experiments that the CH4 uptake is inhibited by N input, especially NH4 p+-N input. To investigate the effect of the natural N input by throughfall and other factors on the CH4 uptake in forest soils, we measured the CH4 uptake rates for 6 months during the snow-free period of the year and N input by throughfall throughout the year at 10 sites in Hokkaido, Japan, from 1997 to 2002. Water filled pore space (WFPS) and pH values in the soils varied widely among the sites (38-93% and 3.9-6.2, respectively). The rates of NH4 p+-N and NH3 p--N inputs ranged from 1.3 to 6.9 kg N hap-1 yearp-1 and from 0.8 to 2.9 kg N hap-1 yearp-1, respectively. The NH4 p+-N input was generally higher than the NH3 p--N input. Total N input by throughfall amounted to 2.3-9.4 kg N hap-1 yearp-1. The highest CH4 uptake rate occurred within the period from July to September (41-215 μg CH4 mp-2 hp-1) each year at most sites. CH4 uptake rate was relatively low (~50 μg CH4 M-2 hp-1) at northern sites, while a high CH4 uptake rate was observed throughout the year 100 (≽ CH4 mp-2 hp-1) at southern sites. The mean CH4 uptake rates were significantly different among the sites. Cumulative CH4 uptake ranged from 1.4 to 6.6 kg CH4 hap-1 [184 d]p-1 with a mean values of 3.22 ± 1.36 kg CH4 hap-1 [184 d]p-1. Cumulative CH4 uptake increased with increasing temperature and decreased with an increase in precipitation (Rain), NH4 p+-N input (TFNH4) WFPS, soil total C (TC), and total N (TN). There was a quadratic relationship between the CH4 uptake and NH3 p--N input (TFNO3), soil pH, and C / N ratio in soil. A regression equation was obtained as follows to predict the CH4 uptake in forest soils: Cumulative CH4 uptake = 0.47 / Rain + 0.38 / TFNH4 + 0.34 / TC - 0.30 / TFN03 (R p2 = 0.74, p = 0.0001). This equation indicates that atmospheric N input into forest soils is one of the main factors that control cumulative CH4 uptake with precipitation, total carbon content in soil in Hokkaido, Japan.

Environmental Factors Influencing Attenuation of Methane and Hydrochlorofluorocarbons in Landfill Cover Soils

The influence of different environmental factors on methane oxidation and degradation of hydrochlorofluorocarbons (HCFCs) was investigated in microcosms containing soil sampled at Skellingsted Landfill, Denmark. The soil showed a high capacity for methane oxidation resulting in a maximum oxidation rate of 104 μg CH4 g−1 h−1 and a low affinity of methane with a half-saturation constant of 2.0% v/v. The hydrochlorofluorocarbons HCFC-21 (dichlorofluoromethane) and HCFC-22 (chlorodifluoromethane) were rapidly oxidized and the oxidation occurred in parallel with the oxidation of methane. The maximal HCFC oxidation rates were 0.95 and 0.68 μg g−1 h−1 for HCFC-21 and HCFC-22, respectively. Increasing concentrations of HCFCs resulted in decreased methane oxidation rates. However, compared with typical concentrations in landfill gas, relatively high HCFC concentrations were needed to obtain a significant inhibition of methane oxidation. In general, the environmental factors studied influenced the degradation of HCFCs in almost the same way as they influenced methane oxidation. Temperature had a strong influence on the methanotrophic activity giving high Q10 values of 3.4 to 4.1 over the temperature range of 2 to 25°C. Temperature optimum was around 30°C; however, oxidation occurred at temperatures as low as 2°C. A moisture content of 25% w/w yielded the maximum oxidation rate as it allowed good gas transport together with sufficient microbial activity. The optimum pH was around neutrality (pH = 6.5–7.5) showing that the methanotrophs were optimally adapted to the in situ pH, which was 6.9. Copper showed no inhibitory effect when added in relatively high concentrations (up to 60 mg kg−1), most likely due to sorption of copper ions to soil particles. At higher copper concentrations the oxidation rates decreased. The oxidation rates for methane, HCFC-21, and HCFC-22 were unaltered in ammonium-amended soil up to 14 mg kg−1 Higher ammonium concentrations inhibited the oxidation process. The most important parameters controlling oxidation in landfill cover soil were found to be temperature, soil moisture, and methane and oxygen supply.

Methane consumption from ambient atmosphere by a Typic Ustochrept soil as influenced by urea and two nitrification inhibitors

The effect of urea and urea mixed with different doses of two nitrification inhibitors, dicyandiamide (DCD) and karanjin [a furanoflavonoid, extracted from seeds of the karanja (Pongamia glabra Vent.) tree], on methane (CH4) consumption was examined in a Typic Ustochrept (alluvial inceptisol) soil, collected from a field under rice-wheat rotation. The soil, fertilized with urea (100 mg N kg-1 soil) and urea combined with different doses of the two inhibitors, DCD and karanjin (each added at 5%, 10%, 15%, 20% and 25% of applied N), was incubated at 25°C, at field capacity moisture content for 35 days. The methane consumption rate ranged between 0.2 and 1.7 µg CH4 kg-1 soil day-1 with little temporal variation (CV =10–31%). It was significantly higher in the control (no fertilizer-N) than other treatments except for a few cases, while total CH4 consumption in the incubation period was significantly higher in the control than other treatments. Methane consumption rate was found to be negatively and positively correlated with soil NH4+ and NO2- + NO3- content, respectively. Mean CH4 consumption rate, as well as total CH4 consumption, was lower on the addition of karanjin due to slower nitrification and higher conservation of NH4+ released from applied urea. Addition of urea led to a 17% reduction of total CH4 consumption while urea combined with karanjin and DCD had 50–64% and 19–34% reduction, respectively. Karanjin was a more effective nitrification inhibitor than DCD during the incubation period.

Seasonal variability of N2O emissions and CH4 uptake by tropical rainforest soils of Queensland, Australia

Over 1 year we followed the seasonal variations of N2O and CH4 fluxes at a tropical rain forest site in Australia. In addition, meteorological parameters, litter fall and decomposition, plant species composition, and concentrations of NH4+/NO3− in the soil and N2O and CH4 in the soil atmosphere were measured. N2O emissions showed a pronounced seasonal pattern with highest rates in the wet season (108.6 μg N m−2 h−1) and significantly lower rates during dry season (mostly &lt;10 μg N2O‐N m−2 h−1). N2O emissions were positively correlated to N2O‐concentrations in the soil profile and to moisture, but not to concentrations of NH4+ and NO3−. The annual emission of N2O (N = 6015) was 0.97 kg N ha−1 yr−1, and, thus, approximately 7 times lower than a previous estimate for the year 2000. The marked differences in N2O emissions between different years indicate that the interannual variability of N2O emissions from rain forest soils cannot be neglected. With regard to CH4 the soil functioned throughout the entire year as a significant sink. Rates of CH4 uptake during the dry period (35–68 μg CH4 m−2 h−1) were higher as compared to the wet period (4–45 μg CH4 m−2 h−1). A close linear correlation between soil moisture and magnitude of CH4 uptake was found. The calculated annual CH4 uptake (N = 6090) is 3.2 kg CH4 ha−1 yr−1. This implies that tropical rain forest soils function as significant sinks for atmospheric CH4 on a global scale.

Diurnal and Seasonal Variation in Methane and Nitrous Oxide Fluxes in Meadow Steppe of Inner Mongolia

Temperate and tropical oxic soils usually exhibit low levels of atmospheric CH 4 oxidation, which are estimated to consume about 10% of the atmospheric CH 4. It has been reported that the semi_arid grasslands represent a significant global sink for CH 4 and a source of atmospheric N 2O. However, the spatial and temporal variability of methane is usually very high which may result in the uncertainty of the ecosystem’s function in the exchange of greenhouse between ecosystem and atmosphere. In order to help define the possible range of emission of N 2O and CH 4 from temperate grassland of Inner Mongolia, diurnal variation in fluxes of methane and nitrous oxide in meadow steppe in the Xilin River basin were investigated with static_chamber and GC methods on June 1, July 2, August 3 and September 1 of 1998. Suitable sampling time was also discussed with the data of diurnal variation investigation. The native meadow steppe can act as a source of atmospheric N 2O but a sink of CH 4 in which the fluxes of the two greenhouse gases had obvious diurnal variation. ANOVA results showed that there was significant difference for the fluxes of N 2O in the four months(F=6.359, p0.004), ranging between 0.282-2.134 μg N 2O_N·m -2·h -1. These background emission rates were typically similar to those in other temperate grasslands. The diurnal mean uptake rates of methane were (-52.19±19.67), (-27.20±10.57), (-126.05±9.32) and (-16.45±1.31) μg CH 4 C·m -2·h -1 for the four months respectively, which has a trend of “high_low_high_low” from the end of May through the beginning of September. The methane uptake rates were similar to those in the Colorado short_grass steppe, averaging 31.2 μg CH 4_C·m -2·h -1, compared with varieties of temperate ecosystems. It was proved that selecting 9∶00-13∶00 as sampling time for each sampling day is suitable in Xilin River basin according to the diurnal variation measurement.

Distribution and relationships of mercury, lead, cadmium, copper and zinc in perch ( Perca fluviatilis) from the Pomeranian Bay and Szczecin Lagoon, southern Baltic

The concentrations of selected metals, such as Hg, Cd, Pb, Cu and Zn, were determined in muscle and liver of perch ( Perca fluviatilis) from the Pomeranian Bay and Szczecin Lagoon, southern Baltic. The concentrations of Hg in muscle and Cd, Pb and Cu in liver increased with the age of the specimens analysed. The positive relationship between muscle Hg and age (weight-length) is probably attributed to the specific bioaffinity for organic matter of CH 3Hg with a high biological half-life, which generally constitutes the dominant pool of the total Hg in the fish muscle. ANOVA analysis clearly demonstrated that in the Pomeranian Bay there were significant seasonal variations of muscle Hg and hepatic Cd, Pb and Cu. Factor analysis supported seasonal differences in muscle and especially hepatic samples; specifically, summer muscles were clearly separated from winter ones. Muscle samples corresponding to the winter season had relatively high concentrations of Hg Cd and Pb. The concentrations of muscle Hg (corresponding to 70–105 μg CH 3Hg eaten weekly) are comparable to the PTWI (permissible tolerable weekly intake) recommended by WHO (200 μg CH 3Hg). The muscle Cd and Pb levels are significantly lower than the PTWI's and do not constitute any threat for man.

Exchange of trace gases between soils and the atmosphere in Scots pine forest ecosystems of the northeastern German lowlands: 1. Fluxes of N 2O, NO/NO 2 and CH 4 at forest sites with different N-deposition

This study summarizes the results obtained from measurements of the exchange rates of N 2O–N, NO–N, NO 2–N and CH 4 between Scots pine forest soils of the northeastern German lowlands and the atmosphere in the years 1995–1998. In order to further identify the effects of atmospheric N-deposition on the magnitude of N- and C-trace gas fluxes, five Scots pine forest sites with different loads of atmospheric N-input (15–22 kg N ha −1 per year) were investigated. The measurements show an increase in NO and N 2O fluxes at the higher N-affected sites (mean values, NO: 21–39 μg NO–N m −2 h −1, N 2O: 16–32 μg N 2O–N m −2 h −1) as compared to the sites with moderate atmospheric N-input (mean values, NO: 3–9 μg NO–N m −2 h −1, N 2O: 5–10 μg N 2O–N m −2 h −1). In addition, it could be demonstrated that atmospheric N-deposition did not only effect N-trace gas fluxes at our study sites, but also the magnitude of atmospheric CH 4-uptake by the forest soils, since at the pine forest sites with moderate atmospheric N-deposition CH 4-uptake rates were approximately two- to five-fold higher (mean values: −140 to −165 μg CH 4 m −2 h −1) than at the sites with high atmospheric N-input (−24 to −77 μg CH 4 m −2 h −1).