Flood effect on CH4 emission from the alas in Central Yakutia,East Siberia

During four years (2006–2009), methane (CH₄) emission was measured at different biomes (dry, wet grasslands, lake and lake vegetation) of mature thermokarst depression located at the most typical thermokarst terrain on the east bank of the Lena River, Central Yakutia, Russia (62°08′N, 130°30′E). To estimate total CH₄ emission from the whole thermokarst depression ecosystem, CH₄ emissions via plant bodies and ebullition were measured in addition to diffusive CH₄ flux measurement. The lake area increased twice from 20.4 ha in 2006 to 43.3 ha in 2007 and then did not change significantly in 2008 and 2009 (46.5 and 44.4 ha, respectively). Ebullition was considered to be a minor source for CH₄ emission from the lake in the studied thermokarst depression. CH₄ emissions from the lake water surface and via the plant body of lake vegetation (hygrophyte and hydrophyte vegetation) were the main sources of CH₄ and these increased by flooding both CH₄ emission rate and area. Using spatial changes of these biomes, the annual emission of CH₄ was calculated taking into account different sources of CH₄. Total CH₄ emission from the studied alas (63.7 ha) was 5.7, 5.2, 20.1 and 50.1 Mg carbon (C) in 2006–2009, respectively, and its difference during this period reached about 10 times. An extreme increase in CH₄ emission from the lake occurred in the second year of continuous flooding (2008), which might have been caused by the decomposition of flooded organic C. So, the lake water ecosystem is the main source of CH₄ in thermokarst depression controlled by the duration of flooding. Under future global climate change, thermokarst depressions in Central Yakutia have potential for lake expansion, causing significant increase in CH₄ emission in the studied region.     

Effects of Plant Species on CH4 and N2O Fluxes from a Volcanic Grassland Soil in Nasu, Japan

To investigate the effects of plant species in grassland on methane (CH₄) and nitrous oxide (N₂O) fluxes from soil, fluxes from an orchardgrass ( Dactylis glomerata L.) grassland, white clover ( Trifolium repens L.) grassland and orchardgrass/white clover mixed grassland were measured weekly from April 2001 to March 2002 using a vented closed chamber method. Related environmental parameters (soil inorganic N content, soil pH (H₂O) value, soil moisture content, soil temperature, grass yield, and the number of soil microorganisms) were also regularly monitored. On an annual basis, CH₄ consumption in the soil of the orchardgrass grassland, white clover grassland and orchardgrass/white clover mixed grassland was 1.8, 2.4, and 1.8 kg C ha⁻¹ year⁻¹, respectively. The soil bulk density of the white clover grassland was lower than that of the other grasslands. Fluxes of CH₄ were positively correlated with the soil moisture content. White clover increased the CH₄ consumption by improving soil aeration. Nitrogen supply to the soil by white clover did not decrease the CH₄ consumption in the soil of our grasslands. On the other hand, annual N₂O emissions from the orchardgrass grassland, white clover grassland, and orchardgrass/white clover mixed grassland were 0.39, 1.59, and 0.67 kg N ha⁻¹ year⁻¹, respectively. Fluxes of N₂O were correlated with the NO₃⁻ content in soil and soil temperature. White clover increased the N₂O emissions by increasing the inorganic N content derived from degrading white clover in soil in summer.     

Strong pH influence on N2O and CH4 fluxes from forested organic soils

Greenhouse gas (GHG) emissions from farmed organic soils can have a major impact on national emission budgets. This investigation was conducted to evaluate whether afforestation of such soils could mitigate this problem. Over the period 1994–1997, emissions of methane (CH₄) and nitrous oxide (N₂O) were recorded from an organic soil site in Sweden, forested with silver birch (Betula pendula Roth), using static field chambers. The site was used for grazing prior to forestation. Soil pH and soil carbon content varied greatly across the site. The soil pH ranged from 3.6 to 5.9 and soil carbon from 34 to 42%. The mean annual N₂O emission was 19.4 (± 6.7) kg N₂O‐N ha^?1 and was strongly correlated with soil pH (r = ?0.93, P < 0.01) and soil carbon content (r = 0.97, P < 0.001). The N₂O emissions showed large spatial and temporal variability with greatest emissions during the summer periods. The site was a sink for CH₄ (i.e. ?0.8 (± 0.5) kg CH₄ ha^?1 year^?1) and the flux correlated well with the C/N ratio (r = 0.93, P < 0.01), N₂O emission (r = 0.92, P < 0.01), soil pH (r = ?0.95, P < 0.01) and soil carbon (r = 0.97, P < 0.001). CH₄ flux followed a seasonal pattern, with uptake dominating during the summer, and emission during winter. This study indicates that, because of the large N₂O emissions, afforestation may not mitigate the GHG emissions from fertile peat soils with acidic pH, although it can reduce the net GHG because of greater CO₂ assimilation by the trees compared with agricultural crops.     

Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlands

Rates of organic carbon mineralization (to CO₂ and CH₄) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid‐boreal Alberta, Canada, two were in low‐boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH₄ production varied significantly as a function of peat type, transplant site, and the type–site interaction. All four peat soils had very small rates of CH₄ production (< 20 nmol g^?1 day^?1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH₄ production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH₄ production (4000 nmol g^?1 day^?1) correlated with large holocellulose content, a large concentration of p‐hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO₂ production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO₂ production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH₄ and CO₂ in Sphagnum‐derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future.     

CH4 flux in an alas ecosystem formed by forest disturbance near Yakutsk,Eastern Siberia,Russia

Abstract

Quartz and mica contents were determined as a function of particle size of soils over quartz and mica-free basalts in northwestern Kyushu and San-in. The contents of both minerals were much higher in the surface soil horizons than in the lower horizons. Quartz particle size distribution (predominantly 2 to 53 μm) and surface morphology (chip or shard, not euhedral) which are similar to those in the north central Pacific pelagic sediments and Hawaiian soils, indicated that quartz is added as aerosolic dust and loess carried by the circumpolar Westerly Winds from Asian semi-arid and arid regions. Close proximity to the eolian sources was deduced by somewhat coarser texture of the present soil quartz. Lower surface soil quartz content, relative to that in the Hawaiian soils was interpreted as indicating a younger landscape age caused by intensive denudation. The covariant relation between the quartz and miea eontents of soils may suggest that at least a portion of the micaceous minerals and quartz in Ando soils of Japan also has a tropospheric origin.     

Diffusion of NH+4 and NO−3 mineralized from organic N in soil

The mineralization of native soil organic matter and the simultaneous diffusion of zero NH⁺₄ and NO^?₃ to a solution sink of zero N concentration was analysed experimentally and theoretically for a fine sandy loam soil. Experimentally, the NH₄ and NO₃ ions produced in an incubated unsaturated soil column were allowed to diffuse through a sintered glass plate into a stirred solution sink. The distribution of NH⁺₄ and NO^?₃ in the soil column was measured after various incubation times. The rate of ammonification was measured directly during incubation and the rate of nitrification modelled from nitrifier growth kinetics. A Freundlich equation was used to describe the equilibrium between soluble and exchangeable NH⁺₄ in the soil. Terms for the microbial transformation of N and the adsorption-desorption of NH⁺₄ were combined with diffusion equations which were solved numerically using finite difference methods. The model constructed was used to predict the NH⁺₄ and NO^?₃ con-centration distributions in the soil column, and good agreement was obtained between the experimental and predicted concentration profiles. The use of the model for predicting the diffusive flux of mineral N to the outer surfaces of soil peds, where it is vulnerable to leaching, was demonstrated.     

Microbial CO2 production, CH4 dynamics and nitrogen in a wetland soil (New York State, USA) associated with three plant species (Typha, Lythrum, Phalaris)

Plants furnish soil with organic carbon (OC) compounds that fuel soil microorganisms, but whether individual plant species – or plants with unique traits – do so uniquely is uncertain. We evaluated soil microbial processes within a wetland in which areas dominated by a distinct plant species (cattail –Typha sp.; purple loosestrife –Lythrum salicaria L.; reed canarygrass –Phalaris arundinacea L.) co‐mingled. We also established an experimental plot with plant shoot removal. The Phalaris area had more acidic soil pH (7.08 vs. 7.27–7.57), greater amount of soil organic matter (19.0% vs. 9.0–11.5%), and the slowest production rates of CO₂ (0.10 vs. 0.21–0.46 μmol kg⁻¹ s⁻¹) and CH₄ (0.040 vs. 0.054–0.079 nmol kg⁻¹ s⁻¹). Nitrogen cycling was dominated by net nitrification, with similar rates (17.2–18.9 mg kg⁻¹ 14 days⁻¹) among the four sampling areas. In the second part of the study, we emplaced soil cores that either allowed root in‐growth or excluded roots to evaluate how roots directly affect soil CO₂ and CH₄. The three plant species had similar amounts of root growth (ca 290 g m⁻² year⁻¹). Fungal biomass was similar in soils with root in‐growth versus root exclusion, regardless of dominant plant species. Rates of soil CO₂ production did not differ with root in‐growth versus root exclusion, and added glucose increased CO₂ production rates by only 35%. Root in‐growth did lead to greater rates of CH₄ production; albeit, addition of glucose had much greater effect on CH₄ production (1.24 nmol kg⁻¹ s⁻¹) compared with controls without added glucose (0.058 nmol kg⁻¹ s⁻¹). Our data revealed relatively few subtle differences in soil characteristics and processes associated with different plant species; albeit, roots had little effect, even inhibiting some microbial processes. This research highlights the need for both field and experimental studies in long‐established monocultures of plant species to understand the role of plant biodiversity in soil function.     

草甸草原模拟氮沉降抑制甲烷吸收、促进氧化亚氮排放

Few studies are conducted to quantify the effects of enhanced N deposition on soil nitrous oxide (N2O) emission and methane (CH4) uptake in the meadow steppe of Inner Mongolia,China.A two-year field experiment was conducted to assess the effects of nitrogen (N) deposition rates (0,10,and 20 kg N ha-1 year-1 as (NH4)2SO4) on soil N2O and CH4 fluxes.The seasonal and diurnal variations of soil N2O and CH4 fluxes were determined using the static chamber-gas chromatography method during the two growing seasons of 2008 and 2009.Soil temperature,moisture and mineral N (NH4+-N and NO3--N) concentration were simultaneously measured.Results showed that low level of (NH4)2SO4 (10 kg N ha-1 year-1) did not significantly affect soil CH4 and N2O fluxes and other variables.High level of (NH4)2SO4 (20 kg N ha-1 year-1) significantly increased soil NO3--N concentration by 24.1％ to 35.6％,decreased soil CH4 uptake by an average of 20.1％,and significantly promoted soil N2O emission by an average of 98.2％.Soil N2O emission responded more strongly to the added N compared to CH4 uptake.However,soil CH4 fluxes were mainly driven by soil moisture,followed by soil NO3--N concentration.Soil N2O fluxes were mainly driven by soil temperature,followed by soil moisture.Soil inorganic N availability was a key integrator of soil CH4 uptake and N2O emission.These results suggest that the changes of availability of inorganic N induced by the increased N deposition in soil may affect the CH4 and N2O fluxes in the cold semi-arid meadow steppe over the short term.     

Estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data in a loamy sand

The degradation rate of the pollutant is often an important parameter for designing and maintaining an active treatment system or for determining the rate of natural attenuation. A quasi‐steady‐state gas transport model based on Fick’s law with a correction term for advective flux, for estimating diesel degradation rates from N₂, O₂ and CO₂ concentration versus depth data, was evaluated in a laboratory column study. A loamy sand was spiked with diesel fuel at 0, 1000, 5000 and 10 000 mg kg⁻¹ soil (dry weight basis) and incubated for 15 weeks. Soil gas was sampled weekly at 6 selected depths in the columns and analysed for O₂, CO₂ and N₂ concentrations. The agreement between the measured and the modelled concentrations was good for the untreated soil (R²= 0.60) and very good for the soil spiked with 1000 mg kg⁻¹ (R²= 0.96) and 5000 mg kg⁻¹ (R²= 0.97). Oxygen consumption ranged from −0.15 to −2.25 mol O₂ m⁻³ soil day⁻¹ and CO₂ production ranged from 0.20 to 2.07 mol CO₂ m⁻³ soil day⁻¹. A significantly greater mean O₂ consumption (P < 0.001) and CO₂ production (P < 0.005) over time was observed for the soils spiked with diesel compared with the untreated soil, which suggests biodegradation of the diesel substrate. Diesel degradation rates calculated from respiration data were 1.5–2.1 times less than the change in total petroleum hydrocarbon content. The inability of this study to correlate respiration data to actual changes in diesel concentration could be explained by volatilization, long‐term sorption of diesel hydrocarbons to organic matter and incorporation of diesel hydrocarbons into microbial biomass, aspects of which require further investigation.     

Assessment of N2O, NOx and NH3 emissions from a typical rural catchment in Eastern China

To evaluate the atmospheric load of reactive gaseous nitrogen in the fast-developing Eastern China region, we compiled inventories of nitrous oxide (N₂O), nitrogen oxide (NO_x) and ammonia (NH₃) emissions from a typical rural catchment in Jiangsu province, China, situated at the lower reach of the Yangtze River. We considered emissions from synthetic N fertilizer, human and livestock excreta, decomposition of crop residue returned to cropland and residue burning, soil background and household energy consumption. The results showed that, for the 45.5 km² catchment, the annual reactive gaseous emission was 279 ton N, of which 7% was N₂O, 16% was NO_x and 77% was NH₃. Synthetic N fertilizer application was the dominant source of N₂O and NH₃ emissions and crop residue burning was the dominant source of NO_x emission. Sixty-seven percent of the total reactive gaseous N was emitted from croplands, but on a per unit area basis, NO_x and NH₃ emissions in residential areas were higher than in croplands, probably as a result of household crop residue burning and extensive human and livestock excreta management systems. Emission per capita was estimated to be 18.2 kg N year⁻¹ in the rural catchment, and emission per unit area was 56.9 kg N ha⁻¹year⁻¹ for NH₃ + NO_x, which supports the observed high atmospheric N deposition in the catchment. Apparently, efficient use of N fertilizer and biological utilization of crop straw are important measures to reduce reactive gases emissions in this rural catchment.     

Evidence of biogenic greigite (ferrimagnetic Fe3S4) in soil

The occurrence of greigite (Fe₃S₄) in soils is reported for the first time. It forms irregularly-shaped aggregations within plant cells in the Gr₂ horizon of a gley soil developed from colluvial material. Greigite was identified by X-ray diffraction and magnetic measurements and was investigated by optical and transmission electron microscopy. Biogenic formation is proposed, based on the elongated shape of single greigite crystals, and sulphur isotope analyses, which showed a depletion in ³⁴S relative to the soil-water sulphate. The cell-edge length of 0.98639±0.00003 nm is significantly smaller than values reported for sedimentary greigite. The mean coherence length of 27 nm agrees with TEM observations and indicates that the single greigite crystals lie in the superparamagnetic region. However, the fine aggregates show magnetically single-domain behaviour. Greigite is the only carrier of a stable magnetic remanence in the soil profile studied.