CH4 Profiles Research Articles

Rapid Sediment Accumulation Results in High Methane Effluxes from Coastal Sediments.

Globally, the methane (CH4) efflux from the ocean to the atmosphere is small, despite high rates of CH4 production in continental shelf and slope environments. This low efflux results from the biological removal of CH4 through anaerobic oxidation with sulfate in marine sediments. In some settings, however, pore water CH4 is found throughout the sulfate-bearing zone, indicating an apparently inefficient oxidation barrier for CH4. Here we demonstrate that rapid sediment accumulation can explain this limited capacity for CH4 removal in coastal sediments. In a saline coastal reservoir (Lake Grevelingen, The Netherlands), we observed high diffusive CH4 effluxes from the sediment into the overlying water column (0.2–0.8 mol m-2 yr-1) during multiple years. Linear pore water CH4 profiles and the absence of an isotopic enrichment commonly associated with CH4 oxidation in a zone with high rates of sulfate reduction (50–170 nmol cm-3 d-1) both suggest that CH4 is bypassing the zone of sulfate reduction. We propose that the rapid sediment accumulation at this site (~ 13 cm yr-1) reduces the residence time of the CH4 oxidizing microorganisms in the sulfate/methane transition zone (< 5 years), thus making it difficult for these slow growing methanotrophic communities to build-up sufficient biomass to efficiently remove pore water CH4. In addition, our results indicate that the high input of organic matter (~ 91 mol C m-2 yr-1) allows for the co-occurrence of different dissimilatory respiration processes, such as (acetotrophic) methanogenesis and sulfate reduction in the surface sediments by providing abundant substrate. We conclude that anthropogenic eutrophication and rapid sediment accumulation likely increase the release of CH4 from coastal sediments.

Kinetic and energy production analysis of pyrolysis of lignocellulosic biomass using a three-parallel Gaussian reaction model

The kinetic and energy productions of pyrolysis of a lignocellulosic biomass were investigated using a three-parallel Gaussian distribution method in this work. The pyrolysis experiment of the pine sawdust was performed using a thermogravimetric–mass spectroscopy (TG–MS) analyzer. A three-parallel Gaussian distributed activation energy model (DAEM)-reaction model was used to describe thermal decomposition behaviors of the three components, hemicellulose, cellulose and lignin. The first, second and third pseudocomponents represent the fractions of hemicellulose, cellulose and lignin, respectively. It was found that the model is capable of predicting the pyrolysis behavior of the pine sawdust. The activation energy distribution peaks for the three pseudo-components were centered at 186.8, 197.5 and 203.9kJmol−1 for the pine sawdust, respectively. The evolution profiles of H2, CH4, CO, and CO2 were well predicted using the three-parallel Gaussian distribution model. In addition, the chemical composition of bio-oil was also obtained by pyrolysis–gas chromatography/mass spectrometry instrument (Py–GC/MS).

Validation of revised methane and nitrous oxide profiles from MIPAS–ENVISAT

Abstract. Improved versions of CH4 and N2O profiles derived at the Institute of Meteorology and Climate Research and Instituto de Astrofísica de Andalucía (CSIC) from spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have become available. For the MIPAS full-resolution period (2002–2004) these are V5H_CH4_21 and V5H_N2O_21 and for the reduced-resolution period (2005–2012) these are V5R_CH4_224, V5R_CH4_225, V5R_N2O_224 and V5R_N2O_225. Here, we compare CH4 profiles to those measured by the Fourier Transform Spectrometer on board of the Atmospheric Chemistry Experiment (ACE-FTS), the HALogen Occultation Experiment (HALOE) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY), to the Global Cooperative Air Sampling Network (GCASN) surface data. We find the MIPAS CH4 profiles below 25 km to be typically higher of the order of 0.1 ppmv for both measurement periods. N2O profiles are compared to those measured by ACE-FTS, the Microwave Limb Sounder on board of the Aura satellite (Aura-MLS) and the Sub-millimetre Radiometer on board of the Odin satellite (Odin-SMR) as well as to the Halocarbons and other Atmospheric Trace Species Group (HATS) surface data. The mixing ratios of the satellite instruments agree well with each other for the full-resolution period. For the reduced-resolution period, MIPAS produces similar values as Odin-SMR, but higher values than ACE-FTS and HATS. Below 27 km, the MIPAS profiles show higher mixing ratios than Aura-MLS, and lower values between 27 and 41 km. Cross-comparisons between the two MIPAS measurement periods show that they generally agree quite well, but, especially for CH4, the reduced-resolution period seems to produce slightly higher mixing ratios than the full-resolution data.

Experimental Study on the Ethane-Reburning Process at Several Air/Fuel Equivalence Ratios and High Temperatures

An investigation of the ethane-reburning process was performed using an electrically heated test rig with a non-intrusive multi-point sampling system. The concentration profiles of CH4, H2, C2H2, O2, CO, CO2, NO, HCN, and NO + HCN at several air/fuel equivalence ratios were measured at various elevated temperatures. The experimental results show that, at high temperatures, the weakly reducing atmospheres associated with air/fuel equivalence ratios in the range of 0.96–0.99 are suitable for the reduction of NO to N2. Under these conditions, C2H2 is able to act as the main reducing component in the ethane-reburning process.

Information‐rich spectral channels for simulated retrievals of partial column‐averaged methane

Space‐based remote sensing of the column‐averaged methane dry air mole fraction (XCH4) has greatly increased our understanding of the spatiotemporal patterns in the global methane cycle. The potential to retrieve multiple pieces of vertical profile information would further improve the quantification of CH4 across space‐time scales. We conduct information analysis for channel selection and evaluate the prospects of retrieving multiple pieces of information as well as total column CH4 from both ground‐based and space‐based near‐infrared remote sensing spectra. We analyze the degrees of freedom of signal (DOF) in the CH4 absorption bands near 2.3 μm and 1.6 μm and select ∼1% of the channels that contain &gt;95% of the information about the CH4 profile. The DOF is around 4 for fine ground‐based spectra (resolution = 0.01 cm−1) and 3 for coarse space‐based spectra (resolution = 0.20 cm−1) based on channel selection and a signal‐to‐noise ratio (SNR) of 300. The DOF varies from 2.2 to 3.2 when SNR is between 100 and 300, and spectral resolution is 0.20 cm−1. Simulated retrieval tests in clear‐sky conditions using the selected channels reveal that the retrieved partial column‐averaged CH4 values are not sensitive to the a priori profiles and can reflect local enhancements of CH4 in different partial air columns. Both the total and partial column‐averaged retrieval errors in all tests are within 1% of the true state. These simulated tests highlight the possibility to retrieve up to three to four pieces of information about the vertical distribution of CH4 in reality.

TITAN’S UPPER ATMOSPHERE FROMCASSINI/UVIS SOLAR OCCULTATIONS

Titan’s atmosphere is composed mainly of molecular nitrogen, methane being the principal trace gas. From the analysis of 8 solar occultations measured by the Extreme Ultraviolet (EUV) channel of the Ultraviolet Imaging Spectrograph (UVIS) onboard Cassini, we derived vertical profiles of N2 in the range 1100 - 1600 km and vertical profiles of CH4 in the range 850 - 1300 km. The correction of instrument effects and observational effects applied to the data are described. We present CH4 mole fractions, and average temperatures for the upper atmosphere obtained from the N2 profiles. The occultations correspond to different times and locations, and an analysis of variability of density and temperature is presented. The temperatures were analyzed as a function of geographical and temporal variables, without finding a clear correlation with any of them; although a trend of decreasing temperature towards the north pole was observed. The globally averaged temperature obtained is (150 ± 1) K. We compared our results from solar occultations with those derived form other UVIS observations, as well as studies performed with other instruments. The observational data we present confirm the atmospheric variability previously observed, add new information to the global picture of Titan’s upper atmosphere composition, variability and dynamics, and provide new constrains to photochemical models.

On the escape of CH4 from Pluto's atmosphere

AbstractWe adapted a multispecies escape model, developed for close‐in extrasolar planets, to calculate the escape rates of CH4 and N2 from Pluto. In the absence of escape, CH4 should overtake N2 as the dominant species below the exobase. The CH4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for Pluto lead to a nearly constant mixing ratio of less than 1% below the exobase. In this case the CH4 escape rate is only 5–10% of the N2 escape rate. Observations of the CH4 profile by the New Horizons/ALICE spectrograph can constrain the CH4 escape rate and provide a unique test for escape models.

TG-MS analysis and kinetic study for thermal decomposition of six representative components of municipal solid waste under steam atmosphere

Thermal decomposition of six representative components of municipal solid waste (MSW, including lignin, printing paper, cotton, rubber, polyvinyl chloride (PVC) and cabbage) was investigated by thermogravimetric-mass spectroscopy (TG-MS) under steam atmosphere. Compared with TG and derivative thermogravimetric (DTG) curves under N2 atmosphere, thermal decomposition of MSW components under steam atmosphere was divided into pyrolysis and gasification stages. In the pyrolysis stage, the shapes of TG and DTG curves under steam atmosphere were almost the same with those under N2 atmosphere. In the gasification stage, the presence of steam led to a greater mass loss because of the steam partial oxidation of char residue. The evolution profiles of H2, CH4, CO and CO2 were well consistent with DTG curves in terms of appearance of peaks and relevant stages in the whole temperature range, and the steam partial oxidation of char residue promoted the generation of more gas products in high temperature range. The multi-Gaussian distributed activation energy model (DAEM) was proved plausible to describe thermal decomposition behaviours of MSW components under steam atmosphere.

An automated, high through‐put method for accurate and precise measurements of dissolved nitrous‐oxide and methane concentrations in natural waters

AbstractWe describe a technique for measuring dissolved CH4 and N2O concentrations from discrete water samples using an automated purge and trap gas extraction system, coupled with a gas chromatograph‐mass spectrometer (PT‐GCMS). The automated system measures blanks, standards, and 25 samples in less than five hours with only ∼ 30 min of operator involvement. Rigorous testing of the PT‐GCMS demonstrates sensitivity, accuracy and precision that is comparable or better than conventional methods for CH4 and N2O analysis. Measured concentrations of CH4 and N2O in air‐equilibrated water samples showed good agreement with expected values derived from solubility calculations, and results of a multilaboratory intercalibration exercise showed that our measurements agree with those made using conventional methods. Precision of replicate water samples is 3.3% for CH4 and 3.0% for N2O. Detection limits are well below the expected concentrations in most natural waters with a five milliliters sample, and can be lowered substantially by analyzing a larger sample volume. To demonstrate the utility of the method, we present depth profiles of CH4 and N2O from Saanich Inlet, a coastal anoxic fjord in British Columbia. The Saanich Inlet water column exhibits rapid changes in CH4 and N2O across depth‐dependent and seasonally variable redox conditions. Our high through‐put, automated method facilitates the measurement of aqueous N2O and CH4 concentrations, and will thus help to improve our understanding of the natural cycling of these climate‐active trace gases.

Modeling the carbon cycle in Lake Matano.

Lake Matano, Indonesia, is a stratified anoxic lake with iron-rich waters that has been used as an analogue for the Archean and early Proterozoic oceans. Past studies of Lake Matano report large amounts of methane production, with as much as 80% of primary production degraded via methanogenesis. Low δ(13)C values of DIC in the lake are difficult to reconcile with this notion, as fractionation during methanogenesis produces isotopically heavy CO2. To help reconcile these observations, we develop a box model of the carbon cycle in ferruginous Lake Matano, Indonesia, that satisfies the constraints of CH4 and DIC isotopic profiles, sediment composition, and alkalinity. We estimate methane fluxes smaller than originally proposed, with about 9% of organic carbon export to the deep waters degraded via methanogenesis. In addition, despite the abundance of Fe within the waters, anoxic ferric iron respiration of organic matter degrades <3% of organic carbon export, leaving methanogenesis as the largest contributor to anaerobic organic matter remineralization, while indicating a relatively minor role for iron as an electron acceptor. As the majority of carbon exported is buried in the sediments, we suggest that the role of methane in the Archean and early Proterozoic oceans is less significant than presumed in other studies.

Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

Abstract. This study makes use of time series of methane (CH4) data from the Halogen Occultation Experiment (HALOE) to detect whether there were any statistically significant changes of the Brewer–Dobson circulation (BDC) within the stratosphere during 1992–2005. The HALOE CH4 profiles are in terms of mixing ratio versus pressure altitude and are binned into latitude zones within the Southern Hemisphere and the Northern Hemisphere. Their separate time series are then analyzed using multiple linear regression (MLR) techniques. The CH4 trend terms for the Northern Hemisphere are significant and positive at 10° N from 50 to 7 hPa and larger than the tropospheric CH4 trends of about 3% decade−1 from 20 to 7 hPa. At 60° N the trends are clearly negative from 20 to 7 hPa. Their combined trends indicate an acceleration of the BDC in the middle stratosphere of the Northern Hemisphere during those years, most likely due to changes from the effects of wave activity. No similar significant BDC acceleration is found for the Southern Hemisphere. Trends from HALOE H2O are analyzed for consistency. Their mutual trends with CH4 are anti-correlated qualitatively in the middle and upper stratosphere, where CH4 is chemically oxidized to H2O. Conversely, their mutual trends in the lower stratosphere are dominated by their trends upon entry to the tropical stratosphere. Time series residuals for CH4 in the lower mesosphere also exhibit structures that are anti-correlated in some instances with those of the tracer-like species HCl. Their occasional aperiodic structures indicate the effects of transport following episodic, wintertime wave activity. It is concluded that observed multi-year, zonally averaged distributions of CH4 can be used to diagnose major instances of wave-induced transport in the middle atmosphere and to detect changes in the stratospheric BDC.

Soil–methane sink increases with soil age in forefields of Alpine glaciers

In upland soils aerobic methane-oxidizing bacteria (MOB) catalyze methane (CH4) oxidation, and thus regulate the sole terrestrial sink for atmospheric CH4. While confirmed in mature upland soils, little is known about this important function in young mountainous soils in glacier forefields, which are progressively formed as a result of glacier recession. We assessed four attributes of the soil CH4 sink, i.e., soil-atmosphere CH4 flux (Jatm), CH4 oxidation activity (k), MOB abundance and variation in community composition along the 6–120-yr soil chronosequence in two Alpine glacier forefields on siliceous and calcareous bedrock. At most sampling locations soil CH4 profiles showed stable uptake of atmospheric CH4, with Jatm in the range of −0.082 to −2.2 mg CH4m−2 d−1. Multiple-linear-regression analyses indicated that Jatm significantly increased with soil age, whereas k did not. Instead, water content and CH4 profiles in the youngest soils often indicated dry, inactive top layers with k < 0.1h−1, and active deeper layers (0.2 h−1 ≤ k ≤ 11h−1) with more favorable water content. With increasing soil age the zone of highest CH4 oxidation activity gradually moved upwards and eventually focused in the 10–40-cm layer (0.2 h−1 ≤ k ≤ 16h−1). Copy numbers of pmoA genes significantly increased with soil age at both sites, ranging from 2.4 × 103 to 5.5 × 105 copies (g soil w.w.)−1, but also correlated with mineral nitrogen content. Terminal restriction-fragment-length-polymorphism and cluster analyses showed differences in MOB community composition apparently related to bedrock type rather than soil age. Yet, regardless of bedrock type, the soil CH4 sink established within a few years of soil development, and Jatm increased to values comparable to mature soils within decades. Thus, young mountainous soils have the potential to consume substantial amounts of atmospheric CH4, and should be incorporated into future estimates of global soil CH4 uptake.

Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River delta

Abstract. Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems, where they are considered to be hotspots of carbon dioxide CO2 and methane CH4 emission. The strength of these emissions is, however, controlled by a variety of physical and biogeochemical processes whose responses to a warming climate are complex and only poorly understood. Small waterbodies have been attracting an increasing amount of attention since recent studies demonstrated that ponds can make a significant contribution to the CO2 and CH4emissions of tundra ecosystems. Waterbodies also have a marked effect on the thermal state of the surrounding permafrost; during the freezing period they prolong the period of time during which thawed soil material is available for microbial decomposition. This study presents net CH4 production rates during the freezing period from ponds within a typical lowland tundra landscape in northern Siberia. Rate estimations were based on CH4 concentrations measured in surface lake ice from a variety of waterbody types. Vertical profiles along ice blocks showed an exponential increase in CH4 concentration with depth. These CH4 profiles were reproduced by a 1-D mass balance model and the net CH4 production rates were then inferred through inverse modeling. Results revealed marked differences in early winter net CH4 production among various ponds. Ponds situated within intact polygonal ground structures yielded low net production rates, of the order of 10-11 to 10-10 mol m-2 s-1 (0.01 to 0.14 mgCH4 m-2 day-1). In contrast, ponds exhibiting clear signs of erosion yielded net CH4 production rates of the order of 10-7 mol m-2 s-1 (140 mg CH4 m-2 day-1). Our results therefore indicate that once a particular threshold in thermal erosion has been crossed, ponds can develop into major CH4 sources. This implies that any future warming of the climate may result in nonlinear CH4 emission behavior in tundra ecosystems.

Methane distribution and sea-to-air flux in the East China Sea during the summer of 2013: Impact of hypoxia

We measured dissolved methane (CH4) at different depths and calculated sea-to-air CH4 fluxes at 65 stations in the East China Sea (ECS) from August 4 to 31 of 2013. CH4 concentrations in surface waters ranged from 2.07 to 27.39nM and concentrations in bottom waters ranged from 1.76 to 31.35nM. The concentration of CH4 also decreased with distance from the Changjiang (Yangtze River) Estuary. Analysis of the depth profiles of CH4 indicated great variations among the different stations due to the influence of different water masses and variations in other factors. A region of significant bottom-water hypoxia, with an oxygen level less than 1.5mgL−1, occurred at the northern region of the ECS. This hypoxic region also had enhanced CH4 production in the water column and sedimentary release of CH4. CH4 saturations in the surface waters ranged from 113% to 1364%, with an average of 317% (±236). We estimated the sea-to-air CH4 flux as 6.5±7.4μmolm−2d−1 using the LM86 equation, and as 11.5±11.9μmolm−2d−1 using the W92 equation. The overall estimated CH4 emission rate from the ECS was 6.4×10−2Tgyr−1. The saturation and sea-to-air flux of CH4 varied significantly among the stations. Taken together, our data suggest that the ECS is a net source of atmospheric CH4.

Validation of XCH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; derived from SWIR spectra of GOSAT TANSO-FTS with aircraft measurement data

Abstract. Column-averaged dry-air mole fractions of methane (XCH4), retrieved from Greenhouse gases Observing SATellite (GOSAT) short-wavelength infrared (SWIR) spectra, were validated by using aircraft measurement data from the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the HIAPER Pole-to-Pole Observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. In the calculation of XCH4 from aircraft measurements (aircraft-based XCH4), other satellite data were used for the CH4 profiles above the tropopause. We proposed a data-screening scheme for aircraft-based XCH4 for reliable validation of GOSAT XCH4. Further, we examined the impact of GOSAT SWIR column averaging kernels (CAK) on the aircraft-based XCH4 calculation and found that the difference between aircraft-based XCH4 with and without the application of the GOSAT CAK was less than ±9 ppb at maximum, with an average difference of −0.5 ppb. We compared GOSAT XCH4 Ver. 02.00 data retrieved within ±2° or ±5° latitude–longitude boxes centered at each aircraft measurement site with aircraft-based XCH4 measured on a GOSAT overpass day. In general, GOSAT XCH4 was in good agreement with aircraft-based XCH4. However, over land, the GOSAT data showed a positive bias of 1.5 ppb (2.0 ppb) with a standard deviation of 14.9 ppb (16.0 ppb) within the ±2° (±5°) boxes, and over ocean, the average bias was 4.1 ppb (6.5 ppb) with a standard deviation of 9.4 ppb (8.8 ppb) within the ±2° (±5°) boxes. In addition, we obtained similar results when we used an aircraft-based XCH4 time series obtained by curve fitting with temporal interpolation for comparison with GOSAT data.

CH4 mixing ratios at microbar pressure levels of Jupiter as constrained by 3-micron ISO data

Infrared Space Observatory (ISO) data of Jupiter are revisited in order to derive CH4 mixing ratios at microbar pressures in the atmosphere. We utilize the most updated radiative transfer programs to construct a 3-μm emission model of CH4 to be compared with the ISO data. From the model-data comparisons, we derive the high-altitude CH4 mixing ratios, which turn out to be at least 10 times smaller than the microbar CH4 mixing ratios assumed in the Galileo probe analysis (Seiff, A. et al., 1998. Thermal structure of Jupiter’s atmosphere near the edge of a 5-μm hot spot in the north equatorial belt. J. Geophys. Res., 103, 22857–22889. doi:10.1029/98JE01766), but which are approximately consistent with ultraviolet airglow observations and with available photochemical models that assume relatively weak atmospheric mixing. We also compare the derived CH4 profile with results from other investigations reported in literature and discuss the implications with respect to photochemistry and vertical transport in the stratosphere of Jupiter.

Methane retrieval from Atmospheric Infrared Sounder using EOF-based regression algorithm and its validation

This paper presents a rapid regression algorithm for the retrieval of methane (CH4) profile from Atmospheric Infrared Sounder (AIRS) based on empirical orthogonal functions (EOF) and its validation. This algorithm was trained using the simulated radiance from an assemble of atmospheric profiles and can be utilized to derive the CH4 profile rapidly with the input of the AIRS cloud-clear radiance. Validation using hundreds of aircraft profiles demonstrates that the root mean square error (RMSE) is about 1.5 % in the AIRS sensitive region of 359–596 hPa, which is smaller than AIRS-V5 product (except in high latitudes). Comparison with the ground-based solar Fourier transform spectrometry observations showed that the RMSE of the retrieved CH4 total column amount is less than 3 %. This EOF-based regression method can be easily applied to other thermal infrared sounders for deriving CH4 and some other gases, and the derived profiles can be used as the first guess for further physical retrieval.

A new Himalayan ice core CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; record: possible hints at the preindustrial latitudinal gradient

Abstract. Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on the northeast saddle of Mt. Qomolangma (Everest) (28°01' N, 86°58' E, 6518 m above sea level) give access to a tentative record of past Himalayan atmospheric mixing ratio of CH4 spanning the past 1200 yr. The major part of the record is affected by artifacts probably due to in situ production. After selecting what may represent the true atmospheric mixing ratio, an average of 749 ± 25 ppbv of CH4 is estimated for the late preindustrial Holocene, which is ~ 36 ± 17 (~ 73 ± 18) ppbv higher than the atmospheric levels recorded in the Greenland (Antarctic) ice cores. A comparison of these new data with model simulations of the CH4 latitudinal gradient suggests either that the models do not get a correct balance between high and low latitude CH4 sources, or that the filtered CH4 profile from the ER cores remains biased by small artifacts.

A field trial of nutrient stimulation of methanotrophs to reduce greenhouse gas emissions from landfill cover soils

Landfills are among the major sources of anthropogenic methane (CH4) estimated to reach 40 × 109kg per year worldwide by 2015 (IPCC, 2007). A 2½-year field experiment was conducted at a closed landfill in western Michigan where methanotrophs, methane-consuming bacteria, were stimulated by nutrient addition to the soil without significantly increasing biogenic nitrous oxide (N2O) production. The effects of the nitrogen amendments (KNO3 and NH4Cl), phenylacetylene (a selective inhibitor of nitrifying bacteria that contribute to N2O production), and a canopy (to reduce direct water infiltration) on the vertical soil gas profiles of CH4, CO2, and O2 were measured in the top meter of the soil. Methane and nitrous oxide fluxes were calculated from the corresponding soil gas concentration gradients with respect to depth and a Millington–Quirk diffusivity coefficient in soil derived empirically from soil porosity, water content, and diffusivity coefficients in air from the literature. Methane flux estimates were as high as 218.4 g m−2 day−1 in the fall and 12.8 g/m−2 day−1 in the summer. During the spring and summer, CH4 fluxes were reduced by more than half by adding KNO3 and NH4Cl into the soil as compared to control plots, while N2O fluxes increased substantially. The concurrent addition of phenylacetylene to the amendment decreased peak N2O production by half and the rate of peak methane oxidation by about one-third. The seasonal average methane and N2O flux data were extrapolated to estimate the reduction of CH4 and N2O fluxes into the atmosphere by nitrogen and inhibitor addition to the cover soils. The results suggest that such additions coupled with soil moisture management may provide a potential strategy to significantly reduce greenhouse gas emissions from landfills. Implications The results of a 2½-year study of effects of nutrient stimulation on methane oxidation in landfill cover soils demonstrates that nutrient addition does decrease methane emissions. The work further underscores the control which soil moisture exerts on methane oxidation. Water management is critical to the success of methane oxidation strategies. Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association.

Benthic ostracode δ13C as sensor for early Holocene establishment of modern circulation patterns in Central Europe

Shells from adult specimen of the benthic ostracodes Limnocytherina sanctipatricii and Leucocythere mirabilis selected from a 8.7 m long piston core provide continuous stable oxygen and carbon records for the past approximately 16 ka. Oxygen isotopes from both species show identical values and track the general North Atlantic and European temperature history since deglaciation in great detail. Values of ostracode δ18O values suggest that about 16 cal ka the average annual air temperatures were about 11 °C colder than today. Carbon isotopic values from both species of ostracodes are similar during the Lateglacial and early Holocene, and show an overall decrease from −4‰ to −7‰ that is probably related to an increase in photosynthetic productivity in the water column, as suggested by an increase in organic carbon, delivering 13C-depleted organic matter to the bottom waters (carbon pump). About 9 cal ka only L. mirabilis δ13C values decreased about −2.5‰ within 300 years. Higher δ13C variability and ecological evidence suggests that L. mirabilis represents a summer signal, whereas L. sanctipatricii displays a more subdued annual average. After about 7 cal ka another −1.5% decrease for both species, accompanied by an increase in magnetic susceptibility, a decrease in carbonate content, and more positive bulk carbonate isotope values followed, suggesting higher detrital-clastic input into the lake.In order to provide a possible mechanism explaining the negative L. mirabilis δ13C-values, sediment pore water profiles of O2 and CH4 in short cores collected from sites distal to proximal to the Alpine Rhine River delta, were inspected. Sediments in cores from more proximal sites to the Rhine delta become anoxic at shallower sediment depth due to the decay of high allochthonous organic carbon input to the sediment, which greatly increases concentrations of methane in pore waters closer to the Rhine inflow. When methane is oxidized close to the sediment–water-interface, 13C-depleted carbon is added to pore water DIC that is then available for incorporation into ostracode shells. This mechanism suggests that about 9 cal ka the oxygen supply to the bottom waters, especially in summer, decreased. This stimulated methanogenesis close to the sediment–water-interface, and provided δ13C-depleted carbon to benthic dwellers. Independent evidence for methanogenesis is provided by the increase in concentration of tetrahymanol after about 9 cal ka coincident with the decrease in δ13C of L. mirabilis.We suggest that about 9 cal ka the northward retreat of the Northern Hemisphere Ice Sheets, and consequently the polar front, left the alpine region affected by a more oceanic climate, characterized by warmer winters as they occur today especially during the positive North Atlantic Oscillation Index phase. More frequently incomplete mixing of the water column may have shifted the decay of organic matter faster to anaerobic conditions in surficial sediments especially during summer. By about 7 cal ka the North Atlantic region had probably warmed sufficiently to increase precipitation in Central Europe and consequently detrital-clastic runoff to Lake Constance.