Improvements in Drill-Core Headspace Gas Analysis for Samples from Microbially Active Depths.
Investigation of the origin of deep hydrocarbons is an important aspect of resource exploration and may lead to an improved understanding of geological environments. In this investigation, gases adsorbed on rock fragments or bore cores were studied by headspace gas analysis (e.g., [1-5]), which provides information on the generation and migration of light hydrocarbons and gases. The IsoJar[TM] (Isotech Laboratories and Humble Instruments, USA) container, which is widely used in such analyses (e.g., [6, 7]) comprises a plastic container of ~600 ml volume with an aluminum screw cap on which there is a rubber septum through which headspace gas can be taken by syringe. The analysis procedure (e.g., ) normally involves storage of wet cuttings or cores in the jar with water and an air headspace for several days or weeks, the addition of a microbicide such as benzalkonium chloride (BKC) to minimize bacterial activity, the partitioning of gas into the headspace during storage, and analysis of these gases (e.g., [9-11]). The use of distilled or tap water avoids contamination from dissolved gases. The [delta][sup.13][C.sub.CH4] values of gases from depths of < 1000 m, in the biogenic region, are usually in the range of -70 [per thousand] to -60 [per thousand], with isotopic compositions becoming heavier as depth increases towards the thermogenic region (e.g., [12, 13]). Large variations in carbon isotopic ratios in C[H.sub.4] and C[O.sub.2] are often reported for depths of < 1000 m, with [delta][sup.13][C.sub.CH4] values sometimes reaching -20 [per thousand] (e.g., [14-17]). These variations are associated with the effects of microbial activity on methane production or oxidation in underground environments . There are a number of factors that control the rate of methanogenesis , including temperature , groundwater salinity , pH , and pore space . Peak microbial activity occurs at 35-45[degrees]C, which corresponds to depths of <1000m [19, 24]. At greater depths, microbial action decreases as thermogenic production increases with the onset of catagenesis (subsequent to diagenesis at shallower depths ). More importantly, pore diameters of at least 1 [micro]m are necessary for in situ methanogenesis, as microbes are in the 1-10 [micro]m size range , which suggests that active methane production occurs at depths of < 1500 m . At shallow depths (less than several meters) below the ocean floor, where the concentration of dissolved gas is relatively low, considerable care was taken to avoid contamination and microbial activity (e.g., ). Hachikubo et al.  adjusted the concentration of BKC in samples to ~2.5% using 25 ml vials to obtain precise depth profiles of gases relative to hydrates. While the concentration and/or amount of microbicide normally added to IsoJar[TM] vessels are often omitted in reports, it is considered that the final concentration in IsoJar[TM] containers should be of the order of 0.01%, which is two orders of magnitude less than that reported by Hachikubo et al. . It is speculated that another possible cause of variations in carbon isotopic composition may be microbial activity in the headspace after sampling, as the amount of microbicide commonly used with samples from microbially active depths might be insufficient to suppress microbial activity.
In a previous study, gas samples from two boreholes (PB-V01 and SAB-1, both ~500m deep) in the Horonobe area, Hokkaido, were processed using IsoJar[TM] containers . In that study, cores were stored in IsoJar[TM] containers with water and a few drops of BKC solution  for up to three months before headspace analysis. Because sampling date of cores and analysis date of gases, which are necessary for the calculation of the storage period, have not been presented in Funaki et al. , these unpublished information are summarized in Tables S1a and S1b. Concentration of the BKC solution and amounts of cores and water also have not been reported in Funaki et al. . In the conventional way of using IsoJar[TM] headspace gas analysis, it is considered that the concentration of BKC solution is lower than 10%, in which case concentrations of BKC in jars are in order of 0.01%. In the construction of the Horonobe Underground Research Laboratory (URL), including two boreholes (PBV01 and SAB-1), water was collected from groundwater at ~50 m depth, and this was used by Funaki et al.  as filling water for the IsoJar[TM] containers. Gases dissolved in deep groundwater from the URL were also analyzed, using an evacuated-vial (EV) method . Measured [delta][sup.13]C values for C[H.sub.4] and C[O.sub.2] from both sets of analyses are plotted against each other in Figure 1. Large variations in [delta][sup.13][C.sub.CH4] values from the IsoJar[TM] measurements (Figure 1) were attributed to methane-oxidizing bacterial activity using sulfate ions in the deep underground environment or to isotopic fractionation during gas migration through fractures . However, these possible causes are considered unlikely because (a) geochemical studies in the Horonobe area indicate that reducing conditions are maintained deep underground and sulfate ions are either absent or present at very low concentrations [29-32]; (b) studies of iodine enrichment  indicates that any traces of methane oxidation by sulfate in pore waters of sediments would have been erased during upward fluid flow due to compaction during burial; and (c) there is no evidence in the study area of isotopic fractionation in gases during migration [34, 35]. The [delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2] values obtained by the EV method (Figure 1) show little scatter plotting in the carbonate reduction field.
Differences between these data sets could be attributed to factors such as aerobic microbial oxidation of methane in the containers after sampling and/or using groundwater from the different depths of core samples. Possible causes were investigated in the present study to improve the methodology of headspace gas analysis using IsoJar[TM]. Gases from the Wakkanai Formation in the Horonobe area were sampled using the methods of Funaki et al.  and Miyakawa et al. . The effects of the sampling method (storage period, water type, and additives) on carbon isotopic ratios in C[H.sub.4] and C[O.sub.2] were investigated, and improvements in headspace gas analysis techniques are suggested.
2. Geological Setting
The Horonobe area is located in northwestern Hokkaido, in a Neogene-Quaternary sedimentary basin (Figure 2). Since August 2006, the Japan Atomic Energy Agency (JAEA) has been excavating the URL for a research associated with the development of technologies related to the geological disposal of high-level radioactive waste. Geologically, the URL area comprises marine sediments of the Wakkanai Formation (Neogene siliceous mudstone containing opal-CT) and Koetoi Formation (Neogene-Quaternary diatomaceous mudstone containing opal-A). Burial and subsidence of these formations occurred throughout the Neogene and Quaternary, when they underwent early diagenetic thermal alteration at temperatures of <60[degrees]C . The URL and surrounding geology are depicted in Figure 3. The high-pressure boreholes have steel casings, with valves allowing the sampling of groundwater from multiple depths or zones . The [delta]D vs. [delta][sup.18]O plots for groundwater from the Wakkanai and Koetoi Formations indicate that it is a mixture of local meteoric water and altered seawater [38, 39]. Methanogenic and methane-oxidizing microbial communities have played an important role in these formations [40-42], where secondary microbial gas with [sup.13]C-enriched isotopic values ([delta][sup.13][C.sub.CH4], -74 [per thousand] to -28 [per thousand]; [delta][sup.13][C.sub.CO2], -7 [per thousand] to +31 [per thousand]) formed through C[O.sub.2] reduction af.sub..sub.ter uplift of the area .
3. Sampling and Analytical Methods
3.1. IsoJar[TM] Samples
3.1.1. Effect of Storage Period. Core samples including in situ pore water (300-400 g), crushed to pieces roughly 30-50 mm in diameter, were placed in IsoJar[TM] containers with 250-300 g of "filling" water. Hg[Cl.sub.2]-saturated or 10% BKC aqueous solution (10 drops (~0.5ml) of either) was added to suppress microbial activity, and the jars were sealed with an air headspace. Final concentrations of both microbicides in the jars were about 0.01%-0.02%. The jars were kept in the dark at room temperature for 5-92 d before analysis. Details of each experiment are summarized in Table 1 and Table S2.
The cores were obtained immediately after drilling of borehole 350-Fz-01 from the bottom of the east shaft (Figure 3). Although distilled or tap water is usually used in the IsoJar[TM] method, groundwater from depths of 53.5-64.5 m and 350 m in borehole 13-350-C01 (drilled in the 350 m gallery; Figure 3) was used to match the 50 m groundwater used by Funaki et al. . The priority in this study was to evaluate the effects of sampling method on the carbon isotopic ratios of C[H.sub.4] and C[O.sub.2], rather than to obtain accurate in situ values. A large portion of C[H.sub.4] dissolved in groundwater around the URL had already escaped due to the pressure decrease associated with excavation, so it was expected that only small amounts of gas would remain in cores. Groundwater, rather than tap water, was used to compensate for this (with water from borehole 13-350-C01 being used because water was not available from borehole 350-Fz-01). Core samples IJ1-IJ25 were from depths of 384-416 m (Table S2). Core samples IJ26-IJ28 were from a depth of 470 m (Table S2) and kept in vacuum storage for one month after drilling. At these depths, the C isotopic ratios for C[H.sub.4] and C[O.sub.2] had similar values to those from 350 m depth .
3.1.2. Effect of Additives. The effective amount of additives was investigated as follows. IsoJar[TM] samples were prepared as described in Section 3.1.1, with up to 20 ml of BKC and Hg[Cl.sub.2] solutions per jar (Table 2 and Table S3). All core samples were from a depth of 480 m in 350-Fz-01. Fresh cores taken immediately after drilling were not available for analysis, and the samples used in this study had been kept in vacuum storage for about six months. Groundwater from borehole 13-350-C01 was used as filling water. Headspace gas compositions were determined after storage in IsoJar[TM] for one month.
3.2. EV Samples. The EV sampling procedure involved the preliminary evacuation of septum-topped 50 ml glass vials containing ~1 ml phosphoric acid (85 wt%). Acidification removed any inorganic carbon as C[O.sub.2], with the C[O.sub.2] concentration being measured as total inorganic carbon (TIC). Groundwater (15-30 ml, from borehole 09-V250-M02#1 drilled from the 250 m gallery; Figure 3) was introduced by a syringe through a 0.22 [micro]m membrane filter to remove microsized carbonate grains and microbes. Samples were stored in the dark at room temperature for 5-98 d, after which ultrapure He was added by a syringe to equalize headspace gas and atmospheric pressures. The sample was left to stand overnight for gas exchange equilibrium to be established between the headspace and dissolved gases. The composition of the headspace gas was determined by GC, with the concentration of dissolved gas being calculated using Henry's law and the ideal gas equation.
3.3. Analytical Procedure. Gases adsorbed on rock fragments in the IsoJar[TM] containers were desorbed into the headspace by ultrasonic shaking. Concentrations of [O.sub.2], [N.sub.2], C[O.sub.2], C[H.sub.4], [C.sub.2][H.sub.6], and [C.sub.3][H.sub.8] in headspace gas were determined by gas chromatography (GC) using a GC7890A Valve System (Agilent Technologies, USA). Carbon isotopic values ([delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2]) were determined by GC combustion isotope-ratio mass spectrometry (GC-C-IRMS), using an IsoPrime GC-MS system (GV Instruments, UK), and are expressed in the usual VPDB [delta] notation. The lower limit of determination of carbon isotope ratios ([delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2]) requires concentrations of 0.01%. Details of Gc and GC-C-IRMS procedures can be found in Waseda and Iwano .
Headspace concentrations of the gases analyzed and [delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2] values for the IsoJar[TM] samples prepared as described in Section 3.1.1 are listed in Table 1 and Table S2, and the results for the EV samples are listed in Table 3 and Table S4.
Sample contamination by air does not affect the present discussion of isotopic ratios because concentrations of C[H.sub.4] and C[O.sub.2] in air are much lower than those in the free gas from groundwater (where C[H.sub.4] = 74%-100%; C[O.sub.2] = 1%-20%; [28, 34]).
C[O.sub.2] in the free gas undergoes isotopic fractionation during exchange with dissolved inorganic carbon (e.g., C[O.sub.2(aq)], HC[O.sub.3.sup.-], and C[O.sub.3.sup.2-]), with HC[O.sub.3.sup.-] being the dominant aqueous species at around neutral pH. To compare [delta][sup.13][C.sub.CO2] values of the IsoJar[TM] samples with those of the EV samples, a fractionation correction (intrinsic isotopic fractionation factor) of +7.9 [per thousand] between C[O.sub.2] gas and HC[O.sub.3.sup.-] at 25[degrees]C  was added to [delta][sup.13][C.sub.CO2] values measured for the IsoJar[TM] samples. The range of room temperatures was 20[degrees]C-25[degrees]C, giving an error of up to -0.6 [per thousand].
Variations in [delta][sup.13][C.sub.CO2] and [delta][sup.13][C.sub.CH4] values with storage time are shown in Figures 4(a) and 4(b), respectively. IsoJar[TM] samples with groundwater (350 m) stored for less than one week give values similar to the EV samples. Storage periods of [less than or equal to] 7 d and [greater than or equal to] 20 d were considered, as no data are available for the interval of 7-20 d.
The [delta][sup.13][C.sub.CO2] and [delta][sup.13][C.sub.CH4] ratios for the EV samples are relatively constant, although [delta][sup.13][C.sub.CH4] values show a small variation (<4%) after 98 d (Figure 4(b)), which is consistent with a previous study . It is possible that some microbes are not removed by 0.22 [micro]m groundwater filtration (e.g., ), and this might have caused the slight variation in [delta][sup.13][C.sub.CH4] values. Differences between carbon isotopic values of C[H.sub.4] and C[O.sub.2] ([delta][sup.3][C.sub.CO2] - [delta][sup.13][C.sub.CH4] = isotopic separation factor; ) in the Horonobe area decrease slightly (<1 [per thousand]) with increasing depth and temperature according to isotopic equilibrium values, with values at depths of 250 m and 350 m being similar to each other within the natural variation of ~2 [per thousand] (1[sigma]) . Therefore, [delta][sup.13][C.sub.CO2] and [delta][sup.13][C.sub.CH4] values of 250 m groundwater obtained by the EV method (Table 3) were used as reference values for the IsoJar[TM] samples with 350 m groundwater.
The [delta][sup.13][C.sub.CO2] values for IsoJar[TM] samples show two separate trends for 350 m and 50 m groundwater, with both showing a slight decrease over time, from +15 [per thousand] at 5 d to +13 [per thousand] at 92 d and from +5 [per thousand] at 17 d to -1 [per thousand] to +3 [per thousand] at 79 d, respectively (Figure 4(a)). The patterns are the same for both BKC and Hg[Cl.sub.2] additives. The two trends suggest that the [delta][sup.13][C.sub.CO2] ratios represent dissolved gases from different depths. The concentration of C[O.sub.2] in the groundwater, as HC[O.sub.3.sup.-], is relatively high even when degassed at atmospheric pressure (30-50 mmol [kg.sup.-1]; ), compared with that of adsorbed C[O.sub.2], so carbon isotopic values should be largely dependent on dissolved C[O.sub.2]. The [delta][sup.13][C.sub.CO2] values of samples with 50 m groundwater (dashed line in Figure 4(a)) are distinct from those of samples with 350 m groundwater, indicating that the former samples are strongly contaminated.
The [delta][sup.13][C.sub.CH4] values for IsoJar[TM] samples (Figure 4(b)) increase markedly with time regardless of additives and fluctuate by more than 30 [per thousand] after 80 d; separate trends for different depths are not evident. The concentration of C[H.sub.4] remaining in the groundwater at atmospheric pressure after sampling is relatively low (~3 mmol [kg.sup.-1]; ), and [delta][sup.13][C.sub.CH4] values for the IsoJar[TM] samples mainly represent gases adsorbed on cores. Therefore, while the relatively large amounts of dissolved C[O.sub.2] reduced the effects of isotopic fractionation on [delta][sup.13][C.sub.CO2] values, [delta][sup.13][C.sub.CH4] values were strongly affected.
The results of the effect of additives as described in Section 3.1.2 are shown and discussed in Section 5.2.
5.1. Methane Oxidation. During methane oxidation, decreasing C[H.sub.4] and increasing C[O.sub.2] concentrations are associated with carbon isotopic fractionation, resulting in enrichment of [sup.13]C in unreacted C[H.sub.4] and depletion in C[O.sub.2] produced. However, there is no clear relationship between headspace gas concentrations and storage period, possibly because of the variability of adsorbed gas levels in natural samples. An apparent carbon isotopic fractionation factor, a, defined as [alpha] = ([delta][sup.13][C.sub.CO2] + 1000)/([delta][sup.13][C.sub.CH4] + 1000), was calculated using the [delta][sup.13][C.sub.CO2] and [delta][sup.13][C.sub.CH4] values in Table 1 (Figure 5). Initial values of a in the Horonobe samples, calculated using the results of the EV method, were around 1.06-1.08, in good agreement with those determined by Miyakawa et al. . The values of a for the IsoJar[TM] samples decreased from ~1.07 to 1.04 with increasing storage time (Figure 5). An earlier study reported a similar trend, where microbial methane oxidation in marine sediments gave an a value of ~1.08 in the methanogenesis zone, decreasing to ~1.02 in the methane oxidation zone .
A bivariate plot of [delta][sup.13][C.sub.CH4] vs. [delta][sup.13][C.sub.CO2] (Figure 6) indicates two trends for the IsoJar[TM] samples (Figure 6(b)), as in Figure 4(a). Thus, data plotted in Figures 4-6 indicate that [delta][sup.13][C.sub.CH4] values in samples stored for more than one week were affected by C[H.sub.4] oxidation to C[O.sub.2]. [delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2] values reported by Funaki et al.  are plotted between the two trends (Figure 6(b)). It seems, therefore, that the variations can be explained by the mixing of the two trends, indicating effects of both methane oxidation and contamination of 50 m groundwater in the IsoJar[TM] container after sampling.
5.2. Effect of Additives. Significant isotopic fractionation occurred in the IsoJar[TM] samples, strongly affecting [delta][sup.13][C.sub.CH4] values despite the addition of BKC or Hg[Cl.sub.2] (Figure 4), suggesting that the amounts of additives used were insufficient to suppress microbial activity. Results of effect of additives as described in Section 3.1.2 are listed in Table 2 and shown in Figure 7. With <10 ml BKC solution or <0.3% BKC concentration, [delta][sup.13][C.sub.CH4] values fluctuated significantly, and isotopic compositions became lighter. This is opposite to the effect of microbial carbonate reduction and may be due to low C[H.sub.4] concentrations (Table 2) resulting from storage of the cores for about six months in a vacuum container (to avoid oxidation by the air and drying), possibly with significant removal of adsorbed gases. An instrumental mass bias of carbon isotope ratio was reported in a very low concentration of hydrocarbons with respect to mass spectrometry . In this study, all the data of C[H.sub.4] concentrations were above the lower limit of determination of 0.01% (Table 2) indicating that large fluctuations of [delta][sup.13][C.sub.CH4] values (Figure 7) are not due to instrumental mass bias. The mechanism of any reaction opposing fractionation is not clear. In a low C[H.sub.4] concentration, the carbon isotope ratio may be easily disturbed by complex microbial metabolism (e.g., methane oxidation and carbonate reduction). With >10 ml BKC solution or >0.3% BKC concentration, the [delta][sup.13][C.sub.CH4] values were relatively constant at about -56 [per thousand] (Figure 7), which is in good agreement with the values for EV samples.
Although the [delta][sup.13][C.sub.CH4] values for IsoJar[TM] samples with Hg[Cl.sub.2] solution are relatively constant (Figure 7), they are consistently 5 [per thousand]-6 [per thousand] lower than those with BKC solution. Concentrations of C[O.sub.2] in the headspace of samples IJ47 and IJ48, to which 20 ml Hg[Cl.sub.2] solution was added, are considerably higher than those in the other samples (Table 2). A possible cause of the decrease in [delta][sup.13][C.sub.CH4] values may be isotopic fractionation associated with mercuric reactions with methane, which generate HCl and lead to C[O.sub.2] outgassing. Although this mechanism is not clear, considerable care should be required using Hg[Cl.sub.2] as a microbicide with respect to carbon isotope fractionation.
This study investigated the possible causes of carbon isotopic variations (in [delta][sup.3][C.sub.CH4] and [delta][sup.13][C.sub.CO2] values) in borehole drillings to 500 m depth, as reported by Funaki et al. . The results have led to improvements in the IsoJar[TM] method for the determination of carbon isotopic ratios in C[H.sub.4] and C[O.sub.2] adsorbed on bore cores. It was found that with air in the IsoJar[TM] headspace, microbes oxidize C[H.sub.4] to C[O.sub.2] during storage, accompanied by isotopic fractionation, especially for samples from depths of < 1000 m where microbes are more active. Isotopic fractionation resulted in [delta][sup.13][C.sub.CH4] and [delta][sup.13][C.sub.CO2] values reaching >30 [per thousand] and >2 [per thousand] after 80 d storage, respectively, while samples analyzed within a week of sampling showed no such effect. The significant isotopic fractionation in C[H.sub.4] was due to its low concentration in the sampling container, while the weaker fractionation in C[O.sub.2] was due to its relatively high concentration. The conventional amount of BKC additive (~0.5 ml of 10% solution) was insufficient to suppress microbial activity at least when using in situ groundwater as filling water. The large variations in isotopic compositions reported by Funaki et al.  thus appear to have been caused by microbial methane oxidation in the IsoJar[TM] containers after sampling and contamination with groundwater from different depths. Important technique improvements are summarized as follows: (1) if long-term sample storage is necessary, >10 ml of 10% BKC solution should be used or >0.3% BKC concentration is required; (2) analysis within a week of sampling is strongly recommended; and (3) for C[O.sub.2] analysis, groundwater from different depths should not be used.
The all data used to support the findings of this study are included within the article and Supplementary information file.
Conflicts of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
The authors are grateful to Hironori Funaki (JAEA) and Taiki Ishikawa (Mitsubishi Materials Techno (MMT)) for providing helpful information regarding sampling methods. Amane Waseda (JAPEX) provided valuable comments that greatly improved the manuscript. The authors would also like to thank Yusuke Kitagawa (MMT) and Eiichi Ishii (JAEA) for the help with sampling. Hiroshi Sasamoto (JAEA) and Aaron Stallard (Stallard Scientific Editing) are gratefully acknowledged for improving the manuscript.
Sampling date, analysis date, sampling depth of cores, and carbon isotope ratios of C[H.sub.4] and C[O.sub.2] of headspace gases in IsoJar[TM] samples of Funaki et al.  (Tables S1a and S1b). Sampling date, analysis date, sampling depth of cores, and chemical compositions of headspace gases in IsoJar[TM] samples and EV samples of this study (Tables S2, S3, and S4). (Supplementary Materials)
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Kazuya Miyakawa (1) and Fumiaki Okumura (2)
(1) Horonobe Underground Research Center, Japan Atomic Energy Agency, Hokushin 432-2, Horonobe-cho, Hokkaido 098-3224, Japan
(2) JAPEX Research Center, Japan Petroleum Exploration Co., Ltd., 1-2-1 Hamada, Mihama-ku, Chiba 261-0025, Japan
Correspondence should be addressed to Kazuya Miyakawa; firstname.lastname@example.org
Received 11 April 2018; Accepted 29 July 2018; Published 1 October 2018
Academic Editor: Andri Stefansson
Caption: Figure 1: Plot of [delta][sup.13][C.sub.CH4] vs. [delta][sup.13][C.sub.CO2] in coexisting gases, showing fields relating to different gas sources and isotopic shifts resulting from production and oxidation (adapted from ). The data are from Funaki et al.  and Miyakawa et al. .
Caption: Figure 2: Maps showing the location of the Horonobe URL site and the boreholes: (a) location map and (b) geological map (after ). The plate boundaries and the direction of plate movement in (a) are from Wei and Seno .
Caption: Figure 3: Layout of the Horonobe URL, locations of boreholes, and surrounding geology. Red color-labelled "borehole 350-Fz-01" indicates core sampling depths (Table S2).
Caption: Figure 4: Temporal variations in (a) [delta][sup.13][C.sub.CO2] and (b) [delta][sup.13][C.sub.CH4] after sampling. Solid arrow indicates the trend for samples with 350 m groundwater; dashed arrow indicates the trend for samples with 50 m groundwater.
Caption: Figure 5: Temporal variations in the apparent carbon isotopic fractionation factor, [alpha], between C[O.sub.2] and C[H.sub.4].
Caption: Figure 6: Plot of [delta][sup.13][C.sub.CH4] vs. [delta][sup.13][C.sub.CO2] in coexisting gases. (a) Grey areas show fields relating to different gas sources and isotopic shifts resulting from production and oxidation (adapted from ). The area indicated by the dashed rectangle is enlarged in (b). (b) Solid arrow indicates a methane oxidation trend for samples with 350 m groundwater; dashed arrow indicates the trend for samples with 50 m groundwater.
Caption: Figure 7: Plot of [delta][sup.13][C.sub.CH4] values vs. (a) amount of microbial suppressant used and (b) concentration of additives.
Table 1: Information on IsoJar[TM] samples and analytical results of headspace gases. Amount Sample of core Amount of Depth of Type of no. sample (g) water (g) groundwater additive IJ1 220 350 350 m None IJ2 369 262 350 m None IJ3 342 304 350 m None IJ4 360 269 50 m None IJ5 239 333 50 m None IJ6 411 247 50 m None IJ7 339 277 50 m None IJ8 338 279 50 m None IJ9 302 274 350 m Hg[Cl.sub.2] IJ10 263 328 350 m Hg[Cl.sub.2] IJ11 380 274 350 m Hg[Cl.sub.2] IJ12 383 241 350 m Hg[Cl.sub.2] IJ13 358 262 50 m Hg[Cl.sub.2] IJ14 225 349 50 m Hg[Cl.sub.2] IJ15 420 252 50 m Hg[Cl.sub.2] IJ16 338 284 50 m Hg[Cl.sub.2] IJ17 341 229 350 m BKC IJ18 264 281 350 m BKC IJ19 388 253 350 m BKC IJ20 333 302 350 m BKC IJ21 320 290 50 m BKC IJ22 345 256 50 m BKC IJ23 392 258 50 m BKC IJ24 368 291 50 m BKC IJ25 360 266 50 m BKC IJ26 388 242 350 m None IJ27 379 272 350 m None IJ28 333 316 350 m None Storage Sample period C[O.sub.2] [O.sub.2] [N.sub.2] no. (days) (%) (%) (%) IJ1 67 6.5 6.9 83 IJ2 41 8.9 2.8 79 IJ3 79 3.1 11.0 80 IJ4 17 0.63 14.6 80 IJ5 68 2.3 9.4 86 IJ6 42 6.7 0.01 79 IJ7 79 2.5 5.4 80 IJ8 79 0.36 18.1 79 IJ9 19 3.9 7.9 80 IJ10 67 5.0 2.4 86 IJ11 41 4.7 5.1 76 IJ12 92 1.49 14.1 80 IJ13 19 2.6 8.1 75 IJ14 68 0.52 16.8 81 IJ15 42 4.0 3.6 83 IJ16 79 0.57 14.2 80 IJ17 19 6.2 6.9 82 IJ18 67 8.9 2.2 80 IJ19 41 7.4 0.02 76 IJ20 79 5.0 4.4 79 IJ21 19 4.7 1.82 85 IJ22 68 3.7 8.2 84 IJ23 42 4.4 3.2 80 IJ24 79 2.2 4.1 80 IJ25 79 2.6 3.0 79 IJ26 5 2.3 14.2 79 IJ27 5 3.0 11.6 78 IJ28 5 2.1 12.7 80 [delta][sup.13] [delta][sup.13] [C.sub.CH4] [C.sub.CO2] Sample C[H.sub.4] ([per thousand] ([per thousand] no. (%) VPDB) VPDB) IJ1 0.030 -45.4 +13.6 IJ2 6.7 -35.5 +13.2 IJ3 2.8 -30.8 +13.2 IJ4 2.2 -49.3 +5.0 IJ5 0.014 -51.4 +2.1 IJ6 12.5 -42.5 +3.5 IJ7 9.6 -36.8 -1.0 IJ8 0.45 -22.3 -1.4 IJ9 5.8 -57.7 +15.2 IJ10 4.8 -40.7 +14.5 IJ11 12.3 -48.8 +15.7 IJ12 0.88 -26.8 +12.9 IJ13 11.9 -55.3 +6.0 IJ14 0.059 +4.7 +2.7 IJ15 7.5 -45.0 +4.7 IJ16 2.0 -38.2 +2.5 IJ17 1.89 -50.3 +14.5 IJ18 5.2 -44.6 +13.5 IJ19 15.5 -48.6 +14.3 IJ20 7.6 -46.2 +14.4 IJ21 5.5 -46.2 +3.7 IJ22 2.3 -26.7 +2.8 IJ23 10.2 -42.7 +4.3 IJ24 10.2 -41.8 +2.2 IJ25 13.4 -43.5 +3.2 IJ26 3.6 -55.4 +14.5 IJ27 6.1 -53.8 +14.8 IJ28 3.5 -55.5 +15.1 Table 2: Information on IsoJar[TM] samples and analytical results of headspace gases for Section 3.1.2. Amount of Amount Sample core of water Type of Amount of no. sample (g) (g) additive additive (ml) IJ29 311 310 None 0 IJ30 299 282 None 0 IJ31 284 324 BKC 1 IJ32 323 297 BKC 1 IJ33 332 312 BKC 3 IJ34 352 279 BKC 3 IJ35 368 290 BKC 6 IJ36 382 278 BKC 6 IJ37 309 299 BKC 10 IJ38 310 280 BKC 10 IJ39 340 285 BKC 20 IJ40 336 309 BKC 20 IJ41 272 319 Hg[Cl.sub.2] 1 IJ42 323 296 Hg[Cl.sub.2] 1 IJ43 348 284 Hg[Cl.sub.2] 5 IJ44 319 314 Hg[Cl.sub.2] 5 IJ45 293 322 Hg[Cl.sub.2] 10 IJ46 362 293 Hg[Cl.sub.2] 10 IJ47 285 308 Hg[Cl.sub.2] 20 IJ48 362 295 Hg[Cl.sub.2] 20 Concentration Storage Sample of additives period no. (wt%) (days) C[O.sub.2] (%) IJ29 0 27 12.8 IJ30 0 27 13.7 IJ31 0.03 27 12.5 IJ32 0.03 27 12.4 IJ33 0.10 27 11.6 IJ34 0.11 28 13.1 IJ35 0.20 28 10.2 IJ36 0.21 28 10.2 IJ37 0.32 28 12.8 IJ38 0.34 28 12.8 IJ39 0.66 29 10.9 IJ40 0.61 29 9.0 IJ41 0.02 29 8.7 IJ42 0.02 29 10.2 IJ43 0.13 29 10.8 IJ44 0.12 29 11.0 IJ45 0.22 30 12.7 IJ46 0.24 30 13.3 IJ47 0.45 30 21 IJ48 0.47 30 23 Sample C[H.sub.4] no. [O.sub.2] (%) [N.sub.2] (%) (%) IJ29 1.0 86 0.039 IJ30 1.0 85 0.029 IJ31 1.0 86 0.036 IJ32 1.0 87 0.040 IJ33 4.2 84 0.053 IJ34 2.0 85 0.046 IJ35 4.1 86 0.067 IJ36 2.9 87 0.067 IJ37 7.3 80 0.054 IJ38 6.6 80 0.052 IJ39 6.2 83 0.068 IJ40 3.7 87 0.105 IJ41 10.9 80 0.042 IJ42 9.9 80 0.041 IJ43 9.2 80 0.037 IJ44 9.0 80 0.044 IJ45 8.4 79 0.043 IJ46 6.9 80 0.046 IJ47 7.0 72 0.033 IJ48 6.0 71 0.045 [delta][sup.13] [delta][sup.13] [C.sub.CH4] [C.sub.CO2] Sample ([per thousand] ([per thousand] no. VPDB) VPDB) IJ29 -48.3 +14.2 IJ30 -74.6 +15.2 IJ31 -74.2 +14.0 IJ32 -84.1 +13.8 IJ33 -88.5 +13.9 IJ34 -75.7 +13.0 IJ35 -58.1 +12.9 IJ36 -90.4 +12.5 IJ37 -56.2 +14.8 IJ38 -57.9 +14.6 IJ39 -54.5 +13.6 IJ40 -57.9 +13.4 IJ41 -59.0 +15.0 IJ42 -63.1 +14.9 IJ43 -65.4 +15.0 IJ44 -60.1 +14.8 IJ45 -62.6 +15.2 IJ46 -61.9 +15.3 IJ47 -62.2 +16.6 IJ48 -62.1 +16.1 Table 3: [delta][sup.13][C.sub.CH4], [delta][sup.13][C.sub.CO2], methane, and TIC contents in EV samples. Sampling depth [delta][sup.13] Storage of groundwater [C.sub.CH4] Sample period (ground ([per thousand] no. (days) level - m) VPDB) EV1 6 248.5 -56.7 EV2 55 248.5 -54.0 EV3 98 248.5 -53.7 EV4 6 248.5 -56.8 EV5 55 248.5 -54.5 EV6 98 248.5 -52.7 [delta][sup.13] Concentration [C.sub.CO2] of dissolved Sample ([per thousand] C[H.sub.4] no. VPDB) (mmol [kg.sup.-1]) EV1 + 17.1 -- EV2 +17.8 7.8 EV3 +17.3 8.5 EV4 +16.9 8.7 EV5 +16.2 6.7 EV6 +16.7 6.7 Concentration of total inorganic Sample carbon (TIC) no. (mmol [kg.sup.-1]) EV1 -- EV2 -- EV3 -- EV4 42 EV5 37 EV6 35
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|Title Annotation:||Research Article|
|Author:||Miyakawa, Kazuya; Okumura, Fumiaki|
|Date:||Jan 1, 2018|
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