A low‐cost automated trap to measure bubbling gas fluxes

Varadharajan, Charuleka; Hermosillo, Richard; Hemond, Harold F.

doi:10.4319/lom.2010.8.363

Cited by 36 publications

(63 citation statements)

References 31 publications

(38 reference statements)

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“…The fill height describes the water level within the gas capturing cylinder and was inferred by measuring the differential pressure between the inside and outside of the cylinder as described in Varadharajan et al (2010). Temperature measurements were performed using an RBR TR-1060 sensor with an accuracy of ± 0.008 • C attached to the ABTs.…”

Section: Measurement Of Ebullition Ratesmentioning

confidence: 99%

Pumping methane out of aquatic sediments – ebullition forcing mechanisms in an impounded river

2014

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Abstract. Freshwater systems contribute significantly to the global atmospheric methane budget. A large fraction of the methane emitted from freshwaters is transported via ebullition. However, due to its strong variability in space and time, accurate measurements of ebullition rates are difficult; hence, the uncertainty regarding its contribution to global budgets is large. Here, we analyze measurements made by continuously recording automated bubble traps in an impounded river in central Europe and investigate the mechanisms affecting the temporal dynamics of bubble release from cohesive sediments. Our results show that the main triggers of bubble release were pressure changes, originating from the passage of ship lock-induced surges and ship passages. The response to physical forcing was also affected by previous outgassing. Ebullition rates varied strongly over all relevant timescales from minutes to days; therefore, representative ebullition estimates could only be inferred with continuous sampling over long periods. Since ebullition was found to be episodic, short-term measurement periods of a few hours or days will likely underestimate ebullition rates. Our results thus indicate that flux estimates could be grossly underestimated (by up to~50%) if the correct temporal resolution is not used during data collection.

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Section: Measurement Of Ebullition Ratesmentioning

confidence: 99%

Pumping methane out of aquatic sediments – ebullition forcing mechanisms in an impounded river

2014

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“…However, theoretical analysis shows that spherical bubbles of realistic size would be mobilized in sediments with reasonable shear strength only under unrealistically large vertical stress variations on the order 10 m of water head [Wheeler, 1990]. The ebullition record from UML [Varadharajan et al, 2010], however, shows gas venting in response to head drops of less than 0.5 m (5 kPa, Figure 102b), which implies that some other mechanism must mobilize bubbles for vertical transport.…”

Section: Model Formulationmentioning

confidence: 98%

“…We constrain and test the model against a record of variations in hydrostatic load and methane ebullition from fine-grained sediments in Upper Mystic Lake (UML), a dimictic kettle lake outside Boston, Massachusetts [Varadharajan et al, 2010] (Figure 102a). Our model is motivated by two key observations: ebullition is triggered by variations in hydrostatic load [Martens and Klump, 1980;Mattson and Likens, 1990;Fechner-Levy and Hemond, 1996;Leifer and Boles, 2005;Varadharajan et al, 2010], and gas migration in fine sediments is controlled by the opening of fractures or conduits [Boudreau et al, 2005;Jain and Juanes, 2009;Algar and Boudreau, 2010;Holtzman and Juanes, 2010]. The high degree of synchronicity in ebullative fluxes among distant venting sites located at different depths (Figure 102) suggests that the release mechanism is governed by the effective stress, which is the average stress between solid grains [Terzaghi, 1943].…”

Section: A Conduit Dilation Model Of Methane Venting From Lake Sedimementioning

confidence: 99%

Mechanisms Leading to Co-Existence of Gas Hydrate in Ocean Sediments [Part 2 of 2]

Bryant¹,

Juanes²

2011

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The experimental boundary conditions do not replicate the situation in gas reservoirs converted to hydrate in the Arctic. The key differences are that in the experiment water can move 117 to the hydrate stability zone only from below, while in nature water can move from below and from above. In experiment gas can move to the hydrate stability zone from below and from above, while in nature it can move only from below. Finally, the fluid phase pressures decrease with time in the experiment (though the conditions remain within the hydrate stability field throughout), while the water phase pressure does not change with time in nature. These differences are minor and do not alter the essential similarities to the natural situation. In the experiment and in nature, the base of the gas hydrate stability zone descends gradually through an existing gas accumulation, and fluid phases are free to move in response to any gradients that arise as hydrate forms. The latter point is important: no fluid flow (neither pressure-driven nor capillarity-driven) is imposed in the experiment. Instead the system evolves a combination of buoyancy-, pressure-and capillarity-driven fluxes of the gas and water phases, and these fluxes balance the various resistances to transport.The model predicts that the contribution of capillarity-driven flux is significant in these experiments. In fact R v~0 .69 when capillary-dominated flow is taken into account while R v~1 when only the viscous dominated portion of the flow was considered. This is consistent with our findings in previous sections of this report, namely, pressure-driven flow cannot supply water from below the BGHSZ fast enough to sustain hydrate formation. Moreover the model predicts that the amount of gas flows to the GHSZ from above quickly diminishes as both the effective permeability, due to hydrate formation within the GHSZ, and gaseous phase relative permeability, due to decrease in gas saturation within the GHSZ, decrease. Therefore, the main contribution for gas flow would be flow from the middle gas inlet. While the gas flux from above and from below could not be independently measured in this experiment, the consistency of the model with other observations suggests that all the fluids needed during conversion to hydrate can be supplied from below. But this is possible only if capillarity-driven flux is accounted for.The consistency of the capillarity-driven flux model with the experimental observations suggests that the finding in the previous section, viz. that the observed hydrate saturation profile in Mt. Elbert arises naturally from the capillarity-driven fluxes, is not a coincidence. That is, these findings suggest that the gas reservoir conversion process is slow, that it introduces modest, even negligible pressure gradients but impose significant gradients in saturation which, along with gas buoyancy, feed the appropriate volumes of fluids to the GHSZ.A complete validation of the model would compare the predicted hydrate saturation profile to the observed profile in F...

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Section: (2009)mentioning

confidence: 99%

“…Ebullition of methane from this lake has been previously documented (Scandella et al, 2011;Varadharajan and Hemond, 2012). We collected gas bubbles using inverted funnel-shaped bubble traps [modified from an inverted-funnel design described previously (Varadharajan et al, 2010;Varadharajan and Hemond, 2012)] deployed~2 m above the lake floor (~18 m water depth) using a custom rope and buoy structure.2 The deep deployment depth was chosen to minimize dissolution and/or oxidation of bubbles during their transit from the sediment to the lake surface. The collected gases were transferred via syringes to serum vials (either pre-evacuated or pre-filled with deionized water that was displaced to make room for the gas sample) sealed with blue butyl septa, fixed with either saturated NaCl solution or 1 M NaOH, and stored at either 4°C or room temperature until analysis.…”

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confidence: 99%

The geochemistry of methane isotopologues

Wang¹

2017

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This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of 12 CH 4 , 13 CH 4 , 12 CH 3 D, and 13 CH 3 D record the formation, transport, and breakdown of methane in selected settings.Chapter 2 reports precise determinations of 13 CH 3 D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of 13 CH 3 D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped-and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H 2 and the reversibility of microbially-mediated methanogenesis in the environment. Determination of 13 CH 3 D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow-and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300• C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O 2 by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of 13 C/ 12 C and D/H isotope fractionation factors alone.: Shuhei Ono, Ph.D. Acknowledgments I fear that this section will not do justice to the people I have not the space to thank individually. Alas, here goes. To those whose names are not specifically listed here, thank you too. I wish first to thank Shuhei Ono. The work this thesis represents could not have happened without his bold vision and the license to explore and question that working in his lab afforded. His unbridled optimism, breadth of scientific curiosity, personal integrity, and accessibility to his personnel are traits I one day hope to emulate. I thank him for his nonjudgmental yet appropriately measured support of many of my ideas-even those that led nowhere-, for believing in me even when I found it difficult to do so myself, and for teaching me to change pump oil, build vacuum lines, and drink Icelandic vodka.I also wish to thank my thesis committee members Jeff Seewald, Roger Summons, and John Pohlman, for their in...

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A low‐cost automated trap to measure bubbling gas fluxes

Cited by 36 publications

References 31 publications

Pumping methane out of aquatic sediments – ebullition forcing mechanisms in an impounded river

Pumping methane out of aquatic sediments – ebullition forcing mechanisms in an impounded river

Mechanisms Leading to Co-Existence of Gas Hydrate in Ocean Sediments [Part 2 of 2]

The geochemistry of methane isotopologues

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