In the summer of 1978, I was invited to give a talk on methanogenesis at the
Gordon Research Conference on Organic Geochemistry which was very well
received. Especially so, since most of the scientists came from a chemical analytical
background, viewing petroleum, kerogen, coal, and hydrocarbon gases as static
things to be collected, structures within identified and origins inferred. Treating
sediments as live, dynamic experimental systems was at the time a novel concept to
these folks. The positive feedback I received had a salutary effect upon me: It
convinced me of the merits of continuing this research. Another invitation to make
a methane biogeochemistry presentation to an International Symposia for Environmental Biogeochemistry further reinforced the positive feedback. Yet I also somehow had to make the entrenched hierarchy grasp the merits of studying anaerobiosis
in regions where such things were not visually evident, such as pristine freshwater
streams. Our discovery of active denitrification in stream periphyton communities
got the ball rolling in this dimension (Triska and Oremland 1981; Duff et al. 1984)
and helped me politically. Our use of dissolved gases (CH 4 and N 2 O) to follow the
propagation and rapid dissipation of a large municipal sewage spill in South San
Francisco Bay reinforced the utility of understanding these processes (Cloern and
Oremland 1983). By this time I had gained a good degree of scientific independence,
and the “entrenched” folks who first doubted me just wanted more in the form of
peer-reviewed research papers, which I was delighted to provide.
30.5 Ethane and Propane and Butane (Oh My)!
One take-away bit of information I acquired from interacting with organic geochemists was their method for classification of natural gases. Much of this was
empirical, inspired by the search for petroleum reserves. The thinking was that
accumulations of biogenic gases consisted almost entirely of methane, with perhaps
only traces of the higher alkanes (ethane and propane) evident. Hence, a ratio of
methane to ethane plus propane of greater than 100 (and usually much greater, say
1000 or higher) indicated a gas of biogenic origin. In contrast, when the ratio was
less than 100 (and usually significantly less, where ethane and propane rise to
percentage levels), it was indicative of a gas of thermogenic origin, which was
often co-associated with petroleum deposits (Bernard et al. 1978; Hunt 1979). Yet
the experimental literature was sparse in this regard to say the least (e.g., Davis and
Squires 1954) and little was known about biogenic mechanisms for higher gaseous
alkane formation.
My USGS colleagues Tim Vogel and Keith Kvenvolden, both marine organic
geochemists, collaborated with me by modifying their sediment hydrocarbon extraction methodology. They routinely employed 1-gallon metal paint cans into which
they placed their recovered, near-surface sediments and partitioned the associated
gases into a small, sealed headspace after the can underwent prolonged violent
shaking on a paint mixer. We modified this by placing anoxic, San Francisco Bay
mud into the cans in order to form a time course of gas production. By using so much
30 BUBBLES in the MUD: A Reminiscence and Perspective
641
Gordon Research Conference on Organic Geochemistry which was very well
received. Especially so, since most of the scientists came from a chemical analytical
background, viewing petroleum, kerogen, coal, and hydrocarbon gases as static
things to be collected, structures within identified and origins inferred. Treating
sediments as live, dynamic experimental systems was at the time a novel concept to
these folks. The positive feedback I received had a salutary effect upon me: It
convinced me of the merits of continuing this research. Another invitation to make
a methane biogeochemistry presentation to an International Symposia for Environmental Biogeochemistry further reinforced the positive feedback. Yet I also somehow had to make the entrenched hierarchy grasp the merits of studying anaerobiosis
in regions where such things were not visually evident, such as pristine freshwater
streams. Our discovery of active denitrification in stream periphyton communities
got the ball rolling in this dimension (Triska and Oremland 1981; Duff et al. 1984)
and helped me politically. Our use of dissolved gases (CH 4 and N 2 O) to follow the
propagation and rapid dissipation of a large municipal sewage spill in South San
Francisco Bay reinforced the utility of understanding these processes (Cloern and
Oremland 1983). By this time I had gained a good degree of scientific independence,
and the “entrenched” folks who first doubted me just wanted more in the form of
peer-reviewed research papers, which I was delighted to provide.
30.5 Ethane and Propane and Butane (Oh My)!
One take-away bit of information I acquired from interacting with organic geochemists was their method for classification of natural gases. Much of this was
empirical, inspired by the search for petroleum reserves. The thinking was that
accumulations of biogenic gases consisted almost entirely of methane, with perhaps
only traces of the higher alkanes (ethane and propane) evident. Hence, a ratio of
methane to ethane plus propane of greater than 100 (and usually much greater, say
1000 or higher) indicated a gas of biogenic origin. In contrast, when the ratio was
less than 100 (and usually significantly less, where ethane and propane rise to
percentage levels), it was indicative of a gas of thermogenic origin, which was
often co-associated with petroleum deposits (Bernard et al. 1978; Hunt 1979). Yet
the experimental literature was sparse in this regard to say the least (e.g., Davis and
Squires 1954) and little was known about biogenic mechanisms for higher gaseous
alkane formation.
My USGS colleagues Tim Vogel and Keith Kvenvolden, both marine organic
geochemists, collaborated with me by modifying their sediment hydrocarbon extraction methodology. They routinely employed 1-gallon metal paint cans into which
they placed their recovered, near-surface sediments and partitioned the associated
gases into a small, sealed headspace after the can underwent prolonged violent
shaking on a paint mixer. We modified this by placing anoxic, San Francisco Bay
mud into the cans in order to form a time course of gas production. By using so much
30 BUBBLES in the MUD: A Reminiscence and Perspective
641