Abiotic Controls on H₂ Production from Basalt−Water Reactions and Implications for Aquifer Biogeochemistry

Abstract

Abiotic production of H 2 from basalt reactions in aqueous solutions is hypothesized to support microbial ecosystems in deep subsurface aquifers, such as those found in the Columbia River Basalt group (CRB). We investigated factors controlling this phenomenon, including rock composition, pH, temperature, sterilization method, reducing agents, and product removal. Ferrous silicate minerals were found to be the basalt components responsible for H 2 production from anaerobic water-rock interactions. H 2 evolution was faster at pH < 7 but occurred from pH 5 to pH 11, which covers the pH range (7-10) measured in CRB groundwaters. The onset of H 2 evolution coincided with the appearance of dissolved Fe 2+ , and an apparent alkaline inhibition could be alleviated by the addition of excess FeCl 2 . This may reflect, in part, the low redox conditions needed for H 2 evolution and suggests that H 2 may be controlled by reaction rates of ferrous silicate minerals. Rates were higher at 60°C than at 30°C, suggesting that the geothermal gradient may lead to increased H 2 production at depth. The results were consistent with the hypothesis that basalt-redox reactions support primary production by microorganisms in some terrestrial subsurface environments.

Temperatures of aqueous alteration and evidence for methane generation on the parent bodies of the CM chondrites

“…We selected a model temperature of 28˚C because it is a reasonable approximation of the temperatures of carbonate growth for most of our samples (though silicate hydration need not occur at the same temperatures as carbonate precipitation) and it is similar to temperatures of aqueous alteration assumed by previous models of this kind (e.g., Clayton and Mayeda, 1999). While we are aware of no definitive reports of serpentinization occurring at 28˚C in terrestrial rocks, both lab experiments and field observations have been used to suggest that serpentinization (and, important for our further discussion of this model in section 3.2 of this paper, concurrent H 2 generation) occurs at earth-surface temperatures (Neal and Stanger, 1983;Stevens and McKinley, 1995;Stevens and McKinley, 2000). The lowest measured temperature of a serpentinization reaction is 45˚C, in the Lost City hydrothermal field, determined using a hydrogen isotope geothermometer (Proskurowski et al, 2006).…”

[FeFe]-hydrogenase in Yellowstone National Park: evidence for dispersal limitation and phylogenetic niche conservatism

“…H 2 in these systems is likely of abiotic origin, derived from subsurface basalt-catalyzed water hydrolysis (Spear et al, 2005) and could further support the notion of an H 2 driven 'deep hot biosphere' (Gold, 1992). Basalt-catalyzed H 2 production is sensitive to both solution pH and reaction temperature, with a near doubling of H 2 production rates with a doubling of incubation temperature (Stevens and McKinley, 2000). Similarly, the rate of basalt-catalyzed H 2 production increases with increasing water acidity (lower pH) (Stevens and McKinley, 2000).…”

“…Basalt-catalyzed H 2 production is sensitive to both solution pH and reaction temperature, with a near doubling of H 2 production rates with a doubling of incubation temperature (Stevens and McKinley, 2000). Similarly, the rate of basalt-catalyzed H 2 production increases with increasing water acidity (lower pH) (Stevens and McKinley, 2000). Coincidentally, hydA was not detected in YNP springs predicted to have elevated geological H 2 production (for example, acidic pH, 436 1C; alkaline pH, 465 1C), an observation that might reflect the unfavorable thermodynamics of bacterial organic carbon fermentation in the presence of high H 2 partial pressure (Schink, 1997).…”

“…Geologically, the production of H 2 occurs through the hydrolysis of reduced meteoric water when in contact with iron-bearing basalts (Apps and van de Kamp, 1993), through the reduction of water during serpentinization reactions in the presence of ultramafic minerals such as olivine (Oze and Sharma, 2007), and through the radiolysis of water (Lin et al, 2005). Basalt-catalyzed H 2 production occurs readily in the presence of reduced acidic fluids (Stevens and McKinley, 2000), whereas H 2 production from serpentinization reactions is more prevalent at alkaline pH (Oze and Sharma, 2005;Cardace and Hoehler, 2009). Thus, geological H 2 production through serpentinization can be expected to predominate in alkaline environments rich in ultramafic minerals, whereas geological H 2 production by hydrolysis can be expected to be predominant in acidic and basalt-rich environments.…”

Hydrogen and bioenergetics in the Yellowstone geothermal ecosystem

“…Hydrogen in Yellowstone geothermal waters is likely geochemical in origin. Sources of geochemical H 2 are not well understood in general (45), but in the Yellowstone environment they probably derive from subsurface interaction of water with Fe[II] (46)(47)(48)(49)(50)(51). Life in the subsurface probably is limited more by the availability of oxidant than of fuels such as H 2 (52).…”