Silicate Dissolution in Las Pailas Thermal Field: Implications for Microbial Weathering in Acidic Volcanic Hydrothermal Spring Systems

Abstract

A longitudinal field microcosm study was conducted in the Las Pailas hot spring system, located on the SW flank of Rincon de la Vieja, Costa Rica, in order to investigate initial microbial attachment and colonization, as well as chemical (abiotic) and biological silicate weathering under hydrothermal conditions. Solution chemistry was pH = 2.42-3.96, T = 43-89.3 • C, Si = 4.45-8.19 mmol L −1 , Fe = 1.50-6.95 mmol L −1 and PO 3− 4 = below detection limits-4.9 μmol L −1 . Microcosms consisted of washed, sonicated primary silicate samples in polycarbonate vessels. The vessels were enclosed either by mesh to observe water/rock/microbial interactions or by 0.2-0.45 μm filters to observe water/rock interactions. Microcosms were incubated for periods of 6 h, 24 h, or 2 mo, fixed in the field, then analyzed in the laboratory. Scanning electron microscopy (SEM) analysis revealed that microbial attachment to mineral samples occurred in as little as 6 h. Microbial colonization and the development of minor etch pits associated with microorganisms occurred within 24 h. The most significant differences in chemical vs. biological weathering were observed after 2 mo. SEM analysis of these incubated surfaces showed that volumetric losses to mineral samples were more than one order of magnitude greater for samples that had been colonized by microorganisms and thus weathered biologically. With time, preferential colonization of anorthoclase mineral samples with Fe-oxides and apatite inclusions occurred. Subsequent weathering, therefore, may be a metabolic strategy by microorganisms to access mineral-bound PO 3− 4 , which is otherwise scarce in solution. Results from this study suggest that microorganisms may play a significant role in weathering in some hydrothermal systems.

The Dissolution Anisotropy of Pyroxenes: Experimental Validation of a Stochastic Dissolution Model Based on Enstatite Dissolution

“…The (100) and (010) faces exhibited similar lenticular pits elongated following the c-axis (the major axis is more than 6 times larger than the minor axis). The shape of the pits projected to the horizontal surface shows a central symmetry, consistent with the shape previously described in the literature for pyroxenes in general 18,60,[63][64][65] . Two types of pits are visible on the (210) face: while the former is similar to the ones observed on the (100) and ( 010) faces (with a small minor axis compare to the major axis), the latter, also elongated following the c-axis, presents a wider minor axis (3 times smaller than the major axis).…”

The Mineralosphere Concept: Mineralogical Control of the Distribution and Function of Mineral-associated Bacterial Communities

“…The authors explained this result by a preferential colonization of mineral surfaces acting as electron donors or acceptors (pyrite, hematite, magnetite). Similarly, Phillips-Lander et al [53] showed that bacteria preferentially colonized minerals with higher Fe and P content.…”

“…Furthermore, the importance of the mineral geochemistry was evidenced in extreme aquatic environments such as in a hot thermal system [53] and subglacial environments [50]. Incubating small crystals of pyrite, hematite, magnetite, olivine, calcite and quartz in the glacial meltwater stream at Robertson Glacier (Canada), Mitchell et al [43] showed that the bacterial communities were quantitatively (higher biomass) and qualitatively (structure and composition) affected by the mineral geochemistry, especially the Fe content.…”

“…Quantitatively, several studies performed in aquatic environments using pure minerals and/or rocks, reported a higher colonization of poorly weatherable minerals such as quartz and K/Na-feldspar [17,53]. Notably, Mitchell et al [50] reported a greater colonization of poorly weatherable minerals such as hematite and magnetite, and conversely a comparatively reduced colonization of highly weatherable minerals such as calcite and pyrite.…”

Effect of carbonic anhydrase on silicate weathering and carbonate formation at present day CO2 concentrations compared to primordial values

“…Physical 2 3 and chemical 4 weathering processes are the main forces driving silicate weathering. In recent decades, the fact that living creatures, especially microorganisms, are involved in mineral weathering has been recognized by a growing number of researchers 5 6 7 . Microbial weathering results from a combination of many factors 8 including: bio-mechanical action, the secretion of organic acids, chelation effects, redox reactions, and others.…”