Experimental studies on New Zealand hot spring sinters: rates of growth and textural development

Abstract

To study the rate of growth of sinters in New Zealand hot springs, field experiments were conducted in seven geothermal areas. At Wairakei, fan-shaped subaqueous deposits of amorphous silica grow rapidly (350 kg a–1 m–2 of drain wall) and are composed of silicified filaments with subordinate bacillus and spirillium-shaped organisms. Characterization of bacteria revealed isolates sharing > 97% 16S rRNA gene sequence homologies affiliated with Thermus, Meiothermus,Bacillus, Tepidomonas, Thermomonas, Porphyrobacter, Thermonema, and, Hydrogenophilus spp., as well as previously uncultured bacteria. At Rotokawa, microstromatolites have a slow growth rate (0.004 mm day–1) that is attributed to low pH, capillary rise, and evaporation. At Champagne Pool, sinter growth (0.023 mm day–1) is dominated by wave action building alternating microbe-rich and microbe-poor layers. Silica sinter was not observed at Waikite, where slides developed a layer of calcite (0.026 mm day–1). Sinter growth at Ngatamariki (0.016 mm day–1) forms by capillary rise, evaporation, and diffusion and at Tokaanu, subaqueous growth is slow (0.002 mm day–1) and contains silicified microbes. Textures at Orakei Korako indicate similar mechanisms to Ngatamariki, except that growth is more rapid (0.023 mm day–1) due to a splash contribution. Silica and calcite saturation indices adequately explain the growth of the sinters and calcite, indicating that microbes are not inducing precipitation where it should not occur. The rate of precipitation is correlated with silica supersaturation, but pH effects can alter this relationship. The degree of preservation of microbial material is explained by the effect of Ostwald ripening on silica spherules. Subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid, Ostwald ripening is inactive, and better preservation can be expected.

Experimental Simulation of Evaporation-Driven Silica Sinter Formation and Microbial Silicification in Hot Spring Systems

“…Water evaporation is, along with cooling, one of the main abiotic drivers of precipitation and consequently of sinter formation (Walter, 1972(Walter, , 1976a(Walter, , 1976bJones et al, 1998;Braunstein and Lowe, 2001;Mountain et al, 2003;Handley et al, 2005;Schinteie et al, 2007;Tobler et al, 2008). Indeed, in situ studies in which sinter growth on glass slides has been examined (Mountain et al, 2003;Handley et al, 2005Handley et al, , 2008Schinteie et al, 2007;Tobler et al, 2008) have shown that sinter growth occurs mainly above the air-water interface as the result of evaporation of silica-rich water supplied by waves, splashes, or capillary action. Evaporation may also occur rapidly wherever the water level is low and in zones irregularly covered by water, such as around geysers or in irregular or terraced hot spring outflows (Walter, 1972(Walter, , 1976aJones et al, 1998).…”

“…By acting as a reactive substratum for passive and heterogeneous silica nucleation, these microorganisms become very rapidly fossilized and eventually encased in the newly formed sinter (Schultze-Lam et al, 1995;Cady and Farmer, 1996;Renaut et al, 1996;Jones et al, 1997Jones et al, , 1998Jones et al, , 2000Jones et al, , 2001Jones et al, , 2003Jones et al, , 2004Jones et al, , 2008Konhauser et al, 2001;Mountain et al, 2003;Kyle et al, 2007;Tobler et al, 2008). The structure of the microbial communities, as well as their daily or seasonal growth variations, thus also contribute to the development of the fabrics and structure of their entombing sinters (Walter et al, 1976;Hinman and Lindstrom, 1996;Konhauser et al, 2001Konhauser et al, , 2004Jones et al, 2005;Berelson et al, 2011).…”

Metagenomics of microbial and viral life in terrestrial geothermal environments

“…Within this area, the Waiotapu region is characterized by a large number of springs exhibiting elevated arsenic concentrations (Mountain et al 2003). With its 65-meter diameter, the Champagne Pool (CP) represents the largest geothermal feature of Waiotapu with arsenic concentrations ranging from 2.9 to 4.2 mg/L (Hedenquist and Henley 1985).…”

Venenivibrio stagnispumantis gen. nov., sp. nov., a thermophilic hydrogen-oxidizing bacterium isolated from Champagne Pool, Waiotapu, New Zealand

“…Champagne Pool discharges siliceous geothermal fluid rich in arsenic and antimony at approximately 75 u C (Jones et al, 2001). Although a few studies have described microbial activity in Champagne Pool in recent years (Ellis et al, 2005;Jones et al, 2001;Mountain et al, 2003;Phoenix et al, 2005), the successful isolation of a micro-organism has not yet been reported. Previous investigations applying cultureindependent approaches, such as denaturing gradient gel electrophoresis analysis and construction of clone libraries based on the bacterial 16S rRNA gene, have indicated that isolate CP.B2 T , a member of the order Aquificales, is one of the few dominant micro-organisms present in Champagne Pool (Hetzer et al, 2007).…”