Biogeochemistry of Stinking Springs, UT Part I: Inorganic carbon dynamics and constraints on nutrient fluxes in a warm, salty, sulfidic spring

METZGER, JOHN GARRECHT; MONTEVERDE, DANIELLE; KELLY, HILARY; BOURNOD, CONSTANZA N.; WANG, DAVID T.; FRANTZ, CARIE; OSBURN, MAGDALENE; BERELSON, WILLIAM; SESSIONS, ALEX L.; HANSELMANN, KURT; JOHNSON, HOPE; STAMPS, BLAKE W.; VUONO, DAVID; SHAPIRO, RUSSELL S.; SPEAR, JOHN R.

San Francisco

Conferencia; AGU Fall Meeting 2013; 2013

American Geophysical Union

Saline microbial mats are among the most phylogenetically and metabolically diverse ecosystems found on Earth; however, we lack a detailed understanding of the controls on genetic and metabolic diversity. Culturing and maintaining mats in lab experiments is difficult making field observations a primary method to study these systems. Modeling of nutrient fluxes within and through mats requires assumptions about the local hydrology that are often difficult to justify. Here, we discuss downstream changes in geochemistry at Stinking Springs, Utah to constrain hydrologic inputs and outputs to a mat system. Stinking Springs, is a warm (40°C), salty (30 ppt), sulfidic (0.5 mM) and bicarbonate-rich (7.8 mM) spring that hosts several morphologically distinct microbial growth structures including layered mats in areas of laminar sheet flow and streamers and floating mats in the faster moving portion of the stream channel. Over a ~80m downstream transect, dissolved inorganic carbon [DIC] decreases from 7.8mM to 4.5mM. This large drop in [DIC] can be explained by the rapid outgassing of CO2 to the atmosphere. Predicted downstream trends in [DIC] and δ13CDIC using a Rayleigh distillation model closely match those of the observed trends. The Rayleigh model assumes no carbon inputs to the stream and only one output mechanism (here, degassing). The best-fit fractionation factor of CO2 degassing from HCO3- was 0.9937.The fit of the [DIC] and δ13CDIC data to a purely physical model was unexpected given the microbial abundance and apparent growth occurring throughout the Stinking Springs system. These results suggest that DIC cycling by the mats leaves only a very small imprint on the overall spring-water DIC signature?a result that indicates life?s biosignatures may be hidden by overwhelming physical processes. The Rayleigh model?s close agreement with in situ measurements implies that the sole source of hydrologic inputs and therefore dissolved nutrient sources to Stinking Springs is the stream that feeds it. Therefore, nutrient fluxes to the mats can be quantified by measurement of water flow rate and nutrient concentration upstream and downstream of the mats. This constraint on dissolved nutrient source allows a great simplification of biogeochemical modeling within the mat system. This constraint can be added to future models of biogeochemical cycling within the mat layers to help elucidate the relationship between taxonomy, metabolism, and geochemistry.