Microbial Cycling of Nitrogen and Carbon in AN Arctic Travertine Spring (jotun Spring, Svalbard Archipelago)

Jotun geothermal spring from Spitsbergen Island (79°27'N, 13°17'E) is dominated by travertine gravel, which has formed a terrace around the spring's source area and down the slope/stream. This spring and associated terraces are dominated by microbial biomass, probably because the shifting environment of the spring offers little opportunity for higher organisms to thrive. We studied two transects to illustrate two different environmental gradients: (1) from the spring source to the end of the stream, which has a continuous source of nutrients, is fully aquatic, and rich in microbial mass; (2) along the gravely travertine plateau, from the spring source to the plateau edge with limited nutrient access, primarily travertine gravel with no visible microbial biomass at the surface. A combination of environmental physicochemical conditions, stable isotopes, and molecular biology were used to determine the characteristics of environmental gradients and communities and to decipher nodes of nitrogen and carbon cycles. Gasses collected from source water were mainly CO2 (30%) and N2 (70%) [see 1]. The NH4 and NO3 concentrations, measured in multiple years between 2004 and 2011 years, showed that along the stream transect the concentrations of NH4 decreased gradually, while those of NO3 increased (i.e. NH4 22.25 to 8.2 μM; NO3 0 to 3.56 μM). The δ15N values of biomass from the stream ranged from -3 to +6‰. Both patterns indicate three possible microbial processes: nitrogen fixation, ammonia incorporation, and nitrification. The NH4 - NO3 pattern measured at the travertine plateau transect showed a high predominance and increase of NO3 over NH4 concentrations (NH4 0.35 to 1.9 μg/gm; NO3 30±5 μg/gm) suggesting that nitrification is significant process in this setting. δ15N of the terrace transect were less variable but generally positive values, which could be related to microbial assimilation and nitrification. Total N content of sediments in the stream transect averaged 1.20 wt.%, whereas the gravel transect had 0.08 wt.% indicates that in the stream samples were enriched in biomass. The δ13C value of total carbon travertine carbonates varied from -1 to 2.5‰, whereas the δ13C of organic carbon ranged from -26.5 to -28‰. In contrast, biofilm δ13C measured within the stream was more negative: -30 to -31.5‰,, utilizing the high concentrations of dissolved CO2 [1]. Nitrogen fixation genes were detected in all of the samples, supported by many of the δ15N measurements in the stream. A variety of ammonium oxidation genes (β-, γ-proteobacteria, archaea) were detected in all of the samples, which supports the nitrification hypothesis suggested by nitrogen analyses. Denitrification genes were detected in all of the settings, showing that microbial organisms from the analyzed habitats do have abilities to complete the nitrogen metabolic circuit. Further work on reverse transcriptase will reveal the metabolic pathways that were active and in what measure genetic analyses reflect the biogeochemical data. [1] Jamtveit B. et al. 2006. Norwegian Journal of Geology 86, 387