Sulfate reduction controlled by organic matter availability in deep sediment cores from the saline, alkaline Lake Van (Eastern Anatolia, Turkey)

Abstract

As part of the International Continental Drilling Program deep lake drilling project PaleoVan, we investigated sulfate reduction (SR) in deep sediment cores of the saline, alkaline (salinity 21.4‰, alkalinity 155 m mEq-1, pH 9.81) Lake Van, Turkey. The cores were retrieved in the Northern Basin (NB) and at Ahlat Ridge (AR) and reached a maximum depth of 220 m. Additionally, 65–75 cm long gravity cores were taken at both sites. SR rates (SRR) were low (≤22 nmol cm-3 day-1) compared to lakes with higher salinity and alkalinity, indicating that salinity and alkalinity are not limiting SR in Lake Van. Both sites differ significantly in rates and depth distribution of SR. In NB, SRR are up to 10 times higher than at AR. SR could be detected down to 19 mblf (meters below lake floor) at NB and down to 13 mblf at AR. Although SRR were lower at AR than at NB, organic matter (OM) concentrations were higher. In contrast, dissolved OM in the pore water at AR contained more macromolecular OM and less low molecular weight OM. We thus suggest, that OM content alone cannot be used to infer microbial activity at Lake Van but that quality of OM has an important impact as well. These differences suggest that biogeochemical processes in lacustrine sediments are reacting very sensitively to small variations in geological, physical, or chemical parameters over relatively short distances.

Microbial abundance in lacustrine sediments: a case study from Lake Van, Turkey

“…This difference cannot be explained by differences in TOC content or C/N ratio. For SRR, Glombitza et al (2013) concluded that differences in the composition and therefore availability of the sedimentary organic matter caused the different rates. Although TOC and C/N ratios were similar at both sites, there were distinct compositional differences in the dissolved organic carbon (DOM) pool, with higher concentrations of more bioavailable compounds like organic acids in sediments from Northern Basin, which also exhibited higher SRR.…”

“…However, Lake Van deviates somewhat from this general rule. While both Lake Van drill sites reveal almost identical cell count records, there are significant differences in sulphate reduction rates (SRR), which is the quantitatively most important electron acceptor process in these sediments (Glombitza et al 2013). This difference cannot be explained by differences in TOC content or C/N ratio.…”

“…Total organic carbon (TOC) was calculated as TOC = TC − TIC and the C/N ratio as C/N = TOC/TN. TOC and C/N data were previously published (Glombitza et al 2013). All data from Potrok Aike were taken from the literature (Vuillemin et al 2013).…”

Eger Rift ICDP: an observatory for study of non-volcanic, mid-crustal earthquake swarms and accompanying phenomena

“…Despite recent advances in microbiological deep subsurface exploration, deep terrestrial environments remain relatively unexplored; mainly due to difficulties in obtaining suitable samples. While microbiological research is already part of the "International Ocean Discovery Program" (IODP) (Parkes et al, 1994;D'Hondt et al, 2007) only a few recent projects within the ICDP have had a microbiological component (Colwell et al, 2005;Gohn et al, 2008;Glombitza et al, 2013;Vuillemin and Ariztegui, 2013).…”

Physical Characterization, Microstructural Evaluation, and Condition Assessment of Ancient Ahlat Tombstones in the Seljukian Cemetery of Ahlat (Turkey)

“…The average snowfall height can reach 130 cm (source: www.ahlat.bel.tr). Cyclic freezing and melting of water carrying soluble substances (note again the salinity, alkalinity and proximity of Lake Van water (Glombitza et al 2013)) through the pores, voids, and capillaries causes efflorescence on the surface and probable ice-and salt-induced spalling. Such a repeat freeze-thaw process and frost damage caused the weak central sites of the high-porosity (approximately 50%) stelae to erode and crater at this particular position over time.…”