Spatial distribution and biogeochemistry of redox active species in arctic sedimentary porewaters and seeps

• Published in: Environmental science--processes & impacts 2022-03, Vol.24 (3), p.426-438
• Main Authors: Hudson, Jeffrey M, Michaud, Alexander B, Emerson, David, Chin, Yu-Ping
• Format: Article
• Language: English
• Subjects: Abundance; Bacteria; Biogeochemistry; Carbon cycle; Ferric Compounds; Geographical distribution; Heterogeneity; Iron; Iron - analysis; Lakes; Lakes - microbiology; Manganese; Microbial activity; Microelectrodes; Microorganisms; Minerals; Oxidation; Oxidation-Reduction; Polar environments; Sediments; Solid phases; Spatial distribution; Spatial heterogeneity; Species; Tundra; Water depth
• ISSN: 2050-7887; 2050-7895
• DOI: 10.1039/d1em00505g

Redox active species in Arctic lacustrine sediments play an important, regulatory role in the carbon cycle, yet there is little information on their spatial distribution, abundance, and oxidation states. Here, we use voltammetric microelectrodes to quantify the in situ concentrations of redox-active species at high vertical resolution (mm to cm) in the benthic porewaters of an oligotrophic Arctic lake (Toolik Lake, AK, USA). Mn( ii ), Fe( ii ), O 2 , and Fe( iii )-organic complexes were detected as the major redox-active species in these porewaters, indicating both Fe( ii ) oxidation and reductive dissolution of Fe( iii ) and Mn( iv ) minerals. We observed significant spatial heterogeneity in their abundance and distribution as a function of both location within the lake and depth. Microbiological analyses and solid phase Fe( iii ) measurements were performed in one of the Toolik Lake cores to determine the relationship between biogeochemical redox gradients and microbial communities. Our data reveal iron cycling involving both oxidizing (FeOB) and reducing (FeRB) bacteria. Additionally, we profiled a large microbial iron mat in a tundra seep adjacent to an Arctic stream (Oksrukuyik Creek) where we observed Fe( ii ) and soluble Fe( iii ) in a highly reducing environment. The variable distribution of redox-active substances at all the sites yields insights into the nature and distribution of the important terminal electron acceptors in both lacustrine and tundra environments capable of exerting significant influences on the carbon cycle. Schematic showing how voltammetric microelectrodes were used to profile arctic lake sediments, where different locations contained different distributions of redox-active species.