Impact of submarine groundwater discharge on biogeochemistry and microbial communities in pockmarks

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Titel: Impact of submarine groundwater discharge on biogeochemistry and microbial communities in pockmarks

Beteiligte: Purkamo, Lotta [Verfasser:in]; von Ahn, Cátia Milene Ehlert [Verfasser:in]; Jilbert, Tom [Verfasser:in]; Muniruzzaman, Muhammad [Verfasser:in]; Bange, Hermann W. [Verfasser:in]; Jenner, Anna-Kathrina [Verfasser:in]; Böttcher, Michael Ernst [Verfasser:in]; Virtasalo, Joonas J. [Verfasser:in]

Erschienen: Elsevier, 2022-10-01

Sprache: Englisch

DOI: https://doi.org/10.1016/j.gca.2022.06.040

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Beschreibung: The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemistry has been demonstrated in many recent studies. However, only a few studies have integrated biogeochemical and microbiological analyses, especially at sites with pockmarks of different degrees of groundwater influence. This study investigated biogeochemical processes and microbial community structure in sediment cores from three pockmarks in Hanko, Finland, in the northern Baltic Sea. Pockmark data were supplemented by groundwater and seawater measurements. Two active pockmarks showed SGD rates of 0.02 cm d−1 and 0.31 cm d−1, respectively, based on porewater Cl− profiles, while a third pockmark had no SGD influence. Reactive transport modelling (RTM) established that the porewater systems of these active pockmarks are dominated by advection, resulting in the focusing of biogeochemical reactions and the microbial community into a thin zone at the sediment surface. The advection further reduces the accumulation of organic matter in the surface sediments, resulting in the absence of a sulfate-methane transition zone (SMTZ) at these pockmarks. Furthermore, the RTM estimated low rates of consumption of SO42−, and low rates of production of CH4, NH4+, DIC at the active pockmarks. Archaeal communities in the active pockmarks were dominated by ammonia-oxidizing archaea of predominantly groundwater origin. In contrast, at the inactive pockmark, the lack of SGD has permitted rapid deposition of organic-rich mud. The porewater system in the inactive pockmark is dominated by diffusion, leading to orders of magnitude higher metabolite concentrations at depth compared to the active pockmarks. The biogeochemical environment in the inactive pockmark resembles typical organic-rich mud seafloor in the area, with sulphate reduction and methanogenesis dominating organic matter remineralization. Accordingly, methanogens dominate the archaeal community, whereas sulfate reducers dominate the bacterial community. RTM results suggest that sulfate-mediated ...

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