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 anaerobic oxidation of methane (S-AOM) also occurs at this site. Although depth-integrated fluxes of SO₄²⁻, CH₄, NH₄, DIC at the inactive pockmark are orders of magnitude higher compared to the active pockmarks, processes at the inactive pockmark represent internal recycling in the coastal sea. Fluxes observed at the active pockmarks, although comparatively small in magnitude, are partly influenced by external inputs to the sea through SGD. Hence, effluxes across the sediment–water interface at these sites partly represent direct external fluxes to the marine environment, in addition to diagenetic recycling at the benthic interface. The study highlights that SGD can result in significant spatial heterogeneity of biogeochemical processes and microbial community structure in the coastal zone, and that the overall effects of SGD and associated solute fluxes at an SGD site are a function of the number of pockmarks, the rate of SGD, and the ratio of active to inactive pockmarks.

最近的许多研究已经证明了海底地下水排放（SGD）对沿海海洋生物地球化学的影响。然而，只有少数研究整合了生物地球化学和微生物分析，特别是在具有不同程度地下水影响的麻点的地点。本研究调查了波罗的海北部芬兰汉科的三个麻点沉积物核心中的生物地球化学过程和微生物群落结构。Pockmark 数据由地下水和海水测量值补充。基于孔隙水 Cl ^{-的两个活动麻点分别显示 0.02 cm d -1}和 0.31 cm d ^-1的 SGD 率个人资料，而第三个麻点没有 SGD 影响。反应输运模型 (RTM) 确定这些活动麻点的孔隙水系统以平流为主，导致生物地球化学反应和微生物群落集中在沉积物表面的薄带中。平流进一步减少了地表沉积物中有机物的积累，导致在这些麻点处不存在硫酸盐-甲烷过渡区（SMTZ）。此外，RTM 估计 SO ₄ ^2-的低消耗率和 CH ₄、NH ₄ ^{+的低生产率}, DIC 在活动麻点处。活跃麻点中的古菌群落以主要来源于地下水的氨氧化古菌为主。相比之下，在不活跃的麻点处，缺乏 SGD 允许富含有机物的泥浆快速沉积。非活动麻点中的孔隙水系统以扩散为主，与活动麻点相比，导致深度处的代谢物浓度高出几个数量级。非活动麻点的生物地球化学环境类似于该地区典型的富含有机物的泥质海底，硫酸盐还原和产甲烷作用主导有机质再矿化。因此，产甲烷菌在古菌群落中占主导地位，而硫酸盐还原剂在细菌群落中占主导地位。RTM 结果表明，硫酸盐介导的甲烷厌氧氧化（S-AOM）也发生在该地点。虽然 SO 的深度积分通量₄ ^2- , CH ₄ , NH ₄, 非活动麻点处的 DIC 比活动麻点高几个数量级，非活动麻点处的过程代表沿海海域的内部循环。在活动麻点处观察到的通量虽然量级相对较小，但部分受到通过 SGD 对海洋的外部输入的影响。因此，除了底栖界面的成岩作用循环外，这些地点的沉积物 - 水界面外流部分代表了直接进入海洋环境的外部通量。该研究强调，SGD 可导致沿海地区生物地球化学过程和微生物群落结构的显着空间异质性，并且 SGD 和相关溶质通量在 SGD 站点的总体影响是麻点数量、麻点率的函数。新元，