Coastal wetlands sequestering abundant blue carbon in soils are biogeochemical hotspots and critical habitats for benthic animals like invertebrate fiddler crabs. Here, we reveal how crab bioturbation (i.e., burrowing activity) drives the redox geochemistry of ferrous iron (Fe(II)), phosphate (PO₄^3-), and sulfide (S(-II)) under contrasting vegetation types and hydrological conditions. We used in-situ approaches of diffusive gradients in thin films to perform detailed mm-scale burrow observations in two subtropical wetlands with a vegetation gradient of mudflat-salt marsh-mangrove. Burrow flushing caused a top-down hydrologic connectivity through the crab burrows and thus created a deep depth for the occurrence of Fe(III) reduction and sulfate reduction which were accompanied by P mobilization. The burrow oxidation zone, indicated by lower concentrations of Fe(II), PO₄^3- and S(-II), were shallower in mudflats and salt marshes than in mangroves due to the unique respiratory roots of mangrove plants. The redox of Fe(II), PO₄^3- and S(-II) in crab burrow was insensitive to the convection flow-induced input of dissolved oxygen through the surrounding soil matrix, indicating the burrow soil is an independent microenvironment. Crab burrowing activities favored Fe-S coupling which is conductive the formation of pyrite and alkalinity generation. Overall, our in-situ high-resolution observations and porewater hydraulic dynamics revealed spatially variable soil geochemistry, active coupled cycling of Fe-P-S in crab burrows, and mm-scale hotspots of redox cycling within burrows.

沿海湿地在土壤中封存大量蓝碳，是生物地球化学热点和无脊椎动物招潮蟹等底栖动物的重要栖息地。在这里，我们揭示了螃蟹生物扰动（即穴居活动）如​​何在对比植被类型和水文条件下驱动亚铁（Fe（II））、磷酸盐（PO ₄ ^3-）和硫化物（S（-II））的氧化还原地球化学条件。我们在现场使用薄膜扩散梯度方法在两个亚热带湿地中进行详细的毫米尺度洞穴观测，其植被梯度为泥滩-盐沼-红树林。洞穴冲刷通过蟹洞引起自上而下的水文连通性，从而为伴随着P动员的Fe（III）还原和硫酸盐还原的发生创造了较深的深度。由于红树林植物独特的呼吸根，泥滩和盐沼中的洞穴氧化区以较低浓度的 Fe(II)、PO ₄ ^{3-和 S(-II) 为标志，比红树林中的浅。}Fe(II)、PO ₄ ^{3-的氧化还原}蟹穴中的S(-II)对通过周围土壤基质的对流诱导的溶解氧输入不敏感，表明洞穴土壤是一个独立的微环境。螃蟹穴居活动有利于Fe-S耦合，这有助于黄铁矿的形成和碱度的产生。总体而言，我们的原位高分辨率观测和孔隙水水力动力学揭示了空间变化的土壤地球化学、蟹穴中 Fe-PS 的主动耦合循环以及洞穴内氧化还原循环的毫米级热点。