Fiddler crabs, found in coastal wetlands worldwide, function as ecosystem engineers. Their burrowing activity can significantly alter biogeochemistry at the local scale, however, the mobility of heavy metals (HMs) in burrow sediments remains unclear. Here, we used diffusive gradients in thin-film probes to obtain bioavailable Fe and HMs (Cu, Zn, Ni, Cd, Pb, Co, and Mo) in crab burrows from coastal wetlands (mudflats, salt marshes, and mangroves). The depth-profile results showed that most HMs were enriched at shallow and deep depths but deficient at middle depths. We highlighted that bioturbation improved oxic conditions, enhanced HM concentrations, and favored dissolved HM retention in burrow sediments, which served as a sink for overlying water HMs via burrow flushing but a potential source of particle HMs via enhanced resuspension. In deep anoxic layers, Fe(III) reduction drove the remobilization of HMs, except Cu and Mo, leading to the co-release of HMs with Fe. This Fe-HM coupling/decoupling was verified using enhanced two-dimensional high-resolution imaging, which revealed highly spatial heterogeneity of multiple HMs. Moreover, the hydrological conditions regulating bioturbation effects on HM behavior varied across different coastal wetlands. With coastal environmental changes, the key role of ubiquitous bioturbation in HM migration and bioavailability should be reconsidered.

在世界各地的沿海湿地中发现的招潮蟹发挥着生态系统工程师的作用。它们的洞穴活动可以显着改变当地规模的生物地球化学，但是，重金属（HMs）在洞穴沉积物中的流动性仍不清楚。在这里，我们在薄膜探针中使用扩散梯度，在沿海湿地（泥滩、盐沼和红树林）的蟹洞中获得生物可利用的 Fe 和 HM（Cu、Zn、Ni、Cd、Pb、Co 和 Mo）。深度剖面结果表明，大多数HMs在浅层和深层都富集，而在中深度则缺乏。我们强调，生物扰动改善了有氧条件，提高了 HM 浓度，并有利于洞穴沉积物中溶解的 HM 保留，这通过洞穴冲洗作为上覆水 HMs 的汇，但通过增强再悬浮作为颗粒 HMs 的潜在来源。在深层缺氧层中，Fe(III) 还原推动了除 Cu 和 Mo 之外的 HMs 的再活化，导致 HMs 与 Fe 共同释放。使用增强的二维高分辨率成像验证了这种 Fe-HM 耦合/解耦，这揭示了多个 HM 的高度空间异质性。此外，调节生物扰动对 HM 行为影响的水文条件在不同的滨海湿地之间存在差异。随着沿海环境的变化，应重新考虑无处不在的生物扰动在 HM 迁移和生物利用度中的关键作用。调节生物扰动对 HM 行为影响的水文条件在不同的滨海湿地之间存在差异。随着沿海环境的变化，应重新考虑无处不在的生物扰动在 HM 迁移和生物利用度中的关键作用。调节生物扰动对 HM 行为影响的水文条件在不同的滨海湿地之间存在差异。随着沿海环境的变化，应重新考虑无处不在的生物扰动在 HM 迁移和生物利用度中的关键作用。