College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, PR China.
State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, Guangdong 518055, PR China.
J Hazard Mater. 2022 Sep 5;437:129380. doi: 10.1016/j.jhazmat.2022.129380. Epub 2022 Jun 15.
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.
招潮蟹广泛分布于世界沿海湿地，是生态系统工程师。它们的掘洞活动可显著改变当地生物地球化学过程，然而，洞穴沉积物中重金属（HM）的迁移仍不清楚。本研究采用薄膜扩散梯度技术，获取了来自沿海湿地（潮滩、盐沼和红树林）的招潮蟹洞穴中生物可利用态 Fe 和 HMs（Cu、Zn、Ni、Cd、Pb、Co 和 Mo）。深度剖面结果表明，大多数 HMs 在浅层和深层富集，而在中层缺失。研究强调，生物扰动改善了好氧条件，增加了 HM 浓度，并有利于溶解态 HM 在洞穴沉积物中的保留，通过洞穴冲洗，沉积物成为上覆水体 HMs 的汇，但通过增强再悬浮作用，成为颗粒态 HMs 的潜在源。在深部缺氧层中，Fe(III)还原驱动了 HMs 的再迁移，除了 Cu 和 Mo 之外，导致 HMs 与 Fe 共同释放。二维高分辨率成像增强技术验证了这种 Fe-HM 耦合/解耦，揭示了多种 HMs 的高度空间异质性。此外，调节生物扰动对 HM 行为影响的水文学条件在不同沿海湿地之间存在差异。随着沿海环境的变化，应重新考虑普遍存在的生物扰动在 HM 迁移和生物可利用性方面的关键作用。
