Institute of Eco-Environmental Forensics, Shandong University, Qingdao 266237, PR China; School of Environmental Science and Engineering, Shandong University, Qingdao 266237, PR China; Department of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada.
Department of Biology, University of Western Ontario, 1151 Richmond Street, London, Ontario, Canada.
Ecotoxicol Environ Saf. 2024 Jul 15;280:116573. doi: 10.1016/j.ecoenv.2024.116573. Epub 2024 Jun 12.
Boreal peatlands are "hotspots" of net methylmercury (MeHg) production and may become drier in the future due to climate change. This study investigates a critical gap by analyzing the nuanced relationship between soil moisture content and the release of MeHg, inorganic mercury (IHg), sulfate (SO), and dissolved organic matter (DOM) in a laboratory incubation of boreal peat soils. Dried peat soils exhibited heightened releases of IHg, MeHg, and SO during re-wetting events. Both dried and saturated peat soils released more DOM than moist peat soils during re-wetting events, and DOM released from dried soils had higher bioaccessibility than that from the saturated soils (p<0.05). There was an equilibrium of IHg concentrations between peat soils and pore waters, but long-term severe drought may disrupt this equilibrium and then release more IHg to pore waters during re-wetting events. Contrary to expectations, positive relationships between IHg concentrations and SUVA did not exist in all treatments. MeHg and SO were depleted quickly because there was no external input of Hg and SO to this static system. More bioaccessible DOM than aromatic DOM was released from peat soils with different soil moisture contents after 32 weeks during the re-wetting event (p<0.05). These results imply that re-wetting of peat soils after droughts can increase the release of MeHg from peat soils and may also increase net MeHg production due to the release of SO and bioaccessible DOM from peat soils, reshaping our understanding of soil moisture's role in mercury dynamics. This novel insight into soil moisture and MeHg dynamics carries significant implications for mitigating mercury contamination in aquatic ecosystems.
北方泥炭地是净甲基汞（MeHg）产生的“热点”，并且由于气候变化，未来可能会变得更加干燥。本研究通过分析土壤湿度与 MeHg、无机汞（IHg）、硫酸盐（SO）和溶解有机质（DOM）释放之间细微关系，在北方泥炭土壤的实验室培养中调查了一个关键差距。在重新润湿事件中，干燥的泥炭土壤表现出更高的 IHg、MeHg 和 SO 释放。与湿润的泥炭土壤相比，干燥和饱和的泥炭土壤在重新润湿事件中释放出更多的 DOM，并且来自干燥土壤的 DOM 具有更高的生物可利用性（p<0.05）。泥炭土壤和孔隙水中的 IHg 浓度之间存在平衡，但长期严重干旱可能会破坏这种平衡，然后在重新润湿事件中向孔隙水中释放更多的 IHg。与预期相反，在所有处理中，IHg 浓度与 SUVA 之间不存在正相关关系。由于Hg 和 SO 没有外部输入到这个静态系统中，MeHg 和 SO 很快就被消耗殆尽。在重新润湿事件期间，不同土壤湿度的泥炭土壤释放出更多的可生物利用 DOM，而不是芳香 DOM（p<0.05）。这些结果表明，干旱后泥炭土壤的重新润湿可以增加泥炭土壤中 MeHg 的释放，并且由于 SO 和可生物利用 DOM 从泥炭土壤中的释放，也可能增加净 MeHg 的产生，从而重塑我们对土壤湿度在汞动态中作用的理解。这一关于土壤湿度和 MeHg 动态的新见解，对减轻水生生态系统中汞污染具有重要意义。
