Data Sheet 1_Atmospheric and river-derived mercury fluxes in distinct natural communities of a river delta.docx

IntroductionRiver deltas play an important role in sequestering and storing mercury (Hg), restricting its release into downstream bodies of water. Delta landscapes encompass a patchwork of distinct wetland soils and vegetation, which accumulate Hg from both atmospheric and watersheds sources, and have varying capacities for long-term Hg retention.
MethodsTo better understand Hg retention in the complex mosaic of delta soils, this study used soil age models based on fallout radionuclides (FRNs, 210Pb, 7Be, 241Am) to measure Hg flux to three distinct natural communities in the Missisquoi River Delta, Vermont.
ResultsSoil profiles of radionuclide and Hg flux from a pitch pine bog, a silver maple floodplain forest, and a wild rice marsh all revealed long-term retention of Hg, despite varying susceptibilities to frequent hydrological disturbances. A mass balance approach was applied to apportion Hg fluxes to each region of the delta based on regional values of Hg wet deposition, measured FRN and Hg inventories, and measured or estimated foliar Hg inputs. Spaghnum peat soils of the pitch pine bog had the lowest Hg flux, consistent with uptake predominantly from wet deposition, while Hg accumulation doubled in bog soils developed under shrub or tree canopies, due to strong foliar and non-foliar uptake of gaseous elemental Hg (GEM). Soils in the silver maple floodplain received the highest Hg flux, driven by both GEM uptake and large riverine sedimentary inputs. Surprisingly, submerged soils in the wild rice marsh recorded substantially lower Hg flux than the adjacent silver maple forest, with low inputs of Hg from both GEM and watershed sources.
ConclusionThis novel chronometry framework for elucidating pathways of Hg accumulation across distinct deltaic environments revealed the variable roles of vegetation type and flooding regime in controlling Hg inputs to delta soils.

引言
河流三角洲在固存与储存汞（Hg）、限制其向下游水体释放方面发挥着重要作用。三角洲景观由多种独特的湿地土壤与植被镶嵌构成，这些介质可从大气与流域来源中富集汞，并具备各不相同的长期汞固存能力。

研究方法
为深入解析三角洲复杂镶嵌土壤中的汞固存机制，本研究基于沉降放射性核素（FRNs，²¹⁰Pb、⁷Be、²⁴¹Am）构建土壤年代模型，对佛蒙特州密西斯阔伊河三角洲三个不同自然群落的汞通量进行测定。

研究结果
对北美油松沼泽、银枫泛滥平原林与野生稻沼泽的土壤剖面放射性核素与汞通量测定结果均显示，尽管三者对频繁水文扰动的敏感性存在差异，但均实现了汞的长期固存。本研究采用质量平衡法，结合区域汞湿沉降数值、实测沉降放射性核素与汞储量，以及实测或估算的叶面汞输入量，对三角洲各区域的汞通量进行分配。北美油松沼泽的泥炭藓（Spaghnum）泥炭土汞通量最低，这与其主要通过湿沉降摄取汞的特征相符；而在灌丛或乔木冠层下发育的沼泽土壤中，由于对气态元素汞（GEM）的高效叶面与非叶面摄取作用，汞积累量提升了一倍。银枫泛滥平原的土壤汞通量最高，这源于气态元素汞摄取与大量河流沉积物输入的共同驱动。令人意外的是，野生稻沼泽的淹水土壤汞通量远低于相邻的银枫林，其气态元素汞与流域来源的汞输入量均较低。

研究结论
本研究构建的新型年代测定框架，可阐明不同三角洲环境下的汞积累路径，揭示了植被类型与水文淹水节律在调控三角洲土壤汞输入过程中的差异化作用。