Collaborative Research: Vegetation assimilation as a source of mercury in a salt marsh ecosystem and implications for soil and tidal water exposures

该奖项的目标是确定马萨诸塞州梅岛湾盐沼生态系统中汞的来源和命运，以及向近岸沿海海洋出口的可能性。汞是一种强效的神经毒素，也是美国和世界各地建议食用鱼类的主要原因。在美国东海岸，盐沼麻雀暴露在汞中，血液中汞含量升高，对繁殖能力构成威胁。这些盐沼中汞的来源在很大程度上是未知的。高汞暴露的可能原因是邻近流域的径流或遗留工业影响的大气输入。该奖项将研究盐沼植物直接吸收大气汞作为这些盐沼生态系统汞源的作用。在这个潮汐系统中，另一个重点在于植物将汞转移到土壤中，并随着植物的死亡将其出口到沿海海洋。该奖项将培训和参与研究的研究生和本科生。该奖项旨在量化汞汇和汞源及其与植物初级生产力、组织周转率和土壤动态的关系，在盐沼生态系统中，据报道存在一些最高的生物汞暴露。第一个假设是，植物汞同化是该河口的主要汞来源，该河口的盐沼在面积上占主导地位（占表面积的50%至90%）。第二种假设是，植物衰老时，汞的植被同化被纳入土壤，导致土壤中汞的高积累，最终被动员到潮汐水中，导致汞从盐沼净出口到潮汐水中。这与碳的“外溢”假说类似，该假说认为，盐沼产生的原生碳超过了被降解和储存的碳，导致向沿海海洋的净出口，从而刺激海洋净初级生产。拟议的测量包括通过部署微气象通量梯度系统对大气汞沉积输入进行量化，该系统允许测量生态系统水平的气态大气汞通量，包括植物汞同化，以及详细的植被汞动态和其他沉积过程。将对从海洋到潮汐水直至淡水源头的潮汐水进行空间样带取样，并分析汞种类（残骸碎屑中所含的溶解汞、颗粒汞、甲基汞和汞结合物），以评估盐沼和潮汐水之间的横向交换。最后，将描述盐沼土壤中总汞和甲基化汞的分布模式，以限制导致这些2500至3500年历史的土壤中汞积累的自然和人为过程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of this award is to determine the origin and fate of mercury in a salt marsh ecosystem in the Plum Island Sound of Massachusetts and potential export to near shore coastal oceans. Mercury is a potent neurotoxin and leading cause for fish consumption advisories in the U.S and across the world. Along the U.S. East Coast, salt marsh sparrows have shown harmful exposures to mercury with elevated blood levels posing risks for reproductive outputs. The origin of mercury in these salt marshes is largely unknown. Possible reasons for high mercury exposure are contributions from runoff from adjacent watersheds or atmospheric inputs from legacy industrial impacts. This award will study the role of direct plant uptake of atmospheric mercury by salt marsh plants as the mercury source for these salt marsh ecosystems. In this tidal system, an additional focus lies on the transfer of mercury to soils by the plants and with death of the plants its export to the coastal ocean. The award will train and involve graduate and undergraduate students in the research.This award aims to quantify mercury sinks and sources and their relationships to plant primary productivity, tissue turnover rates, and soil dynamics, in a salt marsh ecosystem where some of the highest biological mercury exposures have been reported. The first hypothesis is that that plant mercury assimilation is the dominant source of mercury in this estuary where salt marshes dominate in areal extent (50 to 90% of surface area). The second hypothesis is that vegetation assimilation of mercury is incorporated into soils upon plant senesce leading to high mercury accumulation in soils, which ultimately is mobilized to tidal water leading to net export of mercury from salt marshes to tidal water. This is analogue to the “outwelling” hypothesis for carbon that proposes that salt marshes produce an excess of autochthonous carbon over what is degraded and stored resulting in net export to the coastal ocean where it stimulates ocean net primary production. Proposed measurements include quantification of atmospheric mercury deposition inputs via deployment of a micrometeorological flux-gradient system that allows to measure ecosystem-level gaseous atmospheric mercury fluxes including plant mercury assimilation, along with detailed vegetation mercury dynamics and other deposition processes. Spatial transect sampling of tidal water from the ocean through the tidal water up to the freshwater headwater will be conducted and analyzed for mercury species (dissolved, particulate, methyl-mercury and mercury bound contained in wrack detritus) in order to assess lateral exchanges between salt marsh and tidal water. Finally, distribution patterns of total mercury and methylated mercury in salt marsh soils will be characterized to constrain processes — both natural and anthropogenic — that lead to mercury accumulation in these 2,500-to-3,500 year old soils.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.