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子岛海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。汞是一种强有力的神经毒素，在美国和世界各地都是鱼类消费建议的主要原因。在美国东海岸，盐沼麻雀已经显示出有害的汞暴露，血液水平升高对繁殖产出构成风险。这些盐沼中汞的来源在很大程度上是未知的。汞暴露高的可能原因是邻近流域径流的贡献或遗留工业影响的大气输入。该奖项将研究盐沼植物对大气汞的直接吸收作为这些盐沼生态系统的汞来源的作用。在这个潮汐系统中，另一个重点是植物将汞转移到土壤中，并将汞输出到沿海海洋的植物死亡。该奖项将培训和吸引研究生和本科生参与研究。该奖项旨在量化汞的汇和源，以及它们与植物初级生产力、组织周转率和土壤动力学的关系，在盐沼生态系统中，已报告了一些最高的生物汞暴露。第一种假设是，植物对汞的同化作用是该河口汞的主要来源，在该河口，盐沼面积占总面积的50%到90%。第二个假设是，植物对汞的同化作用在植物衰老后进入土壤，导致土壤中汞的高度积累，最终被动员到潮水中，导致汞从盐沼向潮水的净输出。这类似于碳的“外流”假说，该假说认为，盐沼产生的原生碳超过了被降解和储存的碳，导致净出口到沿海海洋，在那里它刺激了海洋的净初级生产。拟议的措施包括通过部署微气象通量-梯度系统来量化大气汞沉积输入，该系统允许测量生态系统一级的气态大气汞通量，包括植物汞同化，以及详细的植被汞动态和其他沉积过程。将对从海洋经潮汐水到淡水源头的潮汐水进行空间横断面采样，并分析汞的形态(溶解的、颗粒的、甲基汞和海藻碎屑中所含的汞结合态)，以评估盐沼和潮汐水之间的横向交换。最后，盐沼土壤中总汞和甲基化汞的分布模式将被表征为限制导致汞在2500至3500年前土壤中积累的自然和人为过程。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.