Mercury is a pervasive environmental contaminant, and it has multiple pathways into ecosystems and watersheds. The primary pathway of mercury distribution is through the atmosphere, 气态汞可以在高空停留长达一年，并且可以长距离运输. A secondary pathway of mercury distribution is through point sources, which are identifiable sources of pollution or contaminants. Once mercury is introduced into landscapes, it has the potential to migrate into other environments, where it can enter marine and freshwater aquatic ecosystems.
研究汞很重要，因为特定类型的汞是环境健康的指标. 这种健康与大气汞浓度甚至与汞总量没有直接关系, 但生物蓄积性甲基汞的生产是环境问题的主要来源(Driscoll等)., 2013). Methylmercury targets the central nervous system, 它作为一种神经毒素的毒性早在20世纪50年代就已为人所知(Castoldi等人)., 2003). 研究表明，在一定的环境条件下，汞可以转化为甲基汞, 因此，研究环境中的汞含量有助于确定潜在的关注场所.
Mill Pond Dam in Durham, NH.
The Mill Pond Dam, a head-of-tide dam in Durham, New Hampshire, separates tidal waters from fresh water in the Oyster River. Though the Town of Durham voted to remove the dam in March 2022, 到2024年3月，大坝仍然在那里，并计划在未来几年内拆除(Dandurant), 2022; New Hampshire Department of Environmental Services, n.d.). Below the Mill Pond Dam lies the Great Bay Estuary environment, 这里是奥伊斯特河的淡水与流入大西洋的盐水混合的地方. 大坝上方的淡水环境包括米尔塘、学院溪和奥伊斯特河.
先前的研究已经确定了米尔池塘(Miller Pond)岩心沉积物中总汞含量升高的地区, 2020). 该项目旨在通过评估汞浓度如何更详细地调查这些发现, together with organic matter, vary above and below the Mill Pond Dam. 该项目于2023年在澳门葡京网赌游戏哈默尔本科生研究中心(Hamel Center for Undergraduate Research)的夏季本科生研究奖学金(SURF)下进行.
Project Overview and Methods
Figure 1. Map of sediment mercury sample sites. Sample sites in the Oyster River: Old Landing (sites OR1 and OR2); Jackson’s Landing (OR3); Wagon Hill (OR4 and OR5). Sample sites above the dam: College Brook (CB1, CB2, CB3, CB4); Mill Pond (MP1, MP2, MP3).
To meet these objectives, sediment samples were collected from Mill Pond, Oyster River, and College Brook on and near the UNH campus. All sample locations are shown in Figure 1. 这些沉积物样本是从水面以下10厘米处的水域边缘收集的, clean plastic scoops and stored in double bags. 样本于2023年7月17日、8月2日和9月5日在每个地点采集，一式三份. 7月13日，在奥伊斯特河和米尔塘的两个地点收集了额外的样本, 7月31日，在奥伊斯特河口附近的马车山采集了一组独特的样本. 在这个项目中，采样是一个挑战，因为在一个暴风雨的夏天开始采样是困难的. 2023年6月和7月的暴雨需要在干燥的日子采集样本，而干燥的日子也没有下过两三天的大雨. 这一点很重要，因为大雨可能会使站点无法进入或造成地面中断，而不一定代表整个系统. Eventually, I obtained samples in mid-July, early August, and early September, allowing for a time series of data through summer 2023.
Samples were then processed in a lab on the UNH campus through freeze drying, which removes all the water from the sample. After processing, the sediment samples have a powderlike texture. 然后，我用Milestone直接汞分析仪分析了处理后的样品中的总汞. 该仪器加热样品以释放汞，并将汞收集并集中在一个金捕集器上, where it is then reheated and released for measurement.
每个样品中有机物的含量是通过一种技术来估计的，这种技术包括测量在加热的炉子中着火时损失的质量. Here, the processed sample is weighed out in crucibles, which are then combusted in a furnace at 450°C for four hours. After this combustion, the inorganic sandlike component of the sediment remains, and the samples are cooled and then weighed again. 原始样品和加热样品之间的质量差提供了样品中有机物百分比的估计. From these data, the estimated amount of organic carbon could be calculated.
确定汞和有机含量的特征有助于了解汞在流域中的承载方式, either with organic matter or merely on sediment. In an uncontaminated estuary, mercury tracks through the watershed with organic carbon, while in a locally contaminated watershed, 汞在流域内循环，并没有显示出与有机碳的密切关系(Seelen等)., 2021). In the measurements for my SURF and undergraduate thesis, 我发现汞和有机碳的关系在污染和未污染的河口地区是不同的.
Figure 2: Total mercury at each site in the Oyster River-Mill Pond watershed. 图表上的线表示每条海洋或淡水沉积物质量准则. ISQG指出了汞可能对生态系统产生负面影响的地方. PEL指出了汞可能对生态系统产生负面影响的地方.
Results and Discussion
As of March 2024, 在2023年夏季运动中收集的大约53个沉积物样本已经进行了充分的处理和分析，以确定点火损失的百分比和总汞分析.
数据分析的重点是将沉积物样品的总汞浓度与加拿大国家资源委员会(NRC)建议的沉积物质量准则进行比较. 加拿大国家研究委员会发布了两个海洋和淡水沉积物浓度指南:临时沉积物质量指南(ISQG)和可能影响水平(PEL)。. ISQG表明一个地区的汞何时开始对生态系统造成不利影响. PEL代表了生态系统中生物可能表现出毒素负面影响的地方. 淡水和海洋沉积物具有不同的ISQG和PEL浓度阈值. The ISQG recommendations were the focus of my data analysis, 而流域中大多数沉积物的浓度都超过了这一标准. Several samples also exceeded the PEL.
在大坝下面的采样点，汞浓度在每个采样点和整个奥伊斯特河都是不同的, as shown in Figure 2.
Figure 3. Breakdown of above and below dam sediment samples, 在每条沉积物质量准则的上方显示了它们的收集位置.
The mercury concentrations in the Oyster River at Old Landing, just below the Mill Pond Dam (site OR2), had total mercury concentrations ten times greater than the marine PEL, with all contents at this site in all but one sample measuring above the PEL. 在奥伊斯特河的其他采样点在老登陆(OR1)和杰克逊登陆(OR3)的站点也有升高的总汞含量, 所有靠近米尔塘大坝的奥伊斯特河地点的汞含量都高于标准. The sites at Wagon Hill (OR4 and OR5), farther downriver, had lower total mercury concentrations, with some samples at OR5 containing mercury concentrations above the ISQG.
For the sample sites above the Mill Pond Dam, 学院溪遗址在个别采样点和整个地区中含有不同数量的总汞. 纪念联合大厦(CB2)下的一个场地的汞浓度超过了淡水标准. 纪念联合大厦(CB4)上游更远的一个地点也含有超过PEL的汞样本.
The remaining College Brook sites, CB1 and CB2, as shown on the sample site map, had mercury concentrations above the freshwater ISQG. The three sites at Mill Pond (MP1, MP2, MP3) had relatively lower mercury amounts, with few samples exceeding the freshwater ISQG at sites MP2 and MP3. 图3显示了大坝上方和下方超过相对ISQG和PEL的样本数量.
Figure 4. Estimated organic carbon at each sample site, calculated from percent of organic matter loss on ignition. The X axis contains the site code for each site: CB (College Brook); MP (Mill Pond); and OR (Oyster River).
The amount of estimated organic carbon in these samples was also variable, more so above the dam than below it, as seen in Figure 4. In the samples below the dam in the Oyster River, 当考虑到所有样品时，有机碳和汞的估计量之间没有关系. When just the samples below the marine PEL were considered, there was some relationship between total mercury and organic carbon. In the freshwater sediments, 在所有样品中，总汞与有机碳之间没有关系, or just the samples below the PEL, were considered. These relationships are displayed in Figure 5.
我的研究结果表明，米尔塘坝流域的总汞量在单个样本点内和所研究的样本点之间是可变的. When evaluating the links between mercury and organic carbon, 坝下海相沉积物的关系具有未污染沉积物的特征, 但是淡水沉积物中有机碳和总汞之间缺乏关系是当地或遗留污染场地的特征.
The high total mercury concentrations above the PEL were unexpected, as were some of the sites with low concentrations recorded in Mill Pond, given findings reported for cores studied by Miller (2020). 其中一个米尔塘地点的低浓度可能是由于 2023年夏季的强降雨可能重新分配了采样地点海岸附近的地表沉积物.
Figure 5. Left; relationship between total mercury and estimated organic carbon in all freshwater sediment samples. Right; Relationship between percent organic carbon and total mercury in the samples below the freshwater PEL.
Taken as a whole, 研究结果进一步表明，在米尔塘大坝上下的沉积物中存在不同数量的汞, 大坝上方的许多沉积物具有当地污染沉积物的特征(Seelen), 2021).
我在2024年3月的美国地质学会东北分会会议上介绍了这项研究(Ward等人)., 2024). 我将与达勒姆镇分享这次演讲和我今年春天完成的论文，希望它能用于指导沉积物清除决策. 计划中的沉积物清除将防止沉积物向下游流入大海湾, ultimately preventing its contamination.
感谢Julie Bryce和Maria Florencia Fahnestock的指导和水银专业知识. Thank you to the Hamel Center for Undergraduate Research—and Mr. Dana Hamel in particular—for the funding for this project.
References
Castoldi, A. F., Coccini, T., & Manzo, L. (2003). Neurotoxic and Molecular Effects of Methylmercury in Humans. Reviews on Environmental Health, 18 (1). http://doi.org/10.1515/reveh.2003.18.1.19
Canadian Sediment Quality Guidelines for the Protection of Aquatic Life. (2002). http://www.popstoolkit.com/Tools/SitePrioritization/Files/Guidelines/Se…
Dandurant, K. (2022, March 8). Durham votes to remove Mill Pond dam with 74% of vote and large turnout. Seacoast Online. http://www.seacoastonline.com/story/news/local/2022/03/08/durham-nh-mi…
Driscoll, C. T., Mason, R. P., Chan, H. M., Jacob, D. J., & Pirrone, N. (2013). Mercury as a Global Pollutant: Sources, Pathways, and Effects. Environmental Science & Technology, 47(10), 4967–4983. http://doi.org/10.1021/es305071v
Miller, H. (2020). 对溃坝科学领域的贡献:Mill Pond and Sawyer Mill泥沙特征分析(2020). Inquiry Journal, 7. http://scholars.rivercitysessions.com/inquiry_2020/7
New Hampshire Department of Environmental Services (2024). Projects: Planned, Completed and Under Consideration. http://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/2020-01/…
Seelen, E. A., Chen, C. Y., Balcom, P. H., Buckman, K. L., Taylor, V. F., & Mason, R. P. (2021). 相对于未受污染的地点，历史污染改变了温带河口的汞来源和循环. Water Research, 190, 116684–116684. http://doi.org/10.1016/j.watres.2020.116684
Ward, J., Bryce, J., & Fahnestock, M.F. (2024). Sediment Mercury Above and Below the Head-of-Tide Mill Pond Dam in Durham, NH, Geological Society of America Abstracts with Programs. Vol. 56, No. 1. doi: 10.1130/abs/2024NE-397667.
Author and Mentor Bios
Oyster River in Durham , NH.
Originally from South Kingstown, Rhode Island, Julia Ward 将于2024年5月毕业，获得环境科学理学学士学位:地球系统. 她通过哈默尔大学本科生研究中心的暑期本科生研究奖学金进行了这项研究，并继续研究这个项目，以完成一篇本科论文. 朱莉娅对地球化学的兴趣吸引了她，她很高兴能参与一个涉及当地事物的项目. She learned that research is a process that has unexpected challenges, 但特别喜欢这个项目的实地考察方面，在外面看到实地的地点. Julia enjoyed connecting the fieldwork with the analysis of this project, collecting the samples that she ended up working with for the next six months. She decided to publish in Inquiry 因为她想把她的研究成果分享到一个人们可以读到的地方，并为更普通的读者写一些东西. 她计划毕业后在自己的领域找到工作，而这段研究经历为她实现这一目标提供了宝贵的技能.
Dr. Julie Bryce 是地球科学教授，也是地球科学系的本科生协调员. 主要研究方向为微量元素和同位素地球化学在地球表面和深部环境中时间和轨道过程的应用. 除了研究元素和同位素是如何在地球系统中循环的之外. Bryce also has projects collaboratively with faculty in other disciplines.
Copyright 2024, Julia Ward
