Granmo Malachi N, Reavie Euan D, Post Sara P, Zanko Lawrence M
Natural Resources Research Institute, University of Minnesota Duluth, Duluth, MN, United States of America.
PeerJ. 2020 May 6;8:e9034. doi: 10.7717/peerj.9034. eCollection 2020.
Geochemical analyses applied to lake sedimentary records can reveal the history of pollution by metals and the effects of remedial efforts. Lakes provide ideal environments for geochemical studies because they have steady deposition of fine grained material suitable for fixation of pollutants. The Laurentian Great Lakes are the most studied system in this field, and they have well-preserved chronological profiles. To date, this important system has been considered in parts for inorganic geochemistry, hampering basin-wide conclusions regarding metal contamination. We filled spatial and temporal gaps in a comprehensive geochemical analysis of 11 sediment cores collected from all five Great Lakes. Hierarchical cluster analysis of all Great Lakes samples divided the metal analytes into five functional groups: (1) carbonate elements; (2) metals and oxides with diverse natural sources, including a subgroup of analytes known to be anthropogenically enriched (Cd, Pb, Sn, Zn, and Sb); (3) common crustal elements; (4) metals related to coal and nuclear power generation; and (5) all of the co-occurring rare earth elements. Two contamination indices (I and EF) applied to sedimentary metals indicated that Na, Co, Mn, Cd, Pb, Ta, and Cu were each, at some point during the Anthropocene, the most enriched metal pollutants in Great Lakes sediments. Land uses correlated with the metal analytes, such as increases in contaminant metals with the rise in catchment population and increases in carbonate elements (e.g. Ca) with agriculture. Certain contamination trends were observed basin-wide, such as for the atmospheric pollutant Pb, which followed a rise associated with fossil fuel combustion and a decline following the ban of leaded gasoline. Other trends were lake-specific, such as recent high concentrations of Na in Lake Superior, likely due to road salt applications, and a late-20th-century peak in Ca associated with algal whiting events in Lake Ontario. Some metals exceeded guidelines for sediment quality, in some cases prior to European settlement of the basin, indicating that a paleolimnological context is important for appropriate management of sediment contamination. The Great Lakes are sensitive to environmental changes such as pollution by metals, and it is clear that while there has been remedial success, results from the uppermost intervals of cores indicate ongoing problems.
应用于湖泊沉积记录的地球化学分析能够揭示金属污染的历史以及治理措施的效果。湖泊为地球化学研究提供了理想的环境，因为它们有细粒物质的稳定沉积，适合污染物的固定。劳伦琴五大湖是该领域研究最多的系统，并且它们拥有保存完好的年代学剖面。迄今为止，这个重要的系统在无机地球化学方面只是部分地被研究，这妨碍了得出关于全流域金属污染的结论。我们填补了从五大湖所有区域采集的11个沉积物岩芯综合地球化学分析中的时空空白。对五大湖所有样本进行的层次聚类分析将金属分析物分为五个功能组：（1）碳酸盐元素；（2）具有多种天然来源的金属和氧化物，包括一组已知人为富集的分析物（镉、铅、锡、锌和锑）；（3）常见地壳元素；（4）与煤炭和核能发电相关的金属；（5）所有共有的稀土元素。应用于沉积金属的两个污染指数（I和EF）表明钠、钴、锰、镉、铅、钽和铜在人类世的某个时期分别是五大湖沉积物中富集程度最高的金属污染物。土地利用与金属分析物相关，例如随着集水区人口增加污染物金属增多，以及随着农业发展碳酸盐元素（如钙）增多。在全流域观察到了某些污染趋势，例如大气污染物铅随着化石燃料燃烧而增加，并在含铅汽油被禁用后下降。其他趋势则是特定湖泊独有的，例如苏必利尔湖近期钠浓度高，可能是由于道路撒盐，以及安大略湖在20世纪后期钙含量峰值与藻类白化事件有关。一些金属超过了沉积物质量指南，在某些情况下甚至早于该流域被欧洲人定居之前，这表明古湖沼学背景对于沉积物污染的适当管理很重要。五大湖对诸如金属污染等环境变化很敏感，很明显虽然治理取得了成功，但岩芯最上部间隔的结果表明问题仍在持续。
