Near-coastal marine sediments often provide high-resolution records of various anthropogenic influences such as the release of heavy metals, which pose a potentially negative influence on aquatic ecosystems because of their toxicity and persistence. In places, the gradual onset of man-made heavy metal emission dates back to ~ 4500 years BP and is difficult to distinguish from potential natural sources. New Zealand offers a perfect setting for studies on anthropogenic impact due to its well-defined three-step development: pre-human era (until ~ 1300 CE), Polynesian era (~ 1300–1800 CE) and European era (since ~ 1840 CE). However, hardly any information exists about the degree of heavy metal input to New Zealand’s coastal areas and the ‘pristine’ natural background values. This study determines the natural background contents of lead (Pb) and zinc (Zn) in marine sediments of the Firth of Thames, a shallow marine embayment on New Zealand’s North Island, and investigates anthropogenic inputs in historic times. Eight sediment cores were analysed by X-ray fluorescence (XRF) for their element composition and temporally resolved by a pollen and radiocarbon-based stratigraphic framework. Sharp increases in Pb and Zn contents occurred simultaneously with the onset of goldmining activities (1867 CE) in the nearby catchment area. The contents of Zn (Pb) increase from very stable values around 60 (13) ppm in the older sediments, interpreted to reflect the natural background values, to an average maximum of 160 (60) ppm near the core top, interpreted to reflect a significant anthropogenic input. These findings unravel the history of contamination in the Firth of Thames and provide an urgently needed database for the assessment of its current ecological state.

中文翻译：

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重金属污染进入新西兰泰晤士河的历史发展

近岸海洋沉积物通常提供各种人为影响的高分辨率记录，例如重金属的释放，由于其毒性和持久性，对水生生态系统造成潜在的负面影响。在某些地方，人为重金属排放的逐渐开始可以追溯到大约 4500 年前的 BP，并且很难与潜在的天然来源区分开来。新西兰因其明确定义的三步发展为研究人为影响提供了完美的环境：前人类时代（直到公元 1300 年）、波利尼西亚时代（公元 1300-1800 年）和欧洲时代（公元 1840 年以来） ）。然而，几乎没有关于新西兰沿海地区重金属输入程度和“原始”自然背景值的任何信息。本研究确定了泰晤士河（新西兰北岛的一个浅海海湾）海洋沉积物中铅 (Pb) 和锌 (Zn) 的自然背景含量，并调查了历史时期的人为输入。通过 X 射线荧光 (XRF) 分析了八个沉积物岩心的元素组成，并通过基于花粉和放射性碳的地层框架进行了时间解析。铅和锌含量的急剧增加与附近集水区的金矿开采活动（公元 1867 年）同时发生。Zn (Pb) 的含量从较老沉积物中的 60 (13) ppm 左右的非常稳定的值增加，解释为反映了自然背景值，到核心顶部附近的平均最大值 160 (60) ppm，解释为反映了重要的人为输入。