Historic development of heavy metal contamination into the Firth of Thames, New Zealand

S Boehnert,D Hebbeln,S Ruiz Soto,B R S Fox,Y Yokoyama

doi:10.1007/s00367-019-00597-9

S Boehnert, D Hebbeln + Show 3 more

Open Access

https://doi.org/10.1007/s00367-019-00597-9

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Abstract

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.

Highlights

Anthropogenic influences on coastal marine ecosystems can date back several centuries or even millennia, with severely increasing impacts during the last two centuries
The objectives of this study are to (i) reconstruct past heavy metal inputs, here Pb and Zn, to the shallow marine environment, (ii) identify the source for humaninduced inputs and (iii) quantify the impact of anthropogenic change by using X-ray fluorescence (XRF) data obtained on subtidal sediment cores from the Firth of Thames
A strong H2S smell was obvious after splitting of the cores NZ-M-1, NZ-M-4, NZ-M-5, NZ-M-6, NZ-M-7 and NZ-M-8

Summary

Introduction

Anthropogenic influences on coastal marine ecosystems can date back several centuries or even millennia, with severely increasing impacts during the last two centuries Often this is accompanied by the rising release of various pollutants into the environment. The causes and the temporal development of enhanced inputs of contaminants, such as heavy metals, to the marine environment, near-coastal sediment depocentres can provide high-resolution sedimentary archives. These have a great potential for the reconstruction of heavy metal inputs through time and to differentiate between anthropogenic or natural causes. With respect to the unique settlement history of New Zealand, it might be speculated that with the onset of the European Era other near-coastal areas in the vicinity to New Zealand mining districts experienced heavy metal pollution similar to the Firth of Thames

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