Tracing and dating past contamination- and extreme weather events in a historical mining area: A multiproxy investigation of peat cores from Falun

Abstract

The contamination history of Falun dates back several centuries due to its extensive mining industry. An occurrence that may have reinforced the spreading of mining contaminants and contributed to extensive erosion was the local extreme weather event that occurred on the 27th of July 1666, which resulted in widespread flooding and put the Falun Copper Mine at risk of destruction. The aim of this investigation is to establish how long-term or extreme weather events can be traced, identified, and dated in peat stratigraphy, especially in an area with past mining contamination. Peat cores extracted from a preserved peat bog northwest of the Falun Copper Mine were analysed using a multiproxy approach, including methods like stratigraphy description, 14C dating, loss on ignition, and portable X-ray fluorescence spectroscopy to pinpoint and analyse fluctuations of organic content, metal concentrations, and geochemical proxies. The obtained age results of deposits within the peat cores indicated ages spanning from pre-mining activity to modern times, thus encompassing the active period of the mine. However, the identification of the extreme weather event proved difficult, as it occurred close to both the peak productivity of the mine, and the great collapse in 1687. Despite this, declines in organic content accompanied by fluctuations in Rb/Sr and Zr/Rb in the uppermost 30 cm in a number of the cores could be an indication of potential flood deposits and would thus be of interest for further investigation. Additionally, the methodology applied in this investigation proved to be an efficient and cost-effective first step when conducting a paleoenvironmental investigation of intact peat cores and could, in future investigations, be further improved.