Quantifying system disturbance and recovery from historical mining-derived metal contamination at Brotherswater, northwest England

Daniel N Schillereff,Richard C Chiverrell,Janet M Hooke,Katharine E Welsh,Neil Macdonald

doi:10.1007/s10933-016-9907-1

Daniel N Schillereff, Richard C Chiverrell + Show 3 more

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https://doi.org/10.1007/s10933-016-9907-1

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Abstract

Metal ore extraction in historical times has left a legacy of severe contamination in aquatic ecosystems around the world. In the UK, nationwide surveys of present-day pollution discharged from abandoned mines are ongoing but few assessments of the magnitude of contamination and impacts that arose during historical metal mining have been made. We report one of the first multi-centennial records of lead (Pb), zinc (Zn) and copper (Cu) fluxes into a lake (Brotherswater, northwest England) from point-sources in its catchment (Hartsop Hall Mine and Hogget Gill processing plant) and calculate basin-scale inventories of those metals. The pre-mining baseline for metal contamination has been established using sediment cores spanning the past 1500 years and contemporary material obtained through sediment trapping. These data enabled the impact of 250 years of local, small-scale mining (1696–1942) to be quantified and an assessment of the trajectory towards system recovery to be made. The geochemical stratigraphy displayed in twelve sediment cores show strong correspondence to the documented history of metal mining and processing in the catchment. The initial onset in 1696 was detected, peak Pb concentrations (>10,000 µg g−1) and flux (39.4 g m−2 year−1) corresponded to the most intensive mining episode (1863–1871) and twentieth century technological enhancements were reflected as a more muted sedimentary imprint. After careful evaluation, we used these markers to augment a Bayesian age-depth model of the independent geochronology obtained using radioisotope dating (14C, 210Pb, 137Cs and 241Am). Total inventories of Pb, Zn and Cu for the lake basin during the period of active mining were 15,415, 5897 and 363 kg, respectively. The post-mining trajectories for Pb and Zn project a return to pre-mining levels within 54–128 years for Pb and 75–187 years for Zn, although future remobilisation of metal-enriched catchment soils and floodplain sediments could perturb this recovery. We present a transferable paleolimnological approach that highlights flux-based assessments are vital to accurately establish the baseline, impact and trajectory of mining-derived contamination for a lake catchment.

Highlights

Historical mining and metal ore processing has resulted in potentially toxic concentrations of metals building up in waterways and lakes (Blais et al 2015)
Pb profiles in the lake sediments show persistent low concentrations (\100 lg g-1) at depth and a pronounced, repeatable stratigraphy in the upper sections of the 12 cores (Fig. 3). This striking pattern varies in depth across the lake, with less sediment accumulating with greater distance from the delta
Remediation work at Hartsop Hall Mine is not a current priority for the UK Environment Agency (Johnston et al 2008); our estimate that metal concentrations may remain above pre-mining levels for up to another 190 years means this decision could merit re-consideration. Lake sediment records such as that preserved at Brotherswater demonstrate geochemical data can provide a quantitative, historical perspective on anthropogenic metal contamination from local mining activity

Summary

Introduction

Historical mining and metal ore processing has resulted in potentially toxic concentrations of metals building up in waterways and lakes (Blais et al 2015). Metal-enriched effluent may discharge directly from a mine, spoil heap or smelter into aquatic systems (Audry et al 2004; Mayes et al 2013; Boyle et al 2015a), while the emission and subsequent atmospheric deposition of metal particulates can be a source of contamination across much wider scales (Renberg et al 1994; Brannvall et al 2001; Rippey and Douglas 2004). A national-scale assessment of contemporary contaminated discharge from abandoned mines has recently been conducted (Mayes et al 2009, 2010), but few assessments have been made of historical metal fluxes during peak ore extraction in the nineteenth century. Sediment records preserved in lakes offer unique opportunities to reconstruct the magnitude of mining-derived contamination (Farmer et al 1997; Couillard et al 2007; Parviainen et al 2012; Schindler and Kamber 2013) and establish

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