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

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 pointsources 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 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 lg 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 agedepth model of the independent geochronology obtained using radioisotope dating ( 14 C, 210 Pb, 137 Cs and 241 Am). 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 postmining 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.

Simulating a century of soil erosion for agricultural catchment management

“…For these two lakes, the linear‐interpolated mineral sediment accumulation rates were combined by taking an average weighted according to the lake area apportioned into sedimentation zones. For Brotherswater, sedimentation zones were characterized by drawing on an additional nine cores that encompass lake‐wide variation in sedimentation rates (Schillereff et al ., ) to apportion a delta‐proximal higher‐rate zone (25% of lake area) versus a lower‐rate zone spanning the remaining lake area. Additional cores were unavailable for Loch of the Lowes.…”

“…Therefore, lake‐centre cores were considered to provide a reasonable approximation of mean lake sedimentation in the absence of pronounced inflow deltas. In contrast, sediment cores ( n = 3 each for dating) were retrieved from delta‐proximal to more distal locations in Brotherswater and Loch of the Lowes, where there is a clear gradient in sedimentation rates away from the inflow delta (Schillereff et al ., ).…”

Deciphering long‐term records of natural variability and human impact as recorded in lake sediments: a palaeolimnological puzzle

“…The exploitation of metal deposits has a long history, and there is increasing evidence of the negative impacts these trace metals have on aquatic ecosystems . Metal pollution can occur in lake ecosystems as a form of point‐source pollution (e.g., from a local mine) with deposited lead and zinc concentrations reaching many thousands of parts per million during industrial mining in the 1800s and 1900s . Trace metals may also be released as particulates and are often distributed atmospherically, far beyond the source; contemporary lead enrichment is globally ubiquitous in lake sediments, and >6 times greater than ‘background’ conditions while two‐thirds of current global mercury emissions are from human activity.…”

“…[110][111][112] Metal pollution can occur in lake ecosystems as a form of point-source pollution (e.g., from a local mine) with deposited lead and zinc concentrations reaching many thousands of parts per million during industrial mining in the 1800s and 1900s. [113][114][115] Trace metals may also be released as particulates and are often distributed atmospherically, far beyond the source 116 ; contemporary lead enrichment is globally ubiquitous in lake sediments, and >6 times greater than 'background' conditions 117 while two-thirds of current global mercury emissions are from human activity. On millennial timescales, atmospherically transported lead emissions are associated with ore exploitation during the Bronze Age (5000-3500 yr BP), Roman (ca.…”

Understanding the impact of millennial to sub-decadal climate and limnological change on the stability of As in lacustrine sediments

“…The use of high-resolution, non-destructive, X-ray fluorescence core scanners (XRF-CS) has become commonplace in the study of paleoenvironments and paleoclimate (Turner et al 2010;Giralt et al 2011;Gregory et al 2015;Profe et al 2016;, sediment provenance (Kujau et al 2010;Hunt et al 2015;Zielhofer et al 2017) and soil and sediment contamination Miller et al 2015;Rodríguez-Germade et al 2015;Lintern et al 2016;Schillereff et al 2016). X-ray fluorescence core scanners are capable of analyzing sediment cores at up to 0.1 mm resolution at < 30 s per interval, offering a major advantage in speed, cost, and resolution over conventional geochemical analysis (ED-or WD-XRF, ICP-MS, INAA).…”