Sediment geochemistry of streams draining abandoned lead/zinc mines in central Wales: the Afon Twymyn

Abstract

Purpose Despite the decline of metal mining in the UK during the early 20th century, a substantial legacy of heavy metal contamination persists in river channel and floodplain sediments. Poor sediment quality is likely to impede the achievement of 'good' chemical and ecological status for surface waters under the European Union Water Framework Directive. This paper examines the environmental legacy of the Dylife lead/zinc mine in the central Wales mining district. Leachable heavy metal concentrations in the bed sediments of the Afon Twymyn are established and the geochemical partitioning, potential mobility and bioavailability of sediment-associated heavy metals are established.Materials and methods Sediment samples were collected from the river bed and dry-sieved into two size fractions (<63 µm and 64-2,000 µm). The fractionated samples were then subjected to a sequential extraction procedure to isolate heavy metals (Pb, Zn, Cu, Cd, Fe, Mn) in three different geochemical phases. Sediment samples were then analysed for heavy metals using ICP-AES. 2Results and discussion The bed sediment of the Afon Twymyn is grossly polluted with heavy metals.Within the vicinity of the former mine, Pb concentrations are up to 100 times greater than levels reported to have deleterious impacts on aquatic ecology. Most heavy metals exist in the most mobile easily exchangeable and carbonate-bound geochemical phases, potentially posing serious threats to ecological integrity and constituting a significant, secondary, diffuse source of pollution. Metal concentrations decrease sharply downstream of the former mine, although there is a gradual increase in the proportion of readily extractable Zn and Cd.Conclusions Implementation of sediment quality guidelines is important in order to achieve the aims of the Water Framework Directive. Assessments of sediment quality should include measurements of background metal concentrations, river water physico-chemistry and, most importantly, metal mobility and potential bioavailability. Uniformity of sediment guidelines throughout Europe and flexibility of targets with regard to the most heavily contaminated mine sites are recommended.

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

“…Falling metal prices, depleted reserves and competition with global markets led to the decline of the UK industry around 1940 (Byrne et al 2010 (Stanley and Vaughan 1982). This vein relates to a regional 'galena-sphalerite' highly saline (marine), low temperature (110-130°C) mineralization phase during the early-Carboniferous (Stanley and Vaughan 1982).…”

“…The significant amplitude of fluctuations in Zn and Cu follows the twentieth century MAR, but this does not fully explain the persistent elevated concentrations contrasted with Pb. One plausible explanation stems from galena deposits being the primary target at Hartsop Hall, leaving greater quantities of sphalerite and copper ores as unworked, exposed waste, leading to a proportionally greater dissolution and efflux of Zn and Cu (Byrne et al 2010). The humid temperate climate and flooddominated hydrological regime generate prevalent oxidizing conditions in the fluvial system (Zoumis et al 2001), which may have accentuated Zn and Cu concentrations in the lake sediments owing to the greater solubility of their oxidized products (Nuttall and Younger 2002).…”

Stormflow hydrochemistry of a river draining an abandoned metal mine: the Afon Twymyn, central Wales

“…This evidence would challenge the picture presented by standard water quality monitoring data that Zn is the primary contaminant from an ecological and water quality perspective (Parsons Brinckerhoff Ltd., 2005). Considering metal loads during stormflows, total Pb loads were up to four times greater than maximum recorded baseflow yields (Byrne 2010; unpublished results). On one occasion (Event 4), the high Pb load was associated with a peak storm discharge which was only exceeded 2% of the time during the study period.…”

Recent advances and future directions in soils and sediments research

“…Tallberg et al 2009;Sutherland 2010;Condron and Newman 2011;Reid et al 2011), and the persistence of chemicals and compounds in deposited sediments (e.g. Byrne et al 2010;Tamtam et al 2011). Studies have also investigated the role of microbial activity in the sorption of chemicals to sediment, and how this may change due to variations in, for example, temperature and redox (e.g.…”