Basin-scale fluxes of metals from historically mined orefields in the UK

摘要

The flux of metals at the tidal limits of major rivers are an importantmetric of freshwater contaminant transfer to marine habitats, reported inNorth-East Atlantic bordering countries under the 1992 OSPAR Convention.This paper critically assesses the OSPAR public archive data to estimate thepollution legacy of base metal mining in the major rivers of England andWales. The data reported for OSPAR are however limited by sample size (12 annual samples to generate a yearly average) and are strongly biased towardslow flow sampling, which is likely to considerably underestimate mean totalcontaminant flux. Alternative methods for assessing long term metal flux areassessed in the River Tyne (2273km~2) which has been subject to extensivehistorical metal mining in its south-western headwaters, coal mining in easternlowlands and heavy industry along tidal teaches. Using an extension of thesediment rating curve/flow duration approach, annual fluxes of contaminantsare estimated at major flow gauging stations based on a 20 year data series ofwater quality and stream flow. At the tidal limit of the Tyne, mean annualfluxes of 128 tonnes Zn/year are estimated which represent a 37% increase onmean annual flux data reported for OSPAR over the period 1991-2003. Whilereasonable relationships can be obtained between flow and contaminantconcentration using these long-term datasets (r~2: 0.4 to 0.8) at larger gaugingstations, there is still considerable bias towards low flow water quality data,highlighting the importance of high flow water quality monitoring to improvecontaminant-flow relations, and thus flux estimates. These data yield usefulinformation for downstream end-users, such as port authorities and ripariandevelopers who dredge and dispose of metal-contaminated sediments atconsiderable cost.