The flux of metals at the tidal limits of major rivers are an important metric of freshwater contaminant transfer to marine habitats, reported in North-East Atlantic bordering countries under the 1992 OSPAR Convention. This paper critically assesses the OSPAR public archive data to estimate the pollution legacy of base metal mining in the major rivers of England and Wales. The data reported for OSPAR are however limited by sample size (12 annual samples to generate a yearly average) and are strongly biased towards low flow sampling, which is likely to considerably underestimate mean total contaminant flux. Alternative methods for assessing long term metal flux are assessed in the River Tyne (2273km2) which has been subject to extensive historical metal mining in its south-western headwaters, coal mining in eastern lowlands and heavy industry along tidal reaches. Using an extension of the sediment rating curve/flow duration approach, annual fluxes of contaminants are estimated at major flow gauging stations based on a 20 year data series of water quality and stream flow. At the tidal limit of the Tyne, mean annual fluxes of 128 tonnes Zn/year are estimated which represent a 37% increase on mean annual flux data reported for OSPAR over the period 1991-2003. While reasonable relationships can be obtained between flow and contaminant concentration using these long-term datasets (r2: 0.4 to 0.8) at larger gauging stations, there is still considerable bias towards low flow water quality data, highlighting the importance of high flow water quality monitoring to improve contaminant-flow relations, and thus flux estimates. These data yield useful information for downstream end-users, such as port authorities and riparian developers who dredge and dispose of metal-contaminated sediments at considerable cost.
Mayes, W. M., Rolls, T., Potter, H. A., & Jarvis, A. P. (2009). Basin scale fluxes of metals from historically mined orefields in the UK. In Proceedings of the 8th International Conference on Acid Rock Drainage