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Contemporary lake transport processes determined from sedimentary records of copper mining activity.

In the recent past (ca. 1850) copper was mined in the catchment of Coniston Water in the English Lake District. Chemical analysis of sediment cores shows a clear record of this activity. Although the mining effluent entered the lake at one place, elevated concentrations of Cu, Fe, Mg, and Ca were observed at all five sites investigated, showing the domination of random transport processes in distributing sediment material. Other effects such as progressive downstream settling, which play a minor but significant role in the local copper loading, are identified. A constant excess Cu:S ratio of 2:1 indicated that Cu is present in the sediments as chalcopyrite and that is was transported from the mine workings in particulate form. Mn accumulation is mediated by redox processes, and so the final concentration in the sediment depends on the depth of the overlying water and the availability of organic carbon.