Sediment sourcing in a catchment heavily influenced by historic metal mining :a case study from the South Tyne, UK

Research has been undertaken into the changing spatial provenance of fine-grained overbank deposits contained within a sedimentation zone along the River Nent, UK. Heavily disturbed by historic lead and zinc mining during the 19th century, the complex geochemistry of the catchment has allowed the use of a sediment fingerprinting technique, employing unique metal signatures and a numerical un-mixing model, to identify sediment sources at sub-catchment level. Unequivocal temporal links between the role of individual mines and sediment generation could not be established, however fluctuations in the relative sediment yields of primary sources entering the sedimentation zone supports the theory that mining practices have strongly influenced sediment generation and supply. A chronology of deposition for the sedimentation zone was determined using a combination of metal stratigraphy (lead and zinc) and mineral statistic records. Absolute dating using optically stimulated luminescence (OSL) was also attempted in order to corroborate the proposed chronology; however, the apparent inaccurate results highlight the limitations of this technique within fluvial settings. At least nine key chronological markers were established and the principle periods of deposition were identified as coinciding with phases of intense mining for lead around the early-1820s to 1866 and for zinc from 1880 to 1912. Volumetric estimates of sediments within the sedimentation zone suggest that a substantial input is recorded prior to intensive lead ore extraction and again prior to intensive zinc ore extraction. These events have been attributed to the process of hushing, a hydraulic technique for removing overburden and metal ore from the hillside. The first event, occurring pre-1825, is considered to be instrumental in the initial formation of the sedimentation zone and pre-dates previous estimates regarding the onset of channel change by about 20 years. Sediment budgets, established for each of the developmental stages of the sedimentation zone have identified the Nenthead mine complex as having the single largest, and most sustained, impact upon channel morphology downstream. The modelling exercise has provided a detailed account of a catchment-scale response to disturbance, highlighting the consequence of mining in generating large volumes of sediment and triggering channel change within the Nent. A contribution is made towards the application of sediment fingerprinting techniques using numerous sediment sources, the strengths and limitations of metal stratigraphy in mining-rich catchments and a greater understanding of effects of anthropogenic disturbance upon rivers within upland Britain. In addition to identifying specific primary and secondary sediment source regions and establishing an improved time series for channel change within the Nent, the results form a basis for future research within this catchment. In particular, the proposed sediment budgets highlight the need to focus attention towards understanding the potential risks posed by the quantities of spoil which remain in the Nent headwaters. Increased erosion and runoff as a result of climate change could result in large quantities of contaminated fine sediment entering the channel once again and the impact of mining may be viewed as indicative of future channel and environmental change within the Nent