Benthic community structure in relation to an instantaneous discharge of waste water from a tin mine

Southwest Cornwall, UK, has a long history of metal mining which has resulted in the establishment, over historical time, of a marked gradient in heavy metal concentrations in the sediments of creeks in the Fal Estuary system. In 1991 Wheal Jane, the last tin mine in the Carnon Valley, closed and the mine workings and Tailings Dam filled with acidic metalliferous water. A plug in the Nangiles adit gave way in January 1992, causing a massive discharge of this water, via the Carnon river, into Restronguet Creek and Carrick Roads. At that time the event was widely reported in national news media as a major catastrophe. Sediment samples for analyses of sediment metal concentrations and associated infaunal communities were collected in November 1991, in anticipation of this event, and again in March, 2 months after the overflow. Analyses of the heavy metals data showed that there was no significant difference in sediment concentrations between these dates. Small changes were found in the meio- and macrobenthic communities but these could be attributed to natural fluctuations in populations over the intervening winter period. We conclude that the overflow had no significant effect on the benthic infauna in the estuary