Estuarine foraminifera from South West England: impact of metal pollution in a mining heritage area

Abstract

The southern coastline of SW England is characterized by a number of drowned river valleys (known locally as rias) that contain a range of important estuarine environments including saltmarsh, mud flats, sea grass meadows and open marine sands. All of these ‘rias’ drain catchments with Devonian and Carboniferous rocks that were intruded by granite during the Variscan Orogeny and which were mineralized at that time. The Cornwall and West Devon Mining Heritage UNESCO World Heritage Site records the exploitation of these minerals since Roman times, though mining ceased in the twentieth century. All these mineralized rocks, mining waste and the occasional ‘flood’ of old mine workings have contaminated the estuaries with Cu, Zn, Sn, As, Cr, Hg, Ag, etc., which, in many places, may have left a record of foraminifera with test abnormalities. Since 1973, in a series of student-led projects, the estuaries of the region have been studied for their foraminiferal assemblages, sometimes including sampling strategies that meant monthly, or 3-monthly, suites of samples being collected. The Fal Estuary is one of the largest and most complex of the ‘rias’ and, while draining mineralized areas, also suffered a major release of acidic mine waste during a flood in January 1992. Recovery from that ‘event’ showed that the total absence of foraminifera began to recover within 2 years and assemblages have now returned to pre-incident levels, though still recording malformed individuals. This re-colonization is probably the result of propagule dispersion from more open waters of the Fal Estuary.