The hydrography and ecology of an estuary polluted by acid mine drainage : Dulas Bay, Anglesey, U.K

• Main Author: Jones, Andrea Parry
• Published: University of Manchester 1995
• Subjects: 551.48
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.550902

The behaviour of Fe, Cu, Zn and Mn and their ecological impact have been examined in Dulas Bay, Anglesey, UK. Dulas Bay receives metal-rich run-off from a disused copper mine via the Afon Goch. Variations in stream discharge conditions affect the concentration and partitioning of metals entering the estuary. Metal concentrations in the Afon Goch (eg. Fe 752, Cu 659, Zn 1810, Mn 526 ~g/l) are one to two orders of magnitude higher than those found in other Welsh streams draining mineralised catchments. During estuarine mixing, a large proportion of the Fe was removed from solution by flocculation, occurring over the salinity range 0-8%0. There was also removal of Cu, and Zn to a lesser extent. The behaviour of Mn was more variable, ranging from conservative to non-conservative. Analysis of the estuarine sediments has revealed gross contamination with metals (Fe 5.08%, Cu 2007, Zn 1200, Mn 427 ~g/g), such that Dulas Bay is among the UK's most metal-polluted sites. High freshwater flows appear to bring about resuspension of estuarine sediments, with the release of porewater enriched in trace metals. Under these conditions, elevated levels of heavy metals will be released to the coastal waters of the Irish Sea. Thus Dulas Bay can act as both a source and sink for metals, depending on the prevailing hydrological conditions. The concentrations of dissolved eu and Zn entering the estuary exceed levels known to produce toxic effects in marine organisms. Analysis of the sediments has revealed a very restricted infaunal community in comparison with nearby unpolluted sites; only two species were present in any number - the polychaete N ereis diversicolor and the amphipod Corophium v olutator. The distribution of rocky shore fauna also appears to be limited. There is evidence for metal tolerance in N. diversicolor and C. volutator from Dulas Bay, and this study has demonstrated tolerance in the gastropod Littorina saxatilis. The only other abundant invertebrate species present at Dulas Bay are barnacles (Semibalanus balanoides and Elminius modestus) and they appear to survive by virtue of their naturally efficient detoxification systems.