Responses of estuarine benthic macrofauna in copper-contaminated sediments to remediation of sediment quality

A 2-year microcosm experiment was undertaken to investigate the impact of copper on the benthic fauna of the lower Tyne Estuary (UK). During a 1-year simulated contamination period, 1 mg l−1 copper was supplied at 2-weekly 30% water changes, at the end of which the sediment concentrations of copper in contaminated microcosms reached 411 μg g−1. Toxicity effects reduced populations of the four dominant taxa (Malacoceros fuliginosus, Capitella capitata, nematodes and Tubificoides spp.). When copper dosage was ceased and clean water supplied, sediment copper concentrations fell by 50% in less than 4 days, but faunal recovery took up to 1 year, with the pattern varying between taxa. Since the copper leach rate was so rapid it is concluded that after remediation, contaminated sediments show rapid improvements in chemical concentrations, but faunal recovery may not be detected until some time later. Reasons for this are discussed.