Changes in Benthos Following the Clean-up of a Severely Metal- polluted Cove in the Hudson River Estuary: Environmental Restoration or Ecological Disturbance?

We studied changes in macrobenthic communities following the environmental clean-up of metal-polluted (cadmium, nickel, and cobalt) sediments in Foundry Cove, a small inlet within the Hudson River estuary of New York. We used a BACI-style experiment to test the hypotheses that high levels of cadmium in sediments change macrobenthic assemblages relative to unpolluted areas, and removal of metals (especially cadmium) by dredging will restore the benthos, such that benthic fauna in Foundry Cove are not different from unpolluted areas. In 1984, prior to the restoration work, there were no significant differences between macrobenthic assemblages in polluted and unpolluted locations, indicating that cadmium had little effect on community structure. The lack of an observed toxicity effect may have been caused by the compensatory evolution of resistance to cadmium in dominant organisms. Six years after the restoration work and despite a substantial reduction in metal pollution, there were lower abundances of oligochaetes, nematodes, and chironomids and a higher abundance of polychaetes at Foundry Cove relative to reference locations. Correlative analyses identified greater sediment compaction caused by dredging at Foundry Cove as a possible cause of faunal differences. The results demonstrate that it is difficult to accurately predict the effects of anthropogenic disturbances and restorations in complex natural systems and that unforeseen side effects are inevitable. Documenting these unpredicted effects and experimentally understanding their causes in past restorations will greatly improve the success and cost-effectiveness of future projects of a similar type.