An Ecological Impact Assessment Framework for Decision-Making Related to Sediment Quality

Until recently, one of the primary tools for evaluating sediment quality has been numeric sediment chemistry criteria. Several regulatory agencies have now adopted a tiered evaluation approach, requiring biological evaluation when chemical criteria are exceeded. Recent decisions have been based on a number of rapidly developing methodologies, including bioassay testing and an increasing array of biomonitoring techniques. Although final decisions may be based on large data sets, presently there is no unifying framework against which decision-making and/or the various biological tests being developed for decision-making are or can be judged. Evaluation of published data sets requires a number of assumptions and extrapolations of results from the laboratory to the field, from exposure data to response data, and from acute to chronic testing procedures. Laboratory evaluation of dredged sediment issues depends upon sediment chemistry data, toxicity responses, bioaccumulation data and, for field validation, upon benthic community structure. Interpretation of the mechanism of impact and evaluation of toxicity in a field setting depends on the ability to distinguish the impacts of changes in survival from impacts associated with changes in food availability or food conversion efficiency. We provide a framework which summarizes the linkages between these responses and levels of organization and provides some perspective on data requirements, utility, and interpretation. Most other approaches to decision-making make simplistic assumptions concerning linearity and ecological processes. This framework makes no such assumptions, yet is not so complex as to be only of academic interest. The framework is discussed in relation to the potential effects of dredged material disposal.