Assessing sediment contamination in estuaries

Historic and ongoing sediment contamination adversely affects estuaries, am ong the most productive marine ecosystems in the world. However, all estuar ies are not the same, and estuarine sediments cannot be treated as either f resh or marine sediments or properly assessed without understanding both se asonal and spatial estuarine variability and processes, which are reviewed. Estuaries are physicochemically unique, primarily because of their variabl e salinity but also because of their strong gradients in other parameters, such as temperature, pH, dissolved oxygen, redox potential, and amount and composition of particles. Salinity (overlying and interstitial) Varies spat ially (laterally, vertically) and temporally and is the controlling factor for partitioning of contaminants between sediments and overlying or interst itial water. Salinity also controls the distribution and types of estuarine biota. Benthic infauna are affected by interstitial salinities that can be Very different than overlying salinities, resulting in large-scale seasona l species shifts in salt wedge estuaries. There are fewer estuarine species than fresh or marine species (the paradox of brackish water). Chemical, to xicological, and community-level assessment techniques for estuarine sedime nt are reviewed and assessed, including chemistry (grain size effects, back ground enrichment, bioavailability, sediment quality values, interstitial w ater chemistry), biological surveys, and whole sediment toxicity testing (s ingle-species tests, potential confounding factors, community level tests, laboratory-to-field comparisons). Based on this review, there is a clear ne ed to tailor such assessment techniques specifically for estuarine environm ents. For instance, bioavailability models including equilibrium partitioni ng may have little applicability to estuarine sediments, appropriate refere nce comparisons are difficult in biological surveys, and there are too few full-gradient estuarine sediment toxicity tests available. Specific recomme ndations are made to address these and other issues.