Longterm Trends

One of the principal reasons for constructing sediment chronologies of particle-associated contaminants is to ascertain whether strategies for reducing contaminant inputs to an estuary are effective. Decreases in contaminant concentration in recently deposited sediments suggest that, although recent inputs may have declined, there remains a reservoir of contaminated sediment that is buried in the sediments. With increasing depth of burial, this material is less likely to be exposed to the fauna of the system. However, it is also possible that large scale, aperiodic events such as major storms can tilt the estuarine dynamic equilibrium in favor of large-scale erosion and transport of the contaminated sediment. The possibility of such large-scale sediment transport events has been recognized recently by Robin Bell of Lamont-Doherty Earth Observatory, Roger Flood of the Marine Sciences Research Center, and their colleagues (Chapter 5). Their work on long sediment cores, combined with a mapping of the sub-bottom morphology using acoustic approaches, indicates that the sediments of the Hudson preserve the record of disruptive events such as major storms that are able to mobilize large quantities of sediment. Such considerations are important in deciding how to handle reservoirs of contaminated sediment that may be buriedbut ultimately exposed if the estuarine equilibrium shifts.

A critical need in deciding between different courses of action withrespect to contaminated sediment in the Hudson is an adequate database of dated sediment cores on which contaminant concentrations have been measured. Unfortunately, this is not a one-time effort but must be done repeatedly (perhaps decadally) over time to ascertain trends in sediment contaminants. The effort can be simplified by locating areas in the estuary where sediment deposition is rapid and using these as reference sites for the developing record ofcon-taminant deposition. Such long-term databases of sediment and contaminant chronologies are critical to effective management of the Hudson River Estuary.

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