HEY WHERE DID THAT COME FROM? - A COMBINED GEOCHEMCIAL AND GEOPHYSICAL APPROACH TO SEDIMENT TRANSPORT DYNAMICS

Material, such as organic industrial chemicals, heavy metals, pharmaceutical chemicals, radio-active isotopes and others, are often linked to anthropogenic events and discharges. Dissolved anthropogenic and natural elements and compounds are often reactive and adsorb to a variety of surfaces prevalent in fine-grained sediments (FGS). Previous research in New York Harbor has located the geochemical fingerprint of the World Trade Center ash in isolated FGS deposits. Understanding the initial spatial distribution and changes to the temporal and spatial aspects of FGS deposits is critically important when prospecting for, evaluating and/or remediating anthropogenic impacts resulting from identifiable events such as this. The temporal aspects are vital when considering sediment transport mechanisms and material fate.

We present a coupled geophysical and geochemical approach to tracing the movement of material through areas of ephemeral, metastable and stable accretion and erosion. This approach assesses the spatial and temporal aspects of sediment transport and provides insight into where certain geochemical species originated, how long they have been in the system and their ultimate fate. Our approach uses high-resolution geophysics to aerially and volumetrically map source and sink areas with an initial survey. Concurrent with this survey, surficial sediment samples and/or sediment cores are collected to geochemically characterize and construct inventories of source and sink areas and provide detailed geochronologies. Repeated surveys and sampling integrate temporal and spatial aspects in a sediment budget and sediment/geochemical transport model that are related to specific events within the basin.

Initial data collected from sites within Boston Harbor will be shown to illustrate the initial geophysical surveying and geochemical inventory construction phases of the integrated approach.