Research
Environmental Geochemistry
Tim Kenna preparing plastic tubes for sediment sampling in the Hudson River
Photo by
F. Nitsche.
The Environmental Geochemistry Group at Lamont-Doherty has been measuring contaminant levels and natural isotope ratios in fine-grained sediment cores from areas throughout the Hudson River Watershed for over twenty years. These measurements are used to trace fine-grained sediment transport in the watershed, establish sediment deposition chronologies for the last 50 to 100 years, distinguish important sources and transport pathways of contaminants over these time scales, and study contaminant behavior both during transport and after deposition.
Recent work includes studying plutonium, neptunium and cesium isotope ratios to trace Mohawk River sediments down the Hudson to the upper part of New York Harbor, using ratios of organic compounds to trace Passaic River sediments throughout the Harbor system, using archived, dated sediment cores to investigate new contaminants of concern such as chemicals used in flame retardants, and using urban lake cores to quantify sources and fluxes of a variety of contaminants transported via atmospheric deposition and road runoff in the New York City area over the last 130 years.
The amount of sediment carried by the river is quite variable. The jar on the right contains 250 mg sediment in one liter of river water --- a typical sediment load for a high-flow event such as a storm or the spring snow melt. The jars on the right and the middle contain approximately 5 mg sediment per liter --- a typical load at lower flow conditions.
Other work aims at collaborating with investigators who have used geophysical tools to map much of the bottom sediments in the Hudson River estuary. The overall goal of this work is to combine the temporal information obtained from geochemical analyses of sediment cores with the spatial (horizontal and vertical) information obtained from the geophysical data to investigate sediment transport and storage over different time-scales. This has included using a handheld XRF spectrometer to rapidly obtain metal profiles on a number of cores and translating this information into better time constraints for sediment deposition on large numbers of cores.
Additional studies have focused on real-time monitoring of sediment transport in the upper Hudson and Mohawk rivers using acoustic Doppler current profilers (ADCPs). This technology has shown promise for providing a detailed record of seasonal and event-driven transport in both rivers and may yield improved estimates of the flux of fine-grained sediments into the estuary and New York Harbor.