PARTICLE DYNAMICS AND SEDIMENT ACCUMULATION IN THE URBANIZED LOWER HUDSON RIVER ESTUARY

Estuaries are dynamic systems that occur at the land-ocean interface. Urbanized estuaries are not only affected by natural processes (such as freshwater discharge, tides, and storms), but also impacted by human activities (such as harbor construction, dredging, and sewage input). In order to discern the spatial and temporal heterogeneity of sedimentation in the lower Hudson River estuary, a combined geophysical, geochemical and geospatial research approach was applied to examine particle dynamics and sediment accumulation in the targeted study area spanning from the George Washington Bridge to the Narrows. The geophysical approach used sidescan sonar and seismic profiling system to image the sediment surface features and the sub-bottom structure. The geochemical approach used two short-lived radioisotopes (¹³¹I and ⁷Be) to examine sediment accumulation over monthly to seasonal time scales. The geospatial approach used GIS as a platform to estimate sediment accumulation over decadal times scales by analyzing historical navigational charts. Our results show that there was a large degree of spatial and temporal heterogeneity in particle dynamics and sediment accumulation within the lower Hudson River estuary. Over monthly and seasonal time scales, sediment accumulation could be as high as 15-20 cm/yr in relatively small areas in the estuaries that are out of equilibrium with their physical regime, such as in the turbidity maximum zone. Over decadal time scales, anthropogenic impacts (such as dredging and dumping) caused sediment accumulation at extremely high rates (> 20cm/yr) on the eastern bank of the Hudson River near George Washington Bridge and sediment erosion in the main river channel, which was balanced by the sediment load input into the system. Future work includes more detailed geochemical and geophysical surveys to better understand particle dynamics over tidal-to-daily time periods and sediment accumulation over the past 18,000 years in association with glacial/interglacial cycles.