Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Carl T. Friedrichs
The transport and fate of fine-grained sediments is a critical factor affecting the physical, chemical, and biological health of estuaries, coastal embayments, riverine, lacustrine, and continental shelf environments. A geophysical and sedimentological study of the York River as a part of the NSF Multi-disciplinary Benthic Exchange Dynamics (MUDBED) project was conducted to determine: 1) the primary drivers of sediment erodibility within a fine-grained system, 2) if these drivers can be accurately measured through sedimentological and acoustic information, and 3) the spatial and seasonal variability of erosion within the estuary. Previous studies indicate that increased erodibility within the York River Estuary is mainly due to recent ephemeral deposition, whereas lower erodibility is associated with eroded or biologically reworked conditions. By studying key physical and biological parameters in the York River estuary, we can more generally apply knowledge gained on relationships among sediment facies, seabed erodibility, and the recent history of deposition, erosion, consolidation, and biological reworking. Three different experiments were conducted to look at erosion, deposition, consolidation, and biological reworking in the Clay Bank region of the York River Estuary, each highlighting varying scales of temporal change. The first experimental approach utilized an Imagenex 881A rotary sonar for one- to three-month deployments to examine surficial changes of the seabed, from hourly to monthly timescales, and allow scientists to track movement of sediment in and out of the system using sonar imagery. Optimized parameters were determined for cohesive sediment environments and a real-time observing rotary sonar was created to analyze the seabed on an hourly basis. In the second experiment, cores were collected on a weekly basis to investigate relationships between sediment properties and erodibility during the post-freshet dissipation of the mid-estuary turbidity maximum as well as over the spring-neap cycle. Grain size, water content, abundance of resilient pellets, the occurrence of 7Be, and x-radiographs were analyzed and compared to the results of Gust microcosm erosion tests to further constrain the controls on erodibility. The third experimental approach utilized seven high-resolution bathymetric surveys conducted between September 2008 and August 2009 within a 3.75 km 2 region at Clay Bank. Seabed height was shown to vary both spatially and temporally in association with the spring freshet, likely related to the presence and migration of a local secondary turbidity maximum.
© The Author
Kraatz, Lindsey M., "Acoustic and sedimentological investigations of seabed conditions and related bio-geological parameters in a tidally energetic, fine-grained environment: York River Estuary, Virginia" (2013). Dissertations, Theses, and Masters Projects. Paper 1539616722.