Date of Award

12-10-2022

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Till J.J. Hanebuth

Second Advisor

Zhixiong Shen

Third Advisor

April Abbott

Abstract

The Georgetown inner harbor is an abandoned oxbow-like river loop and a vital historic site with a wealth of traditional businesses and heavy local industry located within Winyah Bay. Since the modification of the Sampit River in 1949, chronic rapid silting has plagued the inner harbor. With these substantial amounts of fine-grained material accumulating inside the inner harbor, business operations along the waterfront, navigational and maritime operations, and contamination within the harbor are of major concern. The goals of this study were to (a) understand the silting dynamics inside the inner harbor, (b) identify heavy metals which might be of environmental concern and their potential sources, and (c) decipher changes in metal content above and below the stratigraphic boundary indicating the past dredging depth to see if sources may have been different before and after dredging. To accomplish these goals, four sediment cores were taken throughout the inner harbor. Physical and geochemical properties of each core were examined including grain size distribution, total organic content, dry bulk density, X-ray fluorescence core scanner element intensity distribution, X-ray images, and heavy metal concentrations. Supplemental samples were collected and measured for grain size distribution including three suspended sediment samples, 12 piston cores, and six grab samples. In-situ turbidity measurements from two sites within Winyah Bay were also examined. The sediment within the inner harbor is composed of 52 ± 0.47% of cohesive material (finer than 10 μm) with at least 15 ± 0.12% of total organic matter. The mud that reaches the inner harbor settles in the form of flocculated suspension. This process causes 2.65% more coarser material (between 20 and 40 μm) to settle at the two harbor entrances, while 2.87% more finer material (less than 10 μm) is deposited in the backside of the harbor loop. Deposition occurs during periods of slack tide until the accommodation space available has been filled up to less than 4 m in the eastern channel and 0.6 m in the western. This study shows that silting of the inner harbor happens over a few lunar tidal cycles, i.e., within a few months. Heavy metals, including arsenic (19.3 to 23.8 ppm), chromium (77.4 to 105.6 ppm), copper (26.8 to 40.2 ppm), nickel (28.8 to 36.6 ppm), and zinc (90.7 to 180.3 ppm), were found to be above Effects Range Low (ERL) concentrations (Long and Morgan 1990, Long et al. 1995, MacDonald et al. 1996). The lateral and vertical distribution of these metals was found to differ by specific metal. Vertically, in the eastern channel, lead and chromium were observed in higher concentrations below the dredge boundary. Above the dredge boundary, when compared to below, Br was higher in the eastern channel and Mn in at the eastern entrance to the inner harbor. Potential sources identified, based of lateral distribution of metal content, include industrial sources, shipyards and marinas, and local business and tourism along the waterfront.

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