Coastal sediments

On September 28, 2022, Hurricane Ian, a large Category 4 hurricane, caused catastrophic damage and significant morphologic change along the southwest Florida barrier islands. This study evaluates the morphologic changes and sedimentological signatures of deposits resulting from Hurricane Ian through a combination of sediment cores, RTK-GPS beach profiles, and pre- and post-storm digital elevation models. During the storm, bidirectional sediment transport processes occurred along both developed and undeveloped shorelines, producing extensive washover deposits and ebb scour channels from the flood and ebb surges, respectively. Washover deposits contained interbedded sand and shell fragments with vertical grain size distributions dependent on position relative to the dune crest. Both washover deposits and ebb scour channels formed along dune crest elevational lows and were limited by dense vegetation and anthropogenic structures. Results from this study can be used to better constrain morphologic changes resulting from bidirectional sediment transport processes during large magnitude storm events.

Plastic pollution in the marine environment is a global occurrence. Microplastics have been documented in numerous marine systems and organisms. Coastal estuaries and beach systems are at high risk for microplastic pollution. The distribution, abundance, and hazards microplastics present in these marine environments is not fully understood but are widely recognized as needed to support efforts aiming to protect and enhance these extremely valuable marine systems. This project aimed to quantify the abundance and variation of microplastics in estuarine mangrove and open coast beach sediments on Southeast Florida barrier islands, which are vulnerable and important coastal ecosystems. Barrier islands serve as a buffer between Florida’s wetland environments, reefs, and other marine habitats and may serve as a conduit or temporary sink for microplastics entering the ocean. The microplastic pollution present in estuarine mangrove and open coast beach systems may also elucidate patterns of microplastic pollution in the surrounding or similar coastal environments. There have been no extensive studies or monitoring efforts evaluating microplastics in Southeast Florida barrier islands sediments, nor comparing geomorphic properties of an area on microplastic accumulation. Study sites included back barrier estuarine mangroves and open coast beaches at three regionally similar but geomorphically distinct study sites throughout Palm Beach County, Florida. The sites were sampled seasonally in 2022 (i.e., summer and winter) to quantify the spatiotemporal distribution of microplastics.

Harmful organic contaminants, such as petroleum hydrocarbons, are ubiquitous in coastal marine ecosystems around the world, a problem that will only be exacerbated with rising sea level and increased inundation of coastal urban areas. Therefore, it is necessary to understand the fate of these contaminants following their deposition on marine sediment, where they can potentially persist for long periods of time. As organic carbon remineralization rates depend on the respiration process employed by the bacteria in the sediment, it was the goal of this study to determine how the sediment redox environment, with an emphasis on Fe redox chemistry, affects the biodegradation of recalcitrant petroleum hydrocarbon compounds. While amendment of natural sediment with Fe minerals that are commonly transported to coastal areas following erosion from continental crust did successfully catalyze Fe reduction and inhibit sulfate reduction, the effect on the hydrocarbon biodegradation rate was negligible. However, inoculation of the sediment with Shewanella oneidensis, an exoelectrogenic, Fe reducing bacteria known to catalyze the degradation of hydrocarbon compounds found in crude oil, did
significantly affect the redox environment and sediment microbial communities and alter the pattern of hydrocarbon loss in the sediment over time.