Hydrodynamics of artificial and oyster-populated breakwaters: A laboratory study with scaled-down oyster castles under unidirectional flow.

Oyster populations within the Chesapeake Bay have been drastically reduced over the last century mainly due to unregulated human activities and diseases. Regulations and restoration efforts have focused on restoring oyster populations while also considering their ability to provide ecosystem services, such as coastal protection and water quality improvement, among others. To promote oyster growth and the settlement of new populations, a recent technique adopted along the east coast of the US is the use of oyster castles (OCs). OCs have proven effective in recruiting and retaining oysters and in promoting both vertical growth and horizontal expansion of oyster habitats. OCs are widely used in coastal protection as greener alternative to common engineering solutions. We quantified hydrodynamic differences that occur around these OCs during their early stage (i.e. castles without oysters), and with fully developed oysters covering the surface of the castles through a series of laboratory experiments. The experiments were conducted in a recirculating Odell-Kovasznay type channel at the Ecohydraulics and Ecomorphodynamics Laboratory (EEL) at the University of Illinois. OCs (both with and without oysters) were 3D printed at 1:7 scale to fit the canal, and Particle Image Velocimetry (PIV) was used for 2D flow characterization. Data showed noticeable differences in flow acceleration atop the castles when covered with oysters, as well as an increase in the generation and distribution of turbulent kinetic energy atop and around the oyster-covered castles. Magnitudes and spatial distribution of Reynolds stresses were also affected by the presence of oysters in both submerged and near-emergent conditions. Challenges associated with the estimation of the drag coefficient for both gray and oyster-covered OCs highlighted the need for more data besides the centerline 2D PIV output. Further research involving the whole three-dimensional structure of the flow, in both unidirectional and oscillatory conditions, will allow us to provide relevant guidelines on the design and use of oyster-populated breakwaters as a viable nature-based solution for coastal protection within low-energy environments.

Understanding through drone image analysis the interactions between geomorphology, vegetation and marine debris along a sandy spit.

Marine litter (ML) is recognized as one of the main socio-economic and environmental concerns and monitoring operations have been realized worldwide in order to collect information on the types, quantities and distribution of marine debris. In this study, we used Unmanned Aerial Vehicle (UAV) images to map the presence of ML on a coastal spit in relation to geomorphological aspects and vegetation. Our results show that ML is present everywhere, but concentrates in the beach wrack, dunes, and saltmarshes, highlighting the role of the vegetation in trapping ML. Moreover, ML will most probably remain trapped by the saltmarsh vegetation, since they are not visible and easily accessible to allow cleaning operations. On the contrary, cleaning operations may remove the ML present in the beach wrack. Finally, our results provide useful information to support decision-makers for improving beach cleaning activities in the Po river Delta areas (Italy).

What can beach litter tell about local management: A comparison of five pocket beaches of the North Sardinia island (Italy).

Our study provides a first dataset on marine litter collected at five pocket beaches situated in the northern Sardinia (Italy). The monitoring method refers to the operational guidelines for rapid beach assessment of beach waste described by UNEP. We classified the 7975 items collected according to the eight categories and 99 types. Their analysis indicates that plastic is the most common litter category and, plastic fragments are the most frequent debris. The density ranges from 0.05 to 2.82 item/m2. The top 10 highly present marine litter reveals that land-based litter is the main source, probably due to the lack of waste management, massive tourism and recreational activities. In addition, landscape morphology affects the redistribution of marine litter. Overall, these first results are part of a wider study on the presence of marine litter in the pocket beaches of north Sardinia to provide coastal managers and policy makers mitigation strategies.

Examining the dependence of macroplastic fragmentation on coastal processes (Chesapeake Bay, Maryland).

Plastic debris in the coastal environment is subject to complex and poorly characterized weathering processes. To better understand how key environmental factors affect plastic degradation in a coastal zone, we conducted an in situ experiment. We deployed strips of high density polyethylene (HDPE) and polystyrene (PS) in paired coastal areas of contrasting conditions (hydrodynamic activity: erosional or depositional; water depths: subtidal or intertidal). Strips were collected after environmental exposures at 4, 8, and 43 weeks and analyzed for change in mass, algal biofilm growth, and imaged by petrographic and electron microscopy (SEM-EDS). Significant surface erosion was evident on both polymers, and was more rapid and more extensive with PS. Degradation of PS was responsive to intensity of hydrodynamic activity, and was greater at intertidal depths, highlighting the critical role played by photo-oxidation in the coastal zone, and suggesting that algal biofilms may slow degradation by playing a photo-protective role.