A numerical investigation of wave-supported gravity flow during cold fronts over the Atchafalaya Shelf

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(9), (2020): e2019JC015269, doi:10.1029/2019JC015269Wave‐supported fluid mud (WSFM) plays an important role in sediment downslope transport on the continental shelves. In this study, we incorporated WSFM processes in the wave boundary layer (WBL) into the Community Sediment Transport Modeling System (CSTMS) on the platform of the Coupled Ocean‐Atmosphere‐Wave‐and‐Sediment Transport modeling system (COAWST). The WSFM module was introduced between the bottommost water layer and top sediment layer, which accounted for the key sediment exchange processes (e.g., resuspension, vertical settling, diffusion, and horizontal advection) at the water‐WBL and WBL‐sediment bed boundaries. To test its robustness, we adapted the updated model (CSTMS + WBL) to the Atchafalaya shelf in the northern Gulf of Mexico and successfully reproduced the sediment dynamics in March 2008, when active WSFM processes were reported. Compared with original CSTMS results, including WSFM module weakened the overall intensity of sediment resuspension, and the CSTMS + WBL model simulated a lutocline between the WBL and overlying water due to the formation of WSFM. Downslope WSFM transport resulted in offshore deposition (>4 cm), which greatly changed the net erosion/deposition pattern on the inner shelf off the Chenier Plain. WSFM flux was comparable with suspended sediment flux (SSF) off the Atchafalaya Bay, and it peaked along the Chenier Plain coast where wave activities were strong and the bathymetric slope was steep. The influence of fluvial sediment supply on sediment dynamics was limited in the Atchafalaya Bay. Sensitivity tests of free settling, flocculation, and hindered settling effects suggested that sediments were transported further offshore due to reduced settling velocity in the WBL once fluid mud was formed. Although sediment concentration in the WBL was sensitive to surface sediment critical shear stress, cohesive bed behavior was less important in WSFM dynamics when compared with strong hydrodynamic during cold fronts.Research support provided through NSF CyberSEES (Award CCF‐1856359), NASA (Award NNH17ZHA002C), Louisiana Board of Regents (award number NASA/LEQSF(2018‐20)‐Phase3‐11), Bureau of Ocean Energy Management (Cooperative Agreement Award M20AC00007), NSF Coastal SEES (Award EAR‐1427389 ), NSF (Award OCE‐20203676), and LSU Foundation Billy and Ann Harrison Endowment for Sedimentary Geology.2021-02-1

Fate and Transport of the Microbiome in Built Environments

Buildings are complex ecosystems evolving continuously. Indoor components such as occupants, ventilation system, and building structures influence the microbiome. To shed light on how the microbial population in a building will respond to such a fluid system, the fundamental interactions between microbes and the indoor ecosystem must be understood. Buildings are being designed as air-tight structures to save energy; however, this could lead to degradation of indoor air quality through indoor sources of contaminants and/or containment of pollutants in the room or introduce outdoor pollutants indoors depending on the ventilation conditions. In addition, transmission of infectious microbes in indoors threaten the health and well-being of people sharing the indoor spaces. Recent outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have brought to attention the significance of understanding indoor microbial fate and transmission mechanisms. This study focused on transitioning the existing body of knowledge on indoor environment and microbiome towards informing building design and generating insight into the mechanisms governing microbial fate and transport in indoor spaces. An extensive literature review coupled with fractional factorial design approach was applied to identify bacterial families as bio-fingerprints of spaces for the first time. The bio-fingerprints allows the prediction of the possible bacteria present in a building space considering gender, age, and building usage. Field sampling at educational buildings extended knowledge of the influence of occupant characteristics, surface type and the influence of air exchange systems: vents, doors, and windows. While presence of occupants resulted in an increase in particles and microbes, activity significantly influenced bacterial quantity from outdoor sources. Microbial levels were significant depending on whether the age group of the occupants was averaging under or over the 10-year-old, indicating that policies to improve indoor air quality need to account for the distinct nature of elementary schools while high schools and universities may have more similar traits. For surface materials, bacterial levels were lowest on metals and highest on carpets and, tiles. The ventilation system had minimal influence on the removal of microbes generated from indoor sources. The analysis highlighted possible dominance of wall and boundary effects on bacterial transport before occupants’ influence take over. To gain better understanding of boundary effects and surface – microbes interactions, the influence of surface properties, surface types, external forces (inertial force and shear stress) were investigated. Enveloped viruses, vaccinia virus (VACV) and measles virus (MV), bacteria (Corynebacterium sp.) and bovine serum albumin (BSA) were applied. Quartz crystal microbalance with dissipation (QCM-D) was used to measure the change of mass on a range of ‘ideal’ surfaces for varying flow rates and to determine the adhesion kinetics governing the attachment and detachment process. Centrifugal experiments tested bacterial attachment and detachment from ‘real’ surfaces. Attachment and detachment kinetics were unique to each microbesurface combination and shear stress magnitudes governed the extent of detachment