Background
Coastal sediments in the northern Gulf of Mexico have a high potential of being contaminated by petroleum hydrocarbons, such as polycyclic aromatic hydrocarbons (PAHs), due to extensive ...petroleum exploration and transportation activities. In this study we evaluated the spatial distribution and contamination sources of PAHs, as well as the bioavailable fraction in the bulk PAH pool, in surface marsh and shelf sediments (top 5 cm) of the northern Gulf of Mexico.
Results
PAH concentrations in this region ranged from 100 to 856 ng g
−1
, with the highest concentrations in Mississippi River mouth sediments followed by marsh sediments and then the lowest concentrations in shelf sediments. The PAH concentrations correlated positively with atomic C/N ratios of sedimentary organic matter (OM), suggesting that terrestrial OM preferentially sorbs PAHs relative to marine OM. PAHs with 2 rings were more abundant than those with 5–6 rings in continental shelf sediments, while the opposite was found in marsh sediments. This distribution pattern suggests different contamination sources between shelf and marsh sediments. Based on diagnostic ratios of PAH isomers and principal component analysis, shelf sediment PAHs were petrogenic and those from marsh sediments were pyrogenic. The proportions of bioavailable PAHs in total PAHs were low, ranging from 0.02% to 0.06%, with higher fractions found in marsh than shelf sediments.
Conclusion
PAH distribution and composition differences between marsh and shelf sediments were influenced by grain size, contamination sources, and the types of organic matter associated with PAHs. Concentrations of PAHs in the study area were below effects low-range, suggesting a low risk to organisms and limited transfer of PAHs into food web. From the source analysis, PAHs in shelf sediments mainly originated from direct petroleum contamination, while those in marsh sediments were from combustion of fossil fuels.
Bottom-mounted instrumentation was deployed at two sites on a large sandy shoal of an ebb tidal delta offshore of the Port Royal Sound of South Carolina of USA to collect hydrodynamics and sediment ...dynamics data. One site (“borrow site”) was 2 km offshore in a dredge pit for nearby beach nourishment and the other site (“reference site”) was 10 km offshore. In situ time-series data were collected during two periods after the dredging: 15 March–12 June (spring) and 18 August–18 November (fall) of 2012. Data at the reference site indicated active migrating bedforms from centimeters to decimeters tall, and sediment concentrations were highly associated with semidiurnal and fortnightly tidal cycles. In the fall deployment, waves at the reference site were higher than those at the shallow borrow site. Both Tropical Storm Beryl and Hurricane Sandy formed high waves and strong currents but did not generate the greatest sediment fluxes. The two sites were at different depths and distances offshore, and waves contributed more to sediment mobility at the reference site whereas tidal forcing was the key controlling factor at the borrow site. This study provides valuable datasets for the selection of sites, prediction of pit infilling, and the modeling of storm impact in future beach nourishment and coastal restoration projects.
Sandy sediments preserved as paleo-channel fill on the inner shelf, some of which are overlain by modern muds, have been mined for barrier island restoration along the northern Gulf of Mexico. These ...mined areas have been termed “mud-capped” dredge pits. The processes governing the morphological evolution of the pits are poorly constrained due to limited observational data. Physical oceanographic (e.g., currents and waves) and sedimentary data were collected at Sandy Point dredge pit offshore Plaquemines Parish, Louisiana in summer 2015. Currents outside the pit flowed southward and/or southeastward at speeds of 8–20 cm/s, while currents inside the pit had speeds less than 2 cm/s with no clear dominant direction. Wave heights detected inside the pit were less than 0.4 m. A high turbidity layer with suspended sediment concentration around 4 g/L was observed above the pit floor, and its thickness was ~0.5 m. With observational data as input, three 2–D numerical models were employed to predict pit morphological responses, including pit infilling, margin erosion and slope change. The model results suggest that resuspension events were rare on the seafloor adjacent to the pit under summer fair weather conditions. Modeled pit margin erosion was very limited. With little resuspension of seafloor sediment locally, weak margin erosion and stable pit walls, the dominant process governing pit evolution was infilling sourced by the deposition of suspended sediments from the Mississippi River plume.
Beach nourishment has been a strategy widely used to slow down coastal erosion in many beaches around the world. The dredging of sand at the borrow site, however, can have complicated physical, ...geological and ecological impacts. Our current knowledge is insufficient to make accurate predictions of sediment infilling in many dredging pits due to lack of detailed sediment data. Two sites in the sandy shoal southeast of Port Royal Sound (PRS) of South Carolina, USA, were sampled 8 times from April 2010 to March 2013; one site (defined as ‘borrow site’) was 2 km offshore and used as the dredging site for beach nourishment of nearby Hilton Head Island in Beaufort County, South Carolina, and the other site (defined as ‘reference site’) was 10 km offshore and not directly impacted by the dredging. A total of 184 surficial sediment samples were collected randomly at two sites during 8 sampling periods. Most sediments were fine sand, with an average grain size of 2.3 phi and an organic matter content less than 2%. After the dredging in December 2011–January 2012, sediments at the borrow site became finer, changing from 1.0 phi to 2.3 phi, and carbonate content decreased from 10% to 4%; changes in mud content and organic matter were small. Compared with the reference site, the borrow site experienced larger variations in mud and carbonate content. An additional 228 sub-samples were gathered from small cores collected at 5 fixed stations in the borrow site and 1 fixed station at the reference site 0, 3, 6, 9, and 12 months after the dredging; these down-core sub-samples were divided into 1-cm slices and analyzed using a laser diffraction particle size analyzer. Most cores were uniform vertically and consisted of fine sand with well to moderately well sorting and nearly symmetrical averaged skewness. Based on the analysis of grain size populations, 2 phi- and 3 phi-sized sediments were the most dynamic sand fractions in PRS. Mud deposition on shoals offshore of PRS presumably happens when offshore mud transport is prevalent and there is a following rapid sand accumulation to bury the mud. However, in this borrow site there was very little accumulation of mud. This will allow the site to be used in future nourishment projects presuming no accumulation of mud occurs in the future.
•Most sediments are fine sand with <2% organic matter content.•Sediments are well sorted and nearly symmetrical in skewness.•Very little mud accumulation was found in the borrow site for beach nourishment.•Major impacts from dredging are on grain size and carbonate content.
We adapted the coupled ocean-sediment transport model to the northern Gulf of Mexico to examine sediment dynamics on seasonal-to-decadal time scales as well as its response to decreased fluvial ...inputs from the Mississippi-Atchafalaya River. Sediment transport on the shelf exhibited contrasting conditions in a year, with strong westward transport in spring, fall, and winter, and relatively weak eastward transport in summer. Sedimentation rate varied from almost zero on the open shelf to more than 10 cm/year near river mouths. A phase shift in river discharge was detected in 1999 and was associated with the El Niño-Southern Oscillation (ENSO) event, after which, water and sediment fluxes decreased by ~20% and ~40%, respectively. Two sensitivity tests were carried out to examine the response of sediment dynamics to high and low river discharge, respectively. With a decreased fluvial supply, sediment flux and sedimentation rate were largely reduced in areas proximal to the deltas, which might accelerate the land loss in down-coast bays and estuaries. The results of two sensitivity tests indicated the decreased river discharge would largely affect sediment balance in waters around the delta. The impact from decreased fluvial input was minimum on the sandy shoals ~100 km west of the Mississippi Delta, where deposition of fluvial sediments was highly affected by winds.
It was proposed that there are at least 250 enzymes in M. tuberculosis involved in lipid metabolism. Rv0045c was predicted to be a hydrolase by amino acid sequence similarity, although its precise ...biochemical characterization and function remained to be defined.
We expressed the Rv0045c protein to high levels in E. coli and purified the protein to high purity. We confirmed that the prepared protein was the Rv0045c protein by mass spectrometry analysis. Circular dichroism spectroscopy analysis showed that the protein possessed abundant β-sheet secondary structure, and confirmed that its conformation was stable in the range pH 6.0-10.0 and at temperatures ≤ 40 °C. Enzyme activity analysis indicated that the Rv0045c protein could efficiently hydrolyze short chain p-nitrophenyl esters (C₂-C₈), and its suitable substrate was p-nitrophenyl caproate (C₆) with optimal catalytic conditions of 39 °C and pH 8.0.
Our results demonstrated that the Rv0045c protein is a novel esterase. These experiments will be helpful in understanding ester/lipid metabolism related to M. tuberculosis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Biomaterial-associated infection and lack of sufficient osseointegration contribute to a large proportion of implant failures. Therefore, antibacterial and osseointegration-accelerating properties ...are important in implant surface design. In this study, a micro/nanoporous titanium surface was prepared through alkaline and heat treatments, covalently conjugated with aminosilane. Then, varying amounts of chlorhexidine (CHX) were covalently grafted onto the aminosilane-modified surface via glutaraldehyde to obtain different CHX-grafted surfaces. These as-prepared surfaces were evaluated in terms of their surface chemical composition, surface topography, CHX grafting amount, antibacterial activity, and osteoblast compatibility. The results showed that the CHX grafting amount increased with increasing CHX concentrations, leading to better antibacterial activity. CHX (1 mg/mL) resulted in the best antibacterial surface, which still retained good osteoblast compatibility. Meanwhile, competitive bacterial-cell adhesion analysis demonstrated that this surface has great value for osteoblast adhesion at the implant–bone interface even in the presence of bacteria. This effortless, easily performed, and eco-friendly technique holds huge promise for clinical applications.
Gravity core EC2005, located in the mud wedge off the Zhejiang-Fujian coast in the inner shelf of the East China Sea （ECS）, was analyzed for its lithology, grain size, rare earth elements （REE） and ...AMS14C dating. Results revealed high-resolution paleoenvironmental evolution and multiple switches of sediment provenances in the inner shelf of ECS. The lithology, grain size and REE concentrations of sediments varied significantly down the core. Mean grain size ranged from 8 to 121 μm, and the values of ΣREE were 152.8-227.9 μg/g. The chondrite- and shale-normalized REE patterns indicated their similarity to the terrigenous sediments in the study area. Between 17.3-12.3 ka BP the sediments in the inner shelf of ECS were mainly originated from local drainage basins. The source then gradually switched to the Yangtze River between 12.3 and 9.8 ka BP. Since about 10-9.8 ka BP, the sediments in the study area were dominantly derived from the Yangtze River. The continuous rising of sea level and formation of coastal current along the inner shelf played a key role in the switches of sediment provenances.
To restore degraded barrier shorelines of the Mississippi River Delta of coastal Louisiana, sand is dredged from high-quality borrow areas on the adjacent continental shelf. This dredging process ...generally creates a topographic low that facilitates the rapid capture of sediments. Our understanding of sedimentary processes and influences on seabed morphologic evolution is still limited. In this study, Raccoon Island dredge pit in a paleo-river channel on the Louisiana shelf was studied via multiple bathymetric surveys. Physical parameters include pit geometry and topographic change from post-dredging, and infilling sediment sources were analyzed. Raccoon Island pit was 100% filled up less than six years after dredging. The average infilling rate in the Raccoon Island pit was 1.10 m/year from 2013 to 2018. During the surveying period, the pit wall slope decreased by 6.8° within two years. The sediment infilling process in the Raccoon Island pit was likely under the combined influence of topography, wind-driven currents, storm waves, and the dynamic Atchafalaya River dispersal system. The Atchafalaya River reached high discharge in 2016, which likely contributed to a surprisingly high sediment infilling rate at Raccoon Island pit between 2015 and 2018. Raccoon Island pit is in a mixed texture environment in which the sandy pit was fully filled with mud. Mud is useful for marsh restoration but is not considered a quality resource for barrier island or beach restoration. Thus, the Raccoon Island pit is not regarded as a renewable resource for future barrier island restoration.
•A long narrow dredge pit located north of Ship Shoal was excavated and the sandy sediments inside the paleo-channel were excavated and transported to Raccoon Island in 2013.•The sediment infilling process in Raccoon Island pit was likely under the combined influence of wind-driven currents, storm waves, and the dynamic Atchafalaya river dispersal systems.•Raccoon Island pit is not considered as a renewable resource for future restoration due to high mud content. Even after 100% infilling, it will take time for sediment and benthic community to reach a status indistinguishable to ambient seafloor.
The subaqueous delta of the Mississippi River, the largest river system in the conterminous U.S., has entered a stage of retrogradation caused by multiple natural and anthropogenic activities. Since ...the 1950s, the suspended sediment load of the Mississippi River has decreased by ~50% due primarily to the construction of >50,000 dams in the Mississippi basin. The impact of this decreased sediment load has been observed in subaerial environments, but the impact on sedimentation and geomorphology of the subaqueous delta front has yet to be examined. To identify historic trends in sedimentation patterns, we compiled bathymetric datasets, including historical charts, industry and academic surveys, and National Oceanic and Atmospheric Administration hydrographic data, collected between 1764 and 2009. The progradation rate (measured at the 10 m depth contour) of Southwest Pass, which receives 69% of the suspended sediment load reaching Head of Passes, has decreased from ~67 m/yr between 1874 and 1940 to ~26 m/yr between 1940 and 1979, with evidence of further deceleration from 1979 to 2009. At South Pass and Pass a Loutre, the delta front has entered the destructive phase, with the 10 m contour retreating at rates >20 m/yr at both passes since 1979. Advancement of the delta front also decelerated in deeper water (in some areas out to ~180 m depth). Except locally, where mudflow lobes are advancing, deeper contours show a pattern of decreasing progradation rate between 1874–1940 and 1979–2005 time periods. Furthermore, based on differences measured between available bathymetric datasets, the sediment accumulation rate across the delta front decreased by ~73% for the same period. The retention rate of Mississippi River sediment on the delta front ranged from 67 to 81% for the time periods assessed, with total sediment load stored on the delta front equal to 317 ± 54 Mt/yr from 1874 to 1940, 145 ± 25 Mt/yr from 1940 to 1979, and 87 ± 15 Mt/yr from 1979 to 2005. We document for the first time that the Mississippi River delta front has entered a phase of retrogradation, which will likely be accelerated by future upstream activities that divert a portion of the sediment load to the upper delta for coastal protection and restoration projects. The decline of the subaqueous Mississippi River Delta has critical implications for biogeochemical cycling, subaqueous mass wasting, and sediment dispersal to the coastal ocean.
•Rates of sediment accumulation on subaqueous Mississippi River delta have declined.•Progradation of Mississippi River delta has slowed and reversed in some areas.•Mass-wasting on the Mississippi River delta front still appears active.•Recent rates of seafloor erosion suggest the delta front is a temporary depocenter.
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