Development and Characterization of Whey Protein-Based Nano-Delivery Systems: A Review.

Various bioactive compounds (BCs) often possess poor stability and bioavailability, which makes it difficult for them to exert their potential health benefits. These limitations can be countered by the use of nano-delivery systems (NDSs), such as nanoparticles and nanoemulsions. NDSs can protect BCs against harsh environments during food processing and digestion, and thereby, could enhance the bioavailability of BCs. Although various NDSs have been successfully produced with both synthetic and natural materials, it is necessary to fulfill safety criteria in the delivery materials for food applications. Food-grade materials for the production of NDSs, such as milk proteins and carbohydrates, have received much attention due to their low toxicity, biodegradability, and biocompatibility. Among these, whey proteins-from whey, a byproduct of cheese manufacturing-have been considered as excellent delivery material because of their high nutritional value and various functional properties, such as binding capability to various compounds, gelation, emulsifying properties, and barrier effects. Since the functional and physicochemical properties of whey protein-based NDSs, including size and surface charge, can be key factors affecting the applications of NDSs in food, the objectives of this review are to discuss how manufacturing variables can modulate the functional and physicochemical properties of NDSs and bioavailability of encapsulated BCs to produce efficient NDSs for various BCs.

Bacterial biogeography influenced by shelf-basin exchange in the Arctic surface sediment at the Chukchi Borderland.

It has been known that continental shelves around the Arctic Ocean play a major role in the ventilation of the deep basins as a consequence of shelf-basin exchange. In the present study, we found that bacterial assemblage of the surface sediment was different from that of seawater while seawater harboured local bacterial assemblages in response to the Arctic hydrography. This finding suggests that the Arctic seafloor sediments may have distinctive bacterial biogeography. Moreover, the distribution of bacterial assemblages and physicochemical properties in surface sediments changed gradually from the Arctic continental shelf to deep-sea basin. Based on the results, bacterial biogeography in the Arctic seafloor sediments may be influenced by winnowing and re-deposition of surface sediments through the sediment gravity flow. The present study offers a deeper understanding of shelf convection and its role for the construction of bacterial assemblages in the Arctic Ocean.

Resveratrol-loaded Nanoparticles Induce Antioxidant Activity against Oxidative Stress.

Resveratrol acts as a free radical scavenger and a potent antioxidant in the inhibition of numerous reactive oxygen species (ROS). The function of resveratrol and resveratrol-loaded nanoparticles in protecting human lung cancer cells (A549) against hydrogen peroxide was investigated in this study. The 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay was performed to evaluate the antioxidant properties. Resveratrol had substantially high antioxidant capacity (trolox equivalent antioxidant capacity value) compared to trolox and vitamin E since the concentration of resveratrol was more than 50 µM. Nanoparticles prepared from ß-lactoglobulin (ß-lg) were successfully developed. The ß-lg nanoparticle showed 60 to 146 nm diameter in size with negatively charged surface. Non-cytotoxicity was observed in Caco-2 cells treated with ß-lg nanoparticles. Fluorescein isothiocynate-conjugated ß-lg nanoparticles were identified into the cell membrane of Caco-2 cells, indicating that nanoparticles can be used as a delivery system. Hydrogen peroxide caused accumulation of ROS in a dose- and time-dependent manner. Resveratrol-loaded nanoparticles restored H2O2-induced ROS levels by induction of cellular uptake of resveratrol in A549 cells. Furthermore, resveratrol activated nuclear factor erythroid 2-related factor 2-Kelch ECH associating protein 1 (Nrf2-Keap1) signaling in A549 cells, thereby accumulation of Nrf2 abundance, as demonstrated by western blotting approach. Overall, these results may have implications for improvement of oxidative stress in treatment with nanoparticles as a biodegradable and non-toxic delivery carrier of bioactive compounds.

Cellular Uptake and Cytotoxicity of ß-Lactoglobulin Nanoparticles: The Effects of Particle Size and Surface Charge.

It is necessary to understand the cellular uptake and cytotoxicity of food-grade delivery systems, such as ß-lactoglobulin (ß-lg) nanoparticles, for the application of bioactive compounds to functional foods. The objectives of this study were to investigate the relationships between the physicochemical properties of ß-lg nanoparticles, such as particle size and zeta-potential value, and their cellular uptakes and cytotoxicity in Caco-2 cells. Physicochemical properties of ß-lg nanoparticles were evaluated using particle size analyzer. Flow cytometry and confocal laser scanning microscopy were used to investigate cellular uptake and cytotoxicity of ß-lg nanoparticles. The ß-lg nanoparticles with various particle sizes (98 to 192 nm) and zeta-potential values (-14.8 to -17.6 mV) were successfully formed. A decrease in heating temperature from 70°C to 60°C resulted in a decrease in the particle size and an increase in the zeta-potential value of ß-lg nanoparticles. Non-cytotoxicity was observed in Caco-2 cells treated with ß-lg nanoparticles. There was an increase in cellular uptake of ß-lg nanoparticles with a decrease in particle size and an increase in zeta-potential value. Cellular uptake ß-lg nanoparticles was negatively correlated with particle size and positively correlated with zeta-potential value. Therefore, these results suggest that the particle size and zeta-potential value of ß-lg nanoparticles play an important role in the cellular uptake. The ß-lg nanoparticles can be used as a delivery system in foods due to its high cellular uptake and non-cytotoxicity.

Development of Hydrophobically Modified Casein Derivative-Based Delivery System for Docosahexaenoic Acids by an Acid-Induced Gelation.

Although omega-3 fatty acids including docosahexaenoic acid (DHA) contain various health-promoting effects, their poor aqueous solubility and stability make them difficult to be induced in dairy foods. The aims of this research were to manufacture casein derivative-based delivery system using acid-induced gelation method with glucono-σ-lactone and to investigate the effects of production variables, such as pH and charged amount of linoleic acid, on the physicochemical properties of delivery systems and oxidative stability of DHA during storage in model milk. Covalent modification with linoleic acid resulted in the production of casein derivatives with varying degrees of modification. As pH was reduced from 5.0 to 4.8 and the charged amount of linoleic acid was increased from 0% to 30%, an increase in particle size of casein derivative-based delivery systems was observed. The encapsulation efficiency of DHA was increased with decreased pH and increased charged amount of linoleic acid. The use of delivery system for DHA resulted in a decrease in the development of primary and secondary oxidation products. An increase in the degree of modification of casein derivatives with linoleic acid resulted in a decrease in the formation of primary and secondary oxidation products than of free DHA indicating that delivery systems could enhance the oxidative stability of DHA during storage in model milk. In conclusions, casein derivatives can be an effective delivery system for DHA and charged amount of linoleic acid played a key role determining the physicochemical characteristics of delivery system and oxidative stability of DHA.

Development of an Emulsion Gel Containing Peanut Sprout Oil as a Fat Replacer in Muffins: Physicochemical, Tomographic, and Texture Properties.

Peanut sprouts are known to increase their resveratrol content during germination, leading to cultivation in smart farms. Recently, peanut sprout oil extraction and sales have gained traction; however, processed foods utilizing peanut sprout oil have yet to be developed. In this study, water-in-oil (W/O) emulsion gels were structured with water, peanut sprout oil (PSO), sorbitan monostearate (SMS), and candelilla wax (CW) in different ratios, and their potential as shortening substitutes in muffins was evaluated on physicochemical and sensory properties. PSO comprised 67% unsaturated fatty acids and had higher phospholipid (17.97%) and resveratrol (15.95 µg/L) contents and antioxidant activity (71.52%) compared to peanut oil. The PSO emulsion gels were physically structured without changing their chemical compositions. The SMS and CW ratios were found to have a significant influence on the textural properties, solid fat content, rheology, and crystallization of the emulsion gels. The viscoelastic properties of the emulsion gels showed a higher storage modulus than loss modulus and increased with increasing gelator content. Muffins prepared with emulsion gels were characterized by a harder texture and larger pore size, while in the case of muffins mixed with a ratio of 25% SMS and 75% CW, there was no significant difference in overall preference of sensory evaluation compared to shortening muffins. Thus, these findings reveal the potential utility of PSO as a fat substitute and indicate that W/O emulsion gels are suitable for producing muffins without a loss of quality.

Remote impacts of 2009 and 2015 El Niño on oceanic and biological processes in a marginal sea of the Northwestern Pacific.

The significance of long-term teleconnections derived from the anomalous climatic conditions of El Niño has been a highly debated topic, where the remote response of coastal hydrodynamics and marine ecosystems to El Niño conditions is not completely understood. The 14-year long data from a ship-borne acoustic Doppler current profiler was used to examine the El Niño's impact, in particular, 2009 and 2015 El Niño events, on oceanic and biological processes in coastal regions across the Korea/Tsushima Strait. Here, it was revealed that the summer volume transport could be decreased by 8.7% (from 2.46 ± 0.39 to 2.24 ± 0.26 Sv) due to the anomalous northerly winds in the developing year of El Niño. Furthermore, the fall mean volume backscattering strength could be decreased by 1.8% (from - 97.09 ± 2.14 to - 98.84 ± 2.10 dB) due to the decreased surface solar radiation after the El Niño events. Overall, 2009 and 2015 El Niño events remotely affected volume transport and zooplankton abundance across the Korea/Tsushima Strait through climatic teleconnections.

Assessment of potential impact of invasive vegetation on cohesive sediment erodibility in intertidal flats.

In-situ erodibility experiments were conducted to reveal the effects of vegetation on sediment stability in an intertidal flat. Spartina alterniflora (Spartina), one of the most widespread types of vegetation, led to complexity in sediment erodibility. The long stems and leaves of Spartina, which grew to approximately 156 cm from May to November 2019, were effective in trapping suspended sediments in the water columns, eventually promoting the deposition of approximately 2.3 cm within its communities. Sediments eroded by increasing bed shear stress (τb) mainly originated from sediments that were adhered to the stems and leaves of Spartina (May: 76%; November: 54%). They protected subsequent bed erosion against τb. However, this was only an apparent effect because the Spartina caused the erosion rate (E) to stagnate by suppressing the outflow of eroded mass from the bed. As the protective effect of the stems was removed, the uppermost sediment layers in the Spartina communities became more vulnerable to erosion by τb, with the initial erosion thresholds lowered to 0.1 Pa (May) and 0.05 Pa (November). Despite continuous sedimentation by sediment trapping, the sediment bed in Spartina communities had not been consolidated under repeated tidal inundation, showing no distinct development of the critical shear stress for erosion. Thus, the differences in E between cases with or without Spartina's stems reached approximately 1.22 × 10-6 (May) and 1.83 × 10-6 kg m-2 s-1 (November) at τb = 0.6 Pa. Results suggest that the increase in thickness of erodible layers mainly contributed more than sediment volume fraction to the enhancement of erosion potential with τb. This study highlights the necessity to assess both positive and negative effects of Spartina on the stability of sediment beds in intertidal flats.

Disturbance of sedimentary processes in tidal salt marshes invaded by exotic vegetation.

In situ moorings were conducted at salt marsh and bare flat to reveal the environmental disturbance of sedimentary processes in the intertidal flat. Spartina alterniflora (Spartina), an invasive species, grew up to 156 cm in the Ganghwa tidal flat from June to November 2019. This rapid growth has resulted in the dense salt marsh, which complicated hydrodynamics and associated sediment processes. Stems and leaves could effectively trap fine-grained sediments (17.24-20.42 µm) at the bed, increasing the differences in bed elevation between the two sites to up to 5.11 cm. The cohesive sediments accumulated in Spartina communities were resuspended differently by stem-scale turbulence generated from the disturbance of stems and leaves, depending on wind forcing and vegetation conditions. The vegetated sediments, under low wind speeds (<4 m s-1), were hardly resuspended in the water column, compared to those in the bare flat, resulting in sedimentation. Under high wind speeds (>6 m s-1), stem-scale turbulence was sufficiently strengthened to surpass the sedimentation of suspended sediments; thus, it resuspended additional bed sediments without a loss of the trapped sediment, unlike in the bare flat. The flocculation of suspended sediments in Spartina communities was mainly controlled by stem-scale turbulence. The flocs were confined to a size of 40 µm (settling velocity: 0.17 mm s-1) and developed an approaching spherical shape. After the cut-off of Spartina, a favorable condition for the flocs to grow by 57 µm (settling velocity: 0.23 mm s-1) was established with decrease in stem-scale turbulence. These larger flocs were able to develop into a ramified spherical structure. Despite diminishment of stem-scale turbulence, the disturbed sediments were outflowed, resulting in an abrupt decrease in bed elevation (0.12 cm day-1). The results suggest that the sediment accumulated in Spartina communities remained erodible due to frequent disturbances without sufficient consolidation.

Encapsulation of Lactobacillus rhamnosus GG Using Milk Protein-Based Delivery Systems: Effects of Reaction Temperature and Holding Time on Their Physicochemical and Functional Properties.

Microencapsulation is a protective process for materials that are sensitive to harsh conditions encounted during food manufacture and storage. The objectives of this research were to manufacture a milk protein-based delivery system (MPDS) containing Lactobacillus rhamnosus GG (LGG) using skim milk powder and to investigate the effects of manufacturing variables, such as reaction temerpature and holding time, on the physiccohemical properties of MPDS and viability of LGG under dairy food processing and storage conditions. MPDS was prepared using chymosin at varing reaction temperatures from 25°C to 40°C for 10 min and holding times from 5 to 30 min at 25°C. The morphological and physicochemical properties of MPDS were evaluated using a confocal laser scanning microscope and a particle size analyzer, respectively. The number of viable cells were determined using the standard plate method. Spherical-shaped MPDS particles were successfully manufactured. The particle size of MPDS was increased with a decrease in reaction temperature and an increase in holding time. As reaction temperature and holding time were increased, the encapsulation efficiency of LGG in MPDS was increased. During pasteurization, the use of MPDS resulted in an increase in the LGG viability. The encapsulation of LGG in MPDS led to an increase in the viability of LGG in simulated gastric fluid. In addition, the LGG viability was enhanced with an increase in reaction temperature and holding time. In conclusions, the encapsulation of LGG in MPDS could be an effective way of improving the viability of LGG during pasturization process in various foods.

Development and evaluation of probiotic delivery systems using the rennet-induced gelation of milk proteins.

The aims of this study were to develop a milk protein-based probiotic delivery system using a modified rennet-induced gelation method and to determine how the skim milk powder concentration level and pH, which can affect the rennet-induced intra- and inter-molecular association of milk proteins, affect the physicochemical properties of the probiotic delivery systems, such as the particle size, size distribution, encapsulation efficiency, and viability of probiotics in simulated gastrointestinal tract. To prepare a milk protein-based delivery system, skim milk powder was used as a source of milk proteins with various concentration levels from 3 to 10% (w/w) and rennet was added to skim milk solutions followed by adjustment of pH from 5.4 or 6.2. Lactobacillus rhamnosus GG was used as a probiotic culture. In confocal laser scanning microscopic images, globular particles with a size ranging from 10 µm to 20 µm were observed, indicating that milk protein-based probiotic delivery systems were successfully created. When the skim milk powder concentration was increased from 3 to 10% (w/w), the size of the delivery system was significantly (p < 0.05) increased from 27.5 to 44.4 µm, while a significant (p < 0.05) increase in size from 26.3 to 34.5 µm was observed as the pH was increased from 5.4 to 6.4. An increase in skim milk powder concentration level and a decrease in pH led to a significant (p < 0.05) increase in the encapsulation efficiency of probiotics. The viability of probiotics in a simulated stomach condition was increased when probiotics were encapsulated in milk protein-based delivery systems. An increase in the skim milk powder concentration and a decrease in pH resulted in an increase in the viability of probiotics in simulated stomach conditions. It was concluded that the protein content by modulating skim milk powder concentration level and pH were the key manufacturing variables affecting the physicochemical properties of milk protein-based probiotic delivery systems.

A quasi-Monte Carlo based flocculation model for fine-grained cohesive sediments in aquatic environments.

The quasi-Monte Carlo (QMC) method was enhanced to solve the population balance model (PBM) including aggregation and fragmentation processes for simulating the temporal evolutions of characteristic sizes and floc size distributions (FSDs) of cohesive sediments. Ideal cases with analytical solutions were firstly adopted to validate this QMC model to illustrate selected pure aggregation, pure fragmentation, and combined aggregation and fragmentation systems. Two available laboratory data sets, one with suspended kaolinite and the other with a mixture of kaolinite and montmorillonite, were further used to monitor the FSDs of cohesive sediments in controlled shear conditions. The model results show reasonable agreements with both analytical solutions and laboratory experiments. Moreover, different QMC schemes were tested and compared with the standard Monte Carlo scheme and a Latin Hypercube Sampling scheme to optimize the model performance. It shows that all QMC schemes perform better in both accuracy and time consumption than standard Monte Carlo scheme. In particular, compared with other schemes, the QMC scheme using Halton sequence requires the least particle numbers in the simulated system to reach reasonable accuracy. In the sensitivity tests, we also show that the fractal dimension and the fragmentation distribution function have large impacts on the predicted FSDs. This study indicates a great advance in employing QMC schemes to solve PBM for simulating the flocculation of cohesive sediments.

Spatiotemporal variation of extracellular polymeric substances (EPS) associated with the microphytobenthos of tidal flats in the Yellow Sea.

The physical functions of extracellular polymeric substances (EPS), viz., by-product of microphytobenthos (MPB), in tidal flat system are well documented, but some ecological aspects remain unknown. We investigated MPB biomass (Chl-a), EPS, diatom assemblage, and erodibility in two contrasting tidal flat environments (megatidal vs. macrotidal flat) in the Yellow Sea. Thick biofilms were observed when MPB bloomed, with high Chl-a and increased EPS concentrations. Among diatom genera, Navicula was the most dominant taxa found over the year (mean 41%) in both areas. Compared with non-bloom periods, the erodibility decreased by 54-73% as biofilm thickened during the blooms. It was attributed to the elevated abundance of large-sized (>40 µm) Navicula, which was expected to secrete large amounts of EPS. Overall, we successfully demonstrated spatiotemporal differences of sediment stabilization that significantly related to ecological variations of MPB, and identified the key diatom genus as a "sediment stabilizer" in the typical tidal flats of the Yellow Sea.

Influence of tidal forcings on microphytobenthic resuspension dynamics and sediment fluxes in a disturbed coastal environment.

The resuspension dynamics of microphytobenthos (MPB) and sediment fluxes were investigated in a disturbed coastal environment by employing an in situ mooring system. We aimed to identify the interrelationship between microalgal biomass and sediment particles in aspect of their (de)coupling mechanism in a tidal channel system. In specific, the Chl-a (as a proxy of MPB biomass) and the suspended sediment concentration (SSC) were simultaneously measured under natural tidal conditions at different time scales, encompassing daily to fortnightly variations. Looking for the sediment dynamics, the SSC showed a strong positive correlation (p < 0.001) with the Reynolds stress; however, this relationship was not observed for benthic Chl-a. This could be due to more dynamic characteristics of the smaller biological cells, i.e., the decoupled benthic Chl-a from the sediment particles might randomly distribute in the turbid water column above the tidal channel. Notably, the iteration between MPB coupling (prevailing in spring) and segregation (prevailing in neap) with the sediment particles across the flood and ebb tidal cycles was evident during the study period. Meantime, the onshore flux of suspended sediment was almost balanced by its offshore flux, but that of Chl-a appeared to be unbalanced due to an excessive onshore transport. Altogether, the study area seems to experience a time lag in resuspension between MPB and sediment, followed by biological trapping in the tidal channel system, which would support a productive shallow water environment. The present study is the first to address the tidal resuspension of benthic microalgae in relation to sediment dynamics in a disturbed coastal environment of the Yellow Sea.

Manufacture and Physicochemical Properties of Chitosan Oligosaccharide/A2 ß-Casein Nano-Delivery System Entrapped with Resveratrol.

The purposes of this research were to form chitosan oligosaccharide (CSO)/A2 ß-casein nano-delivery systems (NDSs) and to investigate the effects of production variables, such as CSO concentration levels (0.1%, 0.2%, and 0.3%, w/v) and manufacturing temperature (5°C, 20°C, and 35°C), on the production and physicochemical characteristics of CSO/A2 ß-casein NDSs to carry resveratrol. The morphological characteristics of CSO/A2 ß-casein NDSs were assessed by the use of transmission electron microscopy (TEM) and particle size analyzer. High-performance liquid chromatography (HPLC) was applied to determine the entrapment efficiency (EE) of resveratrol. In the TEM images, globular-shaped particles with a diameter from 126 to 266 nm were examined implying that NDSs was successfully formed. As CSO concentration level was increased, the size and zeta-potential values of NDSs were significantly (p<0.05) increased. An increase in manufacturing temperature from 5°C to 35°C resulted in a significant (p<0.05) increase in the size and polydispersity index of NDSs. Over 85% of resveratrol was favorably entrapped in CSO/A2 ß-casein NDSs. The entrapment efficiency (EE) of resveratrol was significantly (p<0.05) enhanced with an increase in manufacturing temperature while CSO concentration level did not significantly affect EE of resveratrol. There were no significant (p<0.05) changes observed in the size and polydispersity index of NDSs during heat treatments and storage in model milk and yogurt indicating that CSO/A2 ß-casein NDSs exhibited excellent physical stability. In conclusion, the CSO concentration level and manufacturing temperature were the crucial determinants affecting the physicochemical characteristics of CSO/A2 ß-casein NDSs containing resveratrol.

Zooplankton and micronekton respond to climate fluctuations in the Amundsen Sea polynya, Antarctica.

The vertical migration of zooplankton and micronekton (hereafter 'zooplankton') has ramifications throughout the food web. Here, we present the first evidence that climate fluctuations affect the vertical migration of zooplankton in the Southern Ocean, based on multi-year acoustic backscatter data from one of the deep troughs in the Amundsen Sea, Antarctica. High net primary productivity (NPP) and the annual variation in seasonal ice cover make the Amundsen Sea coastal polynya an ideal site in which to examine how zooplankton behavior responds to climate fluctuations. Our observations show that the timing of the seasonal vertical migration and abundance of zooplankton in the seasonally varying sea ice is correlated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Zooplankton in this region migrate seasonally and overwinter at depth, returning to the surface in spring. During +SAM/La Niña periods, the at-depth overwintering period is shorter compared to -SAM/El Niño periods, and return to the surface layers starts earlier in the year. These differences may result from the higher sea ice cover and decreased NPP during +SAM/La Niña periods. This observation points to a new link between global climate fluctuations and the polar marine food web.

Bioaccessibility of ß-Lactoglobulin Nanoemulsions Containing Coenzyme Q10: Impact of Droplet Size on the Bioaccessibility of Coenzyme Q10.

The aims of this research were to examine the effect of heating temperature (65, 75, and 85℃) and CaCl2 concentration level (3, 4, and 5 mM) on the physicochemical properties of ß-lactoglobulin (ß-lg) nanoemulsions (NEs) and to study how the droplet size of NEs affects the bioaccessibility (BA) of coenzyme Q10 (CoQ10). The droplet size of NEs and BA of CoQ10 was assessed by particle size analyzer and UV-Vis spectrophotometer, respectively. An increase in heating temperature and CaCl2 concentration level resulted in a significant (p<0.05) increase in the droplet size of NEs while there were no significant differences in polydispersity index and zeta-potential of NEs. When NEs containing CoQ10 were incubated in simulated small intestinal phases, an increase in the droplet size and polydispersity index of NEs was observed. This indicated that NEs were not stable in small intestine and digestion of NEs occurred. As heating temperature and CaCl2 concentration level were decreased, a significant (p<0.05) increase in BA of CoQ10 was observed. There was a significant (p<0.05) increase in BA of CoQ10 with a decrease in the droplet size of NEs. In conclusion, heating temperature and CaCl2 concentration level were key-parameters affecting the initial droplet size of NEs and BA of CoQ10 was negatively correlated with initial droplet size of NEs.

Rainfall effects on the erodibility of sediment and microphytobenthos in the intertidal flat.

The frequent rainfall during the low tide would erode and transport the surface sediment and microphytobenthos (MPB) in the intertidal flat. In order to quantify the rainfall effects on the erodibility of sediment and MPB at the salt marsh and mixed flat, a series of erosion experiments have been conducted with a Gust erosion microcosm system. Surface sediments were sampled for analyzing algal biomass (Chl-a) and primary production (PP) during three typical weather (without rain, rain, and post-rain) conditions. The results of erosion experiment, in both salt marsh and mixed flat, showed that the sediment erodibility under rain condition was higher than that under without rain condition, with increased total eroded mass by 37-86%. It indicated that the rainfall effects caused to significantly disturb the surface sediment. After the rainfall events, the removal of highly-erodible sediments resulted in the reduction in eroded mass. The MPB erodibility under rain condition was lower than that under without rain condition, with decreased total eroded Chl-a by 29%. At the mixed flat, the rainfall effects caused to significantly decrease biological activities of MPB (biomass and PP) associated with surface sediment. The surface Chl-a concentration under post-rain condition decreased by 73%, compared to that under rain condition. At the salt marsh, in contrast, the rainfall effects were barely shown when the biological activities of MPB were rather stable. This implied that the eroded MPB induced by rainfall was retained within the marsh system due to vegetation canopy.

Effects of vegetation and fecal pellets on the erodibility of cohesive sediments: Ganghwa tidal flat, west coast of Korea.

Although the Korean tidal flats in the Yellow Sea have been highlighted as a typical macrotidal system, so far, there have been no measurements of the sediment erodibility and critical shear stress for erosion (τce). Using the Gust erosion microcosm system, a series of field experiments has been conducted in the Ganghwa tidal flat to investigate quantitatively the effects of biogenic materials on the erodibility of intertidal cohesive sediments. Four representative sediment cores with different surficial conditions were analyzed to estimate the τce and eroded mass. Results show that τce of the "free" sediment bed not covered by any biogenic material on the Ganghwa tidal flat was in the range of 0.1-0.2 Pa, whereas the sediment bed partially covered by vegetation (Phragmites communis) or fecal pellets had enhanced τce up to 0.45-0.6 Pa. The physical presence of vegetation or fecal pellets contributed to protection of the sediment bed by blocking the turbulent energy. An inverse relationship between the organic matter included in the eroded mass and the applied shear stress was observed. This suggests that the organic matter enriched in a near-bed fluff layer is highly erodible, and the organic matter within the underlying sediment layer becomes depleted and less erodible with depth. Our study underlines the role of biogenic material in stabilizing the benthic sediment bed in the intertidal zone.

Effects of seasonal variations on sediment-plume streaks from dredging operations.

When mixtures of aggregates and water dredged from the seabed are discharged at the surface into the adjacent water from a barge, coarse sediments sink immediately and fine sediments are suspended forming a plume. Recently, elongated plumes of fine sediment were observed by satellites near a dredging location on the continental shelf. Such plume streaks were longer in certain conditions with seasonality than expected or reported previously. Therefore, the present work studied the appearance of sediment plume with field measurements and numerical simulations and explains the seasonally varying restoring force and thicknesses of the surface mixed layer resulting from the vertical density distribution near the surface, along with mixing by hydrodynamic process. The resulting mixtures, after vertical restoring and mixing with the surroundings, determine the horizontal transport of suspended sediments. A numerical model successfully reproduced and explained the results from field measurements and satellite images along with the seasonal variations.