Morphological identification of <Emphasis Type="Italic">Alexandrium</Emphasis> species (Dinophyceae) from Jinhae-Masan Bay,Korea

Outbreaks of paralytic shellfish poisoning (PSP) and dense blooms caused by Alexandrium species in Jinhae-Masan Bay, Korea have been nearly annual events for many years. However, excluding some Alexandrium species responsible for PSP, there are no critical reports on the morphology of Alexandrium species in this bay. To identify the Alexandrium species based on detailed morphological features, vegetative cells collected water samples and established by the incubation of resting cysts isolated from sediment trap samples were analyzed. Four species of Alexandrium were identified: Alexandrium affine, A. fundyense, A. catenella, and A. insuetum. Morphological features of these species were basically consistent with those outlined in previous studies. However, the ventral pore and the connecting pore on the sulcal plate, which have been accepted as diagnostic characteristics for the identification of A. fundyense and A. catenella, need to be reevaluated, indicating that useful morphological features for identifying these two species should be recommended to avoid confusion in the classification of species in genus Alexandrium.     

Effects of temperature and salinity on the asexual reproduction of <Emphasis Type="Italic">Nemopilema nomurai</Emphasis> (Scyphozoa: Rhizostomeae)

Asexual reproduction of polyps of Nemopilema nomurai, of which massive blooms have occurred in Korean waters every summer since 2003, were tested under 20 combinations of temperature (10, 15, 20, and 25°C) and salinity (12, 17, 22, 27, and 32 psu). Production of podocysts increased with increasing temperature (20 and 25°C), while strobilaton and ephyral liberation occurred at low temperatures (10 and 15°C). Temperature also affected the initiation of ephyral liberation (approximately 25 days at 15°C, and 50 days at 10 and 20°C, respectively). The number of podocysts was only significantly different between 27 and 32 psu, and salinity had no significant effect on the excystment of podocysts, ephyral liberlation, showing N. nomurai is euryhaline. These results demonstrated that temperature is an important factor on both the podocysts production and ephyrae liberation, possibly explaining early spring liberation of ephyrae and continuous introduction of medusae into Korean coastal waters through summer to fall.     

Response of Pile Groups Driven in Sand Subjected to Combined Loads

Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity.     

Wintertime suspended sediment simulation in the Huanghai and East China Seas

A simulation of suspended sediment movement relating to tidal and wave forcing during a winter monsoon in November 1983 in the Huanghai and East China Seas continental shelf is attempted by using the model describing the cohesive/non-cohesive sediment resuspension generated by interactions between currents and waves.model simulation showed that sediment concentration was increased by resuspension at shallow depths during the strong storm conditions due to high bottom stress interacted between currents and waves. This result is in general agreement with observations in horizontal distribution of suspended sediment distribution.At three current meter mooring positions off the southern Shandong Peninsula resuspension occurred only at a depth of 22m,nearest coastal position and at deeper parts at depths of 51 and 80m wave-current interaction effects were not significant. It has shown that the present model simulation demonstrated the capability of reproduction of suspended sediment movement under wintertime extreme event reasonably well.     

Molecular diversity of phytoplankton in the East China Sea around Jeju Island (Korea), unraveled by pyrosequencing

The East China Sea (ECS) around Jeju Island lies in a transitional region between the temperate and subtropical zones and is influenced by the Kuroshio Current. Hence, this area has been considered an important monitoring site for oceanic ecosystem changes. Herein, we assessed the community structure and diversity of the phytoplankton in the ECS around Jeju Island using small subunit ribosomal RNA pyrosequencing. We analyzed eight samples collected from the surface and at 30 m- and/or 50-m depths from two neritic and oceanic stations each from 24–30 April 2011. Comparisons of 15,498 pyrosequences identified 172 phylotypes of phytoplankton, excluding cyanobacteria, from the four surface stations. These pyrosequences were represented by dinoflagellates (29 %), stramenopiles (31 %), and chlorophytes (>39 %), with minor contributions from cryptophytes, haptophytes, and Telonemia. Phylotypes retrieved at 30- and 50-m depths were very similar to the surface samples. However, phylotype diversity and community structure varied considerably with the stations. Dominant phylotypes included Karlodinium veneficum, Ostreococcus tauri, Skeletonema marinoi, and Thalassiosira curviseriata, and many of the detected phylotypes include new records for the present study area. This study provides a valuable phylotype reference for future phytoplankton community structure and diversity studies with regard to marine environmental changes.     

Material characteristics and deterioration evaluation for the 13th century Korean stone pagoda of Magoksa temple

This study focused on the quantitative deterioration evaluation for the Magoksa temple stone pagoda of the thirteenth century in Korea, based on the deterioration map by precise observation and ultrasonic velocity measurements. The stone pagoda is composed mainly of fine-grained quartz diorite with some granodiorite used in the second story and dew bowl, and the replacement stone for restoration in the basement is biotite granite. The deterioration map and the 2D contour map projecting ultrasonic velocity showed that the most serious deterioration was to the north face of the pagoda, which has about 81.2% deterioration rate and a low velocity range compared with the other directions. Thus, it is required to prepare conservation schemes to reduce deterioration and reinforce the structure. It is also required to carry out ground exploitation for calculation of load carrying strength and ground strength together with continuous structural monitoring. The results will be important for the stable and long-term conservation of the pagoda and will further serve to establish scientific conservation systems of stone cultural heritages in the future.     

Hydraulic and Thermal Conductivities of Kaolin–Silica Mixtures under Different Consolidation Stresses

Stable backfill materials for the heat sensitive structures of buried power cables, hot water pipes, and gas pipelines are suggested to have low permeability and high heat transfer characteristics. The hydraulic and thermal conductivities of backfill materials or clay liners are important parameters in proper design and construction of geotechnical structures involved with heat transfers. In this study, to investigate the optimal natural backfill or liner materials, thermal and hydraulic conductivities of kaolin–silica mixtures examined based on the results from laboratory tests under different consolidation conditions. From the experiment results, the thermal conductivity increases while hydraulic conductivity decreases with increasing density during consolidation process. As a result, back-fill materials with high kaolin content under low consolidation stress were desirable materials for burial of heat sensitive structures.     

Stress-Strain Behavior of Light-Weighted Soils

Unconfined and triaxial compression tests were carried out to examine the behavior of light-weighted soils (LWS) consisting of expanded polystyrene (EPS), dredged soils, and cement with respect to initial water content. The stress-strain behavior of LWS are analyzed with varying initial water content and silt contents of dredged soils, cement ratio, and confined stress. As initial water contents increase, the compressibility index increases and the preconsolidation pressure was vice versa. As initial water contents increase, the slope of stress-strain curve in elastic zone increases and strain rate at failure decreases and the strain rate at failure was not changed by the being of foams. As initial water contents increase, a compressive strength of LWS decreases. The decrement ratio of compressive strength of LWS with foams increases as cement content increases and initial water contents decreases. The compressive strength increases as silt contents increases.     

Spring Distribution of Ciliate Plankton in the Southeastern Yellow Sea in 2019

Ocean Science Journal - As planktonic ciliates have been recognized as important players in marine microbial food webs, relevant studies have been conducted in the western coastal waters of the...     

The 2007 Fox Creek landslide,Peace River Lowland,Alberta, Canada

Fox Creek is a small tributary of the Saddle River, a tributary of the Peace River in northwestern Alberta. It has several dormant landslides with degraded scarps and grabens. A new, reactivated landslide on the north bank of the Fox Creek occurred on 5 May 2007. The landslide formed two major sliding blocks. A rapid translational block slide, it mobilized 47 Mm³ of displaced materials, blocked the creek, and made a natural dam with a maximum height of 19 m at the tips of the displaced blocks. The rupture surfaces of the 2007 landslide were within the advance phase glaciolacustrine sediments. The residual friction angles are about 10° similar to those of the previous landslides in the Peace River Lowland. Precipitation and snow melt prior to the landslide are likely triggers of the 2007 Fox Creek landslide. The farmlands on the crest of the river valley and timber resources were impacted. The current landslide dam in Fox Creek does not have any evidence of seepage downstream; it may last for many years. Eventually, the creek will overtop and erode the dam. The same cycle of actions, landsliding, damming, and erosion will continue in the foreseeable future.