Phytoplankton assemblage responses to massive freshwater inputs and anthropogenic toxic substances contamination in the Geum River Estuary, South Korea.

This study investigated the relationships between phytoplankton assemblages and water contamination by persistent toxic substances (PTSs) and nutrients in an estuary with an artificial dam over one year. The distribution of PTSs, including 15 polycyclic aromatic hydrocarbons, 6 alkylphenols, and 8 metal(loid)s, along with nutrients, exhibited relatively high concentrations with irregular temporal fluctuations in the inner estuary. During winter and spring, phytoplankton communities showed good ecological quality, with an average of 28 species and a density of 1750 cells L-1. In contrast, during summer, there was a significant increase in the density of freshwater species (max 45,000 cells L-1). These assemblages were categorized into three seasonal groups, featuring dominant taxa like blue-green algae and diatoms. Temperature and nutrient levels were the principal factors influencing phytoplankton assemblages, while PTSs had a minor impact. Overall, phytoplankton assemblages displayed strong seasonal variation, mainly influenced by freshwater input and nutrient availability.

Spatial distribution of meiofaunal and macrofaunal assemblages in the tidal flats of the southern Korean coast in relation to natural and anthropogenic impacts.

We investigated the spatial variability of macrofaunal and meiofaunal assemblages in intertidal flats on the southern coast of Korea. Abiotic and biotic samples were collected at five stations. The species richness, density, and composition of the assemblages differed significantly among stations. Nematoda and Annelida were the most dominant meiofaunal and macrofaunal taxa, respectively, although taxon dominance differed among stations. Distance-based linear models showed that sediment-related variables and heavy metals were the main environmental factors determining the spatial variability of the assemblages. Macrofauna had only sediment-related variables and heavy metals as major environmental factors, but meiofauna were also influenced by other environmental factors such as sea surface temperature, dissolved oxygen-related variables, and salinity. This study can provide basic ecological data for understanding the spatial distribution of macro-meiofaunal assemblages and aid in the development of marine environmental management strategies on the western south coast of Korea.

Spatiotemporal variability on local-regional scale in subtidal meiofaunal assemblages along the southern coast of Korea.

This study was conducted to investigate the spatiotemporal variability in subtidal meiofaunal assemblages off the southern coast of Korea at local and regional scales. Abiotic and biotic samples were collected by site (three sites at least 10 km apart) within region (three coastal regions at least 50 km apart) over 7 years (2015-2021). The density and taxon richness of meiofaunal assemblages differed significantly among sites, but not among regions or years. The meiofaunal assemblage composition differed significantly among sites, regions, and years. A distance-based multivariate multiple regression analysis revealed that the mean sediment grain size and total nitrogen, lead, nickel, chromium, and aluminum concentrations were key environmental variables determining the variation of the meiofaunal assemblages. This study can provide basic ecological data for understanding the spatiotemporal distribution of meiofauna assemblages and aid in the development of management strategies to mitigate marine pollution on the southern coast of Korea.

Effectiveness of ultra-wide implants in the mandibular and maxillary posterior areas: a 5-year retrospective clinical study.

Objectives: Ultra-wide implants may be used as a replacement if existing implants fail. This study was conducted to evaluate the factors influencing the prognosis and failure of ultra-wide implants. Patients and. Methods: This study evaluated whether sex, age, site, diameter, length, additional surgery, implant stability (primary and secondary), and reason for ultra-wide implant placement affect the 5-year survival and success rates and marginal bone loss (MBL) of ultra-wide implants. Seventy-eight ultra-wide implants that were placed in 71 patients (39 males and 32 females) from 2008 to 2010 were studied. One-way ANOVA analysis was conducted to evaluate the statistical significance of MBL according to the patient's sex, implant site, and diameter. Independent sample t-tests were used to determine the statistical significance of MBL analysis which was used to determine the significance of the 5-year success and survival rates related to the variables. One-way ANOVA was conducted to evaluate the statistical significance of sex, implantation site, diameter, and MBL. Independent sample t-tests were used to evaluate the correlation between implantability and MBL for implantation reasons, while additional surgery, length, and Kaplan-Meier analysis were used to evaluate 5-year survival and success rates. Results: The mean age of patients was 54.2 years with a survival rate of 92.3% and a success rate of 83.3% over a mean 97.8-month period of observation. MBL averaged 0.2 mm after one year of prosthetic function loading and 0.54 mm at the time of final observation. Success rates correlated with primary stability (P=0.045), survival rates correlated with secondary stability (P=0.036), and MBL did not correlate with any variables. Conclusion: Ultra-wide implants can be used to achieve secure initial fixation in the maxillary and mandibular molar regions with poor bone quality or for alternative purposes in cases of previous implant failure.

Comparison of sandblasted and acid-etched surface implants and new hydrophilic surface implants in the posterior maxilla using a 3-month early-loading protocol: a randomized controlled trial.

OBJECTIVES: In this prospective randomized controlled trial, we measured the primary and secondary stability of two surface-treated implants placed in the posterior maxilla, applied 3-month loading protocols, and compared and analyzed the short-term outcomes of the implants. PATIENTS AND METHODS: : From June 2018 to June 2019, patients with a residual bone height of 4 mm in the posterior maxilla were enrolled and randomly divided into two groups to place SA implants (Osstem Implants, Korea) in Group A and NH implants (Hiossen, USA) in Group B. Finally, 14 implants placed in 13 patients in Group A and 17 implants placed in 14 patients in Group B were analyzed. The measured primary and secondary stability of each implant was represented by implant stability quotient (ISQ), and treatment outcomes were evaluated. RESULTS: : Group A consisted of patients with an average age of 62.2 years (range, 48-80 years), and Group B consisted of patients with an average age of 58.1 years (range, 35-82 years). Primary stability was 73.86±6.40 and 71.24±5.32 in Groups A and B, respectively (P=0.222). Secondary stability was 79.07±5.21 in Group A and 78.29±4.74 in Group B (P=0.667). A steep increase in ISQ during the healing period was observed in Group B, though it was not significant (P=0.265). The mean follow-up period was 378.5±164.6 days in Group A and 385.3±167.9 days in Group B. All implants in each group met the success criteria, and the success rate was 100%. CONCLUSION: Two surface-treated implants placed in the posterior maxilla with greater than 4 mm alveolar bone height exhibited successful one-year treatment outcomes if a primary stability of 65 or higher ISQ was obtained and a 3-month early loading protocol was applied.

Macrozoobenthic community responses to sedimentary contaminations by anthropogenic toxic substances in the Geum River Estuary, South Korea.

We investigated the sedimentary pollution by persistent toxic substances (PTSs) and their potential impacts on the macrobenthic faunal community in the Geum River Estuary, South Korea. Sediment and benthic macrofauna samples were collected from eight sites every two months during the period of February to December in 2015. Target PTSs encompassed metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn), one metalloid (As), polycyclic aromatic hydrocarbons (PAHs), and alkylphenols (APs). The significant difference to the environment of the inner and outer parts of the estuary (p < 0.05) was found with relatively high concentrations of PTSs in sediment from the inner estuary. The concentrations of Cu and Zn exceeded the sediment quality guidelines of Korea representing a potential risk to aquatic organisms. The primary source of PAHs was by-products of diesel and gasoline combustion (37%), followed by a coke oven (32%) and oil-burning (31%). The macrofaunal community was spatially distinguished between the inner and outer parts of the estuary (p < 0.05), regardless of the season. In the inner part of the estuary, the density of the macrofaunal community was high, due to the increased opportunistic species and/or some indicator species (organic polluted or enrichment), implying that the given environment was disturbed. Among the environmental parameters analyzed by the distance-based linear model (DistLM), salinity, chlorophyll-a, and nutrient concentrations were found to be key factors controlling the changes in macrofaunal community structure. Such changes in the closed estuary system would indicate that each taxonomic group had to adjust to lower salinities and alternative food sources. Overall, the distribution of PTSs and macrozoobenthic communities in the Geum River Estuary collectively reflected the environmental gradients caused by surrounding activities in the inner part of the estuary together with direct effects by the irregular inflow of freshwater.

A long-term ecological monitoring of subtidal macrozoobenthos around Dokdo waters, East Sea, Korea.

Dokdo's high marine biodiversity has received worldwide attention recently. A total of 578 macrozoobenthos are recorded since the 1960s, but ecology of Dokdo's fauna is unknown. We monitored Dokdo's subtidal macrozoobenthos for 5 years in 2013-17, in the present study. Five stations representing three subtidal habitats were monitored; 1) oceanic plateau, 2) coastal terrace, and 3) island wharf. In total, 13,664 individuals belonging to 141 taxa were recorded during the survey. The number of species and density varied greatly among stations without distinct year-round variation. Faunal compositions significantly differed in time and space, reflecting varied faunal adaptations in a harsh environment. Whilst, temporal stability in faunal assemblages was evidenced for some dominant or cosmopolitan taxa. High spatial heterogeneity reflects site-specific oceanographic conditions. Meantime, sea-surface temperature and wave action were associated with year-round faunal compositions. Overall, the Dokdo's macrozoobenthos significantly contribute to marine biodiversity of the East Sea.

Natural and anthropogenic impacts on long-term meiobenthic communities in two contrasting nearshore habitats.

The present study investigated the spatiotemporal distributions of meiofauna and corresponding environmental variables in two different subtidal environments. The two habitats represent unique geographical localities; (1) Jinhae Bay for semi-enclosed industrial bay (under anthropogenic pressure) and (2) Samcheok coast for open sea area (rather in natural condition) in Korea. Biotic and abiotic data were seasonally collected from six monitoring stations in each area for 3 years (2013-16) at two study areas and all the data were comparatively analyzed. First, abiotic data such as sediment properties and water quality parameters showed significant variations in time (season/year) and space (site/area) cross the study areas and within sites in each area. Second, meiofauna assemblages, such as number of taxa, abundance, and composition, greatly varied between seasons and localities, reflecting (in)direct association(s) to local activities and/or environmental gradients. Of note, the Jinhae Bay community was directly influenced by a hypoxia during summer season. In general, the site-specific variations rather prevailed masking seasonal fluctuations, indicating significance of both oceanographic settings and terrestrial land use activities. Among the environmental parameters measured, sediment grain size appeared to be the key factor in determining the meiofaunal assemblages and distributions, particularly under natural condition shown at Samcheok. Altogether, clear separations in meiofaunal community cross sites (inner vs. outer stations) and areas (enclosed industrial bay vs. open sea) implied anthropogenic pressures and certain impacted boundaries. In addition, association of benthic communities to anthropogenic environments seemed to prevail in macrofaunal community, being simultaneously influenced by abiotic seasonal fluctuations. Overall, two contrasting nearshore habitats exhibited typical spatiotemporal distributions of subtidal benthic communities being collectively influenced by anthropogenic stresses and site-specific environmental gradients.