Variability in blue carbon storage related to biogeochemical factors in seagrass meadows off the coast of the Korean peninsula.

Coastal vegetated habitats such as mangroves, salt marshes, and seagrasses, referred to as blue carbon ecosystems, play an important role in climate change mitigation by an effective CO2 capture from atmosphere and water columns and long-term organic carbon (Corg) storage in sediments. Although seagrass meadows are considered intense carbon sinks, information on regional variability in seagrass blue carbon stock and factors influencing its capacity still remain sparse. In the present study, seagrass blue carbon storage by measuring Corg stocks in sediments and living seagrass biomass, and carbon accumulation rates (CARs) in seagrass meadows were estimated along the Korean coast. Factors affecting variability in Corg stocks were also analyzed using partial least squares (PLS) regression and principal component analysis (PCA). Projected Corg stocks in sediment, extrapolated to a depth 1 m, exhibited substantial variability among sites, ranging from 49.91 to 125.71 Mg C ha-1. The majority of Corg (96-99%) was stored in sediments, whereas the contribution of living biomass was minor. PLS regression and PCA indicated that Corg stocks in seagrass meadows are strongly associated with sediment characteristics such as dry bulk density and water and mud content. Among seagrass traits, above- to below-ground biomass ratio was significantly related to the quantity of Corg stocks in seagrass meadows. Because of the high spatial variability in Corg stocks and CARs, local and regional differences in seagrass blue carbon storage should be considered to accurately assess the climate change mitigation potential of seagrass ecosystems.

Erratum: Correction of Text in the Article "Evidence of Long-Distance Droplet Transmission of SARS-CoV-2 by Direct Air Flow in a Restaurant in Korea".

This corrects the article on p. e415 in vol. 35, PMID: 33258335.

Evidence of Long-Distance Droplet Transmission of SARS-CoV-2 by Direct Air Flow in a Restaurant in Korea.

BACKGROUND: The transmission mode of severe acute respiratory syndrome coronavirus 2 is primarily known as droplet transmission. However, a recent argument has emerged about the possibility of airborne transmission. On June 17, there was a coronavirus disease 2019 (COVID-19) outbreak in Korea associated with long distance droplet transmission. METHODS: The epidemiological investigation was implemented based on personal interviews and data collection on closed-circuit television images, and cell phone location data. The epidemic investigation support system developed by the Korea Disease Control and Prevention Agency was used for contact tracing. At the restaurant considered the site of exposure, air flow direction and velocity, distances between cases, and movement of visitors were investigated. RESULTS: A total of 3 cases were identified in this outbreak, and maximum air flow velocity of 1.2 m/s was measured between the infector and infectee in a restaurant equipped with ceiling-type air conditioners. The index case was infected at a 6.5 m away from the infector and 5 minutes exposure without any direct or indirect contact. CONCLUSION: Droplet transmission can occur at a distance greater than 2 m if there is direct air flow from an infected person. Therefore, updated guidelines involving prevention, contact tracing, and quarantine for COVID-19 are required for control of this highly contagious disease.

Mechanical Complication Rates and Optimal Horizontal Distance of the Most Distally Positioned Implant-Supported Single Crowns in the Posterior Region: A Study with a Mean Follow-Up of 3 Years.

PURPOSE: The purpose of this retrospective study was to determine the 3-year mechanical complication rates of the most distally positioned implant-supported single crowns (ISSCs) in the posterior region, and how these complication rates are affected by several clinical factors (i.e., gender, mean age, horizontal distance [HD], position in the jaw, placement location, duration of functional loading, clinical crown-to-implant length ratio [C/I ratio], and crown height space of the implant). MATERIALS AND METHODS: The mechanical complications (i.e., abutment screw loosening [ASL], abutment screw fracture [ASF], and ceramic fracture [CF]) associated with the implants were identified by examining the patients' treatment records, clinical photographs, and intraoral periapical radiographs. Statistical analyses were performed using chi-square and Student's t-test to identify the relationship between various clinical factors and the mechanical complication rates. Receiver operating characteristics analysis was conducted to determine the optimal cut-off value for the HD between the most distally positioned ISSCs and the mesially adjacent natural tooth beyond which complications occur. RESULTS: The study inclusion criteria were met by 183 patients who had undergone implant surgery in the period 2004 to 2011, involving a total of 221 implant treatments. Mechanical complications were present in 40 (18.1%) of the 221 investigated ISSCs. ASL was the most common complication (n = 28, 12.7%), followed in order by CF (n = 9, 4.1%) and ASF (n = 3, 1.4%). Repeated ASL and CF occurred in four (1.8%) and two (0.9%) implants, respectively. The mechanical complication rates differed significantly between implants with different HDs (p = 0.009) and clinical C/I ratios (p = 0.019); however, there was no significant association between the other clinical factors and the mechanical complication rates. CONCLUSION: Within the limitations of this study, it appears that the incidence of mechanical complications is higher for the most distally positioned ISSCs in the posterior region than for those positioned at other sites. Furthermore, since the rate of mechanical complications increases with increasing HD, an HD of 3.7 mm or less is recommended.

Space maintenance using crosslinked collagenated porcine bone grafted without a barrier membrane in one-wall intrabony defects.

The aim of this study was to determine the efficacy of crosslinked collagenated porcine bone (CPB) for the repair of surgically prepared one-wall intrabony defects in dogs. Buccolingually opened, one-wall, box-type periodontal defects (4 × 5 mm) were prepared bilaterally at the mesial side of the mandibular fourth premolars in beagle dogs (N = 5). Block-type CPB (4 × 5 × 5 mm) was placed on either the left or right side for the CPB site; the opposite site served as a sham-surgery control. Micro-computed tomographic and histological analyses were performed on block specimens obtained from the dogs after a 3-month healing period. There was less mean bone regeneration and cementum regeneration at the experimental sites than at the sham-surgery control sites. Most of the porcine bone particles were located under the floor of the defect and were sequestered from pristine bone. These findings show that CPB can be localized within the defect during the wound-healing period by a process of crosslinking; however, the application of CPB alone without a barrier membrane may not be effective in promoting periodontal regeneration in noncontained-type defects.

An effective transplanting technique using shells for restoration of Zostera marina habitats.

Significant declines in seagrass coverage have occurred in many parts of the world. In recent decades, transplanting projects for seagrass restoration at die-off areas have been attempted, but most current seagrass transplanting techniques are cost and labor intensive. We have developed a new seagrass transplanting method in which oyster shells are used as an anchoring device, and does not require SCUBA diving for sub-tidal planting. Here, we tested the shell method for feasibility and efficiency in large-scale seagrass restoration. Planting units consisting of two Zostera marina shoots anchored to one oyster shell were dropped from a boat to settle on the sediment at the test site. Four transplanting trials were conducted throughout the experimental period (December 2003, January, February, and November 2004) in Koje Bay on the southern coast of Korea. Eelgrass shoots planted using the shell method successfully established at the test areas, and the survival rates of transplants were comparable to those obtained using other common planting techniques. The transplant shoot density declined during the first 2-3 months following transplantation due to the initial transplant shock, and then surviving shoots became established at the sites and produced new lateral shoots after these periods. Plant size and leaf productivity of transplants 7 months post-transplanting were similar to or exceeded those of pre-existed shoots, suggesting that the physiological status of transplants is similar to that of natural population after 7 months. Because the shell method did not require workers to be in the water, the method was cost and labor effective. Additionally, given that shells originate from marine environments, the shell method did not leave any hazardous materials in the transplanting areas after restoration.

Site-specific success of three transplanting methods and the effect of planting time on the establishment of Zostera marina transplants.

Eelgrass, Zostera marina, is the most abundant seagrass species on the coast of Korea, but most large eelgrass meadows have disappeared since the 1970s due to human-induced disturbance. To restore disturbed seagrass habitats in die-off areas, seagrass transplanting has been attempted using various methods. Here, we assessed the feasibility and efficiency of seagrass transplanting methods depending on the sediment type at the planting site. Additionally, the effect of planting time on the establishment of transplant was examined to determine the optimal season for planting. We conducted an eelgrass transplanting experiment from fall 2003 to summer 2004 at three sites with different sediment types using three planting techniques. The staple method resulted in the highest transplant survival rate (77.1-93.8%) at all three sites, but was labor intensive. Transplanting Eelgrass Remotely with Frame Systems (TERFS) method also resulted in relatively a high survival rate (58.7-69.0%) at all sites. The shell method is a newer eelgrass transplanting method in which oyster shells are used as an anchoring device, and does not require SCUBA diving for subtidal transplanting. The shell method resulted in high survival rates in muddy (81.3%) and silty sediments (76.5%), but remarkably low survival rate in sandy sediments (5.0%). The TERFS, and shell methods reduced underwater labor; thus, these methods is suitable for large-scale seagrass restoration. Eelgrass transplants planted in summer had exhibited significant mortality due to high summer water temperatures. Although transplants planted in fall to spring had relatively high survival rates, transplanting and collection of vegetative shoots are difficult in winter and spring. Therefore, fall was suggested as the most effective transplanting season off the coast of Korea.