Yazhi Bai

Sources and mass inventory of sedimentary polycyclic aromatic hydrocarbons in the Gulf of Thailand: Implications for pathways and energy structure in SE Asia

Surface sediments obtained from a matrix of 92 sample sites in the Gulf of Thailand (GOT) were analyzed for a comprehensive study of the distribution, sources, and mass inventory of polycyclic aromatic hydrocarbons (PAHs) to assess their input pathways and impacts of the regional land-based energy structure on the deposition of PAHs on the adjacent continental margins. The concentration of 16 PAHs in the GOT ranged from 2.6 to 78.1ng/g (dry weight), and the mean concentration was 19.4±15.1ng/g. The spatial distribution pattern of 16 PAH was generally consistent with that of sediment grain size, suggesting the influence of regional hydrodynamic conditions. Correlation and principal component analysis of the PAHs indicated that direct land-based inputs were dominantly responsible for the occurrence of PAHs in the upper GOT and the low molecular weight (LMW) PAHs in the coastal region could be from petrogenic sources. A positive matrix factorization (PMF) model apportioned five contributors: petroleum residues (~44%), biomass burning (~13%), vehicular emissions (~11%), coal combustion (~6%), and air-water exchange (~25%). Gas absorption may be a significant external input pathway for the volatile PAHs in the open GOT, which further implies that atmospheric loading could be important for the sink of PAHs in the open sea of the Southeast Asia (SE Asia). The different PAH source patterns obtained and a significant disparity of PAH mass inventory in the sediments along the East and Southeast Asia continental margins can be ascribed mainly to different land-based PAH emission features under the varied regional energy structure in addition to the depositional environment and climatic conditions.

Extensive study of potential harmful elements (Ag, As, Hg, Sb, and Se) in surface sediments of the Bohai Sea, China: Sources and environmental risks ☆

This study analyzed 405 surface sediment samples, obtained from across the Bohai Sea, for concentrations of five potentially harmful elements (Ag, As, Hg, Sb, and Se) and several ancillary parameters (Al, Fe, Mn, total organic carbon (TOC), and grain size). Statistically, the spatial distributions of these elements were correlated positively with Al, Fe, TOC, and grain size, indicating natural sources for these elements or common accumulation mechanisms. The assessment of potential environmental risk with empirical sediment quality guidelines showed that a significant proportion of the samples had As and Sb concentrations that exceeded the effects range low (ERL) or T20 values in the Bohai Sea, indicating the potential for adverse biological effects. However, the assessment results differed when using evaluation methods that considered background values. Based on the geoaccumulation index (Igeo), Hg and Ag were found to have the highest percentages (35% and 60%, respectively) in samples that were moderately contaminated. The estimated contamination degree (Cd) suggested higher contamination levels for the entire area, with 69% of the samples being moderately contaminated. Generally, except for some local hotspots, such as Jinzhou Bay, the contamination levels of these elements in the Bohai Sea were established as slight to moderate. Samples from the Jinzhou Bay area had concentrations that were 10-100 times higher than in the rest of the Bohai Sea, indicating severe contamination.

DISTRIBUTION PATTERN OF POC OF THE SPRING SUSPENDED MATTER IN THE YELLOW SEA AND EAST CHINA SEA: DISTRIBUTION PATTERN OF POC OF THE SPRING SUSPENDED MATTER IN THE YELLOW SEA AND EAST CHINA SEA

A survey of the suspended matter in the South Yellow Sea and the north part of the East China Sea was conducted in April to May 2006.Based on the data from the samples collected at 45 stations,the horizontal and vertical distribution patterns of the particulate organic carbon(POC) of the Yellow Sea and the East China Sea were presented in this paper.And the sources of the POC and the influencing factors were further discussed according to the particulate nitrogen(PN) and C/N.The results show that the highest concentration of surface suspended POC appear at the area around 123° E,31° N in the East China Sea,while the value was lower in the south Yellow Sea and the area to the east of 124° E in the East China Sea.The concentration of surface POC in the vicinity of the Changjiang Estuary is obviously higher than that in other areas,indicating the primary influence by the Changjiang diluted water.However,the highest concentration of bottom suspended POC occurs at the area adjacent of 121.5° E,33.5° N in the south Yellow Sea.And also there was a second highest concentration around 124.5° E,31.5° N in the East China Sea.The value was relative lower in areas to the south of 31° N in the East China Sea.It could be inferred that the high concentration of bottom POC was mainly controlled by the resuspension of sediments.The C/N suggests that the POC of the study area was mainly from the ocean.It is concluded that currents play a critical role in the distribution of POC of suspended matters.Therefore,different areas under the contral of the Yellow Sea Warm Current,the Subei Coastal Current and the Yangtze Diluted Water could be distinguished.The distribution pattern of the POC in the study area was controlled by both the sources of the organic matter and the ocean currents.

Diversity and distribution of catechol 2, 3-dioxygenase genes in surface sediments of the Bohai Sea

Catechol 2, 3-dioxygenase (C23O) is the key enzyme for aerobic aromatic degradation. Based on clone libraries and quantitative real-time polymerase chain reaction, we characterized diversity and distribution patterns of C23O genes in surface sediments of the Bohai Sea. The results showed that sediments of the Bohai Sea were dominated by genes related to C23O subfamily I.2.A. The samples from wastewater discharge area (DG) and aquaculture farm (KL) showed distinct composition of C23O genes when compared to the samples from Bohai Bay (BH), and total organic carbon was a crucial determinant accounted for the composition variation. C6BH12-38 and C2BH2-35 displayed the highest gene copies and highest ratios to the 16S rRNA genes in KL, and they might prefer biologically labile aromatic hydrocarbons via aquaculture inputs. Meanwhile, C7BH3-48 showed the highest gene copies and highest ratios to the 16S rRNA genes in DG, and this could be selective effect of organic loadings from wastewater discharge. An evident increase in C6BH12-38 and C7BH3-48 gene copies and reduction in diversity of C23O genes in DG and KL indicated composition perturbations of C23O genes and potential loss in functional redundancy. We suggest that ecological habitat and trophic specificity could shape the distribution of C23O genes in the Bohai Sea sediments.