Significance of mangrove–mudflat boundaries as nursery grounds for the mud crab, Scylla paramamosain

Fisheries managers frequently try to protect juveniles in order to preserve stocks. Juveniles can be protected by either implementing changes designed to avoid catching immature animals (e.g. increasing mesh size or altering fishing techniques) or protecting nursery grounds. To prevent the capture of immature animals, an estimate of size at maturity is required as well as a knowledge of both fishing methods and the exact location of the nursery grounds. Strong demand for juvenile mud crabs to stock aquaculture ponds has resulted in development of fisheries targeting crabs of all sizes from instar 1 to mature individuals. Using five different fishing methods, different stages in the life cycle of Scylla paramamosain were followed for a period of 16 months in an estuarine population in the Mekong Delta, Vietnam. Mangrove habitat utilisation begins when crabs settle out from the plankton at instar 1 [modal internal carapace width (ICW), 0.5 cm] amongst the pneumatophores at the mangrove fringe. Increasingly larger crabs were found deeper into the mangrove but they were still living on the surface (modal ICW size class, 1.5 cm). As their size increases, the crabs either dig burrows (modal ICW size class, 4.5 cm) or they live in the sub-tidal zone, migrating into the mangrove with each tide to feed (modal ICW size class, 4.5 cm). Larger crabs were caught offshore (modal ICW size class, 12.5 cm) where females accounted for 60% of the catch although of these, only 63% were mature. Recruitment of early instars was continuous but peaked in December to February. Subsequent peaks in the catch rates of larger size classes indicated the development of a single cohort with an estimated growth rate of 2.0 cm ICW per month. On the basis of abdominal width, females were estimated to mature at 10.2 cm ICW although at 9.7 cm ICW, 50% of females had disengaged abdomens. Abdominal disengagement occurred in males at the slightly smaller size of 9.1 cm ICW. Allometric relationships between chela height and carapace width suggested 50% of males acquire mature chelae at 10.2 cm ICW. These results demonstrate the close linkage between early life stages of S. paramamosain and certain specific niches within mangrove habitats, with the main adult population found to be living sub-tidally at some distance from the mouth of the estuary. The study also highlights the special importance of the mangrove fringe, the border between the mangrove forest and the sea, an area which is particularly vulnerable to physical and anthropogenic impacts.     

Smoke aerosols dispersion and transport from the 2013 New South Wales (Australia) bushfires

Environmental monitoring and modelling, especially in the regional context, has seen significant progress with the widely usage of satellite measurement in conjunction with local meteorological and air quality monitoring to understand the atmospheric dispersion and transport of air pollutants. This paper studies the application of these data and modelling tools to understand the environment effects of a major bushfire period in the state of New South Wales (NSW), Australia, in 2013. The bushfires have caused high pollution episodes at many sites in the greater Sydney metropolitan areas. The potential long-range transport of aerosols produced by bushfires to other region and states has been seen by regulators as a major concern. Using data and images collected from satellites, in addition to the results obtained from different simulations carried out using HYSPLIT trajectory model and a regional meteorological model called Conformal Cubic Atmospheric Model (CCAM), we were able to identify at least 2 days on which the smoke aerosols from bush fires in NSW has been transported at high altitude to the northern state of Queensland and the Coral Sea. As a result, widespread high particle concentration in South East Queensland including the Brisbane area, as measured by nearly all the air quality monitoring stations in this region, occurred on the day when the smoke aerosols intruded to lower altitude as indicated by the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Lidar measurements on the CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The use of meteorological or air quality modelling to connect the ground-based measurements with satellite observations as shown in this study is useful to understand the pollutant transport due to bushfires and its impact on regional air quality.     

Application and validation of a biotic ligand model for calculating acute toxicity of lead to Moina dubia in lakes of Hanoi,Vietnam

Environmental Science and Pollution Research - It is increasingly being recognized that biotic ligand models (BLMs) can successfully predict the toxicity of divalent metals toward aquatic biota...     

Arsenic contamination in groundwater and its possible sources in Hanam, Vietnam

This study investigated the arsenic (As) level in groundwater, and the characteristics of aquifer sediment as related to the occurrence of As in groundwater in Hanam, Vietnam. The deposition and transport of As-containing substances through rivers were also examined. Arsenic concentrations in 88% of the groundwater samples exceeded the As limit for drinking water based on the WHO standards. The dominating form of arsenic was As(III). The maximum total As content in bore core sediment was found in a peat horizon of the profiles and generally, elevated levels of As were also found in other organic matter-rich horizons. Total As contents of the bore core sediments were significantly correlated with crystalline iron oxide, silt and clay contents, suggesting that As in aquifer sediment was mainly associated with iron (hydr)oxides and clay mineral. In the groundwater, As concentration showed significant correlations with the total concentrations of Fe and HCO (3)(-). Significant correlations between HCl-extractable As and non-crystalline Fe oxide, total C, N, and S were also observed in the profiles. The results support the hypothesis that under favorable reductive conditions established by the degradation of organic matter, the dissolution of iron (hydr)oxides releases adsorbed As into the groundwater. The deposition of As in the sediments from the Red River were significantly higher than that in the Chau Giang River, suggesting that the Red River is the main source of As-containing substances deposited in the study area.     

Pesticide residues in soils, sediments, and vegetables in the Red River Delta, northern Vietnam

This study assessed pesticide residues in soils, sediments, and vegetables in the Xuan Khe and Hop Ly communes located along the Chau Giang River in the Red River Delta, northern Vietnam. Samples were collected from agricultural areas within and outside of embankments built to prevent flooding. In Xuan Khe, the soils outside of the embankment were more clayey with higher organic matter contents compared with the inside, due to selective deposition during river flooding. Many of the soils contained significant amounts of pesticides including dichlorodiphenyltrichloroethane (DDT), dicofol, isoprothiolane, and metalaxyl although their levels were below the maximum allowable concentration set by the Vietnamese government. The spectrum of DDT derivatives found suggested that the source of DDTs was not contaminated dicofol. Soils in Hop Ly resembled soils in Xuan Khe but were relatively sandy; one field showed appreciable contents of DDT derivatives. The ratios of (p,p ^′-dichlorodiphenyldichloroethylene + p,p ^′-dichlorodiphenyldichloroethane)/∑DDT in the surface and subsurface soils in Hop Ly were 0.34 and 0.57, suggesting that the DDTs originated from recent application. Pesticide residues in soils were not likely to translocate into vegetable crops, except for metalaxyl. High concentrations of cypermethrins in kohlrabi leaves could be ascribed to foliar deposition.     

基于VSG的微电网逆变器控制策略研究

针对微电网中的分布式电源出力的间歇性导致微电网功率不稳定的问题,基于虚拟同步发电机(Virtual Synchronous Generator,VSG)技术的控制方法,建立VSG的数学模型,设计了一种基于电流、电压和功率控制的反馈控制器,提出了一种全新的VSG控制策略,实现分布式电源动态特性对微电网中有功功率和无功功率的均分控制。并通过Matlab/Simulink仿真,验证了所提控制算法的有效性。结果表明:该控制策略对抑制因新能源发电并网导致的电网波动、提高电能质量具有重要意义。     

Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration

Two artificial wastes (A and B) whose contents reflect regional differences in municipal solid waste composition, were used to investigate the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) during incineration. Flue gas samples were simultaneously collected at three ports in the post-combustion zone corresponding to flue gas temperatures of 400, 300, and 200 °C. The combustion of Waste B, which had a higher chlorine and metal content than Waste A, produced greater levels of highly-chlorinated homologues, as demonstrated by a higher degree of chlorination. The total concentrations of PCDDs, PCDFs, PCBs, and PCNs formed in the combustion of both wastes increased as temperature decreased along the convector. There were no significant differences in total concentrations between Waste A and Waste B combustion at specific temperatures, with exception of PCDFs at 400 °C. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) modeling, used to evaluate the data for all compound groups, suggest that during flue gas quenching at temperatures of 400 °C low-chlorinated homologues are preferentially formed in the presence of copper, which is known to be a very active catalyst for this process. At 300 and 200 °C, the formation of highly-chlorinated homologues is favored.     

Effects of chelates (EDTA,EDDS, NTA) on phytoavailability of heavy metals (As,Cd, Cu,Pb, Zn) using ryegrass (Lolium multiflorum Lam.)

Environmental Science and Pollution Research - This paper summarises a study of the application of the synthetic chelate ethylenediaminetetraacetic acid (EDTA), and the natural chelates...     

Steel slag quality control for road construction aggregates and its environmental impact: case study of Vietnamese steel industry—leaching of heavy metals from steel-making slag

Environmental Science and Pollution Research - Steel slag is an industrial by product of steel manufacturing processes and has been widely utilized within civil and construction materials for road...     

Antibiotic and antiparasitic residues in surface water of urban rivers in the Red River Delta (Hanoi,Vietnam): concentrations,profiles, source estimation,and risk assessment

Environmental Science and Pollution Research - Antibiotic residues and antimicrobial resistance in surface water are issues of global concern, especially in developing countries. In this study, the...