An assessment of potential responses of Melaleuca genus to global climate change

The genus Melaleuca consists of around 260 species covering over eight million hectares (including native and introduced species) and distributed mostly in Australia, but also occurring in South-East Asia, the Southern United States and the Caribbean. Melaleuca populations predominantly occur in wetland or/and coastal ecosystems where they have been significantly affected by climate change. This paper assesses the potential responses of the Melaleuca genus to climate change, based on the synthesis of worldwide published data. The main findings include: (i) that the Melaleuca genus has a rich species diversity, and significant phenotypic diversity in a variety of ecosystems; (ii) they demonstrate significant local adaptation to harsh conditions; and (iii) the fossil records and taxon biology indicate the evolution of the Melaleuca genus began around 38 million years ago and they have survived several significant climatic alterations, particularly a shift towards cooler and drier climates that has occurred over this period. These findings show that the Melaleuca genus is highly resilient and adaptable and based on this, this paper argues that Melaleuca can adapt to climate change through Wright’s ‘migrational adaptation’, and can be managed to achieve sustainable benefits.     

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.     

Enhanced phosphate removal by thermally pretreated waste oyster shells

Journal of Material Cycles and Waste Management - Waste oyster shells were used to remove phosphate and the effects of thermal pretreatment were studied. Thermal pretreatment under different...     

Cadmium desorption in sand

Desorption of cadmium (Cd) from sand was studied by both batch and flow-through methods. Batch experiments were conducted at three pH values (5.5, 6.0 and 6.5). In each case, the amount of Cd desorbed was low compared with the quantity of Cd adsorbed previously. Desorption of Cd in the batch experiments can be described adequately by a Freundlich isotherm. The Freundlich isotherm coefficient, Kf, increased with pH. Hysteresis between the sorption/desorption isotherms was observed in all batch experiments. Flow-through experiments in soil columns were conducted for the same three pH values, with the results used to determine transport and sorption/desorption parameters. Again, the desorption isotherms bore little resemblance to the corresponding adsorption isotherms. The experimental breakthrough curves were well fitted by a nonequilibrium desorption model, however the time scale of the desorption process was much larger than measured in batch experiments. This model was therefore rejected as lacking realism. A simple linear retardation (including hysteresis) model that utilises different isotherms was found to simulate column breakthrough curves well. The Freundlich isotherm coefficients, Kf, in all batch and flow-through desorption experiments were different to values evaluated from the corresponding adsorption experiments. However, in contrast to adsorption, desorption in flow-through experiments was not noticeably affected by changes in pH. The effect of pore-water velocity on desorption was also studied at pH 6.0. No trend was established between flow velocity and the desorption coefficient.     

Self-Organizing Maps for Integrated Environmental Assessment of the Mid-Atlantic Region

A new method has been developed to perform environmental assessment at regional scale. This involves a combination of a self-organizing map (SOM) neural network and principal component analysis (PCA). The method is capable of clustering ecosystems in terms of environmental conditions and suggesting relative cumulative environmental impacts of multiple factors across a large region. Using data on land-cover, population, roads, streams, air pollution, and topography of the Mid-Atlantic region, the method was able to indicate areas that are in relatively poor environmental condition or vulnerable to future deterioration. Combining the strengths of SOM with those of PCA, the method offers an easy and useful way to perform a regional environmental assessment. Compared with traditional clustering and ranking approaches, the described method has considerable advantages, such as providing a valuable means for visualizing complex multidimensional environmental data at multiple scales and offering a single assessment or ranking needed for a regional environmental assessment while still facilitating the opportunity for more detailed analyses.     

Effects of C/N ratio on nitrate removal and floc morphology of autohydrogenotrophic bacteria in a nitrate-containing wastewater treatment process

The effects of C/N ratio of a nitrate-containing wastewater on nitrate removal performed by autohydrogenotrophic bacteria as well as on the morphological parameters of floc such as floc morphology, floc number distribution, mean particle size(MPS), aspect ratio and transparency were examined in this study. The results showed that the nitrate reduction rate increased with increasing C/N ratio from 0.5 to 10 and that the nitrogen removal of up to 95% was found at the C/N ratios of higher than 5(between 0.5–10). Besides, high C/N ratio values reflected a corresponding high nitrite accumulation after 12-hr operation, and a fast decreasing rate of nitrite in the rest of operational time. The final p H values increased with the C/N ratio increasing from 0.5 to 2.5, but decreased with the C/N ratio increasing from2.5 to 10. There were no significant changes in floc morphology with the MPSs ranging from35 to 40 μm. Small and medium-sized flocs were dominant in the sludge suspension, and the number of flocs increased with the increasing C/N ratios. Furthermore, the highest apparent frequency of 10% was observed at aspect ratios of 0.5 and 0.6, while the transparency of flocs changed from 0.1 to 0.7.     

Persistent organochlorine residues in human breast milk from Hanoi and Hochiminh City, Vietnam: contamination, accumulation kinetics and risk assessment for infants

Despite the ban on persistent organochlorines (OCs) in most of the developed nations, their usage continued until recently in many Asian developing countries including Vietnam, for agricultural purposes and vector-borne disease eradication programs. In this study, we collected human breast milk samples from the two big cities in Vietnam: Hanoi (n=42) and Hochiminh (n=44) and determined the concentrations of persistent OCs such as PCBs, DDT and its metabolites (DDTs), hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), chlordane compounds (CHLs) and tris-4-chlorophenyl-methane (TCPMe). The contamination pattern of OCs was in the order of DDTs > PCBs > HCHs > CHLs approximately HCB approximately TCPMe. Compilation of available data indicated that DDT residue levels in human breast milk from Vietnam were among the highest values reported for Asian developing countries as well as developed nations. This result suggests recent usage of DDTs in both north and south Vietnam. Interestingly, in both cities, the p,p'-DDT portion was higher in multiparas than those in primiparas. Considering the fact that the interval between the first and the second child of a mother in Vietnam is usually short, this result probably indicates continuous intake of DDTs in the population. Analysis of infant exposure to DDTs via breast milk suggested that the daily intake rates for number of individuals are close to or above the threshold for adverse effects which may raise concern on children health.