Response of meiofaunal and nematode communities to sewage pollution abatement: a field transplantation experiment

To assess the recovery rate of meiofaunal and nematode communities upon abatement of sewage pollution, a field transplantation experiment was conducted in Tai Tam, which is a non-polluted, shallow subtidal habitat on the southern portion of Hong Kong Island. The sediments used were from one site located in Victoria Harbour that was heavily influenced by sewage pollution, and one site in the outside-harbor area, which was relatively clean. In addition, sediments from Tai Tam were used as a control. Fresh sediments with meiofauna were collected from the aforementioned sites, placed in plastic trays and transplanted to Tai Tam. Sediments were retrieved at the beginning of the experiment and at 1-, 3-, and 8-weeks after transplantation for analysis of the meiofaunal and nematode communities as well as the sediment characteristics. The results showed that the meiofaunal and nematode communities in the control sediments were consistent at the four sampling periods, while it took three and eight weeks, respectively, for the nematode communities from the outside-harbor and inside-harbor sites to become similar to the control. These findings indicated that the relatively poor habitat quality and the nematode community composition in the sewage polluted inside-harbor sediments required a longer time for recovery than samples from the better habitat quality and the nematode community composition in the outside-harbor sediments.     

Forward Symplectic Integrators for Solving Gravitational Few-Body Problems

We introduce a class of fourth order symplectic algorithms that are ideal for doing long time integration of gravitational few-body problems. These algorithms have only positive time steps, but require computing the force gradient in addition to the force. We demonstrate the efficiency of these Forward Symplectic Integrators by solving the circular restricted three-body problem in the space-fixed frame where the force on the third body is explicitly time-dependent. These algorithms can achieve accuracy of Runge–Kutta, conventional negative time step symplectic and corrector symplectic algorithms at step sizes five to ten times as large.     

Assessing regional virtual water flows and water footprints in the Yellow River Basin, China: A consumption based approach

The Yellow River, the second longest river in China, is facing increasing water scarcity due to rising water consumption of a fast growing economy and an increasingly urbanized population with water-intensive consumption patterns. The Yellow River Basin (YRB) is divided into three regions: the upper, middle and lower reaches; each with very different characteristics in terms of water resources, economic structure and household income and consumption patterns. Virtual water has been recognised as a potentially useful concept for redistributing water from water-rich to water-poor regions. In this study, we develop a Multi-Regional Input-Output model (MRIO) to assess the regional virtual water flows between the three reaches of the basin and the rest of China distinguishing green and blue water, as well as rural and urban household water footprints. Results show that all three reaches are net virtual water exporter, i.e. production and consumption activities outside the basin also put pressure on the water resources in the YRB. The results suggest a reduction of the export of virtual blue water that could instead be used for producing higher value added but lower water-intensive goods. In particular, the lower reach as the most water scarce region in the basin should increase the import of water intensive goods, such as irrigated crops and processed food products, from other more water abundant regions such as the South of China. Thus, trading virtual water can help sustain the economic growth of the regions within the basin thus easing the pressure from water shortage. In addition, there is a huge gap between urban and rural household water footprints in the basin. The average urban household’s water footprint is more than double the water footprint of a rural household in the basin. This is due to the higher urban household consumption of water-intensive goods and services, such as processed food products, wearing apparel and footwear, hotel and catering services and electricity.     

Sensitivity of AUV response to variations in hydrodynamic parameters

The sensitivity of the response of a typical AUV to changes in hydrodynamic parameters is examined. The analysis is primarily performed using a computer model of an axi-symmetric vehicle typical of many AUVs in service today. The vehicle used is the Canadian Self-Contained Off-the-shelf Underwater Testbed (C-SCOUT), designed and built by graduate and work term students. The fully nonlinear computer model is based on Newton–Euler equations of motion, and uses the component build-up method to describe the excitation forces. The hydrodynamic parameters are varied in a series of simulations with the computer model; the response being analyzed for specific performance indicators.     

The use of selected genotoxicity assays in green-lipped mussels (Perna viridis): a validation study in Hong Kong coastal waters

In Hong Kong, discharges of domestic and industrial wastewaters and disposal of contaminated muds into coastal waters have resulted in high levels of persistent organic contaminants in the water column, biota and bottom sediments. Although the acute toxicity of effluents has been tested by government regulators using mortality-based bioassays, the sublethal effects of many of the pollutants, including environmental carcinogens, have not been well studied. The objective of the present work was to examine the efficiency and efficacy of using: (1) DNA strand breaks (comet assay and alkaline agarose gel electrophoresis assay); (2) oxidative DNA damage (levels of 8-hydroxy-2-deoxyguanosine in cellular DNA) and (3) micronuclei (MN) formation as early warning toxicological indicators of potential environmental carcinogen exposure. Green-lipped mussels (Perna viridis) were transplanted to study sites and retrieved after 4, 8, 12, 16 and 30 days. The bioaccumulation of organic pollutants, including the polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OC pesticides) and polychlorinated biphenyls (PCBs) was observed, and compared with biomarker assays. Some significant dose- and time-dependent inductions of the genotoxic biomarkers, including 8-OHdG, DNA strand breaks and micronuclei were observed. In particular, several very strong (r>0.9) and significantly positive relationships were found at all sites during days 0-12. In addition, significant strong relationships between certain organic contaminants (carcinogenic PAHs and 4 common OC pesticides) and micronuclei were detected at the polluted sites, Tsim Sha Tsui and Sai Wan Ho. The results suggest that the use of micronuclei as a biomarker is potentially effective, especially at the more polluted sites. Nonetheless, further research is required to validate their effectiveness under varying field conditions, especially to elucidate responses under lower contaminant loads, interactions between the environmental and physiological factors affecting organisms in differing coastal environments, and changes in biotransformation and DNA repair enzymes in test organisms.     

Field observations on correlation of fatty acid profiles between suspended particulate matter and green-lipped mussels in subtropical waters of Hong Kong

By analysis of the fatty acid profiles in mussel tissues and suspended particulate matter (SPM) in water, the present study showed a significant relationship of the trophic linkage between mussels and the SPM. At seven locations from inner to outer areas along the eutrophic Tolo Harbour and Tolo Channel, Hong Kong, the composition (as percentage of total fatty acids) of both monoenoic and polyunsaturated fatty acids in the tissues of green-lipped mussels Perna viridis and SPM in water had significant correlation (p<0.01). In particular, the composition of docosahexaenoic acid (DHA, 22:6n3) (as percentage of total fatty acids) in mussel tissues was statistically correlated with that in SPM (p<0.01), implying that mussels incorporate DHA, the biomarker of dinoflagellates. Principal component analysis further demonstrated that the fatty acid profiles of SPM were different among locations in the harbour, mid and outer channel of the study area, so were the mussel tissue fatty acid profiles. Cluster analysis of phytoplankton data also revealed the dominance of diatoms in the inner harbour and channel areas, whereas dinoflagellates were abundant in the outer channel waters. The possible implications of using benthic suspension feeders such as green-lipped mussels P. viridis for controlling phytoplankton abundance in coastal waters are discussed.