Preliminary study on biodegradation of phenanthrene by bacteria isolated from mangrove sediments in Hong Kong

Elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) have been found in mangrove sediments due to anthropogenic pollution, and microbial degradation has been suggested as the best way to remove PAHs from contaminated sediments. The degradation of phenanthrene, a model PAH compound by bacteria, either the enriched mixed culture or individual isolate isolated from surface mangrove sediments was examined. The effects of salinity, initial phenanthrene concentrations and the addition of glucose on biodegradation potential were also investigated. Results show that surface sediments collected from four mangrove swamps in Hong Kong had different degree of PAH contamination and had different indigenous phenanthrene-degrading bacterial consortia. The enriched bacteria could use phenanthrene as the sole carbon source for growth and degrade this PAH compound accordingly. A significant positive relationship was found between bacterial growth and percentages of phenanthrene degradation. The phenanthrene biodegradation ability of the enriched mixed bacterial culture was not related to the degree of PAH contamination in surface sediments. The growth and biodegradation percentages of the enriched mixed culture were not higher than that of the individual isolate especially at low salinity (0 and 10 ppt). High salinity (35 ppt) inhibited growth and biodegradation of phenanthrene of a bacterial isolate but less inhibitory effect was found on the mixed culture. The inhibitory effects of salinity could be reduced with the addition of glucose.     

Removal of tributyltin (TBT) by live and dead microalgal cells

The removal of tributyltin (TBT) from artificial wastewater by dead and live cells of four microalgal species, Chlorella miniata, C. sorokiniana, Scenedesmus dimorphus and S. platydiscus was investigated. Dead cells were generally more efficient in removing TBT during three days exposure. More than 90% and 85% TBT were removed by dead cells of Scenedesmus and Chlorella, respectively. Although the removal percentages of live microalgae were smaller, TBT was continuously absorbed and degraded, and TBT removal percentages similar to respective dead cells were achieved at the end of 14 days treatment. Degradation products, DBT and MBT, were recorded mainly inside the cells, and intracellular MBT concentrations were significantly higher than DBT. In terms of TBT removal, Scenedesmus cells were more effective than Chlorella, probably due to larger cell sizes and biomass. However, TBT specific uptake and degradation by Chlorella was higher than in Scenedesmus. The highest specific TBT uptake values, as well as the highest degradation, were recorded in C. miniata, a Hong Kong isolate.     

Estimation of damping ratio of soil sites using microtremor

It is widely known that the seismic response characteristics of a soil site depends heavily on several key dynamic properties of the soil stratum, such as predominant frequency and damping ratio. A widely used method for estimating the predominant frequency of a soil site by using microtremor records, proposed by Nakamura, is investigated to determine its effectiveness in estimating the damping ratio. The authors conducted some microtremor measurements of soil sites in Hong Kong and found that Nakamura’s method might also be used to estimate the damping ratio of a soil site. Damping ratio data from several typical soil sites were obtained from both Nakamura’s ratio curves using the half power point method and resonant column tests. Regression analysis indicates that there is a strong correlation between the damping ratios derived from these two different approaches. Supported by: Research project (PolyU 5076/97E), of the Department of Civil and Structural Engineering, The Hong Kong Polytechnic University     

Opening geometry of the Kurile Basin (Okhotsk Sea) as inferred from structural data

Abstract   The Kurile Basin in the Okhotsk Sea, northwestern Pacific, is a back-arc basin located behind the Kurile Island Arc. It is underlain by oceanic crust and its origin has been attributed to back-arc spreading. Two models for the opening of the Kurile Basin exist, for which the spreading axis is oriented northeast–southwest and northwest–southeast, respectively. New data are presented here on the morphostructure of the slope of the northern Kurile Basin and of the central Kurile Basin which support a strike of the spreading axis in the latter direction. Bathymetric as well as single-channel and multichannel seismic reflection data demonstrate the existence of dominant northwest-striking normal faults on the northern slope of the Kurile Basin. In the central Kurile Basin a basement rise striking north-northwest–south-southeast (here named the Sakura Rise) was mapped. The rise morphology has the distinct imprint of a rift structure with symmetrical volcanic edifices on the rise axis and faulted blocks that tilt in opposite directions on the flanks. These data suggest that the Kurile Basin opened in a northeast–southwest direction. In the generally accepted plate tectonic reconstructions, northwest–southeast spreading associated with dextral strike–slip along the north–south-striking shear zone of Sakhalin and Hokkaido islands has been assumed. In the present model, spreading in the Kurile Basin was presumably connected with dextral displacement along a northeast-striking shear zone on the southern segment of the Okhotsk Sea.     

The influence of tectonic regime on chalk deposition: examples of the sedimentary development and 3D-seismic stratigraphy of the Chalk Group in the Netherlands offshore area

The sediments of the Upper Cretaceous to lower Palaeogene Chalk Group were deposited through a wide range of depositional processes. Chalk was originally formed by settlement of coccolithophorid skeletal remains from suspension in the water column, with bottom currents redistributing the sediment shortly after deposition. Locally, tilting of the sea‐floor resulted in mass‐movement of chalk at scales varying from decimetre‐thick turbidites to slumps and slide sheets that were up to hundreds of metres thick. Syn‐depositional tectonic activity, therefore, constituted an important control on chalk facies. To study this relation in more detail, a three‐dimensional (3D)‐seismic stratigraphical analysis was carried out, comparing two study areas that experienced contrasting syn‐depositional tectonic evolutions. The Vlieland offshore area, which underwent gradual subsidence and westward tilting during deposition of the Chalk Group, is characterised by parallel and continuous reflections thought to represent pelagic chalk deposits. In the Dutch Central Graben, which was tectonically inverted during the Late Cretaceous to early Palaeogene, discontinuous and irregular seismic reflections that indicate large‐scale reworking of sediment are found. The improved image quality of 3D‐ vs. 2D‐seismic data allowed us to study the detailed geometry of allochthonous chalk bodies and aided the identification and tracing of the often subtle intra‐Chalk Group unconformities, resulting in a subdivision of the Chalk Group into seven seismic sequences.     

Formulating a General Spatial Segregation Measure*

Most traditional segregation measures, such as the index of dissimilarity D, fail to distinguish spatial patterns effectively. Previously proposed spatial measures modifying D suffer from several shortcomings. This article describes a general spatial segregation index based upon the concept of composite population counts, which are derived from grouping people in neighboring areas together to account implicitly for spatial interaction of groups across unit boundaries. The suggested spatial index can overcome the disadvantages of previous indices and can assess the spatial extent of the segregated clusters. The results offer a more comprehensive depiction of spatial segregation of a region.     

Spatial and temporal variations of heavy metal contamination in sediments of a mangrove swamp in Hong Kong

Spatial and temporal variations of heavy metal contamination in sediments of a small mangrove stand in Hong Kong were examined by laying two transects perpendicular across the shore. Surface sediment samples were taken along the two transects running landward to seaward at intervals of 5 or 10 m during December 1989, and March, July and September 1990. Total concentrations of Cu, Zn, Mn and Pb did not show any specific trend along each transect, although the maximum concentration of heavy metals tended to occur at the landward edge. There was a high level of variability among locations within each transect; for instance, the Cu concentrations fluctuated from 1 to 42 μg g⁻¹. Certain sites contained exceptionally high levels of total metals. Total concentrations of Cu, Zn, Mn and Pb as high as 42, 150, 640 and 650 μg g⁻¹, respectively, were recorded, implying contaminated sediment. A comparison of the two transects indicated that the sediments of Transect B seemed to contain higher total Zn but lower Cu and Mn concentrations than those of Transect A. Most of the heavy metals accumulated in the sediments were not extractable with ammonium acetate and no Cu or Pb was detected in these extracts. The concentrations of extractable Zn and Mn were low, less than 10% of the total metal concentration in the sediment, and appeared to decrease from the landward to seaward samples. For both total and extractable metals, there were significant seasonal fluctuations for both transects, but no specific trends could be identified. These spatial and temporal variations suggest that the scale and representativeness of sampling require careful planning, and a single sample might not give a satisfactory evaluation of the levels of heavy metal contamination in mangrove ecosystems.     

Characterization of sewage sludge and toxicity evaluation with microalgae

Heavy metal contents (Cd, Cr, Cu, Pb, Ni and Zn) of digested sludge, collected from sewage treatment works (Shatin (ST), Shek Wu Hui (SWH), Tai Po (TP) and Yuen Long (YL)) in 1992, 1993 and 1994, were analysed by atomic absorption spectrophotometry after sequential extraction by 1 KNO₃, 0.5 KF, 0.1 Na₄P₂O₇, 0.1 EDTA and 6 HNO₃. It was found that the major forms of Cu, Pb, Ni and Zn were in the sulphide phase, organically-bound phase, adsorbed phase and carbonate phase, respectively. A dinoflagellate (Dunaliella tertiolecta) and a diatom (Thalassiosira sp.) were used as bioindicators to test the toxicity of digested sludge samples collected in 1994. Each of the algae were inoculated to elutriates of digested sludge at different concentrations. The toxicities of the four types of sludge, according to 96 h-IC₅₀s, were ranked as follows: TP > ST > SWH > YL for D. tertiolecta and ST > SWH > TP > YL for Thalassiosira sp. For D. tertiolecta, a significant correlation was found between algal inhibition and ammonium-N, both in sludge (p<0.05) and elutriates (p<0.01).     

Effects of copper on survival, development and growth of Metapenaeus ensis larvae and postlarvae (decapoda: Penaeidae)

Effects of copper on survival, development and growth of the early developmental stages of the penaeid shrimp, Metapenaeus ensis, were studied in the laboratory. High variability in survival rates were observed among animals from different spawners. Larvae exposed to 0.06 and 0.10 mg Cu l⁻¹ over a 10-day period had lower survival rates and exhibited slower development than control animals. No significant treatment effects were found at 0.04 and 0.08 mg Cu l⁻¹. Effects of copper on survival and growth of postlarvae were studied over an 8-day period. Copper concentrations lower than 0.10 mg l⁻¹ did not affect survival rates. Slower growth rates were observed in postlarvae exposed to 0.08 and 0.10 mg Cu l⁻¹.     

Measuring water use efficiency of Eucalypt trees with chambers and micrometeorological techniques

Enclosure appears to be the only feasible way to examine the gas exchange of small groups of trees or to answer questions about the effects of increased atmospheric CO₂ on the assimilation, evaporation and water use efficiency of forests. To be effective, enclosures must necessarily change the microclimate, but few studies have been made of the consequences. In this paper, the assimilation, evaporation and water use efficiency of a community of Eucalyptus trees inside a ventilated chamber are compared with the same attributes for the surrounding forest. Assimilation and evaporation for the chamber were measured by the depletion in CO₂ and the enrichment in water vapour of air passing through the chamber. For the forest, assimilation and evaporation were determined by micrometeorological techniques based on the energy balance, and for CO₂, additional chamber measurements of the soil effiux. Water use efficiencies were calculated as the ratio of mol CO₂ assimilated to mol water evaporated. There are some important microclimatic differences between chamber and forest: net radiation is reduced by about 30% in the chamber, the vapour pressure deficit of the chamber air is lower, and the light climate there tends to be diffuse rather than direct. Despite these differences, evaporation rates for both chamber and forest were generally similar, perhaps due to compensating effects in the chamber from higher boundary layer conductances (because of greater ventilation rates) and higher stomatal conductances (because of increased humidity). However, assimilation rates and water use efficiencies were markedly different for the two communities in clear sky conditions, with higher values of both being recorded in the chamber for most of the daylight hours. Only on cloudy days, when the light climate was diffuse in both chamber and forest, were similar assimilation rates and water use efficiencies observed. This behaviour seems to be attributable in part to the light climate in the chamber being predominantly diffuse and that in the forest predominantly direct. Diffuse light enhances the photosynthesis of lower leaves in the canopy. This contention is supported by model calculations of canopy assimilation under diffuse and direct radiation which produced qualitatively the same light response functions as observed for chamber and forest. The study suggests that the use of chambers for exploring questions of forest productivity and water use efficiency must be circumspect. The act of enclosure, by itself, can change the daily water use efficiency of the tree community by as much as 50%.