Mai Po Research Articles

Epidemiological Baseline of Influenza Virus in Wild Aquatic Birds in Hong Kong during the Pre-H5N1 Endemic Era

AbstractInfluenza virus surveillance was conducted on wild ducks and shorebirds in Hong Kong at the Mai Po Nature Reserve to determine whether East Asian wild aquatic birds passing through or overwintering in Hong Kong are reservoirs of H5N1 influenza viruses and to establish an epidemiological baseline of influenza virus in wild aquatic birds during the pre-H5N1 endemic era. Three influenza viruses were isolated from 3178 faecal samples collected over three sampling periods from 1988 to 2001 during the southern and northern migration periods. The isolation rates and viruses were, respectively 0.08% (H10N5) in 1988 – 1990, 0.12% (H11N1) in 1998 and 0.09% (H3N8) in 1999 – 2001. Whereas tracheal and intestinal colon explants from representative shorebirds were susceptible to in vitro infection by the H10N5 virus, orally infected shorebirds were apparently not. Genetic analyses indicated that the nucleoprotein, matrix and nonstructural genes of the three viruses were related to those of aquatic bird viruses in Asia, but not to those of the human H5N1 virus. The present study provided epidemiological baseline information for future influenza virus surveillance in wild aquatic birds in southeast China.

Summer fluxes of atmospheric greenhouse gases N 2O, CH 4 and CO 2 from mangrove soil in South China

The atmospheric fluxes of N 2O, CH 4 and CO 2 from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83 μmol m − 2 h − 1, 11.9 to 5168.6 μmol m − 2 h − 1 and 0.69 to 20.56 mmol m − 2 h − 1 for N 2O, CH 4 and CO 2, respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N 2O and CH 4 fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N 2O and CO 2 fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH 4 +-N contents, as well as the soil porosity. However, only soil NH 4 +-N concentration had significant effects on CH 4 fluxes.

Ecotoxicological study on sediments of Mai Po marshes, Hong Kong using organisms and biomarkers

Sediments from Mai Po Ramsar site, Hong Kong were in general shown to be highly toxic based on the results of four toxicity tests (Microtox ® solid-phase test, Daphnia mortality test, algal [ Microcystis aeruginosa] growth inhibition test and ryegrass [ Lolium perenne] seed germination/root elongation test). Sediment of the mudflat (which is open to Deep Bay, i.e., the pollution source) was the most toxic while sediment of gei wai 24g (an enclosed freshwater pond) was the least toxic. Results of biomarker studies (tilapia hepatic metallothionein; glutathione (GSH) and EROD activity using H4IIE rat hepatoma cell) were also concordant with those in the toxicity tests. Significant liner relationships ( p<0.01) were found between GSH contents in the rat hepatoma cells and PAHs, OCPs contents in the sediment extracts. It is recommended that the present suite of bioassays is useful and is biologically relevant for future ecotoxicological studies focusing on similar wetlands.

Complete Sequence of Plasmid pMP1 from the Marine Environmental Vibrio vulnificus and Location of Its Replication Origin

A novel cryptic plasmid, pMP1, from an environmental Vibrio vulnificus MP-4 isolated from Mai Po Nature Reserve in Hong Kong, has been characterized. The 7.6-kb plasmid had guanine-cytosine content of 40.03% and encoded four open reading frames (ORFs) with >100 amino acids. The predicted protein of ORF1 contained 478 amino acids showing 29% identity and 50% similarity over 309 amino acids to the integrase of Vibrio cholerae phage VP2. ORF2 encoded a putative protein of 596 amino acids, which were 23% identity and 42% similarity over 455 amino acids to the tail tape measure protein TP901 of Chromohalobacter salexigens phage. ORF3 and ORF4 encoded putative proteins of 103 and 287 amino acids, respectively, but showed no homologies to any known proteins. Further experiments indicated that a 3.2-kb fragment from EcoRI digestion could self-replicate. Analysis indicated that a sequence upstream of ORF4 had the features characteristic of theta-type replicons: AT-rich region, six potential direct repeats (iterons) spaced approximately two DNA helical turn apart (about 23 bp), two copies of 9 bp dnaA boxes, three Dam methylation sites, and five inverted repeats. Complementation experiments confirmed that the protein encoded by ORF4 was required for plasmid replication. We propose that ORF4 encode a new type of Rep protein and pMP1 is a new type of theta plasmid.

Fungal endophytes associated with Kandelia candel (Rhizophoraceae) in Mai Po Nature Reserve, Hong Kong

Abstract We examined the endophytic fungi associated with the dominant mangrove plant, Kandelia candel, in Mai Po Nature Reserve, Hong Kong. Bark, woody tissue and leaves from four mature healthy trees were sampled for fungal endophytes in April and June, 2001. A total of 880 isolates was obtained, 595 from the June sampling. The highest number of fungal endophytes was cultured from bark (674 isolates) with only 63 from leaves. Three taxa of ascomycetes, 18 of anamorphic fungi and 29 mycelial morphotypes were identified. These results indicate a degree of tissue recurrence with similar endophytic fungal assemblages in bark and wood, and a different assemblage in the leaf samples. Dominant sporulating fungi of K. candel were Phomopsis sp., Pestalotiopsis sp., Guignardia sp. and Xylaria sp., which are cosmopolitan and common endophytic species.

New species of anthurid and arcturid isopod (Crustacea: Peracarida: Isopoda) from Hong Kong

Three new species of anthurid isopod are described, one each of the genera Caenanthura and Amakusanthura from within or adjacent to Conic Island Cave, eastern Hong Kong, and a new species of Cyathura from the Mai Po Marshes in northwestern Hong Kong. The anthurid isopods of Hong Kong waters are reviewed. In addition, a new arcturid isopod species of the genus Arcturina is described, also from the vicinity of Conic Island Cave.

Sorption behavior of bisphenol A on marine sediments

Bisphenol A (BPA) is a known endocrine disrupting chemical (EDC) that has been widely used for the production of polycarbonate plastics and epoxy resins. In this experimental study, the sorption behavior of BPA on the marine sediments sampled from 6 different sites in the Mai Po Nature Reserve in Hong Kong was investigated. BPA sorption on the sediments can be well described by a linear sorption isotherm, suggesting a partition of BPA between the aqueous solution and the organic matter of the sediments. The BPA partition coefficient, K d , for the raw sediment samples varied from 4.43 to 8.54 L/kg (R2 : 0.91–0.96) in nearly proportion to the organic content of the sediments. After the treatment of H2O2 oxidation for organic removal, the sediments had the K d value reduced by more than 50%. However, the organic residue or black carbon of the sediments after the H2O2 treatment had a much greater sorption capacity than the natural organic matter on the sediment which was oxidized by H2O2. The organic normalized partition coefficients (K oc ) averaged around 1355 L/kg for the H2O2-treated sediment, which was more than three times greater than the K oc value of 447 L/kg for the raw organic matter of the sediments. In addition to the organic content of the sediment, BPA sorption also was affected by a number of environmental factors. A pH drop, a temperature decrease and a reduction in salinity would increase the sorption of BPA on the sediment. The research findings are of significance to the description and assessment of the fate and transport of BPA and other similar EDCs in marine water-sediment systems.

Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes, Hong Kong

This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) ≈ P) being the dominant P fraction. Given the considerable average Fe(OOH) ≈ P concentration of 912 μg g −1, Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m −2 d −1 recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642–3582 mg kg −1), the high zero equilibrium P concentrations (0.02–0.51 mg L −1) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes.

Environmental fate and non-target impact of glyphosate-based herbicide (Roundup ®) in a subtropical wetland

Mai Po Nature Reserve (Hong Kong) is an internationally important wetland for waterbirds. Roundup ®, a formulation based on glyphosate, has been used to control the widespread weeds within the reserve for many years but the fate and non-target impact of the herbicide is unknown. To fill this knowledge gap, we applied Roundup ® by hand-held sprayer to an estuarine and a freshwater pond in the dry season of year 2002. The surface water and sediment were sampled routinely for glyphosate concentrations following one month of application. In situ bioassays using local edible fish species were performed along with the herbicide application. Up to 52% of glyphosate in the surface water was transported to the unapplied regions by wind-driven current in the estuarine pond at 1 DPT (day post treatment). For both ponds, glyphosate concentrations in the water decreased rapidly after 1–3 DPT, but then decreased gradually over time. Both physical adsorption to the bottom sediments and microbial degradation are thought to contribute to these decreases. Interestingly, the persistence of glyphosate in the freshwater pond was longer than in the estuarine system, which is likely due to the considerably higher concentrations of chelating metals (i.e. Cu and Fe) present in the sediment (4.5 and 11-fold higher, respectively) which potentially reduced the bioavailability of glyphosate to the microbial decomposers. Lastly, fishes used in the in situ bioassays (both in applied and unapplied areas) showed similar survival rates, indicating that the use of Roundup ® at the provided application rate posed no serious hazard.

Metal Concentrations of Common Freshwater and Marine Fish from the Pearl River Delta, South China

Sediments and fish, including tilapia (Oreochromis mossambicus), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idellus), and mandarin fish (Siniperca chuatsi) were collected from different fish ponds in the Pearl River Delta (Tanzhou, Sanjiao, Guangzhou, Shipai, Changan, and Mai Po) for the analysis of metalloids and heavy metals [arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb)]. The pollution of As in pond sediments was great; however, As in the edible parts of pond fish were within the international permissible safety levels for human consumption. Axial muscles from 10 species each of freshwater and marine fish purchased from markets in Hong Kong were also analyzed for As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. Freshwater fish contained 0.24 to 2.13 mg/kg As, 0.10 to 0.17 mg/kg Cd, 0.09 to 0.36 mg/kg Cr, 0.06 to 0.35 mg/kg Cu, 0.07 to 0.34 mg/kg Hg, 0.04 to 0.36 mg/kg Ni, 0.11 to 0.52 mg/kg Pb, and 2.67 to 19.1 mg/kg Zn (wet weight). Marine fish had higher Hg and lower Pb concentrations than freshwater fish. A few fish species had average concentrations greater than the international standards for Cd and Pb established by the European Union and the China National Standard Management Department. Total Hg concentrations in 10 of 20 market fish species were generally greater than those of the World Health Organization's recommended limit of 0.2 mg/kg for at-risk groups, such as children and pregnant women. Daily intake through fish consumption of these metals were compared with the Provisional Tolerable Weekly Intake proposed by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives. There appears to be potential threat to local people from Hg contamination because of the high marine fish consumption rate (142 g/d/person).

Conservation and economic viability of nature reserves: An emergy evaluation of the Yancheng Biosphere Reserve

Evaluating the ecological and economic benefits of nature reserves in a fair way is a difficult problem confronting not only conservation scientists and managers but also governments and private land owners. Nature reserves and other social and economic land uses must be evaluated on an objective basis to provide an accurate measure of relative benefits for decision-making. The ecological and economic benefits of various land uses can be expressed in equivalent terms using emergy as a common denominator. Emergy synthesis is a biophysical, donor-based method of valuation that we used to assess the ecological-economic system of the Yancheng Biosphere Reserve (YBR) in North Jiangsu Province, China. In this paper, we introduce new emergy measures designed especially to capture the conservation value of natural lands, as well as a measure of the economic viability of nature reserves. The network structure of natural resources, economic production, and conservation activities in Yancheng reserve was examined and compared to the Maipo Nature Reserve (MNR) in Hong Kong, and a salt marsh ecological-engineering system also in Yancheng. This study showed that there is about a 10:1 return on the emergy invested by government in operating the Yancheng Biosphere Reserve, which is a major migratory stop-over and wintering site for the endangered red-crowned crane ( Grus japonensis). Only 2.2% of the support for conservation in YBR comes from the private sector compared to 41.4% for MNR. One way to improve social self-sufficiency of the reserve is to develop ecotourism and private donors, which will increase economic vitality and mitigate the intense economic competition for reserve land.

Polybrominated diphenyl ethers in fish and sediment from river polluted by electronic waste

The present study investigated contamination of polybrominated diphenyl ethers (PBDEs) in sediment and fish samples collected from rivers in Guiyu, China where electronic waste (e-waste) is recycled and disposed. PBDE congeners with mono-to hepta-brominated and deca-brominated substitutions were detected using (13)C(12) isotope dilution GC/MS/MS and GC/MS methods, respectively. The total PBDE concentrations ranged from 4434 to 16088 ng/g (dry weight) in Nanyang River bank sediment, from 55 to 445 ng/g in Nanyang River bottom sediment and 51.3 to 365 ng/g in Lianjiang River bottom sediment in Guiyu compared with those from 16.1 to 21.4 ng/g in wastewater discharged from a vehicle repairing workshop in Lo Uk Tsuen in Hong Kong. No PBDE congeners were detected in bottom sediment and fish from Mai Po Marshes in Hong Kong. The mean concentrations of total PBDEs in mixed muscles of tilapia (Oreochromis spp) from Lianjiang River were 115 ng/g wet weight (ww) and from wastewater in Hong Kong were 4.1 ng/g ww. Highest mean PBDE concentration was obtained in liver (2687 ng/g ww), followed by abdomen muscle (1088 ng/g ww) of bighead carp (Aristichthys nobilis) collected from Nanyang River. A significant correlation of concentration of each PBDE congener between sediment and muscle from Guiyu was observed. The present results of total PBDEs in sediment and fish were 10 and 1000 times higher than other studies. Open burning and dumping of e-waste are the major causes of PBDE contamination.

Metabolism and biochemical pathway of n-butyl benzyl phthalate by Pseudomonas fluorescens B-1 isolated from a mangrove sediment

n-Butyl benzyl phthalate (BBP) is an endocrine-disrupting chemical. Biodegradation of BBP was investigated using the bacterium Pseudomonas fluorescens B-1 isolated from mangrove sediment of Mai Po Nature Reserve of Hong Kong. The microorganism was capable of utilizing BBP as the sole source of carbon and energy while BBP was degraded in 6 days under aerobic batch culture conditions. The optimum pH, temperature, and salinity for BBP degradation by P. fluorescens B-1 was found to be 7.0, 37 °C, and 15‰, respectively. Biodegradation of BBP was fitted to the first-order kinetics model. The process of BBP biodegradation was monitored by reversed-phase high-performance liquid chromatography with ultra-violet detection after solid-phase extraction. The major metabolites of BBP degradation were identified as mono-butyl phthalate, mono-benzyl phthalate, phthalic acid, and benzoic acid by gas chromatography-mass spectrometry. BBP-degrading activity of P. fluorescens B-1 was found mostly in the soluble fraction associated with the smaller fragments of cellular membranes. Results suggest that mineralization of BBP can be achieved by microorganism of the mangrove environment.

Distribution patterns of polycyclic aromatic hydrocarbons (PAHs) in the sediments and fish at Mai Po Marshes Nature Reserve, Hong Kong

Sediment samples were collected monthly from eight shrimp shallow ponds (local name gei wais) from July 2003 to January 2004, and from mangrove swamps and inter-tidal mudflats in July and November 2003, respectively. Fish samples (tilapia) were also collected. Polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography and mass spectrometry (GC/MS). The results indicated that under wet season wet deposition and suspended particulates brought in by nearby rivers, such as the Peal River, served as an important source of PAHs entering Mai Po Marshes. Total organic matter in the sediments showed significant correlations ( p<0.01) with PAHs in the sediments, mainly due to the mechanism that organic matter such as humic substances increased PAH persistence by binding and occluding PAHs. Except for naphthalene, biota-sediment accumulation factors (BSAF) of the PAHs in tilapia were below 1.7, which may be caused by biotransformation and the lower uptake in fish. In addition, aqueous route dominated accumulation of non-biodegradable PAHs in tilapia because higher levels were detected in larger fish than in smaller ones. A general trend was observed that BSAFs declined with the increase of K ow values, which suggested that bioavailability of low K ow isomers was high due to higher gill transfer efficiencies (aqueous uptake) in fish but enhanced biotransformation and decreased gut assimilation (dietary uptake) resulted in decreased accumulation of more hydrophobic PAHs (high K ow). Lastly, viscera appeared to be a promising tissue for biomonitoring, as it contained much higher concentrations than the muscle (3.5 magnitudes), and the levels in the muscle were significantly correlated with those in the viscera ( r 2=0.938, p<0.0001).

Distribution patterns of octylphenol and nonylphenol in the aquatic system at Mai Po Marshes Nature Reserve, a subtropical estuarine wetland in Hong Kong

Spatial and temporal distribution of octylphenol (OP) and nonylphenol (NP) in Mai Po Marshes, a subtropical estuarine wetland in Hong Kong, were investigated. Surface water samples were collected every month from 11 sites during the period of September-December 2004. Concentrations of OP and NP ranged from 11.3 to 348 ng/L and from 29 to 2591 ng/L, respectively. The high levels of NP and OP were found in November and December than in September and October. The levels of OP and NP have no significant spatial differences except September. Total organic matter in the sediments appeared to be an important factor in controlling the fate of these compounds in the aquatic environment.

Benthic Infaunal Composition and Distribution at an Intertidal Wetland Mudflat

Benthic infaunal communities at Mai Po Inner Deep Bay mudflat, Hong Kong were investigated between August 2002 and August 2003. A total of 55 species belonging to 8 Phyla from more than 99,074 specimens were recorded. The species richness varied between 13 at Station B in August 2002 and 28 at Station D in August 2003 with an average of 21 across the mudflat and the species diversity was low [H′(log2) = 0.7–3.5 with an average H′ = 2.4]. Seasonal variations were also observed through abundance and biomass across the mudflat among the seasons. The abundance density was between 8,977 individuals m−2 at Station D in February 2003 and 77,256 individuals m−2 at Station B in November 2002 and the overall average density was 25,274 individuals m−2 for the four stations. The benthic infauna were dominated by pollution tolerant species at this wetland mudflat.

A new chloro-monoterpene from the mangrove endophytic fungus Tryblidiopycnis sp. (4275)

A new chloro-monoterpene (compound 1) and three known compounds, peroxyergosterol, uracil and methylisocoumarin, were isolated from the ethyl acetate extract of the fermentation broth of the mangrove endophytic fungus Tryblidiopycnis sp. (4275) obtained from Kandelia woody tissue from Mai Po, Hong Kong. Its structure was determined spectroscopically and by X-ray crystallographic analysis.

Biodegradation of 1-Methylindole and 3-Methylindole by Mangrove Sediment Enrichment Cultures and a Pure Culture of an Isolated Pseudomonas Aeruginosa Gs

Indolic compounds are N-heterocyclic aromatic chemicals and have been detected at contaminated sites. Biodegradation of 1-methylindole (1MI) and 3-methylindole (3MI) was investigated initially using enrichment cultures with mangrove sediment obtained from Mai Po Nature Reserve of Hong Kong and subsequently with a pure culture of Pseudomonas aeruginosa Gs confirmed with 16S rRNA gene. At 2.0 mM, 1MI and 3MI were degraded in 4 and 3 days, respectively, by the respective 1MI- and 3MI-degrading enrichment cultures. When substrate concentrations were increased to 3.0,mM and 3.5,mM, slower degradation of 1MI and 3MI was observed indicating inhibitory effects from the substrates, possibly due to toxicity. In addition, no colony of bacteria could be observed on the agar plates amended with 3.5,mM 1MI or 4.0,mM 3MI, indicating that 1MI was more toxic than 3MI. Pseudomonas aeruginosa Gs, isolated from the enrichment culture, effectively utilized both substrates as the sole source of carbon and energy. Complete degradation of 1MI and 3MI was achieved after more than 40 days and 24 days, respectively, at an initial concentration of 2,mM in the culture. Effects of initial substrate concentration, pH and salinity on degradation of 1MI and 3MI by P. aeruginosa Gs were also studied in batch culture. The optimum pH and salinity for degrading both substrates by P. aeruginosa Gs was 7.0 and 5Ȩ, respectively. Biodegradation kinetics of 1MI and 3MI by P. aeruginosa Gs could be described using a first-order kinetic model. Our results suggest that both 1MI and 3MI are biodegradable in the mangrove environment and that toxicity of 1MI could be a potential factor limiting the removal of the chemical in the environment by microorganisms.

Critical Shear Stress for Deposition of Cohesive Sediments in Mai Po

Abstract A series of tests was conducted to investigate the deposition behaviors of the cohesive sediments collected from Mai Po (Hong Kong) in wet seasons when the salinity was low. The sediment suspended by high shear stress in water with zero salinity was allowed to deposit by lowering the shear stress level. The results show that the sediment has a unique transport characteristic. The sediment began to deposit steadily once it undergoes a weaker shear stress. The underlying reasons of this phenomenon and the application to a sediment transport model are discussed in this paper.

Antibiotic resistance and plasmid profile of environmental isolates of Vibrio species from Mai Po Nature Reserve, Hong Kong

In this study, three environmental isolates of Vibrio species were isolated from water and sediment samples of Mai Po Nature Reserve, Hong Kong SAR. They were identified to be Vibrio cholerae MP-1, Vibrio aestuarianus MP-2 and Vibrio vulnificus MP-3 by both biochemical test and subsequent full-length 16S rDNA sequencing. Both disc diffusion susceptibility test and microplate dilution technique were used to investigate the antibiotic resistance profile of these three bacteria. Results from both assays were in generally good agreement. All three isolates were strongly resistant to beta-lactam family of antibiotics while susceptible to tetracycline, chloramphenicol, nalidixic acid and streptomycin. In addition, V. cholerae MP-1 was very tolerant to high concentration of vibriostatic agent O/129 to 40 microg/ml, at which the growth of V. aestuarianus MP-2 and V. vulnificus MP-2 was completely inhibited. A small naturally occurring plasmid was found in V. cholerae MP-1 while no plasmid was detected in the other two bacteria. This study suggests that Mai Po Nature Reserve harbors bacteria of unique characteristics that warrant further investigation.