Estrogens, a group of steroid hormones, are serious environmental pollutants due to their persistence, ubiquity, and endocrine-disrupting toxicity. Natural and synthetic estrogens, such as 17β-estradiol (E2) and 17α-ethinylestradiol (EE2), respectively, have been found in the influent of municipal wastewater treatment plants. The removal and biotransformation of mixed or single E2 and EE2 by six microalgal species, including three local isolates of Chlamydomonas sp. (WW), Chlorella sp. (2f5aia), and Chlorella sp. (1uoai) and three commercially available species, namely Scenedesmus quadricauda (= Desmodesmus communis) (SQ), Selenastrum capricornutum (SC), and Chlorella vulgaris (CV), were compared. The biological removal of estrogen was incubation time- and species-dependent. Among six species, SC had the highest removal ability for both E2 and EE2; their removal increased with incubation time and achieved 93.9 and 75.3 % removal, respectively, at the end of incubation. After 7-day incubation, the removal percentage of mixed EE2 by SC was significantly higher than that of single EE2 (P ≤ 0.05). Differences in the removal percentages of E2 and EE2 between commercial and local species were not significant, as reflected by the comparable removal efficiency among three Chlorella species, CV, 1uoai, and 2f5aia, with the highest removal of E2, either in mixed or in single treatment, at day 2. In all species, the percentages of E2 or EE2 taken up into cells were very low (0.2–9.6 %) when compared to the respective biological removal percentages. E2 was easily transformed into estrone (E1) and some unknown products by all microalgal species, while the products for EE2 transformation could not be identified due to the limited availability of the standards for metabolites.

•The performance of a 10-years old constructed mangrove wetland was stable and achieved satisfactory.•The abundance of nitrogen cycle related bacteria was rich in planted belts.•Most of these dominant species could be grouped into Proteobacteria.•The steady performance was affected by the abundance and diversity of bacterial community in substrate.Constructed mangrove wetland has been used for wastewater treatment but its long-term performance has not been reported. One-year monitoring of a 10-years old horizontal subsurface-flow constructed mangrove wetland consisting of three belts, two with mangrove plants and one without, revealed that the system maintained high and stable removal percentages of organic matter and nutrients, and planted belts performed better than unplanted control. Substrates in belts planted with Aegiceras corniculatum or Kandelia obovata had higher abundance of ammonifiers, nitrifiers and denitrifiers but lower total heterotrophic bacteria than unplanted substrate. Denaturing gradient gel electrophoresis showed that microbial diversity in planted substrate was significantly lower than that in unplanted one. The bacteria in substrates, irrespective to belts, were phylogenetically related to Proteobacteria (most dominant), Acidobacteria, Firmicutes, Nitrospirae, Gemmatimonadetes, Chloroflexi and Cyanobacteria. The steady performance of this 10-year old constructed mangrove wetland was affected by the abundance and diversity of bacterial community in substrate.Download high-res image (164KB)Download full-size image

•No significant differences in CC and growth traits of Sonneratia between Hainan and Shenzhen•Sonneratia had lower CC and caloric values but higher SLA than native mangroves.•Sonneratia did not lose advantage in the new habitat and were competitive in both wetlands.•CC trend was, Sonneratia < Am < other natives, while the trend for SLA was the opposite.•The invasive potential of Sonneratia in Shenzhen should not be ignored.Exotic species invasions are serious ecological problems. Leaf construction cost (CC) and growth traits of two Sonneratia (Sonneratia caseolaris and S. apetala) and four native species (Bruguiera gymnorrhiza, Kandelia obovata, Aegiceras corniculatum and Avicennia marina) in Hainan and Shenzhen mangrove wetlands were compared to evaluate invasive potentials of Sonneratia after introduced to Shenzhen, their new habitat. There were no significant differences in CC and growth traits between two wetlands, suggesting Sonneratia did not lose any advantage in the new habitat and were competitive in both wetlands. CC per unit mass (CCM), CC per unit area (CCA) and caloric values of Sonneratia were significantly lower than those of native mangrove species while specific leaf area (SLA) was just the opposite. CCM of S. caseolaris and S. apetala were 6.1% and 11.9% lower than those of natives, respectively. These findings indicated the invasive potential of Sonneratia in Shenzhen after their introduction.

•Germination of Kandelia obovata was not affected by PBDEs in contaminated sediment.•BDE-99 contamination was more toxic than BDE-209 during germination.•Both PBDEs increased production of reactive oxygen species in mangrove seedlings.•POD activity was a good indicator for BDE-99 toxicity.•CAT activity was an effective bio-indicator for BDE-209 contamination.A 3-months microcosm experiment with mangrove sediment spiked with PBDEs and planted with propagules of Kandelia obovata was conducted to investigate PBDE toxicity and antioxidative responses of the germinated seedlings. BDE-99 suppressed germination rate, leaves formation and growth of mangrove seedlings. The leaves and roots of BDE-99 treated seedlings had significantly higher superoxide (O2−) release, malondialdehyde (MDA) and total polyphenol (TP) content, and peroxidase (POD) activity than the control. BDE-209 increased activities of all three antioxidative enzymes, catalase (CAT), POD and superoxide dismutase (SOD) in roots, but in leaves, only CAT activity was stimulated. The MDA content of BDE-209 treated seedlings was less than the control. PBDEs were found in plant tissues of the treated seedlings. These results indicated that even though PBDEs were taken up in tissues, K. obovata, due to its antioxidative defense enzymes, could tolerate PBDEs and could be used for the bioremediation of PBDE-contaminated environments.Download high-res image (174KB)Download full-size image

•Total and functional bacteria had the highest abundances in surface layer sediment.•Higher removal rate of BDE-47 was found in surface layer.•Removal of BDE-47 in mangrove sediment was mostly affected by Dehalococcoides spp.The removal and degradation of polybrominated diphenyl ethers (PBDEs) in sediments are not clear. The vertical distribution of total and dehalogenating bacteria in sediment cores collected from a typical mangrove swamp in South China and their intrinsic degradation potential were investigated. These bacterial groups had the highest abundances in surface sediments (0–5 cm). A 5-months microcosm experiment also showed that surface sediments had the highest rate to remove BDE-47 than deeper sediments (5–30 cm) under anaerobic condition. The deeper sediments, being more anaerobic, had lower population of dehalogenating bacteria leading to a weaker BDE-47 removal potential than surface sediments. Stepwise multiple regression analysis indicated that Dehalococcoides spp. were the most important dehalogenating bacteria affecting the anaerobic removal of BDE-47 in mangrove sediments. This is the first study reporting that mangrove sediments harbored diverse groups of dehalogenating bacteria and had intrinsic potential to remove PBDE contamination.Download high-res image (152KB)Download full-size image

•An example of how a group of small wetlands supports diverse waterbirds is provided.•Biodiversity management zones plan creates diverse habitats for waterbirds.•Visitation of waterbirds in different habitats follows the management plan.•The control of key habitat factors is crucial for the success of habitat management.The loss of coastal wetlands in Hong Kong Mai Po Nature Reserve adversely affected wetland-depended species. To mitigate this impact, gei wai ponds were reconstructed according to a set of biodiversity management zones (BMZs). This study, based on Canonical Correspondence Analysis (CCA), investigated if waterbird distribution was related to BMZ characteristics. Based on habitat characteristics, ponds in the same BMZ generally clumped in the same quadrant or within a short distance on CCA scatter plots, indicating that a BMZ zone produced common habitat traits. Ponds in a close distance on the plot had similar bird abundance or community structure. Significant correlations were noted between the abundance of cormorants and tall tree, and between waders and bare ground areas within study ponds. This study indicated that the control of key habitat factors was important for the success of reconstruction of gei wais and management of waterbirds in Mai Po.

•The effect of EDCs on bacterial communities was investigated.•EDCs showed no significant effect on bacterial population in sediments.•Bacterial structure affected by EDCs varied greatly with types of sediments.•EDCs affected bacterial structure in sediments during re-developing process.The diversity and composition of bacterial communities in mudflat and mangrove sediments were investigated under the stresses of endocrine-disrupting chemicals (EDCs) using high-throughput sequencing technique. Bacterial diversity in the original sediments was highest among all samples, followed by non-sterilized and sterilized sediments after 84-day incubation. Proteobacteria were the predominant phylum in both mangrove and mudflat sediments, which accounted for 40–60% of the total tags, followed by Cyanobacteria, Chloroflexi, Planctomycetes and Acidobacteria. Although the total population of bacteria was not significantly declined due to the addition of EDCs, bacterial community structures were considerably altered. The number of bacterial genera promoted or inhibited by EDCs was 288 and 324, respectively. Bacterial genera affected by EDCs varied greatly with the types of sediments and the initial status of bacterial communities. Overall, our results suggested that bacterial community structure in mangrove sediments were closely related to their re-development and responses to EDC contamination.Download high-res image (116KB)Download full-size image

•Tidal flushing regime affected plant uptake of toxic organic pollutants in water.•Fe plaque formed on root surfaces could effectively immobilize organic pollutants.•Percentages of organic pollutants taken up by plant tissues were relatively small.•Thin root outer layer of Kandelia obovata facilitated uptake of organic pollutants.•Excoecaria agallocha immobilized more toxic pollutants in Fe plaque than K. obovata.Wastewater often contains mixed toxic pollutants, and the contribution of plant uptake in constructed wetland treatment systems is affected by environmental conditions, particularly tidal flushing. In this study, the uptake of wastewater-borne pollutants, including a mixture of polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs) congeners, by two mangrove plant species, namely Excoecaria agallocha L. and Kandelia obovata Sheue, Liu & Yong, under different tidal flushing regimes was investigated. Results showed that Fe plaque formed on root surfaces could immobilize wastewater-borne PAHs and PBDEs. At the end of 8-month wastewater treatment, most of the pollutants removed by plants ended up in Fe plaque, with 0.12–20.83% of total PAHs and 0.78–24.76% of total PBDEs added to the microcosm retained in Fe plaque. On the contrary, the percentages of PAHs and PBDEs taken up by plant tissues were relatively small, ranging from not detected to 0.09% and from 0.01 to 2.00%, respectively. More uptake of Fe plaque-immobilized PAHs and PBDEs was found in K. obovata than in E. agallocha, leading to more plant damages in the former species due to its weaker root outer layers. While E. agallocha with stronger root protective outer layer was able to uptake more PAHs and PBDEs from wastewater but immobilize in Fe plaque than that of K. obovata. In both plant species, tidal flushing regimes significantly affected the immobilization of PAHs and PBDEs in Fe plaque, and more frequent tidal flushing led to higher percentages of immobilization. This is the first study demonstrating that E. agallocha was a more suitable mangrove plant species to remove wastewater-borne PAHs and PBDEs than K. obovata, and the significance of tidal flushing on performance of constructed mangrove wetlands.Download high-res image (190KB)Download full-size image

This study investigated the efficiency of 12 pilot-scale constructed wetlands (CWs) with different configurations on the removal of estrone and estradiol from raw domestic sewage. An orthogonal design was employed to evaluate the impact of four principal design parameters of CWs, including four wetland types, three substrates, three plant conditions, and three hydraulic loading rates, in summer and winter. A bench-scale anoxic simulation test was performed in the laboratory to clarify the photolysis, sorption, and degradation of estrogens. Estrogens were more effectively removed by the 12 CWs during summer. The experiment showed that target estrogens were efficiently removed by wetland substrate under anoxic conditions through exothermic sorption and degradation even in winter. This suggests that the inefficient removal in CWs in winter likely resulted from subsequent cleavage of a considerable amount of estrogen conjugates in influent due to insufficient decomposition at low temperatures. The transformation from estradiol to estrone could be driven by residual microbial activities not inhibited by azide, and the reversible process was then driven by active microorganisms but not solely abiotic redox reactions. Among the four design parameters, wetland-type was the most important and downward-vertical flow CWs performed best.

The fate of BDE-153 (BDE = brominated diphenyl ethers) in different mangrove, fresh water pond, and marine subsurface sediments collected from Hong Kong SAR was investigated. Under anaerobic conditions, all sediments showed good intrinsic abilities to reductively debrominate BDE-153, producing debromination products ranging from hexa- to mono-BDEs in 90 days. The half-lives of BDE-153 in eight different sediments varied from 7.6 to 165 days, with higher debromination in mangrove than marine and fresh water pond sediments. All sediments exhibited the preference in removing the bromine in para, followed by meta, and the lowest in ortho positions; however, fresh water pond sediments had relatively higher fractions of meta (BDE-99) and ortho substitution (BDE-118) of the three penta-BDE products. Mai Po mangrove and fresh water pond subsurface sediments were also capable of debrominating BDE-47 in 90 days of anaerobic incubation with half-lives of 76.2 and 56.9 days, respectively; but not BDE-209. BDE-47, -153, and -209 in Mai Po surface sediment were not transformed under 30 day aerobic incubation. This study demonstrated that the microbial-mediated debromination of BDE-47 and -153 occurred in natural subsurface sediments under anaerobic conditions although the rates and pathways varied among the sediment types.

The microbial community plays an essential role in the high productivity in mangrove wetlands. A proper understanding of the spatial variations of microbial communities will provide clues about the underline mechanisms that structure microbial groups and the isolation of bacterial strains of interest. In the present study, the diversity and composition of the bacterial community in sediments collected from four locations, namely mudflat, edge, bulk, and rhizosphere, within the Mai Po Ramsar Wetland in Hong Kong, SAR, China were compared using the barcoded Illumina paired-end sequencing technique. Rarefaction results showed that the bulk sediment inside the mature mangrove forest had the highest bacterial α-diversity, while the mudflat sediment without vegetation had the lowest. The comparison of β-diversity using principal component analysis and principal coordinate analysis with UniFrac metrics both showed that the spatial effects on bacterial communities were significant. All sediment samples could be clustered into two major groups, inner (bulk and rhizosphere sediments collected inside the mangrove forest) and outer mangrove sediments (the sediments collected at the mudflat and the edge of the mangrove forest). With the linear discriminate analysis scores larger than 3, four phyla, namely Actinobacteria, Acidobacteria, Nitrospirae, and Verrucomicrobia, were enriched in the nutrient-rich inner mangrove sediments, while abundances of Proteobacteria and Deferribacterias were higher in outer mangrove sediments. The rhizosphere effect of mangrove plants was also significant, which had a lower α-diversity, a higher amount of Nitrospirae, and a lower abundance of Proteobacteria than the bulk sediment nearby.

Barnacle fouling has shown to impede gas exchange ability of mangroves. Fouled mangrove plants may therefore obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production, but such hypothesis remains untested. The objective of the present study compared the stomata density (essential for obtaining carbon dioxide and water molecules) and leaf chlorophyll concentration (essential for photosynthesis) of fouled and non-fouled (control) of seedlings, juveniles and adults of the mangroves Kandelia obovata, in Hong Kong and Taiwan. The seedlings and juveniles of the dominant mangrove plant species, Kandelia obovata, in Hong Kong and Taiwan had a higher density of stomata but a lower chlorophyll concentration in the leaves, when the trunks and twigs were fouled by the barnacle Fistulobalanus albicostatus. Fouled K. obovata appears to develop more stomata in the leaves to compensate the blocking effect of the lenticel from barnacle fouling. As fouling impacts the gaseous exchange ability of mangroves, fouled plants could obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production. Fouled adult plants, however, had variable responses in leaf chlorophyll concentrations among the study sites, suggesting adults were more tolerant of barnacle fouling. The present study reveals seedling and juvenile mangrove plants are very susceptible to barnacle fouling, which impedes the gaseous exchange mechanism and food production, which can subsequently result in reduced growth, fitness and survival.

Mangrove sediment is well known for its susceptibility to anthropogenic pollution, including polycyclic aromatic hydrocarbons (PAHs), but knowledge of the sediment microbial community structure with regards to exposure to PAHs is limited. The study aims to assess the effects of PAHs on the bacterial community of mangrove sediment using both 16s rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and traditional enrichment methods. Both the exposure time and the PAH concentration reduced the microbial diversity, as determined by the DGGE bands. Although PAHs could act as carbon sources for microorganisms, PAHs, at a concentration as low as 20 mg l−1, posed a toxic effect to the microbial community. Sequencing of DGGE bands showed that marine bacteria from the genera of Vibrio, Roseobacter, and Ferrimonas were most abundant after PAH exposure, which suggests that both marine and terrestrial bacteria coexisted in the mangrove sediment, but that the marine microbes were more difficult to isolate using the traditional culture method. DGGE determination further demonstrated that the consistency among triplicates of the enriched consortia was significantly less than that of the sediment slurries. The present study reveals that the mangrove sediment microbial structure is susceptible to PAH contamination, and complex microbial community interactions occur in mangrove sediment.

A fully automated sample pretreatment method was developed for the detection of mono and dihydroxy metabolites of polycyclic aromatic hydrocarbons (PAHs) by gas chromatography–mass spectrometry in the selected ion monitoring mode. Direct immersion solid-phase microextraction for the extraction of target compounds and the headspace on-fiber silylation with N,O-bis(trimethylsilyl)trifluoroacetamide were performed automatically by a multipurpose autosampler (MPS2). The operating conditions including extraction time, derivatization time, ionic strength, pH, and incubation temperature were optimized. Calibration responses of nine metabolites of PAHs over a concentration range of 0.1–100 μg L−1 with a correlation coefficient of 0.999 were obtained. The detection limits of the nine metabolites in mini pore water, minimal salts medium and soil extract culture medium were in the range of 0.001–0.013, 0.002–0.024 and 0.002–0.134 μg L−1, respectively, while the respective quantification limits were 0.003–0.044, 0.005–0.081 and 0.008–0.447 μg L−1. The reliability was confirmed by the traditional solid-phase extraction method. The proposed method could be used to analyze the metabolites of PAHs degraded by microorganisms such as algae and to determine the biodegradation pathways of PAHs.

The influence of growth medium on cometabolic degradation of polycyclic aromatic hydrocarbons (PAHs) was investigated when Sphingomonas sp. strain PheB4 isolated from surface mangrove sediments was grown in either phenanthrene-containing mineral salts medium (PMSM) or nutrient broth (NB). The NB-grown culture exhibited a more rapid cometabolic degradation of single and mixed non-growth substrate PAHs compared to the PMSM-grown culture. The concentrations of PAH metabolites were also lower in NB-grown culture than in PMSM-grown culture, suggesting that NB-grown culture removed metabolites at a faster rate, particularly, for metabolites produced from cometabolic degradation of a binary mixture of PAHs. Cometabolic pathways of single PAH (anthracene, fluorene, or fluoranthene) in NB-grown culture showed similarity to that in PMSM-grown culture. However, cometabolic pathways of mixed PAHs were more diverse in NB-grown culture than that in PMSM-grown culture. These results indicated that nutrient rich medium was effective in enhancing cometabolic degradation of mixed PAHs concomitant with a rapid removal of metabolites, which could be useful for the bioremediation of mixed PAHs contaminated sites using Sphingomonas sp. strain PheB4.

The mechanism involved in the removal of Cr(III) by a green microalgal isolate, Chlorella miniata, was examined based on a series of batch experiments and microscopic analyses, and a mathematical model was proposed. Results showed that Cr(III) biosorption increased with the increase of pH from 2.0 to 4.5, and no significant changes in biosorption outside this pH range. Langmuir isotherm indicated that the maximum Cr(III) sorption capacity of Chlorella miniata was 14.17, 28.72, and 41.12 mg g−1 biomass at pH 3.0, 4.0, and 4.5, respectively. Results from desorption studies, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and EDX (energy-dispersive X-ray spectroscope) analyses confirmed that surface complexation was the main process involved in Cr(III) biosorption. Potentiometric titration revealed that carboxyl (pKa1=4.10pKa1=4.10), phosphonate (pKa2=6.36pKa2=6.36) and amine (pKa3=8.47pKa3=8.47) functional groups on the surface of Chlorella miniata were the possible sites for Cr uptake, and their average amounts were 0.53, 0.39, and 0.36 mmol g−1 biomass, respectively. A surface complexation model further indicated that carboxyl group played the main role in Cr(III) complexation, with a binding constant of K11=1.87×10−4K11=1.87×10−4 and K12=6.11×10−4K12=6.11×10−4 for Cr3+ and Cr(OH)2+, respectively. This model also suggested that the hydroxy species was more easily to complex with the cell surface of Chlorella miniata.A microalgae isolate, Chlorella miniata was used to remove Cr(III) in solution and the results indicated the surface complexation but not the well accepted ion exchange was the main biosorption mechanism.

The biodegradation ability and initial dioxygenase genes of 21 PAH-degrading bacteria isolated from mangrove sediments were investigated. Most of the isolates belonged to the genera of Sphingomonas and Mycobacterium, and the other included Rhodococcus, Paracoccus and Pseudomonas. All the isolated Mycobacterium strains could completely degrade a mixture of polycyclic aromatic hydrocarbons (PAHs) comprising phenanthrene (Phe), fluoranthene (Fla) and pyrene (Pyr) in 14 days. On the other hand, the sphingomonads differed in the extent to which mixed PAHs were degraded from 3% to 79%. The co-culture of Sphingomonas and Mycobacterium strains enhanced the degradation and all three PAHs were completely removed in 7 days. Among the three PAHs, only Pyr was completely degraded by three Mycobacterium strains (SBSW, YOWG and SKEY), whereas Fla, and then Phe were degraded by these three and other isolates. The isolated Mycobacterium strains possessed the nidA gene encoding the initial dioxygenase required for Pyr degradation, while nahAc and phnAc were not detected in the sphingomonads.

•Macrobenthic infaunal community is affected by the presence of mangrove plants.•Sonneratia plantation creates a unique macrobenthic infaunal community.•Deposit and filter feeders prefer to inhabit the Sonneratia site.•Effect of Sonneratia plantation on sediment properties is not discernible.•Change in habitat complexity is the main reason leading to different communities.Sonneratia caseolaris, a superior mangrove species characterized by rapid growth and proliferation, has been introduced to Futian Mangrove National Nature Reserve, Shenzhen, China for mangrove restoration since 1993. However, the effect of Sonneratia plantation on the macrobenthic infaunal community, a vital component of energy flow and nutrient recycling in mangrove ecosystems, remains obscure. The present study aimed to answer this question by determining the macrobenthic infaunal community, habitat characteristics and physico-chemical properties of sediment in the vegetated sites, dominated by different mangrove species (Kandelia obovata, Avicennia marina and S. caseolaris), and un-vegetated mudflat at four sampling times from August 2008 to September 2009. Results showed that the presence of Sonneratia can enhance the biodiversity of macrobenthic infauna in terms of Shannon–Weaver index (H′), compared to the mudflat, since August 2008 onwards. Multivariate analyses (CLUSTER and SIMPER) showed that the macrobenthic infaunal community in the Sonneratia site was different from all the other sites due to higher abundance of deposit and filter feeders, including Limnodriloides sp., Capitella capitata, Potamilla acuminata, Tharyx sp. and Ampharete arctica. The presence of Sonneratia, however, could not significantly alter the sediment properties. Spearman correlation analysis revealed that H′ was negatively correlated with cadmium concentration whereas distance-based linear model (DistLM) suggested that cadmium was a significant predictor variable correlating with the macrobenthic infaunal community. The higher cadmium concentration in August 2008 explained why H′ was lower and different macrobenthic infaunal communities were observed compared to the other sampling times. However, cadmium was the only significant predictor variable explaining 14.9% total variation, suggesting that the macrobenthic infaunal community was generally not affected by the sediment properties. Therefore, we concluded that Sonneratia plantation in the open mudflat can enhance the biodiversity of macrobenthic infauna in view of higher habitat complexity (e.g. presence of pneumatophores, below-ground vegetation and litter) on condition that the cadmium concentration was below the harmful level.

Marine ecosystems are a known net source of greenhouse gases emissions but the atmospheric gas fluxes, particularly from the mangrove swamps occupying inter-tidal zones, are characterized poorly. Spatial and seasonal fluxes of nitrous oxide (N2O) and carbon dioxide (CO2) from soil in Mai Po mangrove swamp in Hong Kong, South China and their relationships with soil characteristics were investigated. The N2O fluxes averaged from 32.1 to 533.7 μg m−2 h−1 and the CO2 fluxes were between 10.6 and 1374.1 mg m−2 h−1. Both N2O and CO2 fluxes in this swamp showed large spatial and seasonal variations. The fluxes were higher at the landward site than the foreshore bare mudflat, and higher fluxes were recorded in warm, rather than cold, seasons. The landward site had the highest content of soil organic carbon (OC), total Kjeldahl nitrogen (TKN), nitrate (NO3−–N) and total phosphorus (TP), while the bare mudflat had the highest ammonium nitrogen (NH4+–N) concentration and soil denitrification potential activity. The N2O flux was related, positively, to CO2 flux. Soil NO3−–N and TP increased N2O flux, while soil OC and TP concentrations contributed to the CO2 flux. The results indicated that the Mai Po mangrove swamp emitted significant amounts of greenhouse gases, and the N2O emission was probably due to soil denitrifcation.Highlights► We investigate the spatial and seasonal fluxes of N2O and CO2 in Mai Po mangrove. ► Both gases fluxes are significant and show large spatial and seasonal variations. ► Soil NO3−–N and TP increase N2O flux. ► Soil OC and TP concentrations contribute to the CO2 flux. ► N2O emission is probably due to soil denitrifcation.

The effect of lubricating oil on germination, early growth and physiological responses of Bruguiera gymnorrhiza (L.), a common mangrove plant species in Hong Kong was investigated. Both fresh and spent (or used) lubricating oil at a single initial dose of 5 L m−2 did not have any effect on germination (i.e. initial establishment). All the oil-treated propagules were successfully developed into new seedlings within 30 days, same as the control (without any oil addition). This viviparous species had long slender propagules with an average size of 15 cm long, and only 1/3 of the exposed section of the propagule was covered by oil. On the contrary, germination of Aegiceras corniculatum (L.) Blanco and Acanthus ilicifolius L. in sandy as well as muddy mangrove sediments was totally inhibited by fresh and spent lubricating oil at the same dose, probably because their propagules were relatively small in size and were completely covered by oil. Although germination of B. gymnorrhiza was not affected, early growth including height, leaf number and biomass of the oil-treated seedlings was significantly reduced while the content of free radicals and malondialdehyde (MDA), and the activity of superoxide dismutase (an anti-oxidant enzyme) increased with oil treatment. These results indicate that lubricating oil, in particular spent oil, posed oxidation stress and caused lipid membrane damages leading to growth reduction in young seedlings of B. gymnorrhiza, and this impact was more significant in plants grown in sandy than in muddy mangrove sediments.

Sewage disposal is a major environmental issue in both developed and developing countries and removal of pollutants such as organic matter, nutrients, heavy metals and persistent organic compounds is required to protect the environment. Novel biological systems using constructed mangrove wetland and immobilized microalgal beads have been developed as alternative systems for treating different types of sewage and pollution at source. The feasibility and efficiency of constructed mangrove wetland to remove organic matter and nutrients from primary settled municipal sewage were demonstrated through a series of greenhouse experiments and a pilot-scale field trial. The treatment efficiency of constructed mangrove wetland was comparable to, or higher than, the conventional constructed wetland. An immobilized microalgal system was developed to remove toxic persistent pollutants from industrial wastewater. Pollutant-resistant microalgal species were selected for culture in domestic wastewater. The harvested biomass was immobilized in alginate beads. Bench-scale experiments showed the algal beads were effective in removing industrial pollutants such as heavy metals (e.g. Cu, Zn, Ni, Cr, etc.), organometallic compounds (e.g. tributyltin, TBT), and persistent organic compounds (e.g. polycyclic aromatic hydrocarbons, PAHs) through biosorption and biodegradation. The adsorbed metals could be recovered by desorption process, and the beads could be used repeatedly for many adsorption–desorption cycles.

Kandelia obovata, with abundant condensed tannins (CTs), is a typical mangrove species in China, but little is known about the chemical alterations and ecological roles of CTs during leaf litter decomposition. A litterbag experiment was conducted to investigate the changes of CTs in a subtropical mangrove swamp along Zhangjiang River Estuary, China, using the colorimetric assays, reversed/normal-phase HPLC–ESI-MS and MALDI–TOF-MS techniques. Total phenolics (TP), extractable CTs (ECT) and total CTs (TCT) decreased rapidly, while bound CTs (BCT), including protein- and fibre-bound CTs in leaves, increased during decomposition, and these temporal changes were well-expressed by exponential functions. Negative correlations between nitrogen (N) and TP, as well as N and ECT were found; however, a positive correlation between N and BCT was detected, suggesting that CTs played an important role in humification during N immobilization. The HPLC–ESI-MS analyses showed that the polymerization degree of CTs had an initial increase, due to leaching, followed by a decrease in the subsequent shift towards abiotic or/and biotic degradation. MALDI–TOF-MS confirmed the degradation processes for CTs. A decrease in the degree of hydroxylation, along with an increase in glycosylation-CTs, was obtained during litter decomposition. These chemical changes enhanced the current knowledge on the potential ecological role of N transformation in CTs in mangrove swamps.Highlights► Changes of condensed tannins (CT) during decay of Kandelia obovata leaves were studied. ► Structural changes of CT were analysed by MALDI–TOF-MS and HPLC–ESI-MS. ► Leaching, immobilization and degradation were the fate of CT during leaf decay. ► High CT levels provided a potential nutrient conservation strategy for K. obovata.

•Parent and oxygenated PAHs were ubiquitous in mangrove sediments of Hong Kong.•The contamination of parent and oxygenated PAHs were at the middle-to-high level.•Parent and carbonylic PAHs were originated from petroleum combustion in sediments.•The source of hydroxylated PAHs was more complicated.•TOM was an important factor for regulating the spatial distribution of oxygenated PAHs.Parent and oxygenated polycyclic aromatic hydrocarbons (PAHs) were investigated in mangrove sediments of Hong Kong. Most of the analytes were detected, and the dominant carbonylic and hydroxylated PAHs in mangrove sediments were 9-fluorenone and 2-hydroxy fluorene, respectively. The concentration of 9-fluorenone and 9,10-anthraquinone was higher than their parent PAHs. Moreover, the concentration of total organic matter (TOM) related with those of the parent PAHs and carbonylic PAHs, except for hydroxylated PAHs, which indicated that TOM was not the only factor regulating the distribution of oxygenated PAHs. Nevertheless, the parent PAHs in mangrove sediments was correlated positively with carbonylic PAHs which demostrated not only the similar source but also the fate of these two compound class. However, hydroxylated PAHs had different source by comparing with parent PAHs and carbonylic PAHs, they were probably originated from biodegradation and accumulated in mangrove sediments.