Virtual increase or latent loss? A reassessment of mangrove populations and their conservation in Guangdong, southern China.

Contrary to the global trend, the area of mangrove in Guangdong Province, southern China, has been increasing over the last two decades. Currently, three exotic mangrove species have been introduced for large-scale afforestation since 1985. A reassessment of the overall status of the mangrove species, habitat change, population of introduced species, was conducted through a comprehensive literature review as well as field investigations covering 96 sites. The success of conservation efforts is also evaluated. Upstream and high intertidal habitats are more vulnerable than downstream and lower intertidal ones, with habitat alteration being the biggest threats. Five mangrove species have narrow distributional extents with small populations, which could incur regional extinction. With the introduced species having naturalized at 42 sites, their role in mangrove management needs to be reconsidered. These findings collectively suggest a need to manage latent species loss and habitat degradation beyond the apparent increase in mangrove area and protection.

The effect of mangrove reforestation on the accumulation of PCBs in sediment from different habitats in Guangdong, China.

To investigate the influence of mangrove reforestation on the accumulation of PCBs, the concentrations and homologue patterns of polychlorinated biphenyls in surface sediments from different mangrove forests and their adjacent mud flats in Guangdong Province were determined. The total PCB concentrations in the sediments ranged from 3.03 to 46.62 ng g⁻¹ (dry weight). Differences in the accumulation and distribution of PCBs were found between the mangrove sites and the mud flats. Furthermore, the natural forests and restored mangrove forests of native species showed slight PCB contamination, whereas the exotic species Sonneratia apetala exacerbated the PCB pollution at certain sites. It was suggested that the native mangrove species Kandelia candel and Aegiceras corniculatum could represent good choices for the phytoremediation of PCB contamination.

Interactions among Fe2+, S2-, and Zn2+ tolerance, root anatomy, and radial oxygen loss in mangrove plants.

Root anatomy, radial oxygen loss (ROL), and tolerances to ferrous (Fe(2+)), sulphide (S(2-)), and zinc (Zn(2+)) ions were investigated in seedlings of eight species of mangrove, including three pioneer species, three rhizophoraceous and two landward semi-mangrove species. The results showed an interesting co-tolerance to Fe(2+), S(2-), and Zn(2+). The three rhizophoraceous species (Bruguiera gymnorrhiza, Kandelia obovata and Rhizophora stylosa), which possessed the thickest lignified exodermis and the 'tightest barrier' in ROL spatial pattern, consistently exhibited the highest tolerance to Fe(2+), S(2-), and Zn(2+). B. gymnorrhiza could directly reduce ROL by increasing lignification within the exodermis. Such an induced barrier to ROL is a probable defence response to prevent further invasion and spread of toxins within plants. The data also indicated that, in B. gymnorrhiza, Fe(2+) or S(2-), or both, induced a lignified exodermis that delayed the entry of Zn(2+) into the roots and thereby contributed to a higher tolerance to Zn(2+). This study provides new evidence of exclusive strategies of mangrove seedling roots in dealing with contaminations. The information is also important in the selection and cultivation of tolerant species for the bioremediation of contaminated waters or soils.

[Health assessment of Qi'ao Island mangrove wetland ecosystem in Pearl River Estuary].

Based on the theories of wetland ecosystem health and by using "Pressure-State-Response" model, a health assessment indicator system for Qi' ao Island mangrove wetland ecosystem in Pearl River Estuary was built, and the assessment indices, assessment criteria, indices weighted values, assessment grades, and assessment methods were established to assess the health state of this ecosystem. In 2008, the overall health index of this ecosystem was 0.6580, health level was of grade II (healthy), and the pressure, state, and response indices were 0.3469, 0.8718, and 0.7754, respectively, suggesting that this ecosystem was good in state and response, but still had definite pressure. As a provincial nature reserve, this ecosystem was to be further improved in its health level. However, the research on the health assessment of mangrove wetland ecosystem was still young. Further studies should be made on the selection of assessment indices, long-term oriented monitoring of these indices, and quantification of the relations between ecosystem health level and ecosystem services.

Influence of mangrove reforestation on heavy metal accumulation and speciation in intertidal sediments.

To investigate the influence of mangrove reforestation on heavy metal accumulation and speciation in intertidal sediments, core sediments from a restored mangrove forest and adjacent mud flat in Yifeng Estuary (southeastern China) were analyzed. The chemical speciation of heavy metals (Pb, Zn, Cu, Cr and Ni) was determined according to a sequential extraction procedure. Special attention was paid to the upper 20cm of sediment, in which metal accumulation was enhanced and speciation was obviously modified. Mangrove reforestation decreased the concentrations of all metals in the acid-soluble fraction and increased metal concentrations in the oxidizable fraction. Increased Pb, Zn and Cu concentrations and decreased Ni and Cr concentrations were observed in the reducible fraction. These results suggest that mangrove reforestation facilitated the accumulation of heavy metals in the upper sediment layers but decreased their bioavailability and mobility.

Toxicity of bisphenol A and its bioaccumulation and removal by a marine microalga Stephanodiscus hantzschii.

The toxicity of bisphenol A (BPA) to Stephanodiscus hantzschii, a diatom isolated from tidal water of Futian Mangrove Nature Reserve, China, and the bioaccumulation and removal capability of the marine microalga to BPA were investigated in the present study. Toxicity experiments showed that the 96-h EC50 of BPA was 8.65+/-0.26 mg/L, and the cell number and chlorophyll a content of S. hantzschii decreased significantly with increases in BPA at concentrations higher than 3.00 mg/L. S. hantzschii had high removal capability at low BPA concentrations as BPA was bioaccumulated and biodegraded by cells. After 16-day treatment, 88%, 99%, 92%, 61%, 48%, 28% and 26% of BPA were removed by the diatom in the media supplemented with 0.01, 0.10, 1.00, 3.00, 5.00, 7.00 and 9.00 mg/L BPA, respectively. The present study demonstrated that S. hantzschii was a tolerant isolate that could be used to remove BPA from contaminated waters.

[Distribution and migration of zinc in Avicennia marina plant-soil system].

Zinc is a major anthropogenic contaminant in estuarine ecosystem, and has potential ecotoxicological consequences for aquatic animals and plants. An artificial mangrove wetland was set up in greenhouse to study the distribution and migration of zinc in synthetic wastewater in Avicennia marina plant-soil system. Different concentration synthetic wastewater and 1.5% salinity artificial seawater (control) were discharged into the system in fixed quantity twice a week for a year. The results showed that most part (> 67%) of zinc in the artificial wastewater discharged into the system was remained in the soil, and only a small portion (1.24%-10.4%) of it was entered into plant and litter, indicating that this artificial plant-soil system had a stronger purifying effect on the zinc in synthetic wastewater. The calculation with matter balance model indicated that soil subsystem had a higher environmental capacity of bearing zinc.

[Effects of PCBs on Aegiceras corniculatum seedlings growth and membrane protective enzyme system].

With pot experiment, this paper studied the effects of PCBs (0, 180, 900, 1800 and 2700 microg x kg(-1)) on the seedlings growth and the leaves chlorophyll content, MDA content, and membrane protective enzyme system of Aegiceras corniculatum. The results showed that PCBs had definite stimulative effects on the seedlings growth. The stem height, basal stem diameter, and stem volume were all increased with increasing PCBs concentration. Within the test range of PCBs, the chlorophyll content and chlorophyll a/b ratio maintained at a relatively stable and normal level. The decrement of chlorophyll content and the increment of chlorophyll a/b ratio were less than 25% and 10% of the control, respectively. With increasing PCBs concentration, SOD activity increased first and decreased then, while POD activity and MDA content were in adverse. It was suggested that A. corniculatum could endure and adapt definite concentrations of PCBs through physiological and biochemical mechanisms, being available to the phytoremediation of PCBs pollution.

Partitioning and removal of Cd and Mn using a simulated mangrove wastewater treatment system.

A greenhouse experiment was conducted to study the partitioning and removal of Cd and Mn from wastewater using constructed mangrove (Kandelia candel) wetland treatment system. Three different strengths of artificial wastewater passed through the system in fixed quantities. Artificial seawater was used as a control. Three different compositions were natural wastewater concentration (C1), medium wastewater concentration (C5) and concentrated wastewater concentrations (C10). C1 had the characteristics and strength similar to natural municipal wastewater while C5 and C10 contained five and ten times of the nutrients and heavy metals in C1, respectively. Results showed that the major portion of the Cd and Mn entering the simulated wastewater treatment system entered the sediment pool where approximately 88% to 95% of the Cd, and between 63% and 89% of Mn, was retained. The amount of added Cd and Mn in the wastewater found in plants were between 0.16% to 1.1%, and 1.7% to 13.9%, respectively. Within the total plant pool, roots accounted for between 30% and 39% of Cd, and from 0.65% to 7.3% of Mn; leaves contained between 19.9% to 30.5% of Cd, and from 7.8% to 41.0% of Mn; litterfall contained 12.3% to 20.6% of Cd, and from 15.2% to 70.3% of Mn, respectively. The averaged accumulative coefficients concentration in plant tissues/concentration in sediment in plant for Cd and Mn were 1.22 to 2.40 and 0.02 to 0.08, respectively. Assimilated Cd and Mn were stored in non-activity plant zones such as cell wall, supplimentary cells of the lenticel, stone cells, cell gaps in root and stem, etc. Kandelia candel seedlings had a relative high toxicity resistance to the two heavy metals.

[Resistant physiology of three mangrove species in a constructed wetland sewage treatment system].

This paper studied the resistant physiology of three mangrove species, Sonneratia caseolaris, Aegiceras corniculaturn and Bruguiera gymnorrhiza in a subsurface flow-constructed wetland sewage treatment system under freshwater condition. The results showed that in a year period, the superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of three mangrove species increased gradually and maintained at a high level, the proline content reached the maximum from July to September, while the plasma membrane permeability did not show any obvious change. In comparing with those grown in the Futian Nature Reserve of Shenzhen, three mangrove species in the test sewage treatment system had lower SOD, POD and CAT activities and higher proline content, while no significant difference was observed in the malondialdehyde (MDA) content and plasma membrane permeability. It was suggested that three mangrove species could adapt to the subsurface flow-constructed wetland sewage treatment system under freshwater condition.

[Research advances in phytoremediation of polychiorinated biphenyls (PCBS)].

This paper reviewed the research advance in PCBs phytoremediation, with the focus on the roles and mechanisms of plants in the removal of PCBs from the environment. In the process of PCBs removal, plants acted not only as a supporter of biodegradation, but also as an active participator in metabolism. Plants could absorb and accumulate PCBs from the environment, and store the non-toxic metabolic products in their tissues. Root exudates could degrade PCBs directly by the contained ectoenzymes, or indirectly through stimulating the activity of rhizospheric microbes. The internal and external factors affecting the phytoremediation of PCBs, including plant species, their culture types and biomass, as well as the initial concentration of PCBs and their physical and chemical characters, were also discussed.

[Degradation of main ecosystems in South China Sea and corresponding conservation countermeasures].

South China Sea is a significant area of global biological diversity. Due to the long-term unreasonable exploitation and utilization, the habitat there degenerates obviously, and the biodiversity loses seriously. The estimated annual loss of mangrove area ranges from 0.5% to 3.5% , and that of seaweed area is from 20% to 50%. A total of 82% of coral reefs in the Sea display evident degradation. In this paper, a trans-boundary diagnostic analysis of ecosystem degradation in South China Sea was conducted, with the focus on mangrove, seaweed and coral reef. Based on the analysis of the destruction state of the existing ecosystems as well as the main causes of habitat degradation and its trans-boundary impacts, some countermeasures on habitat conservation and management were put forward, aimed to promote the cooperation both at national and at regional levels to implement appropriate approach to reverse the ecosystem degradation trend in South China Sea.

[Net primary productivity of several mangrove species under controlled habitats].

Three mangrove species Sonneratia caseolaris, Kandelia candel and Aegiceras corniculatum were planted in different fishponds in April 2002 with three planting--breeding area proportions of 45 : 55, 30 : 70 and 15 : 85, respectively, and the growth of test mangrove plants were surveyed during 2 years after planting. The results showed that S. caseolaris and A. comiculatum could grow well in the coupling system, while K. candel could not. The survival percentage of S. caseolaris, K. candel and A. corniculatum was 92.9%, 93.9% and 44.7%, respectively. During the 2 years, the height of S. caseolaris increased 457.0 cm, and its basal diameter increased from 12.6 mm to 98.7 mm. A. corniculatum had an increment of 26.1 cm in height and 36.5 mm in basal diameter, while K. candel only had an increment of 20.4 cm in height and 26.4 mm in basal diameter. Based on the height, basal diameter, and biomass of trunk, branch, leaf and root, regressive equations of the four organs' biomass were obtained, and the whole biomass of standing trees in the coupling system was calculated. The average biomass of S. caseolaris was 5 597.8 g x m(-2) in April 2004, being increased 5 559.5 g x m(-2) in 2 years. At the same period, the standing biomass of A. corniculatum and K. candel was 962.5 g x m(-2) and 66.0 g x m(-2), with an increase of 932.7 g x m(-2) and 57.0 g x m(-2), respectively. The biomass of plant organs was in the order of stem > branch > root > leaf for S. caseolaris, leaf > branch > stem > root for A. corniculatum, and stem > root > leaf > branch for K. candel. The litter fall production of mangrove plants in 2 years was 1 149.2 g x m(-2), 170.8 g x m(-2) and 7.1 g x m(-2) for S. caseolaris, A. corniculatum and K. candel, respectively. Leaf litter took up more than half of the whole litter fall. From April 2002 to April 2004, the net primary production of S. caseolaris, A. corniculatum and K. candel was 7 048.9 g x m(-2), 1 105.9 g x m(-2) and 93.0 g x m(-2), respectively. The litter fall production occupied 20.5% of the net primary production for S. caseolaris, 15.4% for A. corniculatum, and 7.6% for K. candel, which meant that high productivity was accompanied by high return rate.

[Distribution, migration and purifying effect of cadmium in artificial Avicennia marina wetland system].

An artificial mangrove Avicennia marina wetland was set up in a greenhouse, and an irrigation experiment with synthetic wastewater was performed to research the behavior of cadmium in the artificial wetland system. The synthetic wastewater C1 had the characteristics and strength similar to normal municipal sewage, while C5 and C10 had the nutrients and heavy metals as five and ten times as those in C1, respectively. The control was of 15 per thousand salinity. All the test wastewater was quantitatively irrigated weakly for a year. The results showed that the cadmium in the synthetic wastewater discharged into the system was mainly stagnated in soil subsystem (87.67%-96.74%), and only a small portion (0.43%-3.23%) migrated into plants and litters. After a year trial, the Cd content in roots was more than that in stems and leaves. The artificial Avicennia marina wetland system did have a significant effect on purifying cadmium in synthetic wastewater, and the purification rate for C1, C5 and C10 was 90.43%, 97.17% and 97.06%, respectively.

[Bacteria ecology in planting-culturing system].

Planting-culturing system in inter-tidal zone is a new type eco-culturing model. The survey on bacteria biomass and water quality in the designed planting-culturing system in inter-tidal zone showed that the mangrove planted in the system improved water quality and made water quality to II-III type, better than the IV and V type in the control pond. Designed ponds made heterotrophic bacteria, vibrio, phosphorus bacteria and enzyme-producing bacteria populations 1-2 order lower than the control pond without mongrove planting. Correlation analyses with CORREL software showed that the biomass of these bacteria was positively related with the nitrogen and phosphorus contents in water of the system, and the correlation coefficient for heterogeneous bacteria and vibrio was up to 0.9205. Heterotrophic bacteria and vibrio could be used as the water-quality monitoring organisms.

[Application of mist net in studies of forest bird communities].

It had been more than twenty years for using mist net to study forest avian community. Mist net was very useful for studying cryptic, less vocal or non-vocal, and non-territorial birds, particularly understory birds in forest. The accuracy of mist net was relatively independent of observer biases and skills. It allowed identical and simultaneous sampling of numerous sites and straightforward comparisons among studies done at different sites by different people. So, a lot of ornithologists considered it as a necessary way for studying forest bird communities. Few studies had been reported on bird communities by using mist nets in China. In this paper, some examples on studying forest bird community by using mist nets were introduced, and studies on forest bird community with mist net should be used widely in China in the future.