A field study was conducted to clarify the effect of rhizosphere processes on the accumulation and partitioning of heavy metals (Pb, Zn, Cu, Cr, Cd and Ni) in mangrove sediments. Metals were fractionated by a sequential extraction procedure into three chemically distinct fractions: water soluble, exchangeable and carbonate bound (B1), Fe–Mn oxide bound (B2), and organic and sulfide bound (B3). Results indicate that rhizosphere processes tend to increase the metal concentrations in the rhizosphere sediments. However, plant uptake may result in the decrease of the metal concentrations in the rhizosphere sediments when the metal concentrations are relatively low in the bulk sediments. Compared with the bulk sediments, the rhizosphere sediments have low concentrations of heavy metals in the B1 and B2 fractions and high concentrations in the B3 fraction. Either an increase or decrease in the residual fraction of heavy metals in the rhizosphere sediments may appear, depending on whether the formation of the refractory metal-organic compounds or the activation of the residual fractions dominates. Results also indicate that mangrove plants absorb and store non-essential metals in the perennial tissues, thus reducing the export of non-essential metals via leaf litter transport. Mangrove plants are excellent candidates for phytostabilization of heavy metals in intertidal substrates.

The effects of mangroves restored with different species on nitrogen of coastal surface sediments were studied.Results showed that TN increase significantly after the mangrove restoration.Compared to nude flats,restoration of Sonneratia apetala and Sonneratia caseolaris(introduced) improved the contents of NH 4+-N and NO x--N of surface layer soils,which was entirely opposite to Aegiceras corniculatum and Kandelia candel(indigenous).When matter transfer between the surface sediment and the water in shore,different potential environmental effects of nutrient transport and exchange process may exist in the tidal flat sediment-water interface between introduced and indigenous mangrove restoration.

In nature, Mangroves grow at estuarines and coastal intertidal area. They have adaptive mechanism of physiological, morphological and structural characters to the water-logging conditions induced by the tidal effects. The development of mangrove aerenchyma was proved to be highly related to their adaptability to inundation, and also considered as the major factor to evaluate the mangrove tolerance to inundation. The root aerenchyma developments were compared between natural and artificial habitats by porosity measurement and paraffin section for Avicennia marina (Am), Rhizophora stylosa (Rs), Bruguiera gymnorrhiza (Bg), Kandelia candel (Kc) and Aegiceras corniculatum (Ac), five dominant mangrove species in southern China. The leaf and stem aerenchyma of these five mangrove species were also studied by paraffin section. Results indicated that the measurements of two methods were statistically significantly correlative (P < 0. 05) for root aerenchyma. The most of aerenchyma resulted from the roots for these five mangrove trees. The roots aerenchyma accounted for more than 50% except that root aerenchyma of Am in tidal habitats was 48. 16%, and Ac in non-tidal habitats was 43. 81% of the sum (in root, stem, and leaf). The aerenchyma of Ac, Bg, Am, Kc, and Rs was (14.98 ±3.34)%, (27.83 ±2. 3)%, (29. 64 ± 3. 17)%, (30.09 ± 4. 12)%, and (42. 12 ± 3. 14)% in natural intertidal habitats, respectively. This distribution of aerenchyma was accordant to the mangrove tidal zonation and vegetation successional sequence in the southern China coast. The root aerenchyma of Rs, Bg, Kc, Am, and Ac increased in non-tidal artificial habitats compared to natural tidal habitats, indicating adaptability to non-tidal conditions flooding for these mangrove species in some degree. The increase of root arenchyma development was least in Ac, while most in Rs. It was inferred that those species of less adaptive to inundation, i. e. Bg and Rs, increased their root arenchyma more to tolerate steady water level condition. They could be considered as more sensitive to water level change. By contrast, the species of more adaptive to inundation, i. e. Ac and Am, increased their root arenchyma less. This could be considered as a less sensitive phenomenon to water level change. Under non-tidal conditions, the aerenchyma of Ac, Am, Kc, Bg and Rs was (56.38 ±2.41)%, (40.88 ±1.03)%, (39. 18 ± 1. 21)%, (35. 70 ±0. 57)% and (19. 28 ±0. 63)%, respectively. Judging from root aerenchyma developments in non-tidal habitats, their adaptabilities to the steady inundation condition were as following sequence: Ac > Am > Kc > Bg > Rs. The adaptability of mangrove to non-tidal inundation condition increased the feasibility. The result was important to enhance the survival rate of mangrove planting, and expand planting area for improving coast ecological services.

The macrobenthos are the primary consumers in the mangrove ecosystem and play an important role on nutrient transformation and energy transportation. By conducting the indoor feeding experiment,the feeding characteristics of two common macrobenthos in the Southern China coastal region mangroves,Sesarma dehaani and S. bidens,to the leaf litter of the exotic mangrove species Sonneratia apetala,and two native species,Kandelia obovata and Aegiceras corniculatum were studied. The results showed that the leaf litter of Kandelia obovata had the greatest changes in Tannin content and C/N value during the leaching process,which decreased (45.85±7.74) g·kg-1 and 11.24%. Meanwhile,the decreasing rates of Tannin content and C/N value are (45.15±11.14) g·kg-1 and 2.43%,(18.75±15.15) g·kg-1 and-1.36% respectively for Sonneratia apetala and Aegiceras corniculatum. With the decrease of Tannin content and C/N value,the two Sesarmid crAbs' predation of leaves presented a slightly rising trend accordingly,which rised from 3.097 g to 10.079 g and 2.480 g to 8.723 g for Sesarma dehaani and S. bidens,respectively. In addition,there was no significant difference with the food preference between the two crAbs (P0.05),but there was significant difference between the three mangrove species. Both of the crAbs were significantly prefer to Sonneratia apetala and Kandel obovata rather than Aegiceras corniculatum due to the high Tannin content and low nutritive value in the litter's leaves (P0.01). The results proved that introducing the exotic species Sonneratia. apetala at a large scale would incur the potential impact on the food chain structure in the Southern China coastal regeion mangroves,and also provided the reference for mangrove ecological restoration and reasonable afforestation.

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degradation and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obovata , and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different tolerabilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia . It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aquaculture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.

As polychlorinated biphenyls(PCBs) in mangrove ecosystem may cause ecological risk,monitoring of PCBs in sediments is of great importance.This work presents the determination of trace PCBs in mangrove sediment samples,under the condition of quality assurance/quality control(QA/QC).In this study,both ultrasonic extraction(USE) and microwave-assisted extraction(MAE) are tried.According to properties of the samples,PCBs are cleaned up with copper,sulfuric acid and alumina-silica chromatography column.Then,PCBs are detected by the apparatus of GC/MS.The results show that both USE and MAE have high recoveries.The recoveries of the whole analysis range from 47.45% to 100.76% by USE and from 77.04% to 98.00% by MAE,respectively,and MAE has higher accuracy.The method detection limits for PCBs range from 0.30 to 1.74 ng/g by USE and from 0.30 to 0.47 ng/g by MAE.So MAE is a better choice.