Identification of gaps in mangrove forests with airborne LIDAR

Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for investigating this issue. Airborne light detection and ranging (LIDAR) technology provides an effective way for identifying gaps by remotely obtaining direct measurements of ground and canopy elevations. A method based on an alternative sequential filter and black top-hat mathematical morphological transformation was developed to extract gap features. Comparison of identified gap polygons with raw LIDAR measurements and field surveys shows that the proposed method successfully extracted gap features in mangrove forests in Everglades National Park. There are 400–500 lightning gaps per square kilometer in mangrove forests at the study sites. The distribution of gap sizes follows an exponential form and the area of gaps with sizes larger than 100 m² account for 55–61% of the total area of gaps. The area of gaps in the mangrove forest in Everglades National Park is about 4–5% of the total forest area and the average gap formation rate is about 0.3% of the total forest area per year, indicating that lightning gaps play an important role in mangrove forest dynamics.     

Mangrove forests as a nature-based solution for coastal flood protection: Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk. It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection. However, to use mangroves effectively as a nature-based measure for flood risk reduction, we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure. In this perspective, we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence. We show that the forest properties that comprise coastal flood protection are well-known, but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation. Overall, there is relatively good understanding of the ecological processes that drive forest structure and size, but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics, and on the role of combined stressors influencing forest retreat. Integrating simulation models of forest structure under changing physical (e.g. due to sea-level change) and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.     

Chemical composition of degrading mangrove leaf litter and changes produced after consumption by mangrove crabNeosarmatium smithi (Crustacea: Decapoda: Sesarmidae)

The leaves of the mangroveCeriops tagal contained 3.2–4.1% (all percentages relate to dry weight) ofd-1-O-methyl-muco-inositol previously unreported in mangroves. They consisted of 37% aqueous acetone-water-soluble material, 18% water-insoluble polysaccharides, and ca. 50% polyphenols, which include soluble and insoluble tannins and lignin. The polysaccharide component sugars were glucose, arabinose, uronic acids, mannose, xylose, galactose, and rhamnose in the proportions 28262210752, respectively. The leaves were pectate rich, and the low level of glucan was presumed to consist mainly of cellulose. After four weeks of biodegradation, ca. 60% of the acetone-water-soluble material was lost from the leaves. Degradation processes greatly altered the polysaccharide components in the leaves. Pectates were rapidly degraded, while other polysaccharides, although reduced proportionately, resisted degradation at about the same level, and all component sugars were found in the 8-week-old leaves. Apparent lignin contents increased from 15 to >30% during biodegradation up to eight weeks. The yields of the major fractions in corresponding fecal material fromNeosarmatium smithi showed a similar trend to the diets. An enrichment of the insoluble residue was noticeable due to the digestion of dialyzable material. The fecal carbohydrate content was greatly reduced (7–11%) and the apparent lignin increased (27–39%) due to its resistance to degradation. All dietary polysaccharide component sugars were found in the fecal residues, including some uronic acids. The leaves also contained a readily water-soluble fraction (15%) which consisted of pectates strongly complexed with proanthocyanidins.     

Spatial and vertical distribution of polycyclic aromatic hydrocarbons in mangrove sediments

The distribution and historical changes of polycyclic aromatic hydrocarbons (PAHs) contamination in mangrove sediments in Hong Kong SAR were investigated. Surface sediments (2-3 cm) collected from four mangrove swamps exhibited significant spatial variations in concentrations of total PAH (with SigmaPAHs ranging from 56 to 3758 ng g(-1) dry wt), as well as the composition of 16 USEPA priority PAH compounds. Within a small swamp with an area of 0.68 ha, the total PAH concentrations also differed from sampling site to site, indicating that the PAH contamination is localized and confined to a very small area within the same swamp. Discharges from municipal and industrial wastewater, urban runoff, oil leakage from boats and ships, and accidental oil spill are possible sources of the PAH contamination. The sediment depth profiles reveal that the surface sediment layer (0-5 cm) had lower total PAH concentrations than that in the bottom layer (15-20 cm), and PAH composition also changed with the sediment layers. Based on the estimated annual sediment deposition rate in Hong Kong SAR of around 0.4-0.5 cm, the present findings suggest that the PAH contamination was most serious between 1958 and 1979 but started to decline thereafter. Such decline was probably due to changes in petroleum usage in urban areas and a better control of wastewater discharges from 1980 onwards in this region.     

Bacteriocin-producing Enterococcus faecalis KT2W2G isolated from mangrove forests in southern Thailand: Purification,characterization and safety evaluation

The aim of this work was to purify and characterize the bacteriocin produced by Enterococcus faecalis KT2W2G isolated from the mangrove forest in southern Thailand, in order to evaluate its potential as a new food protective agent. The active peptide from the cell-free supernatant of Ent. faecalis KT2W2G was purified in 4 steps: (i) precipitation with 70% saturated ammonium sulfate, (ii) elution on a reversed phase cartridge (Sep-Pak C₈) using different concentrations of acetonitrile, (iii) cation-exchange chromatography and (iv) final purification by reversed phase-HPLC on a C₈ column. Each purification step increased the specific activity and reduced the amount of contaminating non-bacteriocin proteins. The specific activity of purified bacteriocin was 13,470.53 AU/mg of protein, which corresponded to a 48.10-fold increase. Tricine–SDS-PAGE of the purified bacteriocin gave molecular weight ranging between 3.5 and 6.5 kDa. The activity of the partially purified bacteriocin was unaffected by pH (2.0–12.0) and thermostable, but was sensitive to proteolytic enzymes. This bacteriocin maintained full stability after storage at −20, 4 and 37 °C for 2 months. It was stable when incubated for 1 month at 4 °C in 0–30% NaCl. Inhibitory spectrum of this bacteriocin showed a wide range of activities against other LAB, food-spoilage and food-borne pathogens. Ent. faecalis KT2W2G was sensitive to kanamycin, tetracycline and vancomycin but resistant to ampicillin, gentamicin and penicillin. PCR amplification demonstrated that Ent. faecalis KT2W2G does not harbor virulence genes cylA, cylB and esp but has virulence genes ace, asa1 and efaAfs. The bacteriocin and its producing strain may find application as bio-preservatives for reduction of food-spoilage and food-borne pathogens in food products.     

红树林土壤风干前后鞭毛虫群落差异性分析

研究分析了海南东寨港三种不同生境红树林土壤风干前后鞭毛虫群落的变化情况,结合环境因子对风干前后鞭毛虫的现存量、物种多样性进行了对比分析。结果表明:在新鲜土样和风干土样中,鞭毛虫的种类数和多样性指数都呈递增趋势(裸滩<人工红树林<天然红树林);但现存量却是递减的(裸滩>人工红树林>天然红树林)。此外,在裸滩、人工红树林和天然红树林中,新鲜土样和风干土样的第一优势类群都为动基体目(Kinetoplastida),这与中国典型地带土壤鞭毛虫群落分布是一致的。     

Effects of water quality on mangroves in an urban lake system

This study assessed the extent of anthropogenic stresses on two mangrove species (Sonneratia caseolaris and Cerbera odollam) in a tropical coastal lake system. An anaerobic factor, organic pollution and salt factors were identified as being responsible for the risks to mangroves. A flora risk tolerance index was developed to ascertain the spatial and temporal risk of plants to water pollution. This study revealed the risk to the Cerbera odollam species is high, compared to Sonneratia caseolaris. Further, the flora risk tolerance index is a good index for assessing the risks to the mangrove species.     

Denitrification associated N loss in mangrove soil

Despite the well-known mechanism of N loss through denitrification in wetland, little information is available for mangrove soil. The aim of this study is to quantify N loss via denitrification in mangrove soil, to clarify factors affecting denitrification and to evaluate the role of plants in the mechanism of nitrification–denitrification in mangrove soil. The N loss from mangrove soil was 76%, possibly 55% through denitrification, measured using a ¹⁵N tracer technique. The N loss was reduced to 45% when a nitrification inhibitor, N-serve, was added. Planting reduced the N loss from mangrove soil more than the nitrification inhibitor. The combination of planting and applicasion of nitrification inhibitor completely prevented N loss from mangrove soil. Denitrification in fresh soil samples from a mangrove forest declined markedly from the surface to the sub-surface soil. Available C limited denitrification. The ability of glucose to induce denitrification declined with soil depth, suggesting a decline in the denitrifier population with depth. Significant reduction in N loss from mangrove soil after adding nitrification inhibitor indicates that nitrification is the key factor in N loss of mangrove soil. As there was no significant difference in denitrification between rhizosphere and non-rhizosphere soil, the cause of N loss in the mangrove soil may occur primarily in the surface soil rather than in the rhizosphere soil.     

白鹭落枝头，鱼蟹栖根底——以自然生态为基础的三亚河城市设计

通过对三亚河城市设计地域特色和现状的分析,对设计理念、设计目标、设计原则以及规划布局的介绍,探讨了生态设计思想和方法在城市规划工作中的应用。