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Based on field measurements from two typical intertidal transects at Dan’ao Estuary, groundwater-surface water and associated nutrient exchanges are quantified. Both groundwater discharge rate (39.1 ± 7.0 cm d −1 ) and surface water inflow rate (7.7 ± 1.4 cm d −1 ) at the upstream mangrove swamp transect are much higher than those (1.6 ± 0.3 and 2.1 ± 0.4 cm d −1 , respectively) at the downstream bare flat one. This large difference leads to their contrasting nitrogen forms. Much higher water exchange rates at the upstream transect generate much higher net dissolved inorganic nitrogen (DIN, including NH 4 + , NO 2 - , and NO 3 - ), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi) fluxes (− 160.3 ± 39.2, − 14.6 ± 2.7, − 38.6 ± 7.0 mmol m −2 d −1 , respectively) than those (2.9 ± 0.9, − 0.08 ± 0.03, 1.1 ± 0.4 mmol m −2 d −1 , respectively) at the downstream one. The mangrove swamp at the upstream transect discharges substantial groundwater and associated nutrients to the estuary. The net nutrient loads by water exchange in this estuary can reach 23.5–78.7% of those by local river discharge. [ABSTRACT FROM AUTHOR] more...

A surface and subsurface water coupled ecological model is presented to describe material cycling in a mangrove area, to which an ecosystem model is applied in order to account for chemical and biological reactions as well as physical processes. In this model, the nutrient transport from the groundwater to the river is estimated by the combined use of field measurements and numerical simulation of subsurface flow. The water movement and temporal variations in nutrient concentration obtained from the numerical simulation show a good agreement with the field observations, indicating that this model is valid for simulating material cycling in a mangrove area. The numerical simulation reveals that the supply of dissolved nutrients from the mangrove to the coastal area during spring tides is about 1.6 to 5.5 times larger than that during neap tides. [ABSTRACT FROM AUTHOR] more...

Sediments in eight types of mangroves were sampled in the Leizhou Peninsula. Heavy metals were analyzed to investigate the effects on metal distribution of mangrove communities, to evaluate contamination levels, identify sources and relationships between the two. Results showed that mangrove communities have effects on most heavy metal distributions in sediments, especially in the sediment with shrub communities of Aegiceras corniculatum where the contents of many metals are highest. As, Cr and Ni were identified as metal pollutants of primary concern, while Cd was of no concern. Zn, Pb, As mainly originated from anthropogenic source while the other metals are geogenic. Heavy metal distributions were affected by the independent and joint effects of landscape and sediment context; landscape context explains more variations in heavy metals than does sediment physicochemical variables. Total sulfur, total phosphorus and total potassium in sediment, and the existence of paddy field and forest land within 2000 m around the sampling sites are significant variables also. [ABSTRACT FROM AUTHOR] more...

This study aimed to conduct the isolation, screening and identification of bacteria with a high level of cellulolytic activity from the muddy sediments of mangrove swamps in Thailand. One hundred and ninety aquatic bacterial isolates were isolated from different muddy sediments and eighty one isolates were determined to be cellulolytic bacteria. The cellulolytic bacterium identified as Bacillus cereus JD0404 showed maximum hydrolysis activity on carboxymethylcellulose agar plates. Its cellulolytic performance for CMCase activity, Avicelase activity and β-glucosidase activity was 1.778 ± 0.003 U/mL, 0.079 ± 0.001 U/mL and 0.048 ± 0.002 U/mL, respectively. The optimum temperature and pH for the enzyme activity were determined to be 50 °C and 7.0 respectively. The cellulolytic activity was greatly enhanced by Mn 2+ and considerably inhibited by EDTA and toluene. Preliminary bioconversion application showed that the B. cereus JD0404 could be used for the hydrolysis of cellulose-based biomass. This study demonstrated a feasible bacterium for environmentally friendly industries and biotechnology. [ABSTRACT FROM AUTHOR] more...

Abstract: The atmospheric fluxes of N2O, CH4 and CO2 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 23.83μmolm− 2 h− 1, 11.9 to 5168.6μmolm− 2 h− 1 and 0.69 to 20.56mmolm− 2 h− 1 for N2O, CH4 and CO2, 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 N2O and CH4 fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N2O and CO2 fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH4 +-N contents, as well as the soil porosity. However, only soil NH4 +-N concentration had significant effects on CH4 fluxes. [Copyright &y& Elsevier] more...

Abstract: Gambiense human African trypanosomiasis is still assumed to be endemic in many part of West Africa, particularly in Guinea coastal area with mangrove swamp. Diagnosis is usually made during active medical screening or by passive initiative. Objectives: To describe clinical and epidemiological characteristics of Gambiense human African trypanosomiasis in the coastal area of Guinea. Methods: Exhaustive and retrospective analysis of all patients attending the trypanosomiasis center in the coastal area of Guinea between January 2005 and December 2007 with a diagnosis of human African trypanosomiasis. Results: A total of 196 patients were recruited for the study. Out of them, 55 % of the 73 patients diagnosed during active screening were classified stage 1 (haemolymphatic stage) or early stage 2 (meningoencephalitic stage). Contrarily, 115 of the 120 diagnosed by passive procedure were classified late stage 2, which features more specific signs and neurological symptoms, and leads to coma and death. More than 90 % of all cases presented cervical lymph nodes with identification of trypanosome on direct examination of fluid puncture. Less than one third of the patients were reexamined three months later. Discussion: In the coastal area of Guinea with mangrove swamp, direct examination of lymph node fluid puncture seems to be the most contributive test for the diagnosis of human African trypanosomiasis. Hence, associating clinical examination of cervical lymph nodes area and direct examination of fluid puncture may allow an early diagnosis of Gambiense human African trypanosomiasis and favor the implementation of efficient therapeutic strategies. [Copyright &y& Elsevier] more...

Abstract: The vertical distribution of polycyclic aromatic hydrocarbons (PAHs) at different sediment depths, namely 0–2cm, 2–4cm, 4–6cm, 6–10cm, 10–15cm and 15–20cm, in one of the most contaminated mangrove swamps, Ma Wan, Hong Kong was investigated. It was the first time to study the intrinsic potential of deep sediment to biodegrade PAHs under anaerobic conditions and the abundance of electron acceptors in sediment for anaerobic degradation. Results showed that the total PAHs concentrations (summation of 16 US EPA priority PAHs) increased with sediment depth. The lowest concentration (about 1300ng g−1 freeze-dried sediment) and the highest value (around 5000ng g−1 freeze-dried sediment) were found in the surface layer (0–2cm) and deeper layer (10–15cm), respectively. The percentage of high molecular weight (HMW) PAHs (4 to 6 rings) to total PAHs was more than 89% at all sediment depths. The ratio of phenanthrene to anthracene was less than 10 while fluoranthene to pyrene was around 1. Negative redox potentials (Eh) were recorded in all of the sediment samples, ranging from −170 to −200mv, with a sharp decrease at a depth of 6cm then declined slowly to 20cm. The results suggested that HMW PAHs originated from diesel-powered fishing vessels and were mainly accumulated in deep anaerobic sediments. Among the electron acceptors commonly used by anaerobic bacteria, sulfate was the most dominant, followed by iron(III), nitrate and manganese(IV) was the least. Their concentrations also decreased with sediment depth. The population size of total anaerobic heterotrophic bacteria increased with sediment depth, reaching the peak number in the middle layer (4–6cm). In contrast, the aerobic heterotrophic bacterial count decreased with sediment depth. It was the first time to apply a modified electron transport system (ETS) method to evaluate the bacterial activities in the fresh sediment under PAH stress. The vertical drop of the ETS activity suggested that the indigenous bacteria were still active in the anaerobic sediment layer contaminated with PAHs. The biodegradation experiment further proved that the sediment collected at a depth of 10–15cm harbored anaerobic PAH-degrading bacterial strains (two Sphingomonas, one Microbacterium, one Rhodococcus and two unknown species) with some intrinsic potential to degrade mixed PAHs consisting of fluorene, phenanthrene, fluoranthene and pyrene under low oxygen (2% O2) and non-oxygen (0% O2) conditions. This is the first paper to report the anaerobic PAH-degrading bacteria isolated from subsurface mangrove sediment. [Copyright &y& Elsevier] more...

Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms. In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1–>100μM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide-oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses. [Copyright &y& Elsevier] more...

Abstract: Four transects including sixteen stations were established in the Fugong mangrove (117°54′-117°55′E, 24°22′-24°24′N) of the Jiulong River Estuary, Fujian, China. Besides geochemical characterization and estimation of bacterial abundances, the distribution of α- and β-glucosidase activity was studied to explore the degradation of carbohydrates which can be expected to occur in high quantities in mangrove systems. The distribution pattern of microbial α-glucosidase and β-glucosidase activities was investigated using a fluorogenic model substrate (FMS) technique in order to allow better understanding of in situ enzyme activities, as well as their relation to bacterial biomass, metabolic activity and environmental factors in mangrove sediments. The results showed that the enzyme activities of α-glucosidase (10.83~100.86 µmol g-1 h-1) and β-glucosidase (39.60~222.75 µmol g-1 h-1) varied among the different stations, and the enzyme activities of β-glucosidase were higher than those of α-glucosidase at all stations. The extracellular enzyme activities were positively related to organic C, organic matter and bacterial abundance. In addition, the use of the FMS technique to measure extracellular enzyme activities of mangrove sediments could help us to evaluate their catabolic behavior in situ and so lead to a better understanding of the bacterial role in material cycle of mangrove swamp ecosystems. [Copyright &y& Elsevier] more...

Abstract: 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 ∑PAHs 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. [Copyright &y& Elsevier] more...

Modern diatom assemblages were analyzed in 85 surface sediment samples collected in the Kaw estuary and adjacent mangrove swamps. Samples were collected according to seasonal variations (wet versus dry) and mudbank stability phases, from fluid mudflat to mangrove swamps overgrown with vegetation. According to the diatom species habitat and salinity affinities, the modern distribution shows three main diatom assemblages more related to the sediment stability than the seasonal variations. The fluid mudflat was primarily dominated by marine planktonic species (Coscinodiscus centralis, Cyclotella stylorum, Thalassionema nitzschioides) carried by oceanic waters. These species also dominated the samples located in the estuarine channel of the Kaw River and in adjacent mangrove swamp areas in the upstream portion of the estuary. The occurrence of these marine planktonic species suggests a deep penetration of oceanic water into the estuary. The fluid mudflat was characterized by epipelic species, mostly dominated by species from the genera Gyrosigma, which are characterized by a high motility inside the sediments. This autochthonous epipelic assemblage could be considered as a biological indicator of the fluid mudflat stability. In the mangrove swamp stabilized by vegetation, the diatom assemblages are more diverse and dominated by species from the genera Nitzschia and Navicula. [Copyright &y& Elsevier] more...

• Tidal signals are detected in groundwater of a silty mangrove swamp. • Tidal effects are stronger at fringe forests and mudflats than riverine forests. • Mangrove zones appear to help retain groundwater at low tides. • Active root zone at fringe forests responds instantaneously to tide. • Less tidal pattern exists below active root zone likely due to capillary attenuation. Tides are one of the main factors affecting coastal aquifers, and thus they are important in supporting material transport and carbon circulation. In coastal mangrove swamps, the groundwater responses to tidal variations become more complicated owing to the complex topography, soil types, and the interactions of groundwater with fauna and flora. Perhaps because of this, quantitative relationships between the groundwater dynamics and the tidal actions of coastal mangrove swamps remain unclear. There is still a lack of studies that consider the integrated tidal effects on subsurface aquifers of different soil zones and topographic types. From January to December 2018, we simultaneously monitored the fluctuations of the piezometric head and salinity at the active root zone (shallow zone) and the low-permeability silty zone (middle zone) in the riverine forest and fringe forest and on the mudflat of a coastal mangrove swamp. Tidal signals were extracted from high-resolution time-series groundwater data using a Bayesian statistics modeling method-based code (Baytap08). Different time lags between tidal elevation fluctuations and the fluctuations of the piezometric head and salinity were detected. At the inland riverine forest and seaward mudflat, the upper aquifer quickly dried at low tides, whereas that of the fringe forest in between remained wet all the time. Although the groundwater fluctuations, especially the salinity fluctuations, were highly attenuated owing to capillary effects in the middle zone, the shallow zone showed high dependence on the tidal variations. Most previous studies have focused either on the macropore function (animal burrows and decayed roots) of mangrove swamps or on the capillary attenuation of coastal aquifers. Our results indicate that we need to consider both when analyzing the tidal responses of groundwater in mangrove swamps. The insights obtained from this study may help track the movement of water and materials in the coastal aquifers of mangrove swamps and provide references for better management of these valuable ecosystems and other similar coastal aquifers with complicated structures. [ABSTRACT FROM AUTHOR] more...

The degree of heavy metal contamination in the fine-grained (<63 Mum) and sand-sized (2 mm/63 Mum) fractions of surface sediments in 18 different mangrove swamps (144 random samples) in Hong Kong was examined. Higher concentrations of heavy metals were found in the fine-grained than the sand-sized fractions of the sediment; however, the differences between these two fractions became less significant when the swamp was more contaminated. The principal component analyses show that the 18 mangrove swamps, according to the median concentrations of total heavy metals, were clustered into four groups. The first group included three mangrove swamps in Deep Bay region which are seriously contaminated, with heavy metal concentrations in sediments around 80 Mug g-1 Cu, 240 Mug g-1 Zn, 40 Mug g-1 Cr, 30 Mug g-1 Ni, 3 Mug g-1 Cd and 80 Mug g-1 Pb. The second cluster, made up of another four swamps distributed in different geographical locations (two in Sai Kung district and two in Tolo region), also had elevated levels of Cu, Pb, Ni and Cr in the sediments. Field observation reveals that these seven stands received industrial, livestock and domestic sewage as well as pollution from mariculture activities, suggesting that anthropogenic input is the main source of heavy metal contamination in Hong Kong mangroves. The sediments from other mangrove swamps were relatively uncontaminated. [ABSTRACT FROM AUTHOR] more...