Transport of sediment in mangrove swamps

The transport of suspended sediment in mangrove swamps is controlled by three dominant processes. First, the transport processes in the estuaries and coastal waters draining the swamp, including flocculation, tidal pumping, baroclinic circulation, trapping of the smallest particles in the turbidity maximum zone, and the effect of the mangrove tidal prism. Second, the mechanical and chemical reactions in mangrove waters destroying flocs of cohesive sediment in suspension. Third, biological processes have a dominant influence on the ultimate fate of clay particles in mangroves.     

Sensitivity of dissolved organic carbon exchange and sediment bacteria to water quality in mangrove forests

Poor water quality affects the biogeochemistry functions and the biological community structure of coastal ecosystems. In this study we investigated the effect of water quality on: (a) The exchange of dissolved organic carbon (DOC) between floodwater and mangrove forests, (b) the abundance of sediment bacteria, (c) the microbial community composition, and (d) the microbial catabolic activity. We selected six mangrove forests that were flooded by creeks with differing water qualities to test for thresholds of nutrient concentrations associated with changes in DOC dynamics and the microbial community. Our results show that in sites flooded by water high in soluble reactive phosphorus (SRP) (>20 μg l⁻¹) and NH₄ ⁺ (>30 μg l⁻¹) the DOC concentrations in the floodwater were higher than in ebb water, suggesting DOC import by the mangroves. In contrast, in sites flooded by water low in SRP (<20 μg l⁻¹) and NH₄ ⁺ (<30 μg l⁻¹), DOC concentrations in the floodwater were lower than in the ebb water, suggesting DOC export by the mangroves. Bacterial abundance was higher in sediments with low bulk density, high organic carbon and when flooded by water with low N:P (1–2), but the microbial composition and total catabolic activity assessed using Biolog Ecoplates™ did not differ among sites. The relationship between water quality, microbial communities and DOC exchange suggests that, at least during some periods of the year, poor water quality increases bacterial abundance and modifies DOC exchange of mangrove forests with floodwater and thus, their role in supporting near-shore productivity.     

Diversity and abundance of ammonia-oxidizing archaea and bacteria in polluted mangrove sediment

Ammonia oxidation by microorganisms is a critical process in the nitrogen cycle. Recent research results show that ammonia-oxidizing archaea (AOA) are both abundant and diverse in a range of ecosystems. In this study, we examined the abundance and diversity of AOA and ammonia-oxidizing beta-proteobacteria (AOB) in estuarine sediments in Hong Kong for two seasons using the ammonia monooxygenase A subunit gene (amoA) as molecular biomarker. Relationships between diversity and abundance of AOA and AOB and physicochemical parameters were also explored. AOB were more diverse but less abundant than AOA. A few phylogenetically distinct amoA gene clusters were evident for both AOA and AOB from the mangrove sediment. Pearson moment correlation analysis and canonical correspondence analysis (CCA) were used to explore physicochemical parameters potentially important to AOA and AOB. Metal concentrations were proposed to contribute potentially to the distributions of AOA while total phosphorus (TP) was correlated to the distributions of AOB. Quantitative PCR estimates indicated that AOA were more abundant than AOB in all samples, but the ratio of AOA/AOB (from 1.8 to 6.3) was smaller than most other studies by one to two orders. The abundance of AOA or AOB was correlated with pH and temperature while the AOA/AOB ratio was with the concentrations of ammonium. Several physicochemical factors, rather than any single one, affect the distribution patterns suggesting that a combination of factors is involved in shaping the dynamics of AOA and AOB in the mangrove ecosystem.     

A review on the present status and management of mangrove wetland habitat resources in Bangladesh with emphasis on mangrove fisheries and aquaculture

The mangrove forest of Bangladesh, the largest continuous mangrove bulk, is one of the most important features of the coastal area of the country. The existence of the mangrove has increased the values of other coastal and marine resources such as the coastal and marine fisheries by increasing productivity and supporting a wide biological diversity. The deltaic mangrove of Bangladesh is ecologically different from the other, mostly nondeltaic mangroves of the world and is unique also in its floral and faunal assemblage; therefore, a number of endangered plants and animals that are extinct from other parts of the world, are existing in Bangladesh mangrove. However, the mangrove has been under intensive pressure of exploitation for the last few decades which, in addition to direct clearance and conversion have placed the mangrove under extreme threat. Shrimp farming is the most destructive form of resource use the mangrove has been converted to, which contributed significantly to mangrove destruction with a corresponding loss of biological resources. Concerns have been raised among the ecologists, biologists, managers and policy makers since the early 1990s; deliberate destruction of mangrove and unplanned development of coastal aquaculture particularly shrimp aquaculture have been put under extreme criticism and the sustainability has been questioned. The present status of the mangrove resources including mangrove fisheries and aquaculture and management practices have been reviewed in this paper; impacts of different forms of human interventions and resource use have also been discussed. It is suggested that the management options and the policy aspects should be critically reviewed and amended accordingly; beneficiaries and stakeholders at all levels of resource exploitation must take part and contribute to conservation and management. An immediate need for mangrove conservation has been identified.     

Diversity and biotechnological potential of culturable bacteria from Brazilian mangrove sediment

Mangrove ecosystems are environments subject to substantial degradation by anthropogenic activities. Its location, in coastal area, interfacing the continents and the oceans makes it substantially important in the prospection for biotechnological applications. In this study, we assessed the diversity of culturable bacteria present over the seasons at two depths (0–10 and 30–40 cm) in a mangrove sediment and in a transect area from the land to the sea. In total, 238 bacteria were isolated, characterized by Amplified Ribosomal DNA Restriction Analysis (ARDRA) and further identified, by Fatty Acid Methyl Esther (FAME-MIDI), into the orders of Vibrionales, Actinomycetales and Bacillales. Also the ability of the isolates in producing economically important enzymes (amylases, proteases, esterases and lipases) was evaluated and the order Vibrionales was the main enzymatic source.     

Microbial diversity and anaerobic hydrocarbon degradation potential in an oil-contaminated mangrove sediment

ABSTRACT: BACKGROUND: Mangrove forests are coastal wetlands that provide vital ecosystem services and serve as barriers against natural disasters like tsunamis, hurricanes and tropical storms. Mangroves harbour a large diversity of organisms, including microorganisms with important roles in nutrient cycling and availability. Due to tidal influence, mangroves are sites where crude oil from spills farther away can accumulate. The relationship between mangrove bacterial diversity and oil degradation in mangrove sediments remains poorly understood. RESULTS: Mangrove sediment was sampled from 0--5, 15--20 and 35--40 cm depth intervals from the Surui River mangrove (Rio de Janeiro, Brazil), which has a history of oil contamination. DGGE fingerprinting for bamA, dsr and 16S rRNA encoding fragment genes, and qPCR analysis using dsr and 16S rRNA gene fragment revealed differences with sediment depth. CONCLUSIONS: Analysis of bacterial 16S rRNA gene diversity revealed changes with depth. DGGE for bamA and dsr genes shows that the anaerobic hydrocarbon-degrading community profile also changed between 5 and 15 cm depth, and is similar in the two deeper sediments, indicating that below 15 cm the anaerobic hydrocarbon-degrading community appears to be well established and homogeneous in this mangrove sediment. qPCR analysis revealed differences with sediment depth, with general bacterial abundance in the top layer (0--5 cm) being greater than in both deeper sediment layers (15--20 and 35--40 cm), which were similar to each other.     

Meiobenthos of hypersaline tropical mangrove sediment in relation to spring tide inundation

Tropical intertidal sediments often contain porewater of relatively high salinity, especially in areas exposed to longer periods without seawater inundation and high evaporation. Such an area exists on the west coast of Zanzibar: a high intertidal mangrove plateau, flooded only during spring high tides, with sediment porewater salinities commonly exceeding 100 ppt. A field survey was conducted in this area to examine variations in population density of major meiofaunal taxa and the assemblage structure of free-living marine nematodes during spring-neap tidal cycles. Samples were taken on seven occasions for two months, starting from the end of the rainy season. Porewater salinity remained high throughout the sampling period, ranging from 89 to 160 ppt. Neither spring tide inundation nor heavy rains lowered the salinity markedly. The meiofauna consisted only of four taxa, present on all sampling occasions: nematodes, harpacticoid copepods, plathyhelminthes and chironomids. Densities in surface sediments (0–5 cm) were low compared to other mangrove areas, ranging from 271 to 656 animals 10 cm^-2 with nematodes dominant on all sampling occasions (58–87%). Density fluctuations could not be explained by the effects of spring tide inundation, but the meiofauna showed significant correlations with grain size and organic material. Despite the wide range of salinity, only the numbers of chironomids were negatively correlated with increased salinity. Nematode species diversity was low in all samples, although altogether 28 species were recorded in the samples. Four species occurred in more than 50% of the samples (Microlaimus sp. (100%), Metalinhomoeus sp. (76%), Daptonema sp.l (56%), Chromadorina sp. (56%)) while 12 species were found only in one or two samples. Multidimensional scaling ordination (MDS) of the nematode species abundance data indicated little effects of spring tide inundation on the assemblage structure, but rather a successive change from wet to dry season with a reduction in species diversity and increased numbers of the dominant nematode species Microlaimus sp.     

Production and biomass of mangrove roots in relation to hydroperiod and physico-chemical properties of sediment and water in the Mecoacan Lagoon,Gulf of Mexico

Wetlands Ecology and Management - Production and biomass information of roots is valuable for understanding the ecological process within mangroves. In this study, the production, biomass, turnover...     

Correlation between anammox activity and microscale distribution of nitrite in a subtropical mangrove sediment

The distribution of anaerobic ammonium oxidation (anammox) in nature has been addressed by only a few environmental studies, and our understanding of how anammox bacteria compete for substrates in natural environments is therefore limited. In this study, we measure the potential anammox rates in sediment from four locations in a subtropical tidal river system. Porewater profiles of NO(x)(-) (NO2- plus NO3-) and NO2- were measured with microscale biosensors, and the availability of NO2- was compared with the potential for anammox activity. The potential rate of anammox increased with increasing distance from the mouth of the river and correlated strongly with the production of nitrite in the sediment and with the average concentration or total pool of nitrite in the suboxic sediment layer. Nitrite accumulated both from nitrification and from NO(x)(-) reduction, though NO(x)(-) reduction was shown to have the greatest impact on the availability of nitrite in the suboxic sediment layer. This finding suggests that denitrification, though using NO2- as a substrate, also provides a substrate for the anammox process, which has been suggested in previous studies where microscale NO2- profiles were not measured.     

Methanogenic community compositions in surface sediment of freshwater aquaculture ponds and the influencing factors

Aquaculture ponds represent ecologically relevant environments to study the community composition and diversity of methanogenic assemblages, as well as their interactions with cultivated species and chemical indicators. In this study, aquaculture ponds with crab (Eriocheir sinensis), oriental river prawn (Macrobrachium nipponense), perch (Micropterus salmonides) and Wuchang fish (Parabramis pekinensis) were sampled, and Illumina high-throughput sequencing was used to investigate the methanogenic communities. The results revealed that the abundant methanogenic orders in surface sediment were Methanomicrobiales, Methanosarcinales and Methanocellales. The relative abundance of Methanocellales was higher in crab and prawn ponds as compared to other ponds. Methanogenic 16S rRNA gene abundance and beta diversity of the community was affected by the cultivated species. Methanogenic communities in aquaculture ponds with higher contents of total nitrogen and organic matter had decreased species richness, while those with higher contents of ammonia and nitrite had an overall decreased abundance of methanogens and their respective diversities. Overall, in addition to the differences in cultivated species, the consequent differences in farming practices including the types and amounts of feeds used, the contents of total nitrogen, organic matter, ammonia and nitrite could all influence the methanogenic community in surface sediment of aquaculture ponds.     

Diversity of methanogenic archaea in a mangrove sediment and isolation of a new Methanococcoides strain

Mangrove forest sediments produce significant amounts of methane, but the diversity of methanogenic archaea is not well known at present. Therefore, 16S rRNA gene libraries were made using archaea-specific primers and DNA extracted directly from Tanzanian mangrove sediment samples as a template. Analysis of sequence data showed phylotypes closely related to cultivated methylotrophic methanogenic archaea from the marine environment, or distantly related to acetoclastic and hydrogenotrophic methanogenic archaea. In an attempt to isolate relevant methanogenic archaea, we succeeded in obtaining a new mesophilic methylotrophic methanogenic archaeon (strain MM1) capable of utilizing methanol and methylated amines as the only substrates. Under optimum conditions, the cells of strain MM1 exhibited a high specific growth rate (μ) of 0.21±0.03 (i.e. doubling time of 3.2 h) on both methanol and trimethylamine. The 16S rRNA gene sequence of strain MM1 clustered with five environmental clones, indicating that MM1 is an important methanogenic methylotroph in mangrove sediments. Based on physiological and phylogenetic analyses, strain MM1 is proposed to be included in the species of Methanococcoides methylutens .     

Accelerated sulfur cycle in coastal marine sediment beneath areas of intensive shellfish aquaculture

Prokaryotes in marine sediments taken from two neighboring semi-enclosed bays (the Yamada and Kamaishi bays) at the Sanriku coast in Japan were investigated by the culture-independent molecular phylogenetic approach coupled with chemical and activity analyses. These two bays were chosen in terms of their similar hydrogeological and chemical characteristics but different usage modes; the Yamada bay has been used for intensive shellfish aquaculture, while the Kamaishi bay has a commercial port and is not used for aquaculture. Substantial differences were found in the phylogenetic composition of 16S rRNA gene clone libraries constructed for the Yamada and Kamaishi sediments. In the Yamada library, phylotypes affiliated with delta-Proteobacteria were the most abundant, and those affiliated with gamma-Proteobacteria were the second-most abundant. In contrast, the Kamaishi library was occupied by phylotypes affiliated with Planctomycetes, gamma-Proteobacteria, delta-Proteobacteria, and Crenarchaeota. In the gamma-Proteobacteria, many Yamada phylotypes were related to free-living and symbiotic sulfur oxidizers, whereas the Kamaishi phylotype was related to the genus Pseudomonas. These results allowed us to hypothesize that sulfate-reducing and sulfur-oxidizing bacteria have become abundant in the Yamada sediment. This hypothesis was supported by quantitative competitive PCR (qcPCR) with group-specific primers. The qcPCR also suggested that organisms closely related to Desulfotalea in the Desulfobulbaceae were the major sulfate-reducing bacteria in these sediments. In addition, potential sulfate reduction and sulfur oxidation rates in the sediment samples were determined, indicating that the sulfur cycle has become active in the Yamada sediment beneath the areas of intensive shellfish aquaculture.     

The relationship between invertebrate assemblages and bio-dependant properties of sediment in urbanized temperate mangrove forests

Relationships between ecological structure, functions and properties of sediments in intertidal mangrove forests and mudflats are poorly understood. Studies have not yielded consistent results, due to complex interactions between biotic and abiotic components. The benthic macrofauna in mangrove forests are important contributors to ecological functions, mediating various sedimentary properties. They vary in abundance and diversity at scales from centimeters to hundreds of metres in what appears to be similar “habitat”, but properties of sediments are often not measured at such small scales, or small-scale variation is ignored as random noise. Yet, there should be relationships between scales of variation in macrofauna and bio-dependant properties of sediments.This paper describes variation in assemblages of benthic invertebrates and bio-dependant properties of sediments at a hierarchical range of spatial scales, within and among different habitats in an urbanized mangrove forest and the associated intertidal mudflats in Sydney Harbour, Australia. Measurements were made on two occasions, in replicate sites in each habitat. These were used to test hypotheses about relationships of scales of variation in the benthos and sediments. The benthos showed relatively little difference in diversity and abundances among habitats compared to variation within and between sites in each habitat. The bio-dependant properties of the sediment showed less variation at small scales and larger among-habitat variation than did the benthos. Variation in the benthos did not clearly correlate with variation in the selected bio-dependant properties of the sediments at any scales. Neither did the properties of the sediment show consistent correlations in any habitat.These data indicate that the properties and processes driving the benthos are not simply related to the properties of the sediment we measured and that there was very large variation in both benthos and bio-dependant properties within small sites. This highlights the necessity of using experimental designs that sample at a hierarchy of scales for benthic assemblages and bio-dependant properties of sediment.     

Broad-scale effects of marine salmonid aquaculture on macrobenthos and the sediment environment in southeastern Tasmania

A comparison of sediments and associated macrobenthos at sites sampled within 20 fish farm leases distributed across southeastern Tasmania indicated major natural changes along a regional cline. Introduced taxa were strongly represented in the fauna, comprising 45% of total macrofaunal biomass. Large differences were evident between sites affected by different levels of organic farm waste. Sites located adjacent (< 10 m) to farm cages possessed significantly depressed sediment redox levels, a dominance of capitellid and dorvilleid polychaetes, and low macrofaunal species richness. Subtle impacts extended across farm lease areas in the form of depressed redox potential at 40 mm depth and changes to the macrobenthic community, including a prevalence of the dogwhelk Nassarius nigellus and a paucity of the heart urchin Brissus sp. and the maldanid polychaetes Asychis sp. and Rhodine sp. Minor farm effects were also evident at sites sampled 35 m outside farm lease boundaries, most notably as elevated population numbers of the polychaete Terrebellides sp., bivalve Mysella donaciformis and heart urchin Echinocardium cordatum. Amongst the univariate metrics examined, redox potential at 40 mm depth and the ratio of bivalves to total molluscs provided the most sensitive indicators of farm impacts, with the latter metric relatively insensitive to spatial variation between locations within the region studied.     

Solute dynamics in a North Brazilian mangrove: the influence of sediment permeability and freshwater input

Although water in mangrove sediments influences nutrient cycling in both, mangrove forest and estuary, little information exists on seasonal and vertical distribution of dissolved organic and inorganic compounds in the sediment column. We studied the influence of sediment texture and chemistry, permeability (K), tides, and rainfall on dissolved organic carbon (DOC) and nitrogen (DON), dissolved inorganic phosphate (DIP) and salinity in creek and sediment waters of a mangrove in Pará, Brazil. Water samples were taken from boreholes and piezometers in the mangrove forest and from an adjacent tidal creek at neap and spring tides, during the dry and rainy season. Forest sediment was analysed for carbon (C), nitrogen (N), salinity and permeability. Clay, C and N decreased with depth. Sediment permeability (K) was lowest (<0.1 m day⁻¹) in the upper, clay-rich and crab-burrow-free mud layer. In the deeper, fine sand strata, K ranged from 0.7 to 1.8 m day⁻¹. Tidal range in the creek was 3.5 and 5.5 m for neap and spring tides, respectively. Salinity, DOC, DON and DIP in creek water were inversely related to tidal height. Piezometer data revealed significant water level changes in deeper, sandy sediment layer, which followed, time-lagged, the tidal fluctuations. In contrast, tide did not affect the water level in the upper sediment due to low permeability. Compared with creek water, sediment water was enriched in DOC, DON and DIP because of organic matter input and mineralization. In deeper layers, solute concentration was most likely affected by sorption processes (DOC and DIP) and reduction reactions (DIP). During the rainy season, DOC and DON in creek and sediment water were higher than in the dry season. DIP appeared invariant to seasonal changes. In the rainy season, salt flushing from surface sediments resulted in higher salinities at intermediate sediment depths, while in the deeper layers salinity was lower due to exchange with water from the tidal creek.     

Nitrogen availability and uptake by grassland in mesocosms at two water levels and two water qualities

We studied the effect of water table (-5 or -30 cm) and water type (rain- or groundwater) on the above- and below-ground phytomass production, species composition and nitrogen uptake of grassland.Nitrogen mineralization, nitrification, methane production, redox potential and pH at different depths in the profile were measured and used to monitor gradual changes in variables influencing phytomass production.The rise in the water level lowered the nitrogen uptake in the above-ground phytomass from 14.1 to 11.4 g N per m², but the DM production did not decrease and varied from 566 to 690 g per m². The total root mass increased from 82 to 363 g DM per m², with the proportion in the 5 to 10 cm layer increasing the most from 13 to 24%.The high water level lowered the potential N mineralization in the upper 5 cm of the soil from 16.1 to 4.3 g N per m² and in the deeper 5 to 30 cm layer from 12.6 to 9.4 g N per m² respectively, so the importance of the deeper layer as a source of N increased. The total amount of mineral N that accumulated in the 40 cm deep soil cores decreased from 31.3 to 15.5 g N per m². The above-ground vegetation took up 71 to 76% of this amount in the high water level treatment and only 37 to 57% under drier conditions.Redox potential and methane production indicated anaerobic conditions below 5 cm in both level treatments and in the top 5 cm of the high water level treatment. But some nitrification was measured there also, thus aerobic and anaerobic conditions occurred together. The low N mineralization was attributed to low soil respiration.Raising the water level brought about an increase in the above ground biomass of Glyceria fluitans and an increase in root mass, especially deeper in the soil. Both are responsible for the relatively greater fraction of nitrogen that was taken up from the soil, although less N was available. The nitrification indicates that oxygen is transported by the root system to soil microsites and partly compensates for the anaerobic conditions caused by water saturation.The calcareous groundwater raised the pH in the upper soil layer from 5.3 to 5.8 but no effect on N mineralization was measured.     

Characterisation of the effect of a simulated hydrocarbon spill on diazotrophs in mangrove sediment mesocosm

An analysis of the effect of an oil spill on mangrove sediments was carried out by contamination of mesocosms derived from two different mangroves, one with a history of contamination and one pristine. The association between N₂ fixers and hydrocarbon degradation was assessed using quantitative PCR (qPCR) for the genes rrs and nifH, nifH clone library sequencing and total petroleum hydrocarbon (TPH) quantification using gas chromatography. TPH showed that the microbial communities of both mangroves were able to degrade the hydrocarbons added; however, whereas the majority of oil added to the mesocosm derived from the polluted mangrove was degraded in the 75 days of the experiment, there was only partially degradation in the mesocosm derived from the pristine mangrove. qPCR showed that the addition of oil led to an increase in rrs gene copy numbers in both mesocosms, having almost no effect on the nifH copy numbers in the pristine mangrove. Sequencing of nifH clones indicated that the changes promoted by the oil in the polluted mangrove were greater than those observed in the pristine mesocosm. The main effect observed in the polluted mesocosm was the selection of a single phylotype which is probably adapted to the presence of petroleum. These results, together with previous reports, give hints about the relationship between N₂ fixation and hydrocarbon degradation in natural ecosystems.