Dongtan Wetland Research Articles

Effect of Carbon source on dissimilatory nitrate reduction to ammonium in Costal Wetland sediments

15N tracing technique was applied to investigate the effects of various organic carbon (OC) sources on dissimilatory nitrate (NO3-)reduction to ammonium (NH4+) (DNRA) rates in the coastal wetland sediments. Soils collected from the Chongming Dongtan wetland were incubated at 25oC in the dark for 24 h following the additions of OC sources (glucose, acetate, malate, citrate and oxalate (500 μg C g-1 dry soil)) and 15N-labeled NH415NO3 (initial 15N atom% of NO3--N is 20%). The results showed that soil DNRA rates varied from 0.018-0.497 mg N kg-1 dry soil d-1during the whole incubation, and the rates differed significantly among treatments following the order: oxalate> citrate> glucose> acetate> malate> no exogenous C addition over the first 12-h incubation. This was possibly caused by the different decomposition rates of various OC sources, which further influenced the available energy provided for DNRA microorganisms. Soils with no addition of exogenous C showed lower soil DNRA rates, presumably because of the low C/NO3- ratio as well as energy availability. The relative lower soil DNRA rates over the 24-h incubation indicated that DNRA is a fast process. Our results suggest that DNRA could be controlled by OC sources, especially organic acids, demonstrating that the widespread use of glucose in soil laboratory studies might lead to misleading knowledge on understanding the effects of OC on soil DNRA process.

Simulating the Range Expansion ofSpartina alterniflorain Ecological Engineering through Constrained Cellular Automata Model and GIS

Environmental factors play an important role in the range expansion ofSpartina alterniflorain estuarine salt marshes. CA models focusing on neighbor effect often failed to account for the influence of environmental factors. This paper proposed a CCA model that enhanced CA model by integrating constrain factors of tidal elevation, vegetation density, vegetation classification, and tidal channels in Chongming Dongtan wetland, China. Meanwhile, a positive feedback loop between vegetation and sedimentation was also considered in CCA model through altering the tidal accretion rate in different vegetation communities. After being validated and calibrated, the CCA model is more accurate than the CA model only taking account of neighbor effect. By overlaying remote sensing classification and the simulation results, the average accuracy increases to 80.75% comparing with the previous CA model. Through the scenarios simulation, the future ofSpartina alternifloraexpansion was analyzed. CCA model provides a new technical idea and method for salt marsh species expansion and control strategies research.

Indirect effects of non‐native Spartina alterniflora and its fungal pathogen (Fusarium palustre) on native saltmarsh plants in China

Summary Pathogens can affect their hosts and change community composition and structure. Pathogens may be key determinants of biological invasions. However, few empirical studies exist examining how non‐native plants drive their invasions through indirect effects involved with pathogens. Here, indirect effects refer to how one species alters the effect that another species has on a third. Fusarium palustre was associated with the dieback of Spartina alterniflora in its native North American saltmarshes. Native plant Phragmites australis was also found to die back in the Dongtan wetland of the Chinese Yangtze River estuary invaded by non‐native Spartina alterniflora. This phenomenon suggests that Spartina might not escape from its pathogen when being introduced from its native North America and has indirectly caused the dieback of Phragmites in China. To investigate the indirect effect of Spartina involving Fusarium, we sampled plants and soils in dieback patches to isolate the pathogen. Next, we used an artificial inoculation study to determine the virulence of Fusarium to both Phragmites and Spartina. Finally, the spatial distribution of Fusarium was studied through examining its incidence in saltmarshes along the east coast of China. The endophytic fungus F. palustre was found to be closely associated with Phragmites dieback in the Dongtan wetland and it is likely that it was transported by non‐native Spartina from its native North American saltmarshes to the Chinese saltmarshes. The spillover of F. palustre from non‐native Spartina to native Phragmites might subsequently facilitate Spartina invasion. Synthesis. Invasive plants do not only directly compete with native plants, but also indirectly cause pathogen infection on the latter, by acting as vectors and reservoirs for pathogens shared with native plants. Our findings highlight the significance of indirect effects involving pathogens in biological invasions. It is necessary to consider these pathogen‐mediated indirect effects of non‐native plant species in multi‐host‐pathogen systems for management and restoration purposes.

Effects of Winter Harvesting and Salinity on the Structure of Regrowing Reed Stands

Harvest and salinity are two important factors of the growth of common reed (Phragmites australis). We here examined the different impact of winter harvest treatment on the Phragmites australis between high and low salinity (mean soil electrical conductivity is 7.87 ms/cm and 0.91 ms/cm) areas in Dongtan wetland of Yangtze River estuary, China. We measured phenology, Shoot density, stem diameter and height, biomass (total, aboveground and belowground biomass) and spike weight. At high salinity areas, harvest significantly inhibited the individual growth of stem height yet enhanced ramet density, and consequently led to an insignificant change in aboveground biomass. The belowground parts of reed were significantly inhibited. The root shoot ratio and the proportion of asexual reproduction decreased significantly. At low salinity areas, however, winter harvest generally has no significant influence on reed growth. Our results suggest that the winter harvest management may cause a decline of reed populations in the long term under condition of high salinity; however winter harvesting can be suggested as a proper management for sustainable utilization of reed communities at low salinity areas.

A process-based grid model for the simulation of range expansion of Spartina alterniflora on the coastal saltmarshes in the Yangtze Estuary

Spartina alterniflora has been widely introduced to many coastal and estuarine regions of the world as a species for ecological engineering and this species has been spreading rapidly and widely along the Chinese coastline for the past 30 years. Based on four years of field measurements at the Chongming Dongtan wetland in the Yangtze Estuary, a process-based grid model of spatio-temporal range expansion for S. alterniflora was developed. The model incorporated the seasonal patterns of seed bank dynamics, seedling establishment, clonal propagation and vegetative growth, while also considering the effects of hydrodynamic conditions on the range expansion of S. alterniflora in the coastal saltmarshes. Modelling of a survey strip over a single year on the Dongtan wetland showed that the simulated spread pattern agreed with the actual pattern recorded during the growing season (March–September) with an accuracy of 90–95%, based on the estimations of seed bank dynamics and seedling establishment. On a wider spatio-temporal scale, an 8 year simulation showed that the patterns of range expansion of S. alterniflora are amenable to spatially-explicit modelling that takes spatio-temporal processes into account, mainly due to the aggregation effects of clonal integration in patches. Hydrodynamic conditions and niche availability were the most important factors controlling the expansion rate of S. alterniflora on the seaward expansion front. However, the actual expansion rate of S. alterniflora has slowed down in recent years due to the reduction in the sediment load of the Yangtze River following the completion of the Three Gorges Dam Project. There remain several uncertain issues relating to the model setup and its predictive capacity in terms of environmental variability and the stochasticity that is inherent in the modelling of the reproduction, dispersal and survival of S. alterniflora. Furthermore, an update of the model is needed linked to the sediment dynamics seasonality of hydrodynamic conditions in the Yangtze Estuary. In conclusion, this modelling approach provided valuable insights into the life-cycle mechanisms and range expansion processes of S. alterniflora under the current conditions. We suggest the potential application of this model in comparing various control strategies.

Native Phragmites dieback reduced its dominance in the salt marshes invaded by exotic Spartina in the Yangtze River estuary, China

Vegetation dieback occurs frequently in various ecosystems and causes tremendous consequences. We here examined the impact of native reed (Phragmites australis) dieback on the salt marsh communities invaded by exotic Spartina alterniflora through monitoring dynamics of component species of Phragmites-Spartina mixture, and comparing their performances in monoculture, dieback mixture and healthy mixture in Dongtan wetland of Yangtze River estuary, China. Phragmites showed poorer performance in dieback mixture compared with other communities. Survival rate (30±4.08%), ramet density (37±9.15 plants/m2), plant height (130.71±20.39cm) and aboveground biomass (222.64±5.66g/m2) of Phragmites in dieback mixture were all significantly lower than those in healthy mixture (68±4.79%; 99±17.24 plants/m2; 185.06±17.75cm; 837.07±205.13g/m2, respectively) (for all P<0.05). By contrast, Spartina resprouted well with survival rate of 100% over the course of the experiment. Both ramet density and plant height of Spartina tended to be higher in dieback mixture than in healthy mixture, and its aboveground biomass (1042.19±156.46g/m2) was significantly higher than that in healthy mixture (618.76±129.50g/m2) (P<0.05). Our results suggest that reduced dominance of native Phragmites due to its own dieback weakens its competition with exotic Spartina, which favors Spartina invasion in the salt marsh community.

Evolution analysis of Chongming Dongtan wetland in recent 60 years based on digital nautical chart and remote sensing

The spatial variation of Chongming Dongtan wetland was monitored using 10 remote sensing images including Landsat MSS,TM and ETM+ data.Nine nautical charts were employed to analyze the evolution of underwater terrain from 1951 to 2006.With the above/under water topographic changes as an entirety,the authors made quantitative and qualitative analysis of geomorphic evolution in the past 60 years at Chongming Dongtan wetland using waterline method and depth contour overlaying.Some conclusions have been reached: ① The dynamics of Chongming Dongtan tend to be stable,characterized by erosion in the south part,deposition in the north,rapid propagation in the middle and alternate erosion and deposition in some coasts under the stabilities of the current Yangtze estuary;② Human activities made important effect on the wetland.Especially,damn in the Baigang tidal channel accelerated deposition in the wetland.Then the 0 m isobath expanded to the east at a stable rate.Although the wetland area was increasing with the human reclamation year by year,the inter-tidal structure of wetland was deviated from the nature state.The proportion of high tidal flat was decreasing and it showed discontinuous spatial distribution at Chongming Dongtan.Because the damn was directly exposed to the outside marine environment,it would reduce the capability of disaster weather prevention.

Interspecific interactions between Phragmites australis and Spartina alterniflora along a tidal gradient in the Dongtan wetland, Eastern China.

The invasive species Spartina alterniora Loisel was introduced to the eastern coast of China in the 1970s and 1980s for the purposes of land reclamation and the prevention of soil erosion. The resulting interspecific competition had an important influence on the distribution of native vegetation, which makes studying the patterns and mechanisms of the interactions between Spartina alterniora Loisel and the native species Phragmites australis (Cav.) Trin ex Steud in this region very important. There have been some researches on the interspecific interactions between P. australis and S. alterniora in the Dongtan wetland of Chongming, east China, most of which has focused on the comparison of their physiological characteristics. In this paper, we conducted a neighbor removal experiment along a tidal gradient to evaluate the relative competitive abilities of the two species by calculating their relative neighbor effect (RNE) index. We also looked at the influence of environmental stress and disturbance on the competitive abilities of the two species by comparing interaction strength (I) among different tidal zones both for P. australis and S. alterniora. Finally, we measured physiological characteristics of the two species to assess the physiological mechanisms behind their different competitive abilities. Both negative and positive interactions were found between P. australis and S. alterniora along the environmental gradient. When the direction of the competitive intensity index for P. australis and S. alterniora was consistent, the competitive or facilitative effect of S. alterniora on P. australis was stronger than that of P. australis on S. alterniora. The interspecific interactions of P. australis and S. alterniora varied with environmental conditions, as well as with the method used, to measure interspecific interactions.

Effects of Spartina alterniflora invasion on the communities of methanogens and sulfate-reducing bacteria in estuarine marsh sediments.

The effect of plant invasion on the microorganisms of soil sediments is very important for estuary ecology. The community structures of methanogens and sulfate-reducing bacteria (SRB) as a function of Spartina alterniflora invasion in Phragmites australis-vegetated sediments of the Dongtan wetland in the Yangtze River estuary, China, were investigated using 454 pyrosequencing and quantitative real-time PCR (qPCR) of the methyl coenzyme M reductase A (mcrA) and dissimilatory sulfite-reductase (dsrB) genes. Sediment samples were collected from two replicate locations, and each location included three sampling stands each covered by monocultures of P. australis, S. alterniflora and both plants (transition stands), respectively. qPCR analysis revealed higher copy numbers of mcrA genes in sediments from S. alterniflora stands than P. australis stands (5- and 7.5-fold more in the spring and summer, respectively), which is consistent with the higher methane flux rates measured in the S. alterniflora stands (up to 8.01 ± 5.61 mg m−2 h−1). Similar trends were observed for SRB, and they were up to two orders of magnitude higher than the methanogens. Diversity indices indicated a lower diversity of methanogens in the S. alterniflora stands than the P. australis stands. In contrast, insignificant variations were observed in the diversity of SRB with the invasion. Although Methanomicrobiales and Methanococcales, the hydrogenotrophic methanogens, dominated in the salt marsh, Methanomicrobiales displayed a slight increase with the invasion and growth of S. alterniflora, whereas the later responded differently. Methanosarcina, the metabolically diverse methanogens, did not vary with the invasion of, but Methanosaeta, the exclusive acetate utilizers, appeared to increase with S. alterniflora invasion. In SRB, sequences closely related to the families Desulfobacteraceae and Desulfobulbaceae dominated in the salt marsh, although they displayed minimal changes with the S. alterniflora invasion. Approximately 11.3 ± 5.1% of the dsrB gene sequences formed a novel cluster that was reduced upon the invasion. The results showed that in the sediments of tidal salt marsh where S. alterniflora displaced P. australis, the abundances of methanogens and SRB increased, but the community composition of methanogens appeared to be influenced more than did the SRB.

Soil microbiological variability under different successional stages of the Chongming Dongtan wetland and its effect on soil organic carbon storage

Estuarine wetlands undergoing rapid succession have high organic carbon accumulation rates due to their high primary productivity. A previous study indicated that organic carbon storage in soil differed among successional stages of the Chongming Dongtan tidal wetland due to differences in soil microbial respiration (SMR) and plant biomass. To investigate the mechanisms underlying the differences in SMR, variability in microbial and physicochemical characteristics of soil from different successional stages was studied. Bacterial community composition varied among the successional stages. Some dominant and site-specific bacteria inhabiting the tidal flat may have influenced SMR and soil carbon storage capability. Uncultured members of the Cytophagales and Pseudomonas genera, which include efficient degraders of complex organic compounds, were found primarily in the high tidal flat where the highest SMR and relatively low soil organic carbon storage were observed. Soil environment factors such as particle size, salinity, and total nitrogen (TN) may have affected microbial community composition, in particular the dominant bacterial species, and hence, SMR. The relatively small particle size, low salinity, and high TN in the high tidal flat provided suitable conditions for chemoorganotrophic bacteria such as Cytophagales and Pseudomonas species, which are specialized in the degradation of organic matter.

Dynamics of arsenic in salt marsh sediments from Dongtan wetland of the Yangtze River estuary, China

The mobility and transformation of arsenic (As) in salt marsh sediments were investigated in Dongtan wetland of the Yangtze River estuary, China. As in surface water, pore water and the rhizosphere sediments were quantified. The microcosm incubation experiments were conducted during the flooding of the sediments to examine As dynamics that occurred during changing redox conditions. The concentrations of dissolved As in pore water (0.04–0.95 μmol/L) were significantly greater than that in surface water (0.03–0.06 μmol/L). Under anoxic conditions, the reactive As could be initially mobilized by the reductive dissolution of Fe(III) (hydr)oxides. Subsequently, most of the dissolved As was likely to be associated with secondary iron (hydr)oxide phases and remained in solid phases. The seasonal variability of acid volatile sulfide concentrations suggest the anoxic conditions are enhanced during summer by Spartina alterniflora compared to Phragmites australis and Scirpus mariqueter, causing a notable increase in As mobility. Generally, there was a typical variation in redox conditions with season in salt marsh sediments of Dongtan wetland, in which the dynamics of As mobility and transformation possibly were controlled by iron, and all of this could be significantly influenced by the rapid spread of S. alterniflora.

Variability of soil organic carbon reservation capability between coastal salt marsh and riverside freshwater wetland in Chongming Dongtan and its microbial mechanism

Two representative zones in Chongming Dongtan which faced the Yangtze River and East China Sea respectively were selected to study the variability of soil organic carbon (SOC) reservation capability between coastal wetland and riverside wetland in the Chongming Dongtan wetland as well as its mechanism by analyzing soil characteristics and plant biomass. The results showed the SOC content of riverside wetland was only 48.61% (P = 0.000 < 0.05) that of coastal wetland. As the organic matter inputs from plant litter of the coastal wetland and riverside wetland were approximately the same, the higher soil microbial respiration (SMR) of riverside wetland led to its lower SOC reservation capability. In the riverside wetland, the high soil microbial biomass, higher proportion of β-Proteobacteria, which have strong carbon metabolism activity and the existence of some specific aerobic heterotrophic bacteria such as Bacilli and uncultured Lactococcus, were the important reasons for the higher SMR compared to the coastal wetland. There were additional differences in soil physical and chemical characteristics between the coastal wetland and riverside wetlands. Path analysis of predominant bacteria and microbial biomass showed that soil salinity influenced β-Proteobacteria and microbial biomass most negatively among these physical and chemical factors. Therefore the low salinity of the riverside area was suitable for the growth of microorganisms, especially β-Proteobacteria and some specific bacteria, which led to the high SMR and low SOC reservation capability when compared to the coastal area.

Effect of Scirpus mariqueter on nitrous oxide emissions from a subtropical monsoon estuarine wetland

The effects of the wetland plant Scirpus mariqueter on nitrous oxide (N2O) emissions in Yangtze estuary, China, were investigated using an in situ static chamber technique. Field measurements spanned the entire growing season (May to October) and encompassed a wide range of weather conditions typical of the subtropical monsoon climate of this region. Simultaneous measurement of carbon dioxide (CO2) and anatomical measurements were conducted to experimentally determine the gas transport mechanisms of S. mariqueter on N2O flux. S. mariqueter had a significant effect on N2O flux. Based on the comparison of light‐dark and clipped‐unclipped gas flux, N2O flux was negatively correlated with NEE (p &lt; 0.0001) and NPP (p &lt; 0.001) under light conditions when S. mariqueter was present but positively with temperatures in the dark condition or when S. mariqueter was clipped. Besides the plant uptake corresponding to the N2O negative flux in light chamber, it is reasonable to assume that because of the limitation of nitrate in sediment, coupled nitrification‐denitrification is the main process of N2O producing. O2 transported into the S. mariqueter rhizosphere during photosynthesis stimulated denitrifier also would consume the N2O and would be induced to the N2O diffusing from atmosphere into sediment. Although photosynthetic activity of S. mariqueter attenuated N2O flux significantly over the course of the entire study period, creating a net sink for atmospheric N2O under light condition, the marsh of Chongming Island Dongtan wetland was a net source of atmospheric N2O during the active S. mariqueter growth phase (averaged flux was 98.3 μg N2O m−2 h−1).

Effect of Spartina alterniflora invasion and its controlling technologies on soil microbial respiration of a tidal wetland in Chongming Dongtan, China

The exotic species Spartina alterniflora has recently rapidly expanded in the Chongming Dongtan Nature Reserve. As a result, many technologies to control this organism have been developed. To clarify the effects of S. alterniflora invasion as well as the controlling technologies on the organic carbon reservation capability of the Chongming Dongtan Wetland, variations in soil microbial respiration (SMR) after S. alterniflora invasion and the implementation of different controlling technologies in Chongming Dongtan were analyzed, and their influencing mechanisms were studied by analyzing the soil and plant litter characteristics. The results showed that the SMR of S. alterniflora rhizosphere was 1.87 times (P=0.000<0.05) higher than that of the Phragmites communis rhizosphere, but that their annual organic matter input was almost identical. These findings implied that the organic carbon reservation capability of the S. alterniflora wetland was lower than that of the native P. communis wetland. S. alterniflora stalks more easily decayed into soil than P. communis stalks due to their lower lignin content and C/N ratio. This resulted in increased soil organic carbon (SOC) and TN content in soil of the S. alterniflora rhizosphere, which likely promoted microbial activities, thereby accelerating SMR and organic carbon output. In addition, three artificial measures for controlling the spread of S. alterniflora were found to generally improve the soil microbial activities, thereby increasing organic carbon output when compared to the control. However, when compared to other measures, the effects of mowing plus tillage and waterlogging (MTW) on soil microbial activities and SMR were relatively low owing to restriction by waterlogging. Overall, MTW was a relatively low carbon method for control of the spread of S. alterniflora.

A field study on groundwater dynamics in a salt marsh – Chongming Dongtan wetland

Subsurface hydrology plays an important role in governing the behaviour of salt marshes, in particular, nutrient exchange, plant zonation and carbon cycling. The objective of this paper is to examine the hydrological characteristics of a salt marsh based on a field investigation conducted at a cross-creek section in the Chongming Dongtan wetland (Shanghai, China). Field measurements showed complex groundwater table fluctuations, controlled by multiple factors. The groundwater table near the creek responded quickly to the creek water level fluctuation, in contrast with the weak water table response in the marsh interior. The average elevation of the groundwater table near the creek was lower than that in the interior, suggesting that the optimal soil aeration condition occurred near the creek. The variations of pore water salinity along the cross-creek transect also appeared to be complex even though a low salinity zone remained present near the creek levee over the investigation period. Relatively strong pore water circulation near the creek prevented local solute accumulation. These results are essentially consistent with the hypothesis that the area near the creek is better suited for plant growth. In the marsh interior, weakened drainage and flushing effects may leave the soil largely saturated for a long period and suppress carbon exchange between the marsh soil and ambient environments (coastal water and atmosphere).

崇明东滩湿地不同潮汐带入侵植物互花米草根际细菌的多样性

The invasive species of Spartina alterniflora,as an 'ecosystem engineer' was introduced into many places in China,now,had rapidly and widely invaded into the Chongming Dongtan wetland since 1990s.Microorganisms are important components of wetland ecosystems,performing a range of vital ecosystem functions.But,we have not known how microorganisms have an influence on the invasion of Spartina alterniflora in Chongming Dongtan.In order to study the bacterial diversity and abundance in rhizosphere of invasive plants Spartina Alterniflora growing in different tidelands of Chongming Dongtan Wetlands for different seasons,we selected 10 samples collection points,which distributed on the tidal zones with plant and the blare flat zone without plant in Chongming Dongtan wetlands.The tidal zones contain low-tide zone,mid-tide zone and high-tide zone.Total DNA was extracted from soil samples,and 16S rRNA gene-based PCR was performed.A comparative study of diversity of microorganisms in rhizosphere soils of invasive exotic species(Spartina alterniflora) and two native species(Phragmites australis and Scirpus mariqueter) was conducted by denaturing gradient gel electrophoresis(DGGE) of these PCR products,representing microorganisms in rhizosphere soils..Results showed that diversity and abundance of bacterial community were different in the rhizosphere of Spartina alterniflora,Phragmites australis and Scirpus mariqueter in the low-tide zone,mid-tide zone and high-tide zone in Chongming Dongtan wetlands..We found that,in summer,rhizosphere bacterial communities in mid-tide zone had higher abundance than those in low-tide zone and high-tide zone(P = 0.021 0.05).A higher diversity of bacteria in the rhizosphere soils of these plants was observed in summer than in other seasons.The average diversity index of bacterial community was calculated and was found to be the highest in mid-tide zone(H = 4.20).The abundance and diversity of bacterial community in invasive species Spartina alterniflora rhizosphere were significantly higher than in the local plants P.australis and S.mariqueter in mid-tide zone,and the abundance and diversity of S.mariqueter rhizosphere bacteria in summer slightly higher than in other seasons.Also the abundance and diversity of S.alterniflora rhizosphere bacteria were significantly higher in tidal soils than those in the mudflat soils.Overall,these results indicated the tides had a strong influence on the abundance and diversity of the plants rhizosphere bacteria.And the exotic species Spartina alterniflora had a favorable influence on soil microbial community in wetland.We reasoned that high diversity and abundance bacteria in rhizosphere maybe were an important for the invasion of Spartina alterniflora.A higher diversity of bacteria in the rhizosphere soils of these plants observed in summer revealed that the summer is more beneficial for bacteria living in vicinity of plant roots.The fact that the flourishing Spartina rhizosphere was associated with large bacteria assemblage suggested that the high diversity and abundance of microorganisms might be identified as one of the important factors of Spartina invasion mechanisms.

Comparison of Nekton Use for Cordgrass Spartina alterniflora and Bulrush Scirpus mariqueter Marshes in the Yangtze River Estuary, China

To test whether invasive Spartina alterniflora marshes were functionally equivalent to native Scirpus mariqueter marshes, the present study used bottomless lift nets (20 m2) during 12 high-tide events from August to October 2008 to compare nekton densities and biomass between the two marsh types in the Dongtan wetland. A total of eight species of fish, two species of shrimp, and three species of crab were collected. So-iny mullet Chelon haematocheilus, keeled mullet Liza carinata, Asian freshwater goby Acanthogobius ommaturus, and ridge-tail prawn Exopalaemon carinicauda dominated samples from the two marsh types and accounted for over 90% of the total catch. There were significantly greater densities and biomass (p 0.05) between the two marsh types were observed for densities and biomass of any species or total nekton in September and October 2008. Non-metric multidimensional scaling ordination did not show clear separation of samples between the two marsh types (r = 0.071, p = 0.159). Furthermore, there were no habitat-specific differences (p > 0.05) in the size distributions of the three numerically dominant species (C. haematocheilus, L. carinata, and A. ommaturus). We concluded that S. alterniflora marshes were utilized by nekton in a fashion similar to their utilization of native S. mariqueter marshes under similar physical conditions.

Altererythrobacter dongtanensis sp. nov., isolated from a tidal flat

A Gram-negative, rod-shaped and non-spore-forming bacterial strain, JM27(T), was isolated from a tidal flat of Dongtan Wetland, Chongming Island, China. The strain formed smooth yellow colonies on R2A plates. Growth occurred at 10-37 °C (optimum, 30-37 °C), at pH 6.0-10.0 (optimum, pH 7.0-9.0) and in the presence of 0-1 % NaCl (optimum, 0 %). Catalase test was positive and oxidase test was negative. Ubiquinone 10 (Q10) was the major respiratory quinone. C₁₈:₀ω7c and C₁₇:₁ω6c were the most abundant fatty acids. Diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol were the major polar lipids. The DNA G+C content of strain JM27(T) was 66.4 mol%. The 16S rRNA gene sequence of the isolate showed highest similarity to that of Altererythrobacter marinus H32(T) (96.4 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain belonged to the genus Altererythrobacter of the family Erythrobacteraceae of the class Alphaproteobacteria. On the basis of phylogenetic analysis, whole-cell fatty acids, polar lipid compositions, and biochemical and physiological characteristics, strain JM27(T) is proposed to represent a novel species of the genus Altererythrobacter for which the name Altererythrobacter dongtanensis sp. nov. is proposed. The type strain is JM27(T) ( = KCTC 22672(T) = CCTCC AB 209199(T)).

Spatial and temporal distributions of nitrogen, phosphorus and heavy metals in the intertidal sediment of the Chang jiang River Estuary in China

Spatial and temporal distributions of nutrients (N and P) and heavy metals (Cu, Zn, Pb and Cd) in the intertidal sediments at Dongtan wetland of the Changjiang River (Yangtze River) Estuary were examined by laying one transect running seaward to landward during January, April, June, August and October of 2005. Total nitrogen (TN) and heavy metal concentrations in the intertidal sediment showed an increasing trend from open bare flat to the high marsh, with the maximum concentrations in the high marsh and the minimum values in open bare flat. In contrast, sediment total phosphorus (TP) concentrations changed little among sampling sites. One-way ANOVA found that there were significantly temporal variations of nutrients and heavy metals concentrations in the intertidal sediment (P < 0.05). The concentrations of heavy metals generally showed an increasing trend from January to October. As compared with other large estuaries, heavy metal contamination in the intertidal sediment of the Changjiang River Estuary was relatively low.

Effects of crab burrows on pore water flows in salt marshes

Macro-pores such as crab burrows are found commonly distributed in salt marsh sediments. Their disturbance on the soil structure is likely to influence both pore water flows and solute transport in salt marshes; however, the effects of crab burrows are not well understood. Here, a three-dimensional model simulated tidally driven pore water flows subject to the influence of crab burrows in a marsh system. The model, based on Richards’ equation, considered variably saturated flow in the marsh with a two-layer soil configuration, as observed at the Chongming Dongtan wetland (Shanghai, China). The simulation results showed that crab burrows distributed in the upper low-permeability soil layer, acting as preferential flow paths, affected pore water flows in the marsh particularly when the contrast of hydraulic conductivity between the lower high-permeability soil layer and the overlying low-permeability soils was high. The burrows were found to increase the volume of tidally driven water exchange between the marsh soil and the tidal creek. The simulations also showed improvement of soil aeration conditions in the presence of crab burrows. These effects may lead to increased productivity of the marsh ecosystem and enhancement of its material exchange with coastal waters.