Middle Tidal Zone Research Articles

Occurrence, Source Apportionment, and Risk Assessment of Antibiotics in Mangrove Sediments from the Lianzhou Bay, China.

In recent years, the widespread application of antibiotics has raised global concerns, posing a severe threat to ecological health. In this study, the occurrence, source, and ecological risks of 39 antibiotics belonging to 5 classes in mangrove sediments from Lianzhou Bay, China, were assessed. The total concentrations of the antibiotics (∑39 antibiotics) ranged from 65.45 to 202.24 ng/g dry weight (dw), with an average of 142.73 ± 36.76 ng/g dw. The concentrations of these five classes of antibiotics were as follows: Sulfonamides (SAs) > Tetracyclines (TCs) > Fluoroquinolones (QUs) > Penicillin (PCs) > Macrolides (MLs). The spatial distribution of antibiotics varied as high tidal zone > middle tidal zone > low tidal zone. The total organic carbon (TOC), pH, nitrate (NO3--N), and nitrite (NO2--N) of the sediment significantly influenced the distribution of antibiotics (p < 0.05). A source analysis identified untreated sewage from aquaculture as the primary source of antibiotics in the local mangrove. A risk assessment revealed that ciprofloxacin, norfloxacin, ofloxacin of QUs, and tetracycline of TCs exhibited medium risks to algae in certain sampling sites, while other antibiotics exhibited low or no risks to all organisms. Nevertheless, the total risk of all the detected antibiotics to algae was medium in 95% of the sites. The overall ecological risk level of antibiotics in the middle tidal zone was slightly lower than in the high tidal zone and the lowest in the low tidal zone. In summary, the experimental results provided insights into the fate and transport behaviors of antibiotics in mangrove sediments from Lianzhou Bay.

Tidal variation shaped microplastic enrichment patterns in mangrove blue carbon ecosystem of northern Beibu Gulf, China

Mangroves are considered to be a sink for microplastics (MPs) due to their unique characteristics. Previous studies mainly focused on the spatial distribution of MPs, but few researchers have addressed the influence of tidal variation on this distribution, especially since the MP total number in mangroves was unknown. In this study, surface sediment samples were collected in mangroves from the Beibu Gulf, South China Sea, and the abundance, composition, and number of MPs were investigated. The results showed that MPs were widely present in all mangrove sediment samples, with abundances ranging from 26.67 ± 9.43 to 239.94 ± 37.80 items/kg. The distribution of MPs was heterogeneous among different sampling sites, with the highest levels in the Shankou (SK) area. The MP abundance in the same mangrove forest gradually increased from the low tidal zone to the high tidal zone, with the enrichment factor ranging from 1.50 to 4.00. The MP abundance was significantly correlated with particulate organic carbon (POC) (n = 12, R = 0.664, p &amp;lt; 0.05). Results showed that mangroves had an interception effect on MPs and factors affecting MP distribution in mangrove sediments included not only tides but also human activities, such as aquaculture, agriculture, and residential life. Finally, this paper estimated the MP total number in mangroves at different sampling areas and tidal zones, and the middle tidal zone was considered to be more accurate for MP pollution assessment in mangroves.

The Hummocky Patches and Associated Sediment Dynamics Over an Accretional Intertidal Flat

Tidal flat system is composed of multiple sub-scale geomorphological units. We found a new mesoscale geomorphological unit on sand-mud mixed intertidal zone along China coast, which was defined as hummocky patches. Hummock patches are most developed in middle tidal flat, with horizontal magnitude of 10–20 m and vertical magnitude of ∼15 cm. Hummocky patches significantly influence local sediment transport, thus affect morphological evolution of tidal flats. In order to understand the formation and development mechanisms of hummocky patches, we collected hydrodynamics, topography, sediment properties, and substrate erosion thresholds data through an in-situ field observation covering a spring-neap tidal cycle over an accretional intertidal flat in Jiangsu, China. We found that sediment characteristics including sorting coefficient (σ: measuring the uniformity of sediment particles) and silt/clay/organic matter/water content are essentially different between hummocky patches and nearby seabed, which leads to spatially varied substrate erosion resistance. The measured erosion thresholds for patches are two times higher comparing to surrounding seabed sediment, which provides foundation for the formation of hummocky patches. Under the impact of periodical tidal currents and waves, surrounding seabed experiences considerably more erosion than patch area, which finally develops to hummocky patches. Therefore, hydrodynamic forces drive the formation and development of patches. The erosion resistance of patches decreases vertically from seabed surface to sublayer, causing initial erosion in the lower sublayer, followed by a mass collapse of the seabed surface layer. Hummocky patches are commonly found in middle tidal zone and their sizes decrease to the shore as tidal currents and waves attenuate with shoreward propagation. Hummocky patches have distinct seasonal variations, which only appear in summer and autumn when wind waves are comparatively lower than winter and spring. We infer the reason is that the strong hydrodynamics caused by winter storms cause larger bottom shear stress than the erosion threshold of hummocky patches, leading to destruction of hummocky patches and a smooth tidal flat surface. This study shed new insight on the knowledge of mesoscale geomorphological units and their formation and development in intertidal flats, which provides crucial information for developing more realistic tidal flat sediment transport and morphological models.

Corrosion behavior of marine structural steel in tidal zone based on wire beam electrode technology and partitioned cellular automata model

The initial corrosion evolution of marine structural steel in tidal zone is studied using wire beam electrode (WBE). The electrochemical experiment results show that the WBE in the high and middle tidal zones are in the anodic dissolution state for less time than that in the low tidal and immersion zones. The fitting results of WBE experiment provide the boundary conditions for the partitioned cellular automata (PCA) model, which is adopted to simulate the initial corrosion evolutions of steel in the tidal zone. The proposed independent variable of the electrolyte concentration (ρ), corrosion probability (Pc), passivation probability (Pp), and movement direction probability (Pm) on the corrosion behavior of steel are studied. The calculated results demonstrate that ρ and Pm can well characterize the corrosion evolutions of the steel in ocean tidal zones. This model is effective in predicting the corrosion evolution of marine structural steel in tidal zone. It provides a new method for predicting the corrosion evolution of marine structural steel in tidal zone.

N2O emission dynamics along an intertidal elevation gradient in a subtropical estuary: Importance of N2O consumption

Studying nitrous oxide (N2O) production and consumption processes along an intertidal elevation gradient can improve the understanding of N2O dynamics among coastal wetlands. A natural-abundance isotope technique was applied to characterize the processes responsible for N2O emission in high, middle and low intertidal zones in the Yangtze Estuary. The results showed that N2O emission rates in high tidal zones (0.84 ± 0.35 nmol g−1 h−1) were significantly higher than those in middle (0.21 ± 0.04 nmol g−1 h−1) and low tidal zones (0.26 ± 0.05 nmol g−1 h−1). Gross N2O production and consumption rates were greater in high and low tidal zones than in middle tidal zones, whereas N2O consumption proportions generally increased from high to low tidal zones. N2O consumption was quite pronounced, implying that N2O emission in estuarine wetlands accounts for only a small fraction of the total production. Higher degrees of N2O consumption were the pivotal driver of less N2O emission in low tidal zones. Bacterial denitrification (>84%) was the dominant pathway, although hydroxylamine (NH2OH) oxidation/fungal denitrification contributed substantially to N2O production in high tidal flats. The contribution to N2O production exhibited a decrease in NH2OH oxidation/fungal denitrification and an increase in bacterial denitrification with decreasing elevation. Changes in N2O dynamics along the elevation gradient were affected by carbon and nitrogen substrate availabilities as well as the redox environments. Overall, our findings highlight the importance of N2O consumption in controlling N2O emission in intertidal wetlands, especially with higher inundation frequencies and durations.

Spatial Zonation and Diversity of Bivalves and Gastropods in Mangrove Forests of Casiguran, Aurora

This study generally aimed to determine the spatial zonation and diversity of bivalves and gastropods in mangrove forest of Cozo, Esteves and Tinib in Casiguran, Aurora. Specifically, this aimed to determine the species composition and distribution, and determine the relationship between spatial zonation and diversity of bivalves and gastropods as influenced by ecological factors such as vegetation, soil texture, organic matter, soil salinity, and soil pH. A total of 22 taxa comprising eight species of bivalves and 14 species of gastropods were identified. The high tidal zone of Esteves had high diversity (0.66) of bivalve species compared to other tidal zones and areas. On the other hand, the diversity of gastropods was almost equal in the middle tidal zones of Cozo (0.60), Esteves (0.57), and Tinib (0.42). In terms of bivalve species’ density and abundance, Dendostrea folium was the most dense and abundant in the low tidal zone of Cozo (253,333 ind.ha−1 or 25 ind.m2-1, 97.44%) while Gafrarium tumidum in the low tidal zones of Esteves (46,666 ind.ha−1 or 4 ind.m2-1, 73.68%) and Tinib (126,666 ind.ha−1 or 12 ind.m2-1, 50%). In terms of gastropod species’ density and abundance, Cerithidea cingulata was the most dense and abundant in the low tidal zone (666,666 ind.ha−1 or 66 ind.m2-1, 65.79%) of Cozo and the middle tidal zone (5,280,000 ind.ha−1 or 528 ind.m2-1, 61.40%) of Tinib. It was Terebralia palustris in the low tidal zone (1,263,333 ind.ha−1 or 126 ind.m2-1, 63.06%) of Esteves. All tidal zones within each study area had greater dissimilarities in terms of bivalves but had greater similarities in terms of gastropod species’ compositions. On the other hand, all tidal zones between study areas had greater dissimilarities in terms of bivalve and gastropod species present. Most tidal zones had Gafrarium tumidum as common bivalve species while Neritidae sp. and Cerithidea cingulata were common gastropod species. All these species were found thriving in a wide range of vegetation, soil texture, organic matter, soil salinity and pH.

Assessing benthic ecological status in subtropical islands, China using AMBI and Bentix indices

Assessment of the ecological quality status is important for environmental protection and management. Benthic sensitivity-based indices have been considered as effective indicators of ecosystem health assessment. In this paper, two benthic sensitivity-based indices, AMBI and Bentix, were used to assess the benthic ecological status of soft-bottom intertidal zones in China's subtropical islands according to the data obtained in spring, 2007. Simultaneously, the assessment results were compared with the sediment quality in order to test the applicability of the indices for island eco-environmental quality assessment. The results showed that 246 species of macrobenthos were identified in the sampling sites. In the intertidal zone of Meizhou Island, dominant species were tolerant, which accounted for 58.7% of the total individuals. In the other intertidal transects, the dominant species were sensitive, but the percentages of tolerant species were high in the intertidal zone of estuarine islands. The results also showed that the benthic ecological status of most intertidal zones studied was high or good, except for the middle tidal zone of Meizhou Island where it was moderate. The two biotic indices were generally correlated with the contents of heavy metals and petroleum in the sediments, which indicated that the two indices could be used to detect the environmental changes related to pollution in a wide range. However, it seems that the AMBI assessment results more reasonably approximated those of the concurrent sediment quality survey than the performance of Bentix.

Early Stage Evolution of Nourished Beach under High-energy, Macro-tidal Environment

Beach planform evolution, profile equilibration and sediment grain size change have been studied during the first 4 months from 4th September to 24th December 2011 after the construction of beach nourishment project at Longfengtou Beach, Haitan Bay. Monthly beach profiles, shoreline surveys, sediment sampling and nearshore wave measurements were carried out after implementation of the 1.3km long nourishment project which was completed on 20th August 2011. This study indicates that: (1) rapid beach profile equilibration occurred in the early stage after the construction of the project. A null point was observed, which is equal to the height of mean high tide, basically kept dynamic stable during the process of profile evolution. Shoreface sediment accumulated beneath the height of this point while erosion happened above it, the slope between the beach berm and the landward edge of low tidal zone became more gradual accompanied with seaward transportation of beach sediment. The velocity of beach slope adjustment in earlier period is faster than later. (2) Beach planform adjustment initiated simultaneously with the combination of the process of profile equilibration and longshore sediment transport. Shoreline retreated with an average distance of 11.1m and maximum of 31.02m from 4th September to 24th December, erosion in the south part was more serious than in the north, and 3 erosion hot spots were found along the coast. (3) Sediment redistributed with cross-shore profile equilibration, it showed a pattern across beach profile as medium sand (0.4-0.5mm) in beach berm, smaller (0.3-0.4mm) in high and middle tidal zone, coarse sand(0.6-1mm) in beach slope transitional zone, fine sand(0.1-0.25mm) in low tidal zone. The sediment grain size change of foreshore was rapidly response to the passage of storm surge.

Relative importance of sexual and asexual reproduction for range expansion of Spartina alterniflora in different tidal zones on Chinese coast

In this paper, based on spatially explicit individual-based model and global sensitivity analysis, the relative importance of sexual and asexual reproduction for range expansion of Spartina alterniflora in different tidal zones during different invasion stages has been revealed. The results showed that: 1) sexual reproduction is thought to accelerate the range expansion in middle and high tidal zones; 2) seed dispersal and adult survival rate are the two most important for range expansion of S. alterniflora during most invasion stages in all tidal zones. However, in high tidal zone, the importance of seed dispersal distance is much less than in low and middle tidal zones, and that of sexual reproduction is also great, which cannot be ignored. In middle tidal zone, the importance of adult survival rate is less important than in high and low tidal zones, and is very close to asexual reproduction. Moreover, there are significant fluctuations among the importance of different parameters except seed dispersal distance, indicating strong interactions. 3) the importance of adult survival rate and asexual reproduction is much greater than seed dispersal distance during early invasion. Especially, their importance is much higher during early and middle invasion stages in high tidal zone. During early invasion stages, the interactions among different parameters are very strong. To enhance the invasion control efficiency, it is necessary to take different control measures according to different tidal zones and invasion stages.

Meiofauna distribution in intertidal sandy beaches along China shoreline (18°–40°N)

In this study, the distribution pattern of meiofauna from nine sandy beaches at six latitudinal gradients along Chinese coast between 18 and 40°N was studied on their meiofauna abundance to examine the effect of latitudinal gradients. In general, meiofauna abundance was lower in four subtropical beaches in Xiamen (24°N) and Zhoushan (29°N) than that in other beaches. Meiofauna abundance differed little between tropical and temperate beaches. The taxonomic structure of meiofauna showed a dominance of nematode in colder area. The relative composition of turbellarians and polychaetes increased in warmer area. In addition to latitudinal gradient, salinity, oxygenation, sediment grain size affect also the meiofauna latitudinal distribution. As for horizontal distribution, the highest meiofauna abundance was found in low tidal zone at tropical beaches, and in middle tidal zone at temperate beaches. The horizontal distribution of meiofauna was controlled by both physical and biotic factors including feeding and anthropogenic activities. Although meiofauna abundance exhibited a horizontal difference, the composition of meiofaunal main taxa was unanimous horizontally at all beaches at the same sampling latitude.

In Situ Corrosion Monitoring of Mild Steel in a Simulated Tidal Zone without Marine Fouling Attachment by Electrochemical Impedance Spectroscopy

The corrosion behaviors of the isolated short and vertical long scale Q235B steel in a simulated tidal zone were studied by electrochemical impedance spectroscopy (EIS) monitoring and corrosion weight loss calculation in an experimental indoor simulating trough. The results show that the corrosion rate of the isolated short scale Q235B steel in the tidal zone acquired by the EIS agrees with the corrosion weight loss result. The corrosion rates of the short scale steel are in the order of middle tidal zone > the central zone between the middle tidal zone and low tidal zone > high tidal zone > low tidal zone. The fastest corrosion rate in the middle tidal zone is attributed to the longest wet time in a tidal cycle. According to the comparison of corrosion weight loss between the vertical long scale and isolated short scale specimens, the corrosion rate of vertical long scale specimens of Q235B steel is lower than that of the isolated short scale specimens in the tidal zone, but the result is contrary in the immersion zone.

Influence of coralline algae on biodiversity of macrobenthic community in intertidal zone of Nanji Islands

With an aim of describing the influence of coralline algae on other macroalgae and benthic invertebrates in the intertidal zone of the Nanji Islands, an investigation of such organism assemblages was conducted in the Nanji Archipelago Marine Nature Reserve between May 2012 and February 2013. Shannon-Wiener index and Pielou's evenness indices were calculated for macroalgae (including coralline algae), non-Corallinaceae macroalgae (excluding coralline algae) and benthic invertebrates. In addition, the functional diversity of the benthic community was estimated using Rao's Q. Our results are as follows: (1) A total of 52 species of macroalgae belonging to 3 phyla, 3 classes, 16 orders, 21 families and 41 genera were found; 5 species among them belonged to coralline algae; (2) The dominance of coralline algae has reached a high level in the intertidal zone of the Nanji Islands except in the high tidal zone where relatively few macroalgae exist. The biomass of coralline alga accounted for 68.9% of the total algae biomass. Shannon-Wiener indices of macroalgae diversity varied from 1.638–4.044, and non-Corallinaceae macroalgae varied from 1.495– 3.809, while benthic invertebrates’ varied from 5.2890–6.917. Pielou’s evenness of macroalgae communities 第 5 期 汤雁滨等: 珊瑚藻类对南麂列岛潮间带底栖生物群落多样性的影响 641 varied from 0.819–0.971, and non-Corallinaceae macroalgae varied from 0.930–0.973; benthic invertebrates ranged from 0.967 to 0.988; (3) Regression analyses between dominance of coralline algae and Shannon-Wiener and Pielou's evenness indices of macroalgae communities suggested that coralline algae may be reducing the species diversity of macroalgae. The result of correlation analysis between dominance of coralline algae and Shannon-Wiener index, Pielou's evenness of benthic invertebrates showed no significant correlation. (4) The dominance of coralline algae and Rao's Q of benthic invertebrates in low tidal zone were both higher than those in middle tidal zone, but the correlation analysis showed no significant correlation between them. Based on our results, we concluded that: well-adapted coralline algae species may have reduced the species diversity of other macroalgae in these systems via interspecific competition; meanwhile, the benthic invertebrates, perhaps because of their higher dispersal abilities and more diverse life histories relative to macroalgae, were not affected in terms of species or functional diversity by coralline algae.

Habitat heterogeneity influences restoration efficacy: Implications of a habitat-specific management regime for an invaded marsh

Invasive species have to be managed to prevent adverse consequences. Spartina alterniflora has invaded many marshes where salinity and inundation are often key factors affecting vegetation. The former was surface clipped twice and native Phragmites australis was planted in invaded zones to examine the effects of habitat properties on the efficacy of invader control and native restoration. The results showed that two clipping treatments almost eliminated S. alterniflora in the zones with long inundation periods of 80 h/15 d but stimulated compensatory growth of S. alterniflora in the zones with short inundation periods. Transplanted P. australis performed better over time in zones with low salinity (<10.5 psu) but performed poorly in high-salinity zones, indicating that the efficacy of invader management and native restoration activities changes significantly along habitat gradients. With a progression from the dyke to the seaward side of the studied marsh, there was a long then short then long inundation period whereas salinity increased consistently. The study indicates that the high-frequency removal of the above-ground parts of S. alterniflora should be used only in the middle tidal zones and that native vegetation should be planted in zones above the mean high water level while the others zones in the saltmarsh should be restored to mud flats. Usually, invasive plants can flourish in highly heterogeneous habitats, which can influence management efficacy by influencing the re-growth of treated invaders and the performance of restored native species. Therefore, habitat-specific management regimes for invasive species can be expected to be more efficient because of their dependence on specific habitats.

Tempo-spatial variation of macrobenthic communities on a tidal flat of Wenzhou Bay, China

The tempo-spatial variation of macrobenthic communities was studied on a tidal flat of Wenzhou Bay, China from November 2003 to August 2004. We collected 38 macrobenthic species belonging to 23 families, 8 classes and 7 phyla, most of which were arthropods and molluscs. Species richness, density and biodiversity significantly differed between tidal zones, seasons and the interaction between them. The tempo-spatial variations of the macrobenthic communities were also shown in cluster and ordination analysis. The middle tidal zone during autumn tends to have the highest values of the community descriptors. Thus, tidal zone and seasons have significant roles in structuring these communities.

Corrosion of thermally sprayed zinc and aluminium coatings in simulated splash and tidal zone conditions

The corrosion rate in the splash and tidal zones of marine steel structures is very severe. Thermally sprayed coatings of zinc or aluminium and their alloys are among the most important technologies to eliminate this problem. This experimental study on the protective properties of thermally sprayed zinc and aluminium coatings on steel piles was conducted in an apparatus for simulating the marine corrosion environment. Particular attention was given to the anticorrosion performance of thermally sprayed zinc and aluminium coatings in the splash and tidal zones in combination with the cathodic protection of bare steel in the immersed zone. The experimental results showed that top to bottom thermal spraying of zinc or aluminium coatings on steel piles before their installation was effective, but that under cathodic protection conditions, protection of thermally sprayed zinc or aluminium coatings is effective up to the average middle tidal zone.