Tidal Gradient Research Articles

Fate of soil organic carbon in estuarine mangroves: Evidences from stable isotopes and lignin biomarkers

Coastal wetlands are increasingly recognized for their role in climate change mitigation, particularly through the sequestration of soil organic carbon (SOC). Despite widespread acknowledgement of their importance, the variation in organic carbon (OC) sources among different estuarine mangrove wetlands, and how these sources interact with environmental factors, is not fully elucidated. This research focuses on the role of estuarine mangrove wetlands in climate change mitigation through SOC sequestration. It explores the distribution, sources, and decomposition of SOC in a wetland with four mangrove communities along a tidal gradient. These include a tidal flat, a Sonneratia apetala forest, a mixed S. apetala and Kandelia obovata forest, and a K. obovata forest. The study employs biogenic element analysis (C, N, lignin phenols) and natural stable carbon isotope ratios (δ13C and δ15N) to assess SOC. Key findings show a decrease in SOC and total nitrogen (TN) from the upstream K. obovata forest to the downstream tidal flat. A stable isotope mixing model reveals a diminishing mangrove-derived OC contribution in topsoil (0–40 cm), estimated at 62 % in the K. obovata forest, 45 % in the central region, and 24 % in tidal flats. Soil profiles suggest microbial decomposition as the main isotope fractionation mechanism, with lignin analysis indicating woody angiosperms as the primary OC source. These findings enhance understanding of OC origins and decomposition in coastal wetlands and inform “blue carbon” management, highlighting the terrestrial-estuary continuum's significance.

Tidal Freshwater Forested Wetlands in the Mobile-Tensaw River Delta along the Northern Gulf of Mexico

Tidal freshwater forested wetlands (TFFWs) typically occur at the interface between upriver non-tidal forests and downstream tidal marshes. Due to their location, these forests are susceptible to estuarine and riverine influences, notably periodic saltwater intrusion events. The Mobile-Tensaw (MT) River Delta, one of the largest river deltas in the United States, features TFFWs that are understudied but threatened by sea level rise and human impacts. We surveyed 47 TFFW stands across a tidal gradient previously determined using nine stations to collect continuous water level and salinity data. Forest data were collected from 400 m2 circular plots of canopy and midstory species composition, canopy tree diameter and basal area, stem density, and tree condition. Multivariate hierarchical clustering identified five distinct canopy communities (p = 0.001): Mixed Forest, Swamp Tupelo, Water Tupelo, Bald Cypress, and Bald Cypress and Mixed Tupelo. Environmental factors, such as river distance (p = 0.001) and plot elevation (p = 0.06), were related to community composition. Similar to other TFFWs along the northern Gulf of Mexico, forests closest to Mobile Bay exhibited lower basal areas, species density, diversity, and a higher proportion of visually stressed individual canopy trees compared to those in the upper tidal reach. Results indicate a strong tidal influence on forest composition, structure, and community-level responses.

Recruitment niche segregation of halophytes along the tidal gradient

Recruitment is a critical component of the plant life cycle, but little is known about its contribution to community assembly in comparison to later plant stages. We aimed to analyze the relevance of recruitment niche segregation in community assembly using tidal salt marshes in a Mediterranean climate. With this objective, we recorded the spatio-temporal distribution of seedling emergence and its relationships with propagule density and environmental conditions at the community level along the tidal gradient. Results indicate that seedling recruitment was strongly influenced by differential establishment abilities and the effects of sedimentary and meteorological factors that vary seasonally and along the tidal gradient. Taxa colonizing the same habitats showed some similarities in their recruitment patterns, but they also presented enough differences to configure almost a unique recruitment pattern for each taxa. Sediment characteristics segregated recruitment niches at both extremes of the tidal gradient, and the few species colonizing habitats between these two extremes also showed contrasted spatial recruitment patterns. In addition, sequential differences in seedling emergence segregated within high marsh taxa. Most of the taxa exhibited a continuous germination strategy associated to prolonged flowering periods and the ability to germinate along broad salinity ranges. Our results shed light on the importance of recruitment niche segregation to the assembly of plant communities, which is key for understanding their functioning and guiding their management.

Biogeographic effects shape soil bacterial communities across intertidal zones on island beaches through regulating soil properties

Island coastal zones are often mistakenly perceived as “ecological desert”. Actually, they harbour unique communities of organisms. The biodiversity on islands is primarily influenced by the effects of area and isolation (distance from the mainland), which mainly focused on plants and animals, encompassing studies of entire islands. However, the application of area and isolation effects to soil microorganisms on island beaches across the intertidal zones remains largely unexplored. We hypothesized that island area and isolation shape soil bacterial communities by regulating soil properties on island beaches, due to the fact that local soil properties might be strongly influenced by land-use, which may vary among islands of different sizes and isolations. To test this hypothesis, we conducted a study on 108 plots spanning 4 intertidal zones on 9 representative island beaches within Zhoushan Archipelago, eastern China. We employed one-way ANOVA and Tukey's honestly significant difference (HSD) test to assess the differences in diversity, composition of soil bacterial communities and soil properties among intertidal zones. Redundancy analysis and structural equation modelling (SEM) were used to examine the direct and indirect impacts of beach area and isolation on soil bacterial communities. Our findings revealed that the area and isolation did not significantly influence soil bacterial diversity and the relative abundance of dominant soil bacterial phyla. However, soil nitrogen (soil N), phosphorus (soil P), organic carbon (SOC), available potassium content (soil AK), and electrical conductivity (soil EC) showed significant increases with the area and isolation. As the tidal gradient increased on beaches, soil bacterial OTU richness, Chao 1, and relative abundance of Planctomycetota and Crenarchaeota decreased, while relative abundance of other soil bacterial phyla increased. We found that influences of island area and isolation shape soil bacterial communities on beaches by regulating soil properties, particularly soil moisture, salinity, and nutrients, all of which are also influenced by area and isolation. Island with larger areas and in lower intertidal zones, characterized by higher soil water content (SWC), soil EC, and soil AK, exhibited greater soil bacterial diversity and fewer dominant soil bacterial phyla. Conversely, in the higher intertidal zones with vegetation containing higher soil N and SOC, lower soil bacterial diversity and more dominant soil bacterial phyla were observed. These findings have the potential to enhance our new understanding of how island biogeography in interpreting island biome patterns.

The intrinsic alignment of red galaxies in DES Y1 redMaPPer galaxy clusters

ABSTRACT Clusters of galaxies trace the most non-linear peaks in the cosmic density field. The weak gravitational lensing of background galaxies by clusters can allow us to infer their masses. However, galaxies associated with the local environment of the cluster can also be intrinsically aligned due to the local tidal gradient, contaminating any cosmology derived from the lensing signal. We measure this intrinsic alignment in Dark Energy Survey (DES) Year 1 redMaPPer clusters. We find evidence of a non-zero mean radial alignment of galaxies within clusters between redshifts 0.1–0.7. We find a significant systematic in the measured ellipticities of cluster satellite galaxies that we attribute to the central galaxy flux and other intracluster light. We attempt to correct this signal, and fit a simple model for intrinsic alignment amplitude (AIA) to the measurement, finding AIA = 0.15 ± 0.04, when excluding data near the edge of the cluster. We find a significantly stronger alignment of the central galaxy with the cluster dark matter halo at low redshift and with higher richness and central galaxy absolute magnitude (proxies for cluster mass). This is an important demonstration of the ability of large photometric data sets like DES to provide direct constraints on the intrinsic alignment of galaxies within clusters. These measurements can inform improvements to small-scale modelling and simulation of the intrinsic alignment of galaxies to help improve the separation of the intrinsic alignment signal in weak lensing studies.

Changes in Salinity, Mangrove Community Ecology, and Organic Blue Carbon Stock in Response to Cyclones at Indian Sundarbans.

Climate change-induced frequent cyclones are pumping saline seawater into the Sundarbans. Fani, Amphan, Bulbul, and Yaas were the major cyclones that hit the region during 2019-2021. This study represents the changes in the soil parameters, mangrove biodiversity and zonation due to the cyclone surges in the Indian Sundarbans between 2017 and 2021. Increasing tidal water salinity (parts per thousand) trends in both pre-monsoon (21 to 33) and post-monsoon (14 to 19) seasons have been observed between 2017 and 2021. A 46% reduction in the soil organic blue carbon pool is observed due to a 31% increase in soil salinity. Soil organic blue carbon has been calculated by both wet digestion and the elemental analyzer method, which are linearly correlated with each other. A reduction in the available nitrogen (30%) and available phosphorous (33%) in the mangrove soil has also been observed. Salinity-sensitive mangroves, such as Xylocarpus granatum, Xylocarpus moluccensis, Rhizophora mucronata, Bruguiera gymnorrhiza, and Bruguiera cylindrica, have seen local extinction in the sampled population. An increasing trend in relative density of salinity resilient, Avicennia marina, Suaeda maritima, Aegiceras corniculatum and a decreasing trend of true mangrove (Ceriops decandra) has been observed, in response to salinity rise in surface water as well as soil. As is evident from Hierarchical Cluster Analysis (HCA) and the Abundance/Frequency ratio (A/F), the mangrove zonation observed in response to tidal gradient has also changed, becoming more homogeneous with a dominance of A. marina. These findings indicate that cyclone, climate change-induced sea level rise can adversely impact Sustainable Development Goal 13 (climate action), by decreasing organic soil blue carbon sink and Sustainable Development Goal 14 (life below water), by local extinction of salinity sensitive mangroves.

Dynamics of extracellular polymeric substances and soil organic carbon with mangrove zonation along a continuous tidal gradient

The importance of mangroves in blue carbon storage has been widely reported. However, the potential contribution of microbial extracellular polymeric substances (EPS) to the carbon pool is still poorly understood in mangrove ecosystems. Thus, a natural mangrove reserve located in Gaoqiao was chosen to investigate the linkage between microbial EPS and sediment organic carbon. Sequential resin extraction, Fourier transform infrared spectroscopy (FTIR), and 16S high-throughput sequencing were employed to determine the variations in EPS and bacterial taxa in different mangrove communities. Both EPS and EPS-C increased significantly with mangrove zonation from seaward to landward, irrespective of the EPS subfractions (colloidal and bound EPS) and components (extracellular protein and polysaccharide). Moreover, both EPS and EPS-C were found to be positively correlated with soil organic carbon. The present data further showed that EPS-C accounted for 1.84~10.69% of TOC in surface sediments. Multiple functional groups (e.g., O-H, N-H, and C=O), which may provide ligands for particle adsorption and complexation, were identified by FTIR. Consistent with the ascend of EPS with mangrove zonation from seaward to landward, the highest transmittance intensity for all functional groups was consistently exhibited in EPS isolated from landward Rhizophoraceae forest. In addition, the present data also indicated an interesting positive linkage between EPS and the abundance of some specific bacterial taxa, such as Rhizobiales, Corynebacteriales, and Gaiellales. In summary, this study claims the importance of EPS in the carbon pool in mangrove ecosystems. The present study may provide a better understanding of the functions of mangroves in carbon stocks.

Biodegraders of Large Woody Debris Across a Tidal Gradient in an Indonesian Mangrove Ecosystem

There has been limited research on the breakdown, recycling, and flux of carbon from large woody detritus (LWD) in mangrove forests. The breakdown of LWD is caused by guilds of terrestrial and marine biodegrading organisms that degrade wood at a range of rates and efficiencies. Spatial variations in environmental factors within mangroves affect the distribution and community of biodegrading organisms, which, in turn, impacts carbon flow and sequestration. We reveal the role of biodegrading organisms in LWD breakdown and the environmental factors that influence the distribution of biodegrading guilds within a mangrove forest in South East Sulawesi that supports a diversity of mangrove species typical of Indonesian mangrove forests, which constitute 20% of Global mangrove cover. Within the high intertidal regions, terrestrial biodegradation processes dominated upon LWD. After 12 months exposure on the forest floor, experimental wooden panels in these areas remained unchanged in mass and condition. In the low intertidal region, marine wood-boring animals belonging to the family Teredinidae were the dominant biodegraders of LWD, and their activity reduces LWD volume and speeds up the loss of LWD volume. More than 50% of the experimental wooden panels’ weight in these areas was lost after 12 months exposure on the forest floor. Although different biodegrading guilds occupy the same LWD niche, their distribution throughout the mangrove forest is influenced by inundation time. The change of biodegrading guilds within LWD between the terrestrial and the marine organisms was distinct, creating a biodegradation boundary in a distance as narrow as 1 m on the mangrove forest floor. These results are important, as rising sea levels have crucial implications for biodegrading guilds. A full understanding of factors affecting the biodegradation processes of LWD in mangrove forests is critical to accurately assess mangrove carbon stores and the fate of mangrove derived carbon.

Morphological characteristics and abundance of prokaryotes associated with gills in mangrove brachyuran crabs living along a tidal gradient.

Due to the chemico-physical differences between air and water, the transition from aquatic life to the land poses several challenges for animal evolution, necessitating morphological, physiological and behavioural adaptations. Microbial symbiosis is known to have played an important role in eukaryote evolution, favouring host adaptation under changing environmental conditions. We selected mangrove brachyuran crabs as a model group to investigate the prokaryotes associated with the gill of crabs dwelling at different tidal levels (subtidal, intertidal and supratidal). In these animals, the gill undergoes a high selective pressure, finely regulating multiple physiological functions during both animal submersion under and emersion from the periodical tidal events. We hypothesize that similarly to other marine animals, the gills of tidal crabs are consistently colonized by prokaryotes that may quantitatively change along the environmental gradient driven by the tides. Using electron microscopy techniques, we found a thick layer of prokaryotes over the gill surfaces of all of 12 crab species from the mangrove forests of Saudi Arabia, Kenya and South Africa. We consistently observed two distinct morphotypes (rod- and spherical-shaped), positioned horizontally and/or perpendicularly to the gill surface. The presence of replicating cells indicated that the prokaryote layer is actively growing on the gill surface. Quantitative analysis of scanning electron microscopy images and the quantification of the bacterial 16S rRNA gene by qPCR revealed a higher specific abundance of prokaryote cells per gill surface area in the subtidal species than those living in the supratidal zone. Our results revealed a correlation between prokaryote colonization of the gill surfaces and the host lifestyle. This finding indicates a possible role of prokaryote partnership within the crab gills, with potential effects on animal adaptation to different levels of the intertidal gradient present in the mangrove ecosystem.

Pleistocene and Holocene procurement of the clam Donax serra (Bivalvia: Donacidae) along the southern Cape coast of south Africa

Humans began to exploit aquatic resources routinely since the late Middle Pleistocene (c. 162 ka), as evidenced by PP13B Cave in the southern Cape of South Africa. Hard bottom or rocky shore species were among the first to be collected, and although they dominate Pleistocene and Holocene archaeomalacological assemblages locally, the soft-bottom Donax serra clam began to be collected systematically near PP13B by 110 ka. Since then, D. serra appears intermittently in early and Holocene middens. Earlier studies on PP13B D. serra assemblages dated to 110–91 ka concluded that initial collection of D. serra ~ 110 ka was unselective in terms of shell size and was undertaken along the entire tidal gradient. In later visits ~ 91 ka, foragers narrowed their collection to the mid-intertidal where most larger clams live, thus increasing the efficiency of D. serra procurement. In this paper, further metrical data from other Pleistocene and late Holocene assemblages is presented in order to test these conclusions. Pleistocene data from mainly the Klasies River main site also reflect small sizes as in contemporary levels from PP13B; however, it is not possible to generalise that the increase in foraging efficiency observed in PP13B also applies to post 90 ka contexts overall due to a lack of Pleistocene samples dating to this latter period. However, it is clear that foraging efficiency was comparatively higher in the Plettenberg Bay and Mossel Bay areas since the early Holocene. Variability among Holocene D. serra assemblages appear to be explained also in terms of foraging ranges. Settlement patterns, group size and/or its composition may be factors behind the generally intermittent presence of D. serra in the southern Cape middens.

Modelling spatial and temporal patterns in bioturbator effects on sediment resuspension: A biophysical metabolic approach

Tidal flats are biogeomorphic landscapes, shaped by physical forces and interaction with benthic biota. We used a metabolic approach to assess the overarching effect of bioturbators on tidal landscapes. The benthic bivalve common cockle (Cerastoderma edule) was used as model organism. The effect of C. edule on sediment resuspension was approximated as a function of the overall population metabolic rate per unit of area. We combined i) laboratory observations on how C. edule affect sediment resuspension along gradients of bioturbation activity, sediment cohesiveness and hydrodynamic force with ii) spatial data on the natural distribution of intertidal C. edule populations. This allowed us to build an integrated model of the C. edule effect on sediment resuspension along the tidal gradient. Owing to the temperature dependence of metabolic rate, the model also accounted for seasonal variation in bioturbators activity.Laboratory experiments indicated that sediment resuspension is positively related to the metabolic rate of the C. edule population especially in cohesive sediments. Based on this observation, we predicted a clear spatial and seasonal pattern in the relative importance of C. edule contribution to sediment resuspension along a tidal transect. At lower elevations, our model indicates that hydrodynamics overrules biotic effects; at higher elevations, inter-tidal hydrodynamics should be too low to suspend bioturbated sediments. The influence of C. edule on sediment resuspension is expected to be maximal at the intermediate elevation of a mudflat, owing to the combination of moderate hydrodynamic stress and high bioturbator activity. Also, bio-mediated sediment resuspension is predicted to be particularly high in the warm season.Research into metabolic dependency of bio-mediated sediment resuspension may help to place phenomenological observations in the broader framework of metabolic theories in ecology and to formulate general expectations on the coastal ecosystem functioning.

Long-term Salinity, Hydrology, and Forested Wetlands Along a Tidal Freshwater Gradient

Tidal freshwater forested wetlands (TFFWs) commonly occur along coastal rivers; however, sea level rise and changes to river discharge may impact these wetlands. Information that characterizes the hydrology and salinity regime of the TFFW zone is needed to assess risk and predict future viability. A combination of field data and modeling were used to characterize TFFW hydrology, salinity, and vegetation along two distributaries (the East River and St. Marks River) of the Apalachicola River in west Florida, USA. Six gaging stations were established (three per river) roughly equidistant along the TFFW tidal gradient to monitor salinity and water levels at the river-wetland interface. Eighteen 500-m2 forest survey stations (nine per river) were also established roughly equidistant between (and including) the upper and lower gaging stations to measure canopy trees (> 2.54 cm DBH) and calculate species importance values (IV200). Field measures, along with other monitoring and model data, were used to develop a 30-year salinity record (1985–2015) for each gaging station based on an artificial neural network (ANN) model. Optimal ANN models for each TFFW gaging station were selected based on Akaike’s Information Criteria, and 30-year mean daily salinity was interpolated to all forest survey stations based on river distance. Important input variables for the ANN models included daily Apalachicola River discharge, Apalachicola Bay tidal stage, and bay salinity, among others. Based on 30-year salinity models, mean daily salinity ranged between 0.30 and 0.63 ppt at the downriver stations of East and St. Marks Rivers, respectively, to 0.14 and 0.14 ppt at the upriver stations, respectively. Results showed a predictable reduction in mean salinity and salinity ranges further upriver at both rivers; however, the St. Marks River showed a distinct inflection point in reduced salinity compared with the East River. Evaluating tree species IV200, there was a shift to species indicative of non-tidal conditions midway up the study reach of the St. Marks River while tidal species remained prominent throughout the East River study reach. Comparison of salinity, tidal reach, and species IV200 for each river suggests hydrology may be the most important contributor to the downriver extent of TFFWs while salinity may be an important driver of TFFW community composition.

Consequences of nest site selection vary along a tidal gradient.

Parents providing care must sometimes choose between rearing locations that are most favourable for offspring versus those that are most favourable for themselves. Here, we measured how both parental and offspring performance varied in nest sites distributed along an environmental gradient. The plainfin midshipman fish Porichthys notatus nests along a tidal gradient. When ascending from the subtidal to the high intertidal at low tide, both nest temperature and frequency of air exposure increase. We used one lab and two field experiments to investigate how parental nest site choices across tidal elevations are linked to the physiological costs incurred by parents and the developmental benefits accrued by offspring. Under warmer incubation conditions, simulating high intertidal nests, offspring developed faster but had higher mortality rates compared to those incubated in cooler conditions that mimicked subtidal nests. In the field, males in higher intertidal nests were more active caregivers, but their young still died at the fastest rates. Larger males claimed and retained low intertidal nests, where offspring survival and development rates were also highest. Our results suggest that males compete more intensively for nest sites in the low intertidal, where they can raise their young quickly and with lower per-offspring investments. Smaller, less-competitive males forced into higher intertidal sites nest earlier in the season and provide more active parental care, possibly to bolster brood survival under harsh environmental conditions.

Radial oxygen loss is correlated with nitrogen nutrition in mangroves.

The present study aimed to explore the possible functions of radial oxygen loss (ROL) on mangrove nutrition. A field survey was conducted to explore the relations among ROL, root anatomy and leaf N in different mangrove species along a continuous tidal gradient. Three mangroves with different ROL (Avicennia marina [A. marina], Kandelia obovata and Rhizophora stylosa) were then selected to further explore the dynamics of N at the root-soil interface. The results showed that seaward pioneer mangrove species such as A. marina appeared to exhibit higher leaf N despite growing under poorer nutrient conditions. Greater leaf N in pioneer mangroves coincided with their special root structure (e.g., high porosity together with a thin lignified/suberized exodermis) and powerful ROL. An interesting positive relation was observed between ROL and leaf N in mangroves. Moreover, rhizo-box data further showed that soil nitrification was also strongly correlated with ROL. A. marina, which had the highest ROL among the three mangrove species studied, consistently possessed the highest levels of NO3-, nitrification and ammonia-oxidizing bacteria and archaea gene copies in the rhizosphere. Besides, both NO3- and NH4+ influxes were found to be higher in the roots of A. marina when compared to those of K. obovata and R. stylosa. In summary, greater N acquisition by pioneer mangroves such as A. marina was strongly correlated with ROL which would regulate N transformation and translocation at the root-soil interface. The implications of this study may be significant in mangrove nutrition and the mechanisms involved in mangrove zonation.

Distribution and risk of mercury in the sediments of mangroves along South China Coast.

The importance of mangrove was widely reported. However, the potential risks of pollutants (e.g., Hg) accumulated in the mangroves are often ignored. Thus, the present study aimed to explore the distribution and risk of mercury (Hg) in the sediments of mangroves along South China Coast. Results showed that concentrations of total Hg ranged from 0.0815 to 0.6377 mg/kg, with an arithmetic mean value of 0.2503 mg/kg. The contamination index (Pi) showed mild pollution toxicity risks in NS, slight toxicity risks in DZG, QZ, SY, ND, GQ, TLG, and free pollutions in BMW, SJ, ZJK and BLHK. NS, DZG and SY scored the highest values of Igeo among the eleven mangrove regions studied, indicating moderate to heavy pollution inputs in these regions. As for the distribution of Hg in the sediments along tidal gradient, concentrations of Hg in the sediments sharply increased from seaward mudflat to landward mangrove, corresponding with the increases of TOC. In summary, the present data indicated that mangrove ecosystem is efficient in Hg reservoir. However, the potential ecological risks of Hg, especially in some mangrove regions easily affected by human activities, should be noted.

Assessing Impacts of Metallic Contamination along the Tidal Gradient of a Riverine Mangrove: Multi-metal Bioaccumulation and Biomagnification of Filter-Feeding Bivalves

Most riverine mangroves (characterized by salinity fluctuations and tidal inundations), are seriously threatened by metallic pollution. Whether differences in salinity and tidal effects along the river continuum can affect metallic bioaccumulation and the biomagnification of species is still unknown. Bivalves are representative sessile inhabitants in mangrove ecosystems, with a high capacity to bioaccumulate metallic contaminants. The present study used two bivalves, Meretrix lusoria and Mytilopsis sallei, to monitor inter-site changes in metallic contamination and assess the associated ecological impacts along the tidal gradients of riverine mangroves. The concentrations of a total of six metals (Cr, Ni, Cu, Zn, Cd and Pb) in M. lusoria and M. sallei, collected at three different sites along Danshuei Riverine Mangrove, were investigated. The metallic concentrations of the whole soft body of the studied bivalves, and the associated surface sediment from each site, were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) to determine the inter-site effects on the bioaccumulation and biomagnification of metallic contaminants in bivalves. There are increasing concentrations of four metallic contaminants, Zn, Cr, Cd and Cu, in the seaward direction of the bivalves. The increasing mean metallic concentrations along the seaward direction may be the effect of salinity, further decreasing the rate of the elimination of these metals, thus resulting in a net increase in metallic contaminants. Our results clearly show prominent inter-site changes in the metallic burdens of bivalves in our study on riverine mangrove ecosystems associated with different levels of bioaccumulation and biomagnification of metallic contaminants. Thus, it is important to monitor multiple sites along the dynamic environment of riverine mangroves in order to gain a good understanding of the ecological impact of metallic pollution risks. The present findings provide important evidence of the use of simple indices to assess the ecological impacts of metallic pollution in riverine mangroves.

Inducible versus constitutive antioxidant defenses in algae along an environmental stress gradient

Optimal defense theory (ODT) predicts that antiherbivore defenses should be constitutive when plants are frequently attacked and inducible when the probability of attack is low. Like antiherbivore defenses, antioxidant defenses can be inducible or constitutive. We hypothesized the ODT predictions should apply to antioxidant defenses; thus, species inhabiting environments where oxidative stresses occur frequently should produce constitutive antioxidant defenses, whereas species in environments where stresses occur less frequently should produce inducible defenses. We tested this hypothesis by attempting to induce production of the antioxidant precursor dimethylsulfoniopropionate (DMSP) in 4 ulvoid algae species that experience different levels of environmental stress because they are zoned along a tidal gradient. The 2 lower intertidal speciesUlvaria obscuraandUlva fenestrata, which experience oxidative stresses less frequently, induced DMSP production in response to applications of the chemical oxidant hydrogen peroxide within 7 d, whereas the higher intertidal speciesUlva linzaandUlva intestinalis, which regularly experience oxidative stress, did not have increased DMSP concentrations. This study demonstrates a novel waterborne signaling mechanism for DMSP induction in marine macroalgae and provides evidence of selection for inducible antioxidant defenses in organisms experiencing less frequent environmental stresses.

Interactions between topsoil properties and ecophysiological responses of mangroves (Avicenniamarina) along the tidal gradient in an arid region in Qatar

This study investigated the interactions between topsoil properties and ecophysiological responses of Avicennia marina along the tidal gradient in an arid region in Qatar. In February 2017, three plots were established, each at a distance of 0 m D0 , 50 m D50 , and 100 m D100 from the inland boundary of a mangrove forest. Soil samples were collected at 0-10-cm depth in each plot to determine the chemical properties, and the density of seedlings, saplings, and trees was measured. Moreover, above- AGB and below-ground biomass BGB were calculated using an allometric equation for A. marina with the measured diameter at breast height in February 2017. As an indicator of salt stress, chlorophyll fluorescence parameters were measured in October 2017. Salinity 45.60 ppt and exchangeable sodium percentage ESP; 29.02% at D100 were significantly highest. AGB was higher at D100 41.44 Mg ha-1 than at D0 0 Mg ha-1 and D50 7.33 Mg ha-1 , and BGB was higher at D100 44.91 Mg ha-1 than only at D0 0 Mg ha-1 . There was no significant difference in the density of seedlings, saplings, or trees or the chlorophyll fluorescence parameters among the plots. Salt stress was not induced despite the hypersalinity at this site, since A. marina growing in an arid climate can endure strong salinity. Soil pH was highest at D0, followed by at D50 and D100. Organic matter, total nitrogen, available phosphorus, and cation exchange capacity were significantly higher at D100 than at D0 and D50. Higher concentrations of nutrients on the seaward side might result from the tidal gradient and a large input of organic matter and low soil alkalinity.

Influence of the Flood on the Flow Characteristics in Different Flood and Tide Combination Scenarios: A Case Study in Puyang River a Tributary of Qiantang River

Huang, J. and Zhang, H., 2019. Influence of the flood on the flow characteristics in different flood and tide combination scenarios: A case study in Puyang River a tributary of Qiantang River. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 178–184. Coconut Creek (Florida), ISSN 0749-0208.Based on the background of Puyang Jiang River, a 2D hydrodynamic model was built to explore the distribution characteristics of tidal range in the downstream section of Puyang River under different flood tide combinations between Puyang River and Qiantang River. The influence of different frequency floods and flood discharges of Puyang River on the flood level of Puyang River was analysed. The results show that the tidal range at each point of the exit section decreases with the increase of floods in Puyang River. Under the same flood conditions of Puyang River, the tidal range at each point of the river increases with the increase of the Qiantang River rushing tide; under the same characteristic tidal conditions, the tidal gradient along the water flow direction of the Sanjiangkou-Xizhuang section increases with the increase of floods in the Puyang River. When Puyang Jiang River suffered flooding from once ten years to twenty years and then to fifty years, the mean value of water level reduction of east and west river is from 0.66 cm to 0.72 cm and then to 0.63 cm, namely, the sensitivity of the discharge of Gaohu flood retarding basin to the water level of east and west river of Puyang Jiang River is first strengthened and then weakened. The research results provide a guidance for flood regulation of Puyang River and optimization of operation in Gaohu flood detention area.

The cross-shore distribution of epibenthic predators and its effect on zonation of intertidal macrobenthos: a case study in the river Scheldt

Available research is inconclusive on how circatidal habitat use and cross-shore distribution of aquatic epibenthic predators may affect the vertical zonation of infauna in muddy, soft-bottom substrates in estuaries. We placed fyke traps at different heights on the intertidal mudflat to assess the circatidal density of epibenthic predators. Infauna was sampled across the same tidal gradient. The abundance of epibenthic predators in the fykes decreased with elevation (decreasing inundation time), yet for the shrimp Palaemon longirostris abundance did not change with elevation in autumn. When corrected for inundation time, predator density was equal over the tidal range or higher on the high mudflat in some instances, indicating that predators evenly distributed over the mudflat or moved to the highest part during a high tide. The density of epibenthic predators did not correlate with the density of infauna, whereas the latter did show a close relationship with sediment characteristics. Our data suggest epibenthic predator density does not shape the present distribution of infauna across the tidal gradient on the oligohaline mudflats in the Scheldt.