Ebb Tide Research Articles

Effect of Different Rootstocks and Scions Compatibility Study on Rosa sp

An investigation entitled, “Effect of different rootstocks and scion compatibility study on Rosa sp.’’ was conducted to study the graft compatability and growth performance of grafted rose plants and the experiment was conducted in Vegetable Research Station, Tamil Nadu Agricultural University, Palur, Cuddalore district, Tamil Nadu during the year 2022. It was carried out using completely randomized design (CRD) with fifteen treatments (T1- Andhra red rose + Dog rose, T2-Andhra red rose + Button rose, T3-Andhra red rose + Ebb tide rose, T4- Andhra red rose +Fairy rose, T5- Andhra red rose + Edward rose, T6- Edward rose+ Dog rose, T7-Edward rose + Button rose, T8-Edward rose+ Ebb tide rose, T9-Edward rose + Fairy rose, T10-Edward rose+ Edward rose, T11-Damask rose + Dog rose, T12-Damask rose + Button rose, T13-Damask rose + Ebb tide rose, T14-Damask rose+ Fairy rose, T15-Damask rose+ Edward rose) and two replications. The results indicated a significant difference between the different treatment combination for graft union, success percentage, survival percentage, plant height (cm), leaf length (cm), leaf width (cm), days taken for leaf initiation. The experiment data revealed that the maximum graft success (90) and graft survival percentage (80), length of leaves (3.9 cm) and plant height (67.6) was recorded in the treatments T7 (Edward rose + Button rose). It can be concluded that the combination of rootstock as Edward rose and scion as Button rose is said to be most compatible and can be recommended for commercial cultivation.

High-fidelity modeling of a vertical axis tidal turbine model under realistic flow conditions

In the context of the global energy crisis, developing renewable energies is of primal importance. Among the renewable resources available are tidal currents. Tidal currents can be exploited with tidal turbines. Different concepts of tidal turbine exist, we here investigate a vertical axis tidal turbine or VATT prototype made by HydroQuest and CMN. More precisely, we carry on numerical investigations on a Hydroquest/CMN tidal turbine model. Experimental studies are limited to turbine models and thus suffer from scale effects. In situ measurement are still expensive and difficult to acquire. Computational Fluid Dynamics (CFD) is an interesting alternative in order to go beyond what experiments can offer. One major drawback of CFD is that it requires validation of the models used. A validation of our CFD tool is included in this paper. Because the hydrodynamic of vertical axis tidal turbines is highly unsteady, Large Eddy Simulation (LES) are well adapted here. Blade-resolved Computational Fluid Dynamics (CFD) approaches are appropriate to study vertical axis tidal turbines, but their cost is still prohibitive for real size tidal turbine. Simplified approaches are preferred solutions. Literature showed that Actuator Line Model (ALM) LES is well suited to model vertical axis turbine. Most tidal sites are characterized with strong turbulence intensities. The presence of turbulence in most tidal sites has led companies and academics to study the effects of ambient turbulence over tidal turbines. It has been shown that turbulence can have a non-negligible influence on the turbine performances and wake. To account for the effects of turbulence, synthetic turbulence is introduced at the inlet of the simulation. The LBM is an unsteady weakly-compressible CFD approach. It solves the Boltzmann equation using an explicit time discretization and a uniform Cartesian grid called lattice. It has been proven to be an efficient approach for modeling tidal turbines using LES and ALM, Grondeau et al. (2019). In this paper, we study a tidal turbine model of the Hydroquest/CMN VATT using an ALM-LBM-LES approach. This model was tested at the Ifremer Boulogne-sur-Mer testing facilities. We first compare our results with the experimental ones in a scenario without turbulence and for flood and ebb tide configurations. A numerical investigation of the influence of upstream turbulence on the turbine performances and wake is then realized. Prospects of this study include among others the effects of turbines interactions and waves.

Evaluating the influence of environmental and biological factors on migration behavior and residence duration of wild subyearling Chinook Salmon in a fjord estuary using miniature acoustic transmitters

AbstractObjectiveSeaward migration and early marine residence are periods of high mortality in the lifecycle of Pacific salmon Oncorhynchus spp. The conservation of these species requires knowledge of habitat use patterns during early life to address survival bottlenecks. Using new miniaturized transmitters (V3 307‐kHz tag; Innovasea Systems), we investigated the association between biological and environmental factors and the residence behavior of subyearling Chinook Salmon Oncorhynchus tshawytscha in a fjord estuary in British Columbia.MethodsTagged wild subyearling Chinook Salmon (n = 49; 67–95 mm) were experimentally released into an estuary. Using time‐to‐event analysis and model selection, we evaluated the association between biological (size, growth, day of release) and environmental (temperature, salinity, depth, discharge, tide direction) factors and estuary residence patterns.ResultOf the 49 fish released, 36 were inferred to have exited the estuary successfully. In this sample of subyearling Chinook Salmon, the median residence duration was estimated to be 11.2 days (95% CI = 6.5–15.5). We found tide direction and salinity to be important factors influencing the probability of a fish leaving the estuary. Fish were 75% more likely to leave the estuary on an ebb tide. Higher salinity also increased the probability of a fish leaving the estuary. Fish successful in leaving the estuary displayed either direct or indirect movement patterns in the estuary, with most fish (71%) being indirect movers that made multiple trips upstream and downstream. Within the estuary, most movements occurred at night (76%), regardless of tide direction.ConclusionThis study provides the first direct measure of estuary residence duration in wild subyearling Chinook Salmon and a valuable description of movement ecology in this age‐class of fish. While this was a small study in a single year, our results indicate this estuary is likely a stopover habitat for larger subyearlings. Studies indicating the use of habitats by specific populations, as presented here, are integral to the design of habitat‐based conservation measures for mobile species.

UPDATE ON THE STABILITY OF FOUR ESTUARIES ON THE AUSTRALIAN SOUTH-EASTERN SEABOARD

On the New South Wales, Australian east coast there are several estuaries with similar characteristics. Disconcertingly, the construction of training walls and jetties (breakwaters) at four of the medium-to-large sized estuaries have tripped their associated channel and lake (bay) systems from a long-term shoaling mode into an unstable scouring mode (Nielsen and Gordon 1980, 2008, 2017; Couriel et al. 2013. Field data and hydraulic theory confirm that such estuary entrance works have increased the tidal conveyance of entrance channels by modifying channel cross-sections, removing sand bars, extraneous littoral currents and associated sand movements that, previously, impeded ebb tide discharges and ocean tide forcing (Nielsen and Gordon 2017; Escoffier 1940).

Dry season physicochemical characteristics of a tropical meso-tidal estuary: cross river estuary, southeast nigeria


 The Cross River estuary is a tide-dominated coastal plain estuary which empties into the Atlantic Ocean at the Bight of Biafra, Gulf of Guinea. It receives fresh water from major tributaries including Calabar, Great Kwa, Akpa-Yafe, Mbo and Little Kwa rivers; and plays a significant role in anthropogenic activities such as fishing exploitation and commerce. This research focuses on the assessment data from the hydrodynamic variability of the Cross River estuary. Data from April 2017 to March 2018 were generated from monitoring tidal current velocity in the estuary as well as the tidal variations under spring and neap tidal conditions. The result shows that the average current velocity in the water column was 0.85 m/s during flood tides and 0.96 m/s during ebb tides. Residual currents were observed to be seaward, with ebb dominance. In-situ measurements of physicochemical parameters including dissolved oxygen, temperature, pH, salinity, density and transparency were recorded at 55 geo-referenced sampling stations throughout the estuary in the dry season month of January, 2018. Further to this, salinity, temperature and pH varied from 0 – 20 ppt; 27.9-31.4°C; 5.4-8.4 respectively, and in increased seaward direction. The relationship between physicochemical parameters were interpreted using Pearson’s Correlation Matrix. Here, salinity showed significant correlations (p<0.05) with pH while density showed significant correlations with temperature, salinity and pH (add reasons). This research study reveals that changes in tidal cycles and current velocity are important factors contributing to the observed variations in physicochemical properties of the Cross River estuary and thus, useful for effective monitoring of the estuary and similar meso-tidal systems.

Pemodelan Hidrodinamika 2-Dimensi Arus Laut Permukaan Perairan Desa Berakit Kabupaten Bintan

Information related to ocean currents is not yet available in Berakit Village waters, ocean currents are an important parameter to determine the condition of a waters. An alternative that can be used to determine the condition of ocean currents is to use hydrodynamic modeling. The purpose of the study was to analyze the distribution pattern and characteristics of surface ocean currents. This research was conducted by conducting 2-dimensional hydrodynamic modeling simulating ocean currents for 1 (one) year in December 2020-November 2021 using MIKE 21 software by sampling in 6 (six) different conditions, namely at the highest tide, lowest tide, high tide. towards the ebb and flow of the full moon, the ebb towards the negligible tide, the tide towards the ebb tide and the ebb towards the negligible tide. The model results were validated by the RMSE formula with a value of 2%, the model results were very good, so that they could be used as a reference in providing an overview of the real conditions of the pattern and current distribution at the research location. The movement of ocean currents at the time of the full moon and negligible dominant currents move towards the south of the waters, while at the time of the full tide and negligible the dominant currents move towards the north of the waters. In the north season, the current velocity ranges from 0.00006 m/s-0.125 m/s with the dominant movement towards the north. East monsoon currents move predominantly north and south with speeds ranging from 0.0000003 m/s-0.129 m/s. In the south monsoon the dominant current moves to the north and south at a speed of 0.0000007 m/s-0.13 m/s. in the west season, the dominant current moves to the north and south at a speed of 0.00001 m/s-0.12 m/s. The speed of the dominant ocean currents is greater at high tide compared to low tide, this is due to differences in sea level elevation in the opposite direction of motion.

Tidal Currents and Their Reshaping Impact on Estuarine Morphology

The Selagan Jaya River Estuary frequently undergoes shape changes, prompting this study to unravel the influence of currents and tides on its morphological evolution. Field measurements encompassing current and tidal data, supplemented by secondary tidal data from TMD and estuary morphology data from USGS, were employed. Findings reveal a mixed semidiurnal tide with a Formzhal value of 0.491 for the Selagan Jaya Estuary. The lowest ebb elevation stands at 0.0117 m, contrasting with the highest flood elevation of 0.6046 m. Flood current velocities range from 0.193 to 1 m/s, while ebb currents span 0.127 to 0.307 m/s. Validation between field and TMD tidal data attains a 98.44% accuracy. Importantly, currents and tides distinctly shape the Selagan Jaya River Estuary; during flood tides, sediment-laden currents ingress, while ebb tides with slower currents hinder sediment egress, underscoring their profound morphological impact.
 Highlight:
 
 Estuarine Morphological Dynamics: Investigates the dynamic nature of the Selagan Jaya River Estuary's shape changes and its underlying processes.
 Tidal and Current Influence: Unravels the intricate interplay between currents and tides, revealing their significant role in shaping the estuarine morphology.
 Formzhal Analysis: Introduces the Formzhal value as a key indicator of the estuary's tidal characteristics and their implications for morphological evolution.
 
 Keyword: Estuarine Morphodynamics, Currents, Tidal Dynamics, Morphological Evolution, Sediment Transport

Variability in methane emissions from stems and buttress roots of Bruguiera gymnorrhiza trees in a subtropical mangrove forest

AbstractTrees in wetlands emit a significant amount of methane (CH4) into the atmosphere which is produced in the soil where anaerobic conditions prevail. However, only very few studies have considered the role of trees in the CH4 budget of mangrove forests. How tree CH4 emissions () vary between and within individuals, and how these emissions vary with the day/night alternation and the tidal cycle, have not yet been elucidated. We measured from buttress roots and stems on individuals of Bruguiera gymnorrhiza of different sizes. We also measured from trees and sediments over a 24‐h cycle. Higher was measured on the buttress roots than on the stems, with a decreasing trend with height along the stems on a majority of trees. exhibited large variations over a 24‐h cycle which were observed for the first time in this study. from sediment was twice higher at low tide compared to just before or after the flood period. from non‐submerged stem positions at high tide was four times higher during the day than during the night. On buttress roots and on stem portion which were submerged, high were measured at the beginning of the ebb tide even at night. A better understanding of variability from mangrove trees and its controls, at different time scales and along spatial gradients is needed for accurate estimation of CH4 budgets of mangrove forests.

Alternating patterns of cross-shelf suspended sediment transport in the northern East China Sea in winter

Suspended sediment transport across the continental shelf is a key process for the materials exchange between coastal seas and the deep ocean. The cross-shelf transport through the Yangtze Shoal in the northern East China Sea (ECS) exhibits a unique pattern, which is characterized by alternations between high and low values in suspended sediment concentration (SSC). This study is conducted to reveal the underlying mechanisms and their effects on sediment fluxes. Surface SSC retrieved from GOCI data are combined with in situ observations of concentration and particle sizes of suspended sediment to study the temporal and spatial variations of the SSC in the Yangtze Shoal. Additionally, a numerical model for examining ocean circulation based on the FVCOM is established to display the hydrodynamic feature in the study area. The alternating SSC pattern is closely related to the topography of three ridges and two troughs. High SSC with fine particle size can be found over the ridge, while low SSC is detected at the surface layer of water in the trough. Even during the flood and ebb tides, this alternating pattern of high and low SSCs does not change, except for the expansion and contraction of coverage areas of high SSC. The high SSC near the tidal ridge should have resulted from the combined effect of resuspension and upwelling since the stronger bottom shear stress and a surface divergence that may induce an upwelling can be found in this area. Combined with the simulated current, the sediment transport flux between ridges and troughs is estimated. The sediment flux in the ridge is substantially increased than that in the trough, especially during the flood maximum and ebb maximum time. The contribution of suspended sediments from the Yangtze Shoal to the Southwestern Cheju Island Mud (SCIM) is relatively small during the normal weather in winter. However, cross-shelf transport can be remarkably strengthened by strong northerly winds in winter. This work puts forward a detailed cross-shelf transportation process induced by topography.

Numerical study on the impact of wave-current interaction on wave energy resource assessments in Zhoushan sea area, China

Based on MIKE21 SW, the wave-current coupled and uncoupled numerical models were established for Zhoushan sea area. Through analysis of four characteristic moments during spring tide, it can be seen that the influence of tidal level on wave parameters is greater than that of tidal current, but the differences of the annual average wave energy flux are mainly caused by tidal current. The effect of wave-current interaction will cause the wave energy redistribute near the peak of the wave spectrum, resulting in the wave energy near the peak flatted. The wave energy is transferred to low-frequency waves during the flood tide, while is transferred to high-frequency waves during the ebb tide. Through the research on the absorbed power of five wave energy converters in three target areas, it is seen that the effect of wave-current interaction will change the wave energy distribution, thus change the matching between the wave energy distribution interval and the optimal conversion interval of the wave energy converter. Finally, the difference trends of the five wave energy converters on the absorbed power calculated by the two models are obviously different from each other and are also different from the difference trends of their wave energy fluxes.

Sources of Drag in Estuarine Meanders: Momentum Redistribution, Bottom Stress Enhancement, and Bend-Scale Form Drag

Abstract Curvature can create secondary circulation and flow separation in tidal channels, and both have important consequences for the along-channel momentum budget. The North River is a sinuous estuary where drag is observed to be higher than expected, and a numerical model is used to investigate the influence of curvature-induced processes on the momentum distribution and drag. The hydrodynamic drag is greatly increased in channel bends compared to that for straight channel flows. Drag coefficients are calculated using several approaches to identify the different factors contributing to the drag increase. Flow separation creates low-pressure recirculation zones on the lee side of the bends and results in form drag. Form drag is the dominant source of the increase in total drag during flood tides and is less of a factor during ebb tides. During both floods and ebbs, curvature-induced secondary circulation transports higher-momentum fluid to the lower water column through vertical and lateral advection. Consequently, the streamwise velocity profile deviates from the classic log profile and vertical shear becomes more concentrated near the bed. This redistribution by the lateral circulation causes an overall increase in bottom friction and contributes to the increased drag. Additionally, spatial variations in the depth-averaged velocity field due to the curvature-induced flow are nonlinearly correlated with the bathymetric structure, leading to increased bottom friction. In addition to affecting the tidal flow, the redistributed momentum and altered bottom shear stress have clear implications for channel morphodynamics.

Decorporatization and organized interests in public policymaking in Norway: A tide that lifts all ships or an ebb tide leaving only the few afloat?

AbstractOver the past decades, there has been evidence of a shift from corporatist representation to pluralist policymaking in Norway and the neighboring Scandinavian countries. This article examines the policy involvement of voluntary associations and interest groups within the context of decorporatization and pluralization. Should decorporatization be understood as a tide that lifts all groups into public policymaking, or an ebb tide leaving only the few privileged afloat? By analyzing survey data on Norwegian voluntary associations and interest groups regarding their contacts with the parliament, government, and administration in 1983 and 2013, the article presents evidence of a growing mobilization and representation of citizen groups that have traditionally held a less prominent position in the policymaking process. However, economic groups have also increased or maintained their access to the parliamentary and governmental arenas, and insider access appears to persist as a factor in shaping group representation. Furthermore, the results indicate a widening gap in more frequent access between resource‐rich and resource‐poor groups. This leads to a somewhat contradictory conclusion: In one sense, decorporatization has been a tide lifting all ships, but in another, also an ebb tide leaving the few afloat.

Hydrodynamic and anthropogenic disturbances co-shape microbiota rhythmicity and community assembly within intertidal groundwater-surface water continuum

Tidal hydrodynamics drive the groundwater-seawater exchange and shifts in microbiota structure in the coastal zone. However, how the coastal water microbiota structure and assembly patterns respond to periodic tidal fluctuations and anthropogenic disturbance remains unexplored in the intertidal groundwater-surface water (GW-SW) continuum, although it affects biogeochemical cycles and coastal water quality therein. Here, through hourly time-series sampling in the saltmarsh tidal creek, rhythmic patterns of microbiota structure in response to daily and monthly tidal fluctuations in intertidal surface water are disentangled for the first time. The similarity in archaeal community structures between groundwater and ebb-tide surface water (R2=0.06, p = 0.2) demonstrated archaeal transport through groundwater discharge, whereas multi-source transport mechanisms led to unique bacterial biota in ebb-tide water. Homogeneous selection (58.6%-69.3%) dominated microbiota assembly in the natural intertidal GW-SW continuum and the presence of 157 rhythmic ASVs identified at ebb tide and 141 at flood tide could be attributed to the difference in environmental selection between groundwater and seawater. For intertidal groundwater in the tidal creek affected by anthropogenically contaminated riverine inputs, higher microbial diversity and shift in community structure were primarily controlled by increased co-contribution of dispersal limitation and drift (jointly 57.8%) and enhanced microbial interactions. Overall, this study fills the knowledge gaps in the tide-driven water microbial dynamics in coastal transition zone and the response of intertidal groundwater microbiota to anthropogenic pollution of overlying waters. It also highlights the potential of microbiome analysis in enhancing coastal water quality monitoring and identifying anthropogenic pollution sources (e.g., pathogenic Vibrio in aquaculture) through the detection of rhythmic microbial variances associated with intertidal groundwater discharge and seawater intrusion.

Numerical Simulation of Oil Spills in the Lower Amazonas River

In 2013, a slope slide took place at the Santana-AP channel that links to the Lower Amazon River’s North Channel, resulting in the sudden collapse of a substantial section of the Port of Santana and its infrastructure. This area houses liquid bulk terminals and pipelines with high pollution potential. The objective of the research is to evaluate the potential environmental impacts of an eventual oil spill in the very short term using a numerical hydrodynamic simulation model coupled with that of pollutant dispersion. The SisBaHiA® software, experimentally calibrated using acoustic methods (ADCP), was used to generate hypothetical scenarios in these areas with a substantial risk of landslides. Two hydrological scenarios stand out in the simulations: (a) November S-1 (dry) and (b) May S-2 (rainy). In S-1, the plume dispersion was higher during flood tides S-1a and S-1b, reaching 4 h urban slope areas, river mouths, tributaries (Matapi and Vila Nova), and environmental protection areas. At S-2, the plume spread was greater during the ebb tides S-2c and S-2d, affecting Macapá’s water supply system 12 h after the accident. The scenarios suggest the existence of high risks associated with the study hypotheses. The dispersion of the plume is directly proportional to the flow, indicating that local hydrodynamics is probably the most relevant dispersive factor. We conclude that the mitigation time for more severe effects is critical in the first 4 h because the coastal geographic feature tends to keep the plume in the Santana channel.

Influence of hydrodynamic conditions on the fate of halogenated flame retardants along salinity gradients in a highly polluted micro-tidal estuary

Halogenated flame retardants (HFRs) have properties similar to those of hydrophobic organic pollutants (HOPs). However, the understanding of their environmental fate in tidal estuaries remains limited. This study aims to bridge knowledge gaps regarding the land-sea transport of HFRs through riverine discharge into coastal waters. HFR levels were significantly influenced by tidal movement, and decabromodiphenyl ethane (DBDPE) was the predominant compound with a median concentration of 3340 pg L−1 in the Xiaoqing River estuary (XRE), whereas BDE209 had a median concentration of 1370 pg L−1. The Mihe River tributary plays a key role in transporting pollution to the downstream estuary of the XRE in summer, and the increasing suspended particulate matter (SPM) by resuspension in winter significantly affects HFR levels. These concentrations were inversely proportional to diurnal tidal oscillations. Tidal asymmetry caused an increase in SPM during an ebb tide, which increased HFR levels in a micro-tidal estuary such as the Xiaoqing River. The location of the point source and flow velocity influences the HFR concentrations during tidal fluctuations. Tidal asymmetry increases the likelihood of some HFRs being adsorbed by particles exported to the adjacent coast, and some settled down in areas with low hydrodynamic conditions, hindering their flow to the ocean.

Physiochemical Controls on the Horizontal Exchange of Blue Carbon Across the Salt Marsh‐Tidal Channel Interface

AbstractTidal channels are biogeochemical hotspots that horizontally exchange carbon (C) with marsh platforms, but the physiochemical drivers controlling these dynamics are poorly understood. We hypothesized that C‐bearing iron (Fe) oxides precipitate and immobilize dissolved organic carbon (DOC) during ebb tide as the soils oxygenate, and dissolve into the porewater during flood tide, promoting transport to the channel. The hydraulic gradient physically controls how these solutes are horizontally exchanged across the marsh platform‐tidal channel interface; we hypothesized that this gradient alters the concentration and source of C being exchanged. We further hypothesized that trace soil gases (i.e., CO2, CH4, dimethyl sulfide) are pushed out of the channel bank as the groundwater rises. To test these hypotheses, we measured porewater, surface water, and soil trace gases over two 24‐hr monitoring campaigns (i.e., summer and spring) in a mesohaline tidal marsh. We found that Fe2+ and DOC were positively related during flood tide but not during ebb tide in spring when soils were more oxidized. This finding shows evidence for the formation and dissolution of C‐bearing Fe oxides across a tidal cycle. In addition, the tidal channel contained significantly (p < 0.05) more terrestrial‐like DOC when the hydraulic gradient was driving flow toward the channel. In comparison, the channel water was saltier and contained significantly (p < 0.05) more marine‐like DOC when the hydraulic gradient reversed direction. Trace gas fluxes increased with rising groundwater levels, particularly dimethyl sulfide. These findings suggest multiple physiochemical mechanisms controlling the horizontal exchange of C at the marsh platform‐tidal channel interface.

Experimental performance and wake study of a ducted twin vertical axis turbine in ebb and flood tide currents at a 1/20th scale

While studies on horizontal axis tidal turbines are plentiful, those on ducted twin vertical axis alike HydroQuest’s turbines are lacking. For such a device, both the relative counter-rotation direction of the rotors and the tripod base geometry upstream are different between ebb and flood tide. Consequently, this paper analyses the effect of the two opposed flow directions on the hydrodynamic performance and on the wake of the turbine. The study is based on experimental measurements at a 1/20th scale in Ifremer’s wave and current flume tank. The hydrodynamic performance of the model are characterised over a wide range of operating points with the turbine installed on a tripod and on a monopile base. In addition, the 3D wake of the turbine is thoroughly analysed in the two flow directions using 3-component laser Doppler velocimetry. Overall, the drag and the maximum average power coefficient are not affected by the current direction but the optimal tip speed ratio is 7 % lower during ebb with 1.5 times higher power fluctuations compared to flood tide. Besides, the wake of the two rotor columns interact differently depending on the flow direction, leading to a 30 % faster surface averaged velocity recovery in the flood tide configuration. The observed effect of flow direction provides a better knowledge of twin vertical axis turbine wake interactions and highlights the impact of the gravity base geometry on the development of the overall turbine wake. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin-vertical axis tidal turbines.

Residual circulations and wind conditions affect the transport and distribution of Pb

Hydrodynamic conditions affect the dispersion and transportation of pollutants. In this study, 102 surface water samples were collected and numerical simulations were conducted by coupling SWAT (Soil and Water Assessment Tool) and MIKE 21 models to investigate the effect of hydrodynamic conditions on the transport and distribution of Pb in Jiaozhou Bay, China. The tidal current velocity was lowest at flood tide and highest at ebb tide in summer, mainly due to the strong runoff caused by heavy rainfall in summer. The velocity of the residual current near the bay mouth was high, with an average value of 0.32 m/s. The residual currents had alternating clockwise and counter-clockwise circulations of different diameters in the bay mouth and the northern bay. The circulation diameter in the bay mouth area was large, and the circulation extended from the bay mouth to the Yellow Sea. Due to the small circulation diameters and opposite directions of the adjacent circulations in the northern bay, pollutants were easily trapped there. The dissolved Pb particles released from the northern bay mainly migrated to the shore, while the dissolved Pb particles released from the bay mouth tended to migrate to the Yellow Sea. The dominant wind directions and residual currents were the main driving forces affecting the trajectories of the particle tracking simulations. The dissolved Pb concentration in the water was high near shore and in the southwestern bay and under the combined effects of tidal residual current, wind force, and river and wastewater inputs. The low Pb concentration near the bay mouth was mainly influenced by the high residual current velocity. These results can provide improved insights into the mechanism of Pb transport and distribution in a semi-enclosed bay.

Sediment settling process revealed by a bottom-tethered sediment trap at the east tip of the Shandong Peninsula

This paper investigates sediment settling process during summer seasons based on in-situ observation and sediment analysis at the east tip of the Shandong Peninsula, which is a pathway for sediments from the Bohai Sea and the North Yellow Sea to enter the South Yellow Sea in China. Bottom-tethered sediment traps, together with platforms equipped with current profilers/meters and temperature/salinity and turbidity sensors, were deployed for approximately 10 days in August 2017 over an elongated deposit off the coast of the Shandong Peninsula. A computed tomography (CT) scan and grain size and 210Pb analyses of trap sediment were carried out to determine the settling process of suspensions at the study site. Twenty-three couplets were found in the CT images of the trap, the time series of which was established using intervalometer disks. Quantitative characterization of rhythmites using a hounsfield unit indicates that the period of couplets is approximately quarter-diurnal, and the settling process could be divided into three stages during Aug. 21st – 27th. Current, wave, wind, and SSC data illustrate that the diversion of the bottom current leads to the formation of couplets, and the thickness of the couplet is controlled by the vertical current velocity and wind direction. Northerly winds enhance the difference in settlement between flood and ebb tides, whereas southerly winds smoothen the difference. The gale event inhibited the settlement of the suspended matter, and the source of the suspensions was converted from local to remote after the event, as evidenced by 210Pb data. No evident erosion can be detected in the sediment traps. The results are of significance to better understand the sedimentary dynamics near the Shandong clinoform and inspire the practical efficiency of bottom-tethered sediment traps in the settling process in coastal areas.

Heat stress, especially when coupled with high light, accelerates the decline of tropical seagrass (Enhalus acoroides) meadows

Heat stress threatens the survival of seagrass, but its damage mechanisms are unclear. In this study, the results reveal that heat stress exceeding 36 °C in the dark caused inactivation of the PSII reaction center, damaging both the PSII donor and acceptor sides in Enhalus acoroides. High light further increased the damage to the photosynthetic apparatus under heat stress. The stronger the heat stress under high light, the harder the recovery of photosynthetic activity. Therefore, during ebb tide at noon in nature, heat stress combined with strong light would induce a significant, even irreversible decrease in photosynthetic activity. Moreover, the heat stress hindered the transcription of psbA and RuBisCO, enhanced respiratory O2, and induced severe peroxidation even if the SOD, APX, and GPX activities significantly improved. The results clearly suggest that heat stress, especially when coupled with high light, may be an important cause for the decline of E. acoroides meadows.