Tidal Conditions Research Articles

Trajectory of microplastic particles with 2-dimensional hydrodynamic modelling approach at Pekalongan waters, Central Java, Indonesia.

This research aims to understand the extent of microplastic contamination in Pekalongan waters, Central Java, and its potential impact on fishing grounds, aligning with Indonesia's National Action Plan for Handling Marine Debris 2018-2025. The study employs a 2D hydrodynamics modelling approach with Mike 21 Software to map the spatial distribution of microplastic movement concerning fishing areas during the west and east monsoon seasons. The results showed that microplastic particles follow tidal currents in Pekalongan waters, with their movement influenced by factors such as current, wind, and tidal conditions. The trajectory of microplastics entering fishing ground areas poses potential contamination risk for fish caught by fishermen, threatening the health of marine ecosystems and the stability of their structure and function.

Effects of cable bacteria on vertical redox profile formation and phenanthrene biodegradation in intertidal sediment responded to tide

Periodic oxygen permeation is critical for pollutant removal within intertidal sediments. However, tidal effects on the vertical redox profile associated with cable bacterial activity is not well understood. In this study, we simulated and quantified the effects of tidal flooding, exposing, and their periodic alternation on vertical redox reactions and phenanthrene removal driven by cable bacteria in the riverbank sediment. Results show that electrogenic sulfur oxidation (e-SOx) mediated by cable bacteria during exposing process drove the vertical permeation of oxidation potential characterized by a decrease in Fe(II) and sulfide concentrations. The sulfate produced was observed in deep sediment (5–10 mm) and served as an electron acceptor for anaerobic oxidation, thereby triggering the functional succession of microbial community. About 78.2 % and 80.8 % of phenanthrene was degraded in deep sediment where cable bacteria grew well under exposing and tidal conditions. Anaerobic processes during tidal flood were also found to be important for the survival of cable bacteria. Higher cable bacteria abundance (up to 1.5 %) was observed under tidal conditions compared to that under continuous exposing conditions and flooding conditions. This might be attributed to lower oxidation stress and sulfide replenishment via sulfate reduction while flooding. Under tidal conditions, the cable bacteria interacted with sulfate reduction bacteria (e.g. Desulfobacca spp. and Desulfatiglans spp.) and maintained the dynamic balance of HS− and SO42− in sediment profiles. This HS−-SO42− cycle could serve as a “redox connector” that continuously delivers oxidation potential to deep sediments, resulting in the removal of organic pollutants. The findings provide preliminary evidence of the self-purification mechanisms within intertidal sediments and suggest a potential strategy for sediment remediation.

Development and prediction of scour around offshore wind turbine monopile foundations in ebb and flow tides

Monopile foundations are commonly used to support offshore wind turbines (OWTs) in nearshore shallow waters, where the periodic ebb and flow of tides can cause severe seabed erosion around these foundations. Accurately predicting the progression of scour depth under these tidal conditions is crucial for the safety of OWTs. While a few empirical formulas for equilibrium scour depth in periodic tides have been proposed, they often overlook the backfilling effects during their derivation. Consequently, these methods fail to predict the progression of scour depth characterized by recurring scouring and backfilling processes. In this study, the scour progression under different tidal patterns, including square tides, symmetrical sinusoidal tides, and asymmetrical sinusoidal tides with various periods, is investigated using numerical methods. It is indicated by the results that deeper scour depths are produced by symmetrical tides compared to asymmetrical tides, while the highest scour depth is observed under square tides, potentially slightly exceeding that under unidirectional currents. Additionally, asymmetric scour depths at the front and back sides of the pile can result from the asymmetry of tides. Although scour progression is affected by tide periods, their impact on the equilibrium scour depth is limited. Furthermore, a new concept called normalized cumulative effective flow intensity is introduced, which plays a primary role in governing equilibrium scour depth. Based on this concept, prediction methods for both equilibrium scour depth and scour progression under sinusoidal tides, which closely resemble natural tidal patterns, are proposed. The accuracy of these methods is validated by experimental data from previous studies. These findings not only provide a method to optimize the design of monopile burial depth but also aid in the development of appropriate maintenance measures to prevent scour-induced damage to OWT foundations over their long lifespans.

Changes in the suspended floc properties by bed erosion in a macrotidal muddy flat: Case of Asan Bay, Korea

Intertidal flats have closely connected sediment transport systems with tidal channels. The properties of suspended sediments derived by horizontal advection and local erosion were examined under various current and wave. A field campaign was conducted over two weeks (October 17–31, 2021) in the Asan intertidal flat. Suspended sediments were in the form of flocs, which are clumps of particles, with an average floc size (davg) of 70–275 μm. The maximum current velocity and water level at each tidal cycle continuously decreased from 0.19 to 0.04 m s−1 and from 5 to 2 m, respectively. In accordance with the hydrodynamic conditions, continuous decrease in davg from spring to neap tides was superimposed by flood-ebb variations in davg. Geological heterogeneity between channels and flats can be significantly influenced by tide and wind conditions. Under tide-dominant conditions, the spring tidal current was strong enough to transport macroflocs with davg of 200–500 μm into the intertidal flats. The grown macroflocs up to 1.6 times of davg at early flood tide were deposited in the flats during the slack tide and transported back to the channels by ebb tidal current. Under wind-dominant conditions, the suspended flocs originated primarily from the bed by erosion. The deposited macroflocs or microflocs were entrained into water column and transported to adjacent tidal channel as microflocs or flocculi. The structure of the advected flocs had more varied density in the range of 42–147 kg m−3, compared to the eroded flocs. Under severe erosion, the structure of suspended flocs was similar to that of advected flocs despite their smaller size. This suggests that bed erosion supplied more porous flocs into the water column than those transported by advection. Consequently, the intertidal flats are at an increased risk of erosion due to the diverse structure of flocs.

The hypertidal Santa Cruz–Chico River estuary (South Patagonia, Argentina): A hybrid ria-type system under extreme tides, arid climate and active uplift

The present study focuses on the morphosedimentary organization and sediment infilling stratigraphy of one of the largest estuaries of southern Patagonia in Argentina. With a tidal range up to 12 m, the area is subject to extreme tidal conditions, combined with moderate offshore wave climate, strong and constant westerly winds, and contrasted water and sediment discharges from the two tributaries of the estuary, the Santa Cruz and Chico rivers. The estuarine valley is entrenched in the Patagonian coastal plateau due to significant uplift. On the basis of sediment facies (sedimentary structures, grain size, geochemistry, mineralogy), meiofauna (foraminifera and testate amoebae), morphological changes and shallow geophysics (high-resolution seismic reflection, ground-penetrating radar) data, the Santa Cruz–Chico River system is defined as a hybrid system comprising a tide-influenced fluvial mouth (the Santa Cruz River) and a tide-dominated estuary (the Chico River estuary), both converging toward an elongated subtidal ria-type estuarine basin. River-supplied sands and muds by-pass the estuarine basin and are exported offshore where they settle and form an ebb-tidal delta. Sediments in the Santa Cruz–Chico River valley mainly consist of Pleistocene lowstand fluvial gravels resting on the regional Miocene substrate, and thin early Holocene transgressive deposits, deeply incised by a tidal ravinement surface that developed during the highest Holocene sea-level at ca 7500 y. BP. After the maximum stillstand, relative sea level fell and a competition occurred between erosion, promoted by water depth decrease, and deposition, favored by tidal prism reduction. At present, sediment by-passing and offshore sediment export are the dominant processes. The very large size of the ebb-tidal delta, which expands on the continental shelf, suggests that this situation has prevailed for a very long time.

The role of estuarine convergence on the salinity distribution and the estuary response to short river discharge pulses

Estuarine behaviour is primarily controlled by the interaction of river discharge and tidal mixing. Transient increases in river discharge, which occur naturally during the wet season or can be managed in regulated basins, alter estuarine dynamics and reduce salt intrusion. Two characteristic times have been identified in the response to these river pulses: the adjustment time (the time required to adapt to the peak discharge) and the recovery time (the time required to return to steady state conditions). Previous work has analysed the effect of peak discharge and pulse duration in the adjustment process, focusing on long discharges (i.e. longer than the intrinsic estuarine timescale) and straight channels. This paper presents an idealised 3-dimensional model (Delft3D) to assess the effect of estuarine convergence on the response to short river pulses in tide dominated, well-mixed estuaries. The similarity between the tidal period, the estuarine timescale and the duration of the pulse led to the introduction of the time between tidal and river conditions as an additional parameter in the analysis. The results show that salt intrusion in convergent estuaries have a lower sensitivity to variations in river discharge compared to the behaviour of prismatic estuaries. Conversely, the influence of convergence on changes in salt intrusion due to the increased river discharge gains relevance in convergent estuaries. Seaward transport of salt is significantly enhanced by freshwater releases that occur between early and mid ebb, especially during spring tides. Increasing convergence reduces the asymmetry of the estuarine response, shortens the recovery time, and shifts the onset of maximum salt displacement and the minimum adjustment time. The results are particularly relevant for water management and salt intrusion control in regulated basins with limited resources, as the volume of fresh water used to reduce salt intrusion can be optimised considering the timing of the pulse release, which depends on the tidal conditions at the estuary.

Tracking the invasive and euryhaline pikeperch Sander lucioperca in the lower River Thames using acoustic telemetry indicates no movements into areas of relatively high salinity.

Native to Central and Eastern Europe, the euryhaline pikeperch Sander lucioperca can acclimatize to elevated salinity levels (e.g., up to 30‰), but it remains unknown whether their invasive populations use this ability to inhabit and/or disperse through brackish waters, such as estuaries and inshore areas. To test whether invasive pikeperch show a propensity to move into areas of relatively high salinity, their spatial use and movement patterns (e.g., home range, distances moved, and movement rates) were assessed using acoustic telemetry in the upper River Thames estuary, southeast England. Analyses revealed that individual pikeperch were capable of moving relatively long distances in a short time (e.g., speeds up to 70 m min-1), with movement patterns associated more with tidal state and elevation at the water surface (both assumed to relate to changes in salinity) than diurnal changes. There were no recorded movements of any pikeperch into the more saline, downstream waters of the estuary where salinity levels were recorded to over 40‰, with the mean salinity in the most downstream area where pikeperch were detected being 1.39‰ (range of logger: 1.22-1.71). The results suggest that these pikeperch did not use high salinity waters when less saline waters were available, and thus the risk that they will use to move through high salinity areas to expand their invasive range appears low. Accordingly, efforts to minimize risks of the further dispersal of invasive pikeperch populations can focus on control and containment programmes within fresh waters.

Are Thai mangrove managers aware of the potential threat posed by sea level rise?

Rapid sea level rise (SLR) represents a novel threat to mangroves, which could adapt through vertical accretion or landward expansion. Depending on tidal conditions and stressors, managers will likely have to intervene to enhance the adaptive capacity of mangroves. However, managers must be aware of, understand, and anticipate the risks of SLR-induced habitat degradation to plan adaptive measures, which must be supported by administrative resources, political will, and stakeholder engagement. Here, we studied how cognitive, experiential, and organizational factors influence risk awareness and adaptive management capacity of communal and state-based managers. In telephone-based interviews, the risk perception of 60 community-based and 23 governmental mangrove managers in Thailand was assessed to gain insights into their awareness and understanding of SLR risks, current management practices and adaptive measures, and the extent of their collaboration and stakeholder engagement. The findings show that most managers acknowledge the presence of SLR (72%) but perceived the adaptive capacity of mangroves as sufficiently high and the risk of SLR-induced degradation as minimal (63%), regardless of their affiliation. However, few respondents (18%) were aware that SLR would prolong hydroperiods and increase waterlogging stress of mangrove trees. The survey also revealed organization-specific biases. State officials cited a high level of uncertainty due to limited research and monitoring preventing them from planning adaptive measures. Community managers relied on their past experiences of mangrove recovery following disturbances, which might be unsuitable for informing management decisions in response to the novel threat of SLR. These findings indicate a lack of knowledge and guidelines for understanding and addressing SLR impacts. Additionally, there was an observed optimism bias among community managers, where past successful recoveries led to an overestimation of mangroves' adaptive capacity. Knowledge transfer and awareness-raising among mangrove resource stakeholders are critical for developing adaptation measures.

Computational Simulation of Monopile Scour under Tidal Flow Considering Suspended Energy Dissipation

Local scour around bridge foundations significantly impacts the stability and safety of marine structures. The development of scour holes adjacent to the pile foundations of sea-crossing bridges, influenced by tidal currents, involves multidimensional physical fields, multiscale coupling, and complex variations in marine loads. However, experimental models alone are inadequate for investigating the underlying mechanisms. Numerical simulation, a critical tool for studying local scour processes, faces the challenge of accurately modeling sediment transport, particularly under tidal flow conditions near pile foundations. To solve this challenge, this research considers the effect of reciprocating flow on sediment shear as well as its characteristic dissipation based on the immersed boundary method, introduces a reciprocating flow dissipation mechanism, and adds a momentum exchange term between the fluid and the sediment to derive a new controlling equation; a new tidal flow localized scour solver is ultimately constructed, termed TidalflowFOAM. The solver effectively simulates complex flow conditions under tidal currents, extending the modeling capabilities to more realistic three-dimensional bridge scour scenarios under combined wave and current conditions. Validation through cases reported in the literature and a series of controlled experiments, encompassing varying depths, flow velocities, and pile diameters, demonstrates the solver’s proficiency in capturing post-vortex data and accurately reflecting the influence of key factors on scour depth. However, the fidelity of the simulated scour hole morphology under tidal flow conditions behind the piles requires enhancement. The proposed numerical model for tidal flow conditions has high solution accuracy and can guide practical engineering applications.

The combination of detection and simulation for the distribution and sourcing of microplastics in Shing Mun River estuary, Hong Kong

For the first time, combined detection and simulation was performed on microplastic (MP) debris in surface water, sediment, and oyster samples at ten coastal sites of Shing Mun River estuary, Hong Kong at different tidal conditions. The MP debris were extracted and detected using Fourier transform infrared (FT-IR) spectroscopy, and the simulation was conducted using Weather Research & Forecasting Model (WRF) / Regional Ocean Modelling System (ROMS) coupled hydro-dynamic modelling and the subsequent Lagrangian particle tracking.The results demonstrated the majority of polyethylene (with partial chlorine substitution) debris among all the MPs found, and great spatial and tidal variabilities of MP concentrations were observed. The combination of MP observation and simulations referred to the interpretation that a considerable percentage of MPs found in this study originated from South China Sea. Those MPs were probably transported to Tolo Harbour through sea currents and drifted inshore and offshore with tides. This study provided baseline measures of MP concentrations in Shing Mun River estuary and comprehensive understanding for how MPs transport and distribute within a dynamic estuarine system.

Response of Sediment Dynamics to Tropical Cyclones under Various Scenarios in the Jiangsu Coast

The Jiangsu Coast (JC), China, is an area susceptible to the impact of tropical cyclones (TCs). However, due to the lack of available on-site observation data, nearshore sedimentary dynamic processes under the impact of TCs have not been fully explored. This study developed a 3D wave–current–sediment numerical model for the JC based on the Finite Volume Community Ocean Model (FVCOM) to investigate sediment dynamic responses to TCs under various scenarios, including different tracks, intensities of TCs and tidal conditions. The validation results demonstrated the model’s satisfactory performance. According to the simulation results, typhoons can significantly impact the hydrodynamics and sediment dynamics. During Typhoon Lekima in 2019, strong southeasterly winds substantially increased the current velocity, bottom stress, wave height, and suspended sediment concentration (SSC). Three typical landfall-type typhoons, with prevailing southeasterly winds, brought significant sediment flux from southeast to northwest along the coast, while the typhoon that moved northward in the Yellow Sea induced a relatively small sediment flux from north to south. Typhoons could also induce stripe-like erosion and deposition, which is closely related to seafloor topography, resulting in seabed thickness variations of up to ±0.3 m. Additionally, strengthening typhoon wind fields can lead to increased sediment flux and seabed morphological changes. Typhoon Winnie, particularly at spring tide, had a greater impact on sediment dynamics compared to other landfall typhoons. Numerical simulations showed that the typhoon-induced net sediment flux within the spring tidal cycle could increase by 80% to 100% compared to the neap tidal cycle, indicating the significant influence of tidal conditions on sediment transport during TC events.

Analysis of delays in the container loading and unloading process at the stevedoring stage at PT Pelabuhan Indonesia (Persero) Regional 2 Pangkal Balam

This research aims to identify and overcome factors that hinder loading and unloading activities at PT Pelabuhan Indonesia (Persero) Regional 2 Pangkal Balam. This research uses a qualitative approach with primary data sources obtained through interviews, direct observation, and secondary data from related documents at the port office. Some problems faced in the loading and unloading process at Pangkal Balam Port include equipment damage, truck queues, weather conditions and sea tides. These factors have a negative impact on the efficiency and effectiveness of the stevedoring process, resulting in delays in the delivery of goods and losses for exporters and importers. Efforts to reduce these obstacles include improved equipment maintenance, better organization of truck queues, and adaptation to weather and tidal conditions. This research also emphasizes the importance of continuously evaluating existing operational procedures to increase the productivity and satisfaction of port service users. The results of this research can be a reference for PT Pelabuhan Indonesia (Persero) Regional 2 Pangkal Balam in improving port services so that goods can be delivered on time and service users are not disadvantaged. Thus, ports can function optimally as efficient and effective port activity centres.

Diversity of Gastropods in The Mangrove Forest Area of Ujung Kulon National Park

Various kinds of reseources in coastal areas are very important for us to maintain sustainability. We can find coastal area with varios kinds of ecosystems in Ujung Kulon National Park. This study aims to determine the diversity of gastropods in the mangrove forest area of Ujung Kulon National Park. Sampling used the line transect method and the purposive sampling method with low tide conditions. Sampling was carried out at three stations which are divided into three transects at each station. The transect line was drawn along 50 m with each transect made 5 plots with a size 1 x 1 m2 with a distance between plots of 10 m. This research was held in May-June 2021. The data analysis includes the index values of diversity, dominance, evenness, and abundance. The results of the gastropod obtained consist of 20 species from 7 different families so that diversity index value were included in the medium category with the highest diversity index value owned by station 1 with a diversity index value of 2,03 and the lowest diversity index value owned by station 3 with a value of 1,56. The gastropod abundance index value has an average value of 273 ind/m2.

Onshore sediment transport enhancement and evolution of bedforms: Laboratory experiments of beach ploughing

Progressive coastal retreat has been an issue exacerbated in recent years due to climate change. Sand is eroded from beaches during the winter and partially recovered during summer by slow accretion processes. The development of new working with nature techniques that produce enhanced beach accretion could help recover most of the sand lost during winter and thus reduce the impact of climate change on beaches. The presence of bedforms contribute to increasing onshore sediment transport, but few studies have been performed to quantify their effect. In this study, the evolution and effect of artificially created bedforms on onshore sediment transport were analysed in prototype-scale laboratory experiments. The tested bedforms mimicked a beach ploughing of the intertidal area, with a wavelength of 1.6 m and height of 0.25 m, corresponding to the ploughing dimensions that a tractor can perform. Two tests were performed with the same initial morphology, medium sand (D50 = 0.318 mm), sea state conditions (Hs = 0.3 m, Tp = 7 s) that produced accretion, and different water levels that represent two tidal states. The experimental flume was longitudinally split into two equal channels of 1 m wide, allowing the simultaneous simulation of a natural control geometry and a ploughed geometry, facilitating the comparison and assuring the very same sea conditions. The presence of ploughed bedforms produced two effects: (1) an acceleration of natural accretion rates reaching 40%, and (2) onshore sediment transport due to the migration of the bedforms. The acceleration of natural accretion was explained by the extra bottom roughness induced by the bedforms, which produced more wave dissipation through bottom friction and thus more accretive conditions. The ploughed height decreased exponentially as waves broke over the crest of the ridges, which almost disappeared after 2–3 h of wave action. As a result, the extra bottom roughness also decreased as time passed. Consequently, the nature-assisted beach enhancement technique of ploughing should be applied at each low tide to produce a cumulative effect. Plough bedforms migrated onshore at a rate of approximately 0.2 m/h during the first hour, mobilizing onshore up to 61 kg m−1 h−1 of sediment. Ripples appeared on the tops of the ridge crests and migrated faster onshore, contributing to the migration of the ploughed bedforms. These results demonstrated the importance of considering bedforms while studying accretion processes and the potential of ploughing as an innovative strategy of working with nature to enhance beach recovery.

Experimental study on the use of artificial meadows that mimic wave-vegetation interactions for coastal protection

A detailed experimental study was conducted on five artificial meadows made of structures that mimic wave-vegetation interactions. The meadows were of different lengths and leaf thicknesses under regular and random waves, such that the leaf thickness changed as the meadow length increased. Different wave heights, periods, and tidal conditions were examined. The results for regular and random waves were consistent. The meadow length had a stronger influence (30%–50%) on wave transmission than leaf thickness (5%–10%). A lower wave transmission was observed at higher wave energies due to enhanced wave-vegetation interaction, higher wave reflection, and effective energy dissipation. Compared with submerged conditions or when the top of the meadow was at still-water level, a lower wave transmission and higher wave reflection and energy dissipation were noted when the leaves emerged in the air. The longest meadow in the emerged condition reduced the wave height by more than 50% at mid meadow. Furthermore, a wave transmission coefficient of 0.3 was achieved by this model, which is desirable for the design of this wave barrier type. The model with the best overall hydrodynamic performance can be used alone or combined with existing natural vegetation for coastal protection.

Contrasting Methane Seepage Dynamics in the Hola Trough Offshore Norway: Insights From Two Different Summers

AbstractThis study investigates the temporal variations in methane concentration and flare activity in the Hola trough (offshore Norway) during May 2018 and June 2022. Between these time periods, methane seep activity exhibits 3.5 times increase, as evidenced by hydroacoustic measurements. As the seep area in the Hola trough is constantly within the hydrate stability zone, the observed increase cannot be attributed to migration of its shallow boundary due to temperature increase. However, a combination of low tide conditions resulting in a lower sediment pore pressure and a bottom water temperature increase resulting in a lower methane solubility is likely to explain the increase in the number of seeps observed in June 2022. The hypothesis of tide influence is supported by data collected from a piezometer deployed and recovered during the cruise showing that the tidal effect was observed 3 m below the seafloor. Despite the numerous methane seeps detected, methane concentration and gas flow rates near the seafloor were low (<19 nM and <70 mL min−1, respectively) compared to other areas with methane seep activity. This is likely due to strong currents rapidly dispersing methane in the water column. Sub‐seafloor investigations identified pathways for gas migration in methane seep areas, influenced by topography. This study provides valuable insights into the temporal dynamics of methane concentrations, flare activity, and gas distribution in the Hola trough, contributing to our understanding of offshore methane dynamics in the region.

Changes of physiological traits on red chili pepper (Capsicum annum L.) exposed by short-term waterlogging

Abstract Tropical riparian wetland known as non-tidal lowland is potential land for agriculture, especially for vegetable cultivation such as red chili pepper (Capsicum annum L.). Transitional period (dry to rainy season) has a chance for red chili pepper cultivation in the field (at low tide conditions), but has risk of experiencing dynamic water table to waterlogging in early rainy season. The aim of this research was to determine the effects of physiological traits of red chili pepper exposure on short-term (4 days) waterlogging. This study was done at the Tropical Crop Science Laboratory, Kagoshima University, Japan. The experiment was designed as a completely randomized factorial design. The first factor was control/field capacity and waterlogging (entire growing media was submerged). The second factor was chili variety, consisting of Laris and Romario. Treatments began 14 days after transplanting, lasted four days, then followed by seven days of recovery. The results of this study showed that there were changes in photosynthetic characters between before waterlogging, after waterlogging and after recovery time, between control and waterlogging, and also between Laris and Romario. Photosynthetic and transpiration rates decreased sharply under waterlogging in after waterlogging, but increased in after recovery period on Laris, opposite on Romario. Changes occur were associated with the decline in stomatal conductance and chlorophyll fluorescence as a response to waterlogging stress. Laris as a resistant variety has the ability to recover under short-term stress conditions, so it needs to be further developed for cultivation in tropical riparian wetlands.

Mangrove extent reflects estuarine typology and lifecycle events

Ecosystem services provided by mangrove forests are increasingly recognised worldwide. These values have led to numerous ecosystem protection and restoration measures, including recent blue carbon economic incentives to re-establish mangroves at scale. However, our current ability to predict mangrove extent is based mainly on inundation averages (e.g. hydroperiod) or tidal planes of mature mangrove forests. This study investigates the validity of existing methods to accurately predict mangrove extent by comparing the location of existing mangroves at 27 sites (in 23 estuaries in southeast Australia) against commonly used approaches. To this aim, the downslope and upslope surface elevation limits of the mangrove species Avicenna marina were measured on-site using high-resolution RTK-GPS equipment across different estuarine typologies, including drowned river valleys, strong and weakly tidal estuaries, tidal lakes, and intermittently open/closed estuaries. These measurements were analysed against long-term (8–30+ years) tidal records to estimate inundation characteristics within the estuary. Study results indicate that the commonly used tidal plane method for predicting mangrove extent can incorrectly predict vertical extent by over 40 per cent. Likewise, hydroperiod is a poor predictor of extent as similar hydroperiods can be calculated across significantly different estuarine inundation patterns.Interestingly, the results indicate that mangrove elevations and inundation patterns are not uniform within or across estuaries, although there is uniformity across related estuarine typologies. For instance, inundation patterns in drowned river valley estuaries are more consistent (less extreme inundation and exposure events) than in estuaries with a variable tidal range, such as tidal lakes. Ultimately, this study highlights that predictions of mangrove extent should consider estuarine typology, the lifecycle of mangroves, and potential physio-adaptations to changing inundation patterns. Importantly, future tidal conditions may encourage biophysical adaptations in mangroves which may confound the extent of existing predictive techniques.

Estuarine Adjustment: Dependence of Salinity Delay on the Forcing Timescale and Magnitude

AbstractThe salinity in estuaries continuously adapts to varying forcing for example, by discharge and tidal conditions. The changes in salinity lag behind the changes in forcing. Previous work has mostly related this delay to the adjustment time, which depends on an average background state of the estuary. Payo‐Payo et al. (2022), https://doi.org/10.1029/2021jc017523 showed that adjustment time however cannot explain the actually observed delays for a realistic salinity and forcing signal. Inspired by this, this study aims to develop relations between delay time and forcing variations and background state of the estuary. To this end, I first propose a definition of the actual delay of salinity based on wavelet analysis, applicable to observed or modeled salinity signals. To compare delay to estuarine parameters, I use a linear 1D model, but qualitative results carry over to the general case. Using model experiments with harmonic and peaked variations in the forcing, the delay time depends not only on the adjustment time, but also on the timescale of the forcing variation. Even for forcing timescales that are up to a factor 100 longer than the adjustment time, both forcing timescale and adjustment time are important for the delay. A second novel finding is that the delay depends strongly on the position along the estuary where the delay is observed. As verification, model experiments with realistically varying forcing were done, roughly inspired by the Modaomen Estuary (China). Although delay times showed a complicated and scattered dependency on model variables in this case, the above qualitative conclusions were confirmed.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.