Mud Zone Research Articles

Compound- and element-specific accumulation characteristics of persistent toxic substances and metals in sediments of the Yellow Sea

This study investigated the large-scale distributions of persistent toxic substances (PTSs) and heavy metals in sediments of the Yellow Sea, collected from six transects between latitudes 32 and 37 degrees north (n = 35). Elevated concentrations of polychlorinated biphenyls (PCBs) were detected near the mainland, with a predominance of low-chlorinated congeners (di to tetra, ∼60%), indicative of atmospheric deposition. Analysis of traditional and emerging polycyclic aromatic hydrocarbons (t-PAHs and e-PAHs) revealed notable enrichment in the Central Yellow Sea Mud Zone (CYSM), attributing fossil fuel combustion as the significant source. Styrene oligomers and alkylphenols exhibited notable accumulation near the Han River Estuary in South Korea and the Yangtze River Estuary in China, respectively. The accumulation of heavy metals was predominantly observed in the CYSM, with element-specific distribution patterns. Cluster analysis revealed distinct distribution patterns for PTSs and metals, highlighting their source-dependent and grain size-dependent behaviors. In addition, the distribution and accumulation of PTSs tended to depend on their partitioning coefficients, such as the octanol-air partition coefficient (log KOA) and octanol-water partition coefficient (log KOW). This study offers valuable insights into the sources, transport, and fate of hazardous substances in the Yellow Sea, emphasizing the necessity for targeted environmental management strategies.

Geochemical properties of blue carbon sediments through an elevation gradient: study of an anthropogenically impacted coastal lagoon

Global research is showing that coastal blue carbon ecosystems are vulnerable to climate change driven threats including accelerated sea-level rise and prolonged periods of drought. Furthermore, direct anthropogenic impacts present immediate threats through deterioration of coastal water quality, land reclamation, long-term impact to sediment biogeochemical cycling. These threats will invariably alter the future efficacy of carbon (C) sequestration processes and it is imperative that currently existing blue carbon habitats be protected. Knowledge of underlying biogeochemical, physical and hydrological interactions occurring in functioning blue carbon habitats is essential for developing strategies to mitigate threats, and promote conditions to optimise C sequestration/storage. In this current work, we investigated how sediment geochemistry (0–10 cm depth) responds to elevation, an edaphic factor driven by long-term hydrological regimes consequently exerting control over particle sedimentation rates and vegetation succession. This study was performed in an anthropogenically impacted blue carbon habitat along a coastal ecotone encompassing an elevation gradient transect from intertidal sediments (un-vegetated and covered daily by tidal water), through vegetated salt marsh sediments (periodically covered by spring tides and flooding events), on Bull Island, Dublin Bay. We determined the quantity and distributions of bulk geochemical characteristics in sediments through the elevation gradient, including total organic carbon (TOC), total nitrogen (TN), total metals, silt, clay, and also, 16 individual polyaromatic hydrocarbon’s (PAH’s) as an indication of anthropogenic input. Elevation measurements for sample sites were determined on this gradient using a LiDAR scanner accompanied by an IGI inertial measurement unit (IMU) on board a light aircraft. Considering the gradient from the Tidal mud zone (T), through the low-mid marsh (M) to the most elevated upper marsh (H), there were significant differences between all zones for many measured environmental variables. The results of significance testing using Kruskal–Wallis analysis revealed, that %C, %N, PAH (µg/g), Mn (mg/kg), TOC:NH4+ and pH are significantly different between all zones on the elevation gradient. The highest values for all these variables exists (excluding pH which followed a reverse trend) in zone H, decreasing in zone M and lowest in the un-vegetated zone T. TC content is 16 fold higher overall in vegetated (3.43 -21.84%) than uninhabited (0.21–0.56%) sediments. TN was over 50 times higher (0.24–1.76%), more specifically increasing in % mass on approach to the upper salt marsh with distance from the tidal flats sediments zone T (0.002–0.05%). Clay and silt distributions were greatest in vegetated sediments, increasing in % content towards upper marsh zones The retention of water, metals, PAHs, mud, chloride ions, NH4+, PO43− and SO42− increased with elevated C concentrations, concurrently where pH significantly decreased. Sediments were categorized with respect to PAH contamination where all SM samples were placed in the high polluted category. The results highlight the ability of Blue C sediments to immobilise increasing levels of C, N, and metals, and PAH with over time and with both lateral and vertical expansion. This study provides a valuable data set for an anthropogenically impacted blue carbon habitat predicted to suffer from sea-level rise and exponential urban development.Graphical abstractSummarized results from this study demonstrating the geochemical changes through an elevation gradient, with a transect encompassing intertidal sediments through supratidal salt marsh sediments within Bull Island’s blue carbon lagoon zones.

Distribution and Sediment Selection by the Mud Shrimp Upogebia noronhensis (Crustacea: Thalassinidea) and the Potential Effects on the Associated Macroinfaunal Community

Burrowers such as thalassinideans remobilize sediment in benthic ecosystems, altering granulometry, enhancing organic matter cycling and oxygenation. We characterized the distribution of the mud shrimp Upogebia noronhensis and the associated macroinfauna along a depth and granulometric gradient in a shallow subtidal area in the southern Brazilian coast. Mud shrimp densities were estimated by burrow opening count using 0.25 m2 quadrats in three sediment zones: sand, sand-mud transition and mud. Macroinfaunal community descriptors and sediment granulometric characteristics were assessed. U. noronhensis average density varied from 0.6 to 145 individuals m−2 and was highest in the transition zone and lowest in the sand zone. Macrofauna in the sand zone was at least three times more abundant and 1.2 times richer, averaging 436.3 organisms and 39 species, while the transition and mud zones were more even in species distribution (species evenness > 0.7). The shrimp presence seems to be linked to a coarse sand content <80% and clay and silt <40% in the sediment, a compromise between gallery construction ability and filter-feeding suitability. High densities and aggregated distribution of mud shrimp, combined with alteration of sediment grain composition and organic matter, are likely to affect macroinfaunal abundance nearby the burrows.

Research on the Metal Corrosion Process in the Sea Mud/Seawater/Atmosphere Interface Zone

Corrosion in the interface zone is a complicated local corrosion phenomenon. The conventional single-electrode method finds it difficult to obtain the kinetic information of corrosion occurrence and development process. In this paper, metal corrosion was studied by Wire Beam Electrode (WBE) technology on the interfaces of sea mud/seawater and seawater/atmosphere. The study found that the metal corrosion in the interface is a process of coupling a dual corrosion cell into a single corrosion cell. Initially, a corrosion cell is formed with the seawater/atmosphere interface acting as the cathode and the upper part of the metal in the seawater area as the anode. This is due to the oxygen concentration cell caused by the waterline effect. The cathode area is always enriched near the seawater/atmosphere interface. The lower part of the metal in the seawater area and the metal in the sea mud area are the anode and the cathode, respectively, of another corrosion cell. Along with the immersion time, the anodic area of the first corrosion cell gradually extends to the lower part of the metal in the seawater zone and finally the sea mud zone, resulting in the disappearance of the second corrosion cell. In the single corrosion cell stage, the seawater/atmosphere interface is the cathode area; the seawater area and the sea mud area are the anode areas, and the electrode adjacent to the cathode area becomes the anode area with the largest current density. During the whole experiment, the sea mud zone is a process of polarity transition from the cathode zone to the anode zone, and finally forms the anode zone of the whole electrode together with the anode zone in the sea zone.

Distribution, seasonal and age-related dynamics of intestinal cestodoses of sheep and goats in the mud zone of the Republic of Dagestan

Distribution, seasonal and age-related dynamics of intestinal cestodoses of sheep and goats in the mud zone of the Republic of Dagestan

The fate of organic carbon burial in the river-dominated East China Sea: Evidence from sediment geochemical records of the last 70 years

The accumulation of organic carbon (OC) in the sediments of river-dominated continental margins plays a critical role in the global carbon budget and is subject to human modification. However, the relationships between human activities in drainage basins and carbon burial in modern sediments are still poorly understood. Here, a well preserved sediment core from a mud zone in the East China Sea (ECS) was analyzed for isotopes (δ13Corg and δ15N), radioisotopes (210Pb and 137Cs), bulk organic carbon and nitrogen, sediment grain size, major elements, trace metals and chemical properties (pH and Eh), in order to reveal the fate of the OC buried in the studied shelf over the last 70 years. The results showed that the input of terrestrial organic matter (TOM) from the Yangtze River into the ECS declined by 15% between 1980 and 2005, in concomitance with decreasing terrestrial-derived Ca and Zr. These changes were mainly due to alterations in the sediment load and cultivated land, induced by river damming and soil conservation practices. The amount of marine organic matter (MOM) was strongly and positively correlated with chlorophyll a concentrations and the loads of dissolved inorganic nitrogen and phosphate. The discharge of riverine nutrients from artificial fertilizers seems to be one of the key factors influencing marine productivity. OC burial fluxes varied between 33.8 and 54.7 g C m−2 yr−1 and were primarily related to changes in the mass accumulation rates (MARs) and OC%. Notably, due to the construction of the Three Gorges Dam (TGD) in 2003, the input of eroded material from the downstream and subaqueous delta of the Yangtze River increased, profoundly altering the local hydrodynamics and sedimentary redox levels. These changes may, in turn, accelerate the degradation of sedimentary OC, preventing carbon deposition and preservation.

Mud gas play

The presence of methane gas seepage in the mud volcano proves the existence of gas associated with over pressured zone in the subsurface. The analysis of C isotope on samples of methane gas seepage of mud volcano show the gas is thermogenic methane at the level of thermal maturity that is equivalent to the peak of petroleum formation. The mud of mud volcano extruded from overpressures zone beneath is predicted to have high gas storage capacity. The objectives of this paper are to define capacity of the mud of mud volcano system as a potential reservoir gas and its role in petroleum system. Isothermal absorption test is performed to answer the storage capacity of the mud of Kesongo and Lusi mud volcanoes system. Seismic data and velocity data show over pressured mud zone as chaotic zone with low velocity anomaly distributed crossing the reflector layer as chamber. The gas storage capacity of the mud based on adsorption test at the temperature of 65-degree Celsius ranges from 812 scf/ton up to 3,217 scf/ton shows it has capacity of gas reservoir. The adsorbed gas in over pressured mud shows different mechanism with that of the conventional reservoir. Adsorbed gas in over pressured mud can be proposed as unconventional gas reservoirs with new alternative hydrocarbon play: mudgas-play (MGP). Mud-gas-play is defined as the accumulated gas trapped in over pressured zone. Gas accumulations tend to be concentrated in the upper part of over pressured zone.

Halogenated flame retardants in the sediments of the Chinese Yellow Sea and East China Sea

With the phasing out of traditional polybrominated diphenyl ethers (PBDEs), significant volumes of alternative brominated flame retardants (aBFRs) are being used and released into the environment compartment, especially in coastal regions. The levels and distribution of PBDEs, aBFRs, and dechlorane plus (DPs) were investigated in the surface sediments of the Yellow Sea (YS) and East China Sea (ECS) to examine the distribution and sources of these hydrophobic contaminants. The level and distribution of pollutants in the sediments of YS and ECS show obvious regional differences. As a major replacement for decabromodiphenyl ether (BDE 209), decabromodiphenyl ethane (DBDPE) was the dominant compound observed in the surface sediments, with a concentration one order of magnitude higher than that of BDE 209. High concentrations were found in the depositional zones of the YS, indicating that these contaminants may originate from land-based pollution sources (likely from the Laizhou Bay manufacturing base) near the Bohai Sea. The pollutants can be carried by the coastal current together with the sediment from the Yellow River, transported through the Bohai Strait and deposited in the mud zone of Northern and Southern YS. Low levels of halogenated flame retardants (HFRs) were found in the estuary of the Yangtze River and ECS, indicating that Yangtze River contributes less HFRs to the region. Riverine discharge, atmospheric deposition, surface runoff, ocean current system, and mud area deposition effects may be significant factors influencing the distributions of HFRs.

Sediment Depth-Dependent Spatial Variations of Bacterial Communities in Mud Deposits of the Eastern China Marginal Seas.

The mud sediments of the eastern China marginal seas (ECMS) are deposited under different hydrodynamic conditions with different organic matter sources. These events have been demonstrated to exert significant influences on microbial communities and biogeochemical processes in surface sediments. However, the extent to which such effects occur in subsurface microbial communities remains unclear. In this study, both horizontal and vertical (five sites, each for eight layers) distributions of bacterial abundance and community composition in mud deposits of the South Yellow Sea (SYS) and East China Sea (ECS) were investigated by quantitative PCR and Illumina sequencing of the 16S rRNA gene. Both bacterial abundance and diversity were higher in the ECS than in the SYS, and tended to be higher in up than in deep layers. Proteobacteria (JTB255 marine benthic group), Acidobacteria and Bacteroidetes were dominant in the upper layers, whereas Lactococcus, Pseudomonas, and Dehalococcoidia were enriched in the deep layers. The bacterial communities in surface and subsurface sediments showed different inter-taxa relationships, indicating contrasting co-occurrence patterns. The bacterial communities in the upper layer samples clustered in accordance with mud zones, whereas those in the deep layer samples of all sites tended to cluster together. TOC δ13C and TON δ15N significantly affected the bacterial community composition, suggesting that the abundance and composition of organic matter played critical roles in shaping of sedimentary bacterial communities. This study provides novel insights into the distribution of subsurface bacterial communities in mud deposits of the ECMS, and provides clues for understanding the biogeochemical cycles in this area.

The Lusi drone: A multidisciplinary tool to access extreme environments

Extreme and inaccessible environments are a new frontier that unmanned and remotely operated vehicles can today safely access and monitor. The Lusi mud eruption (NE Java Island, Indonesia) represents one of these harsh environments that are totally unreachable with traditional techniques. Here boiling mud is constantly spewed tens of meters in height and tall gas clouds surround the 100 m wide active crater. The crater is surrounded by a ∼600 m diameter circular zone of hot mud that prevents any approach to investigate and sample the eruption site. In order to access this active crater we designed and assembled a multipurpose drone.The Lusi drone is equipped with numerous airborne devices suitable for use on board of other multicopters. During the missions, three cameras can complete 1) video survey, 2) high resolution photogrammetry of desired and preselected polygons, and 3) thermal photogrammetry surveys with infra-red camera to locate hot fluids seepage areas or faulted zones. Crater sampling and monitoring operations can be pre-planned with a flight software, and the pilot is required only for take-off and landing. A winch allows the deployment of gas, mud and water samplers and contact thermometers to be operated with no risk for the aircraft. During the winch operations (that can be performed automatically), the aircraft hovers at a safety height until the tasks controlled by the winch-embedded processor are completed. The drone is also equipped with GPS-connected CO2 and CH4 sensors. Gridded surveys using these devices allowed obtaining 2D maps of the concentration and distribution of various gasses over the area covered by the flight path.The device is solid, stable even with significant wind, affordable, and easy to transport. The Lusi drone successfully operated during several expeditions at the ongoing active Lusi eruption site and proved to be an excellent tool to study other harsh or unreachable sites, where operations with more conventional methods are too expensive, dangerous or simply impossible.

Effects of terrestrial and marine organic matters on deposition of dechlorane plus (DP) in marine sediments from the Southern Yellow Sea, China: Evidence from multiple biomarkers

As an emerging halogenated organic contaminant, Dechlorane Plus (DP) was scarcely reported in marine environments, especially in China. In this work, 35 surface sediments and a sediment core were collected across the Southern Yellow Sea (SYS) to comprehensively explore the spatio-temporal distribution and possible migration pathway of DP. DP concentrations ranged from 14.3 to 245.5 pg/g dry weight in the surface sediments, displaying a seaward increasing trend with the high levels in the central mud zone. This spatial distribution pattern was ascribed to that fine particles with the elevated DP levels were preferentially transported to the central mud zone under hydrodynamic forcing and/or via long-range atmospheric transportation and deposition. DP concentrations in sediment core gradually increased from the mid-1950s to present, which corresponded well with the historical production and usage of DP, as well as the economic development in China. Significantly positive correlation between DP and total organic carbon (TOC) in both surface sediments and sediment core indicated TOC-dependent natural deposition of DP in the SYS. We used multiple biomarkers, for the first time, to explore the potential effects of terrestrial and marine organic matters (TOM and MOM) on DP deposition. The results showed that competition may occur between TOM and MOM for DP adsorption, and MOM was the predominant contributor in controlling DP deposition in the marine sediments from the SYS.

Sources, geochemical speciation, and risk assessment of metals in coastal sediments: a case study in the Bohai Sea, China

To investigate the sources and toxicity of metals in Bohai Sea sediments, concentration and geochemical speciation of metals of surface sediments were measured. Metal distributions and principal component analysis suggested that Zn, Pb, Cd, and Ag were largely derived from anthropogenic sources, whereas the majority of the other metals studied here were found to have been derived from natural rock weathering and calcareous marine biota. The major sources of anthropogenic metal inputs to the study region are from the mining industry, port transport services, vehicle exhausts, and agricultural runoff. Empirical sediment quality guidelines and the risk assessment code were used to evaluate the metal toxicities in this area. Our results show that Cd presents a high risk to the ecological system because it was found in the non-residual phase, which tends to be weakly bound and highly bioavailable; Cu, Pb, Ni, and Co pose a low risk; Zn and Cr present no risk. The use of the threshold effects level and effects range-low values of Cd and Cr as guidelines for the Bohai Sea are of limited use as they do not account for the bioavailability and toxicity of the elements in marine environments. Assessment of the annual metal fluxes from riverine and atmospheric sources indicates that the largest contributions of metals to the Bohai Sea were derived from the suspended particulate load of rivers. Furthermore, it was found that the main depositional zones for metals in the Bohai Sea were in estuaries and the center mud zones.

Influence of Eccentrically Located Drilling String in the Well Bore Over Cleaning Capabilities of a Wellbore

It has been analyzed solution to the problem of definition eccentric location of the drill string in the hole using analytical studies and modern systems of mathematical computer modeling. Practical implementation of technological problem solution was represented as calculated parameters of the formation and changes in the area of stagnant zones in the cross section of the annular space hole in certain baseline characteristics of the process of washing. As a result, studies have found that at lower eccentric placement of both direct and deformed drill string in the well drilling mud flow looks like sickle core flow. The maximum speed of mud while inside the nucleus, and the minimum - in the contact zones flexible pipe and the borehole wall. This change dependencies hydraulic pressure loss pumping mud pump flow rate and distribution of nuclei along the axis of the drill string at its eccentric location in the borehole. It has been determined the conditions of dead mud zones formation in the annular space and offered solutions to solve this problem.

Rapid appraisal links feral buffalo with kunkod (Melaleuca spp.) decline in freshwater billabongs of tropical northern Australia

Freshwater wetlands have great ecological, social, cultural and economic importance and are considered some of the most threatened ecosystems globally, especially in the tropics. In the tropics of northern Australia, much land is owned by Aboriginal people, thus requiring community-based approaches to monitoring and decision making. Herein we present a collaborative community-based rapid appraisal of an observed decline in a culturally and ecologically important tree genus of the freshwater wetlands in northern Australia, locally known as kunkod (Melaleuca spp., Myrtaceae) by Bininj (local Aboriginal people). We conducted collaborative research with the local Aboriginal Djelk Rangers incorporating local and scientific knowledge and preferred research methods. The decline in kunkod was more common in the water zone than in the mud and dry zones of freshwater billabongs in the Djelk Indigenous Protected Area. Kunkod decline and poor regeneration were significantly correlated with high water electrical conductivity, turbidity and ammonium. Feral buffalo activity was also positively correlated with these parameters, suggesting an indirect effect of buffalo on kunkod population health (large and small trees) through reduced water quality rather than direct rubbing on the trees, as was initially expected. Ongoing monitoring will allow assessment of potential recovery of kunkod following planned feral buffalo control.

Diversity, Abundance, and Niche Differentiation of Ammonia-Oxidizing Prokaryotes in Mud Deposits of the Eastern China Marginal Seas.

The eastern China marginal seas (ECMS) are prominent examples of river-dominated ocean margins, whose most characteristic feature is the existence of isolated mud patches on sandy sediments. Ammonia-oxidizing prokaryotes play a crucial role in the nitrogen cycles of many marine environments, including marginal seas. However, few studies have attempted to address the distribution patterns of ammonia-oxidizing prokaryotes in mud deposits of these seas. The horizontal and vertical community composition and abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) were investigated in mud deposits of the South Yellow Sea (SYS) and the East China Sea (ECS) by using amoA clone libraries and quantitative PCR. The diversity of AOB was comparable or higher in the mud zone of SYS and lower in ECS when compared with AOA. Vertically, surface sediments had generally higher diversity of AOA and AOB than middle and bottom layers. Diversity of AOA and AOB showed significant correlation with latitude. Nitrosopumilus and Nitrosospira lineages dominated AOA and AOB communities, respectively. Both AOA and AOB assemblages exhibited greater variations across different sites than those among various depths at one site. The abundance of bacterial amoA was generally higher than that of archaeal amoA, and both of them decreased with depth. Niche differentiation, which was affected by dissolved oxygen, salinity, ammonia, and silicate (SiO), was observed between AOA and AOB and among different groups of them. The spatial distribution of AOA and AOB was significantly correlated with δ15NTN and SiO, and nitrate and δ13C, respectively. Both archaeal and bacterial amoA abundance correlated strongly with SiO. This study improves our understanding of spatial distribution of AOA and AOB in ecosystems featuring oceanic mud deposits.

Corrosion Resistance of X52 Pipeline Steel at Sea Mud Zone

Corrosion resistance of X52 pipeline steel at sea mud zone in Qingdao Huiquan test station was investigated by using Tafel polarization curves and electrochemical impedance spectroscopy (EIS). The morphology and chemical composition of the corrosion products were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that the corrosion current density of X52 pipeline steel increased with immersion time. The corrosion products were loose and mainly included Fe3O4, Fe2O3 and FeOCl, which absorbed on the specimen surface accelerating the cathodic depolarization reaction.

A Study on Sacrificial Anode Cathodic Protection for Wharf Steel Pile of Tripoli Lebanon

In this paper, the sacrificial anode protection system for steel pile of Tripoli wharf (Lebanon) was studied. Optimal average protection current densities were selected for steel pipe/sheet pile of seaside zone back filled zone and sea mud zone. Based on field test and investigation, we found that the optimal average protection current density for seaside zone is 0.060 A/m2, back filled zone 0.030 A/m2 and sea mud zone 0.025 A/m2, respectively.

Sedimentary ladderane core lipids as potential indicators of hypoxia in the East China Sea

Anammox (anaerobic ammonium oxidation) is an important process in many suboxic to anoxic marine environments for converting fixed nitrogen to N2, and has a major impact on the marine nitrogen cycle. Ladderane core lipids have been utilized as an indicator of the contribution of anammox to the marine nitrogen cycles. However, such studies have not been reported for the China seas and little is known about the importance of anammox within the nitrogen cycle of these marginal seas. In the research reported here, the ladderane core lipid contents of 17 surface sediment samples from the East China Sea are reported, and their spatial distribution is investigated. C18 -[5]-ladderane FAME, C20-[5]-ladderane FAME and C20-[3]-ladderane FAME have all been detected, suggesting that the anammox bacteria are widely present within the study area. The total contents of the three ladderane lipids (ΣFAMEs) range from 24–355 ng/g (weight of dry sediments), with higher contents occurring in the Minzhe Mud Zone and broadly coincident with the spatial distribution of hypoxia. It is suggested that the sedimentary ladderane core lipids are mainly produced in the water column and their sedimentary contents can be used as indicators of water column hypoxia.

Simulation of wave damping during a cold front over the muddy Atchafalaya shelf

The Atchafalaya Shelf off the Louisiana coast in the United States is characterized by fine grained sediments dispersing into the shelf from the lower Atchafalaya River and Wax Lake outlets. Rapid seaward flushing of the sediment-laden river plumes, due to water level set-down during cold front passages forms a fluid mud layer close to the bottom, which effectively dampens the wave energy. In this study, the performance of a phase-averaged spectral wave model was skill assessed based on the wave data recorded close to the southern periphery of the mud zone during several days in March 2009. Separation of wave spectra into sea and swell partitions showed that the wave model overestimated the sea waves generated by northerly wind during the cold front passage. A non-stationary scheme was needed to solve the wave action balance equation to include the wind dynamics during the cold front passages over the study area. A recently developed mud-induced dissipation term was improved by modifying its algorithm for solving the implicit dispersion equation. The modified model became efficient enough to be used for non-stationary calculations. The thickness, density, kinematic viscosity of the mud layer, and its offshore extent were determined by trial and error. The mud-induced energy dissipation term enabled the model to reproduce the energy attenuation of short waves by the fluid mud. A high value of mud viscosity (0.01–0.1m2/s) was required to obtain good agreement with in situ measurements when the maximum wave height occurred. However, the model using lower values of mud viscosity (0.001–0.01m2/s) was more successful in reproducing the measured wave spectra from a few hours after the maximum wave activity. The simulation results also showed that presence of fluid mud with high value of mud viscosity hindered the wave growth in shallow water due to suppression of high frequency waves.

A combined field and modeling study of groundwater flow in a tidal marsh

Abstract. Bald mud beaches were found among the mangrove marshes in Dongzhaigang National Nature Reserve, Hainan, China. To investigate the possible reasons for this phenomenon, the intertidal zones of a mangrove transect and a bald beach transect with similar topography and tidal actions were selected for comparison study. Along both transects, observed water table variations were significant in the high and low intertidal zones and negligible in the middle intertidal zones. Despite the same tidal actions and above-mentioned similarities, observed groundwater salinity was significantly smaller along the mangrove transect (average 23.0 ppt) than along the bald beach transect (average 28.5 ppt). These observations invite one hypothesis: the hydraulic structure of tidal marsh and freshwater availability may be the main hydrogeological factors critical to mangrove development. Two-dimensional numerical simulations corroborated the speculation and gave results in line with the observed water table. The two transects investigated were found to have a mud-sand two-layered structure: a surface zone of low-permeability mud and an underlying high-permeability zone that outcrops at the high and low tide lines. The freshwater recharge from inland is considerable along the mangrove transect but negligible along the bald beach transect. The high-permeability zone may provide opportunity for the plants in the mangrove marsh to uptake freshwater and oxygen through their roots extending downward into the high-permeability zone, which may help limit the buildup of salt in the root zone caused by evapotranspiration and enhance salt removal, which may further increase the production of marsh grasses and influence their spatial distribution. The bald beach is most probably due to the lack of enough freshwater for generating a brackish beach soil condition essential to mangrove growth. It is also indicated that seawater infiltrated the high-permeability zone through its outcrop near the high intertidal zone, and discharged from the tidal river bank in the vicinity of the low tide line. These processes thereby formed a tide-induced seawater-groundwater circulation, which likely provided considerable contribution to the total submarine groundwater discharge (SGD). Finally, implications and uncertainties behind this study were summarized for future examinations.