Vertical Distribution Of Salinity Research Articles

Disentangling hydrodynamic drivers of the Southern Venice (Italy) coastal aquifer via frequency decomposition analysis: Insights, challenges, and limitations

Study regionShallow coastal aquifer located in the southern part of the Venice lagoon (Italy). Study focusThis study aims to improve the understanding of coastal aquifers’ hydrodynamics by implementing systematic time-series analyses of data. A collection of non-intrinsically consistent time series from hydrological (surface water and groundwater) and meteo-mareographic monitoring networks was obtained from different institutions. Each signal was broken down through a frequency decomposition analysis, isolating the main driving forces to focus on phenomena that occur at different time and spatial scales. New hydrological insights for the regionResults highlighted that the aquifer is highly connected with the Venice lagoon, with a clear fluctuation of piezometric heads induced by tidal major constituents, decreasing landward. Besides, the effects exerted by reclamation canals and pumping stations were also determined and found to increase landward. Despite the relatively simple behaviour of piezometric heads, the groundwater salinity is influenced by additional local factors, like probe depth, wells’ screen length, and vertical salinity distribution along the aquifer. These findings suggested how to make use of limited and sparse data to enhance the conceptual model of coastal aquifer hydrodynamics, while highlighting the limitations of existing monitoring networks. This outcome justified the need for an intrinsically-consistent network of dedicated multi-level samplers to avoid intra-borehole mixing and reliably characterize the groundwater salinity distribution.

On the Salinity Distribution Induced Mixing at the Mouth of the Estuary

Salinity is an essential parameter in estuaries because it determines the mixing process and distribution of biota in the estuary ecosystem. In the paper, we investigate the dynamics of salinity distribution in the Dumai estuary. Salinity and tidal data observation were carried out during the transitional season around the mouth of the estuary. We get the salinity time series data in a tidal cycle. We observed that the Formzhal number is about 0.239, indicating that the tidal type in Dumai estuary waters is mixed directional, tending to double a day, with the highest and lowest tides in the Dumai estuary being 1.26 and 0.47 m, respectively. The salinity variability due to tides was studied by harmonic analysis, while the spatiotemporal distribution was studied using an analytical solution developed by previous researchers. The results show the presence of time lag between tidal elevation and salinity variation. Low tide and salinity, which indicate the effect of river discharge, are significant. This study further indicated that high salinity occurs during strong mixing conditions. It implied that the high salinity from the offshore entrance to shallower waters allowed for mixing processes. This paper ends with a comprehensive discussion of the vertical distribution of salinity at the mouth of the estuary.

Influence of sluice gate operation on salinity stratification and hypoxia development in a brackish estuary dam

The water quality in the artificially made Saemangeum Lake, located in an estuary, is poor; here, we explored the causes of hypoxia development. The field survey for spatial and vertical distribution of salinity and dissolved oxygen (DO) was conducted three times at 6 sites in the Mankyung Basin during the period when the salinity stratification was developed, and continuous observations for temporal and vertical distribution of water temperature, salinity, DO, and flow direction and velocity were performed at a site in the downstream of the lake for about 40 days. Hypoxia was detected at the bottom layer of the survey sites, which were directly affected by seawater inflow. At these sites, the salinity stratification, one of the causes of hypoxia, was clearly observed. The Richardson number and potential energy anomaly (PEA) calculated from the continuous observation measurement results indicated that the water column was very stable and strongly stratified during the investigation period. The vertical salinity structure due to the stabilization of the water column and the bottom temperature above 20 °C caused hypoxia of the bottom layer when insufficient seawater inflow or non-operation of sluice gate. Due to the horizontal salinity gradient by the seawater flowing in through the sluice gate operation, a baroclinic force acts from the sluice gate to the upstream direction at the bottom layer. In contrast, a barotropic force acts from the upstream inlet toward the sluice gate at the surface layer. The directional flow of each water layer changes in opposite directions to form a repeated reversing current which prevents the supply of DO through the inflow of fresh seawater. Therefore, to improve the water quality of Saemangeum Lake, it is necessary to control the short/ long-term reversing current that obstructs DO supplementation from seawater flowing through the sluice gate.

Effect of Flow‐Direction‐Dependent Dispersivity on Seawater Intrusion in Coastal Aquifers

AbstractFlow‐direction‐dependent (FDD) dispersivity in coastal aquifers (CAs) may strongly affect the inland extend of seawater intrusion (SWI) and the accompanying vertical salinity distribution. FDD dispersivity may predict greater inland intrusion of the saltwater wedge, but less vertical spreading of salinity than does the classical flow‐direction‐independent (FDI) dispersivity, the standard currently employed in most numerical CA models. Dispersion processes play a key role in the SWI process and directly affect CA pumped water quality. Constant FDI dispersivities may be inappropriate in representing mixing processes due to large differences between depth and horizontal salinity transport scales, and due to typical structured heterogeneities in aquifer fabrics. Comparison of FDI and FDD model forecasts for the classical Henry problem (HP) steady‐state SWI, based on a new HP semianalytical solution with FDD and on a numerical FDI model modified to additionally represent FDD, highlights the theoretical types of differences implied by these alternative dispersivity assumptions and exactly how each parameter affects the solution. Large differences between FDI and FDD dispersivity forecasts of time‐dependent SWI in large scale heterogeneous aquifers occur in a typical CA (Akkar CA, Lebanon). The FDD model forecasts that future salinities in pumping wells will exceed the potable water limit, whereas the FDI model greatly underestimates the historic inland intrusion of the saltwater wedge and forecasts no impact on future Akkar CA potable water supply. These results indicate the importance of employing the appropriate dispersion process representation when creating model‐based SWI forecasts, especially for developing effective CA management strategies.

Physical and mechanical properties of winter first-year ice in the Antarctic marginal ice zone along the Good Hope Line

Abstract. As part of the 2019 Southern oCean seAsonal Experiment (SCALE) Winter Cruise of the South African icebreaker SA Agulhas II, first-year ice was sampled at the advancing outer edge of the Antarctic marginal ice zone along a 150 km Good Hope Line transect. Ice cores were extracted from four solitary pancake ice floes of 1.83–2.95 m diameter and 0.37–0.45 m thickness as well as a 12×4 m pancake ice floe of 0.31–0.76 m thickness that was part of a larger consolidated pack ice domain. The ice cores were subsequently analysed for temperature, salinity, texture, anisotropic elastic properties and compressive strength. All ice cores from both solitary pancake ice floes and consolidated pack ice exhibited predominantly granular textures. The vertical distributions of salinity, brine volume and mechanical properties were significantly different for the two ice types. High salinity values of 12.6±4.9 PSU were found at the topmost layer of the solitary pancake ice floes but not for the consolidated pack ice. The uniaxial compressive strengths for pancake ice and consolidated pack ice were determined as 2.3±0.5 and 4.1±0.9 MPa, respectively. Young's and shear moduli in the longitudinal core direction of solitary pancake ice were obtained as 3.7±2.0 and 1.3±0.7 GPa, respectively, and of consolidated pack ice as 6.4±1.6 and 2.3±0.6 GPa, respectively. Comparing Young's and shear moduli measured in longitudinal and transverse core directions, a clear directional dependency was found, in particular for the consolidated pack ice.

The seasonal changes in the position of the upper boundary of the Black Sea hydrogen sulfide zone due to the nature of the dynamic processes development

The position and seasonal fluctuations of the depth of the maximum water salinity gradient in the Black Sea in the upper 150 m layer (halocline), which is interpreted as the upper boundary of the hydrogen sulfide layer in the sea, were estimated based on the analysis of climatic data of the vertical distribution of salinity for the period 1903—1982. Seasonal maps of the depth of this boundary in the water area of the sea were constructed, and extrema (axes of maximum and minimum) were identified. Features of dynamic processes in the Black Sea were estimated by the position of the axes of the convergence and divergence zones, which correspond to the values of the maximum and minimum in the field of the considered characteristic. Water temperature and salinity maps in isolines with extremum axes highlighted on them — the positions of the vergence zones axes were built at this depth in a similar way. Thus, ideas have been obtained where the position of the upper boundary of the hydrogen sulfide layer should be expected in a specific season and region.
 For comparison with the current hydrophysical conditions in the Black Sea, the actual materials of individual surveys carried out three times in 2016, 2017, and 2019 during a warm period on a zonal section in the open sea were analyzed. The depth of the upper boundary of the hydrogen sulfide zone was 55, 56, and 54 m, respectively, while according to climatic data — 62 m. It may indicate ongoing changes due to climate warming.

Imaging the Structure and the Saltwater Intrusion Extent of the Luy River Coastal Aquifer (Binh Thuan, Vietnam) Using Electrical Resistivity Tomography

With the growing population and the adverse effects of climate change, the pressure on coastal aquifers is increasing, leading to a larger risk of saltwater intrusion (SI). SI is often complex and difficult to characterize from well data only. In this context, electrical resistivity tomography (ERT) can provide high-resolution qualitative information on the lateral and vertical distribution of salinity. However, the quantitative interpretation of ERT remains difficult because of the uncertainty of petrophysical relationships, the limitations of inversion, and the heterogeneity of aquifers. In this contribution, we propose a methodology for the semiquantitative interpretation of ERT when colocated well data are not available. We first use existing wells to identify freshwater zones and characterize the resistivity response of clayey deposits. Then, we approximate the formation factor from water samples collected in the vicinity of ERT data to derive a resistivity threshold to interpret the saline boundary. We applied the methodology in the shallow aquifers of the Luy River in the Binh Thuan province, Vietnam, where water resources are under pressure due to agricultural, aquacultural, and industrial production. Twenty-one ERT profiles were collected and revealed a much larger intrusion zone, compared to the previous study. Saltwater is present in lowland areas of the left bank over almost the whole thickness of the aquifer, while the right bank is constituted of sand dunes that are filled with freshwater. At a larger distance from the sea, a complex distribution between fresh and saltwater is observed. Our methodology could be applied to other heterogeneous aquifers in the absence of a dense monitoring network.

Calibration of estuary numerical model by the Powell’s optimization method

In this paper, we attempt to optimize the parameters related to estuarine salt intrusion in Delft3D model. BOBYQA algorithm by Powell, a constrained optimization algorithm was applied to the ？？ ？？ model of Delft3D to calibrate the vertical salinity profiles. The optimization was first demonstrated with the flume data of Ippen and Harleman (1961), then was applied to the observation data of the Seomjin River in Korea. A total of 11 or 15 parameters were optimized with the objective function of salinity RMS error. The observation data were totally 28 sets of the vertical salinity distribution at 14 different stations, obtained by Korea Institute of Ocean Science & Technology. The results showed that the turbulence generation and viscous dissipation terms, and turbulent Prandtl number were relatively more important among the parameters employed in the optimization. It could also be assured that the accuracy of the vertical salinity profile was much improved through the optimization.

Upper Ocean Response to Rain Observed From a Vertical Profiler

AbstractRainfall induces a vertical salinity gradient directly below the ocean surface, the strength and lifetime of which depend on the size of the rain event, the availability of mixing, and the air‐sea heat fluxes. The presence of rain in turn influences the near‐surface turbulent mixing and air‐sea exchange processes. During a campaign in the midlatitude North Atlantic, the Air‐Sea Interaction Profiler (ASIP) was used to investigate changes in the vertical distribution of salinity (S), temperature (T), and turbulent kinetic energy dissipation rate (ϵ) caused by four rain events. During one of the rain events a strong shallow stratification was formed. The buoyancy effect of this freshwater lens changes the dominant wind‐driven turbulent mixing. The surface momentum flux was limited to a shallow layer, and below it ϵ is reduced by 2 orders of magnitude. For a different rain event of higher‐peak rain rate, the salinity anomaly is smaller and is dispersed deeper into the water column. The difference in ocean response shows that the upper ocean is sensitive to changes in the atmospheric forcing associated with the rain events. The observed salinity anomalies as a function of rain rate and wind speed are compared to relationships from studies with the 1‐D turbulence model GOTM and satellite validation. The observations suggest that the vertical salinity anomaly is best described as a function of total rain. A higher‐resolution prognostic model for sea surface salinity and temperature is shown to perform well in predicting the observed S and T anomalies.

Optimal design of combined propulsion Underwater Glider for operation of the East Sea of South Korea

An underwater glider is an autonomous underwater vehicle that is propelled by changes in volume. Due to this propulsion method, it is possible to make observations with these devices continuously for 30–60 days. Of the gliders’ physical properties, the volume change has the greatest influence on the cruising speed. The speed can be increased by increasing the volume change, but this also increases the energy consumption. Therefore, the change in buoyancy is very important for the operation of underwater gliders. Hence, it is necessary to optimize the change in buoyancy. In this study, we describe a technique for optimizing the design of underwater gliders intended to operate in the East Sea of Korea using a combined buoyancy engine and thruster propulsion system. First, we carried out a simulation study to optimize the volume change of the buoyancy engine based on the average flow velocity distribution, water temperature, and vertical salinity distribution in the East Sea. Then, we used our simulations to predict the optimal change in volume of the underwater glider. Finally, we discuss the advantages of operating with thrusters in special environments under specific water temperature, salinity distribution, and ocean current conditions.

Numerical simulation of ice cover of saline lakes

A new version of 1D thermodynamic and hydrodynamic model LAKE 2.1 is presented. The model is supplemented with description of dynamics and vertical distribution of salinity in ice layer. Simulation results are compared to in situ and satellite data on water temperature and ice cover at Lake Uvs (Mongolia) from 2000 to 2015. We demonstrate that underestimation of mixed-layer depth by the model with standard k–ε closure during summer and autumn leads to significant shift of ice-on to earlier dates. If the effects of water salinity are neglected in the model, ice cover establishes 16–17 before the observed dates. This error is removed, if influence of salinity on water density and freezing point is included, still assuming the fresh ice. However, in this case, LAKE model underestimates the maximal winter ice thickness on average by ≈0.2 m. In turn, this discrepancy decreases an order of magnitude if dynamics and vertical distribution of salinity in ice are reproduced. Such an effect does not take place when using constant salinity value in ice.

Numerical Simulation of Ice Cover of Saline Lakes

A new version of the one-dimensional thermo-hydrodynamic and biogeochemical model LAKE2.1 is presented. The model is supplemented with a description of the dynamics and vertical distribution of salinity in an ice cover. Simulation results are compared to in situ and satellite data of water temperature and ice cover at Uvs Nuur Lake (Mongolia) from 2000 to 2015. It is shown that underestimating the mixed-layer depth by the model with standard turbulence closure k−e during summer and autumn leads to a significant shift in the timing of the onset of ice. It is also demonstrated that, while neglecting the salinity of the lake, the freeze-up according to the model happens 16–17 days earlier than in reality. This error is removed if the effect of salinity on water density and freezing temperature is included. However, in this case, the model underestimates the maximal seasonal ice thickness on average by ≈0.2 m. In turn, this error decreases an order of magnitude if the dynamics and vertical distribution of salinity in ice are simulated in the model.

Responding to salinity in a rural African alluvial valley aquifer system: To boldly go beyond the world of hand-pumped groundwater supply?

Effective response to groundwater salinity in the developing world may critically safeguard drinking-water supplies. Groundwater resources throughout rural Africa are exploited by a vast and increasing number of hand-pumped boreholes for community supply. Our research in TA Ngabu (Shire Valley), Southern Malawi aims to: define groundwater-salinity problem occurrence within the semi-arid alluvial-valley aquifer, rural developing-world setting; critique current capacity to respond; and, to discuss future response options - in particular considering the need to explore alternative options that boldly go beyond the world of hand-pumped groundwater supply. Salinity problem definition was achieved through survey of 419 hand-pumped boreholes that revealed widespread brackish groundwater leading to non-potable (unpalatable) drinking-water supplies. Persistent non-functionality or abandonment of boreholes was typically ascribed to salinity. Whilst salinity is conceptualised to arise from shallow-groundwater evaporation, formation-evaporite dissolution and faulted-area upwelling, sparse data locally renders attribution of salinity sources to individual boreholes difficult. There is a significant need to better resolve the vertical distribution of salinity and local controlling processes. Problem response capacity was hampered by multiple factors, including, sector inertia, low drilling costs compromising water-point integrity, and lack of technical vision for alternatives. Various recommendations are made to improve response capacity continuing to work at the hand-pump supply scale. However, in areas where salinity is significant, exploring the feasibility of other options is advocated in conjunction with technical capacity development. Groundwater options may utilise high borehole yields possible from alluvial aquifers, grossly under-exploited by hand pumps. Groundwater at depth, albeit of unknown quality typically, or pipeline transfers of probable good-quality groundwater from valley-margin units, should be considered. Surface-water pipeline supplies may be viable for (growing) population centres. Canal-fed irrigation schemes (pending for the area), should be multiple-use, protective of groundwater and embrace pipeline drinking-water supply and managed-aquifer-recharge opportunities. Advancing desalination technologies, although presently unaffordable, should be kept under review.

Impact of Aquarius Sea-Surface Salinity Assimilation in Improving the Ocean Analysis Over Indian Ocean

ABSTRACTThe distribution of ocean salinity controls the density field and thereby plays a major role in influencing the ocean dynamics. It has been a challenging task to understand the variability of salinity structure in the regions of large fresh water discharge and high precipitation such as Bay of Bengal (BoB). Recent advancement in satellite technology has made possible the measurement of sea surface salinity (SSS). Aquarius is the satellite which measured the global SSS for the period 2011 to 2015. In the present study, we assimilated Aquarius SSS in the Global Ocean Data Assimilation System based on 3DVAR technique. The assimilation of Aquarius SSS resulted in reduced biases in salinity not only at the surface, but also in the vertical distribution of salinity and better captured the temporal variations of salinity structure in sensitive regions, such as the Bay of Bengal. In addition, the assimilation of SSS showed marginal improvement in ocean thermal structure over data sparse regions of Indian Ocean. It is also shown that the assimilation of Aquarius SSS has improved the stratification in the upper Ocean which is the key factor in the observed improvement in ocean analysis.

Spatial heterogeneity of soil salinization and its influencing factors in the typical region of the Mu Us Desert-Loess Plateau transitional zone, Northwest China

Studies on the spatial heterogeneity of saline soil in the Mu Us Desert-Loess Plateau transition zone are meaningful for understanding the mechanisms of land desertification. Taking the Mu Us Desert-Loess Plateau transition zone as the study subject, its spatial heterogeneity of pH, electrical conductivity (EC) and total salt content were analyzed by using on-site sampling followed with indoor analysis, classical statistical and geostatistical analysis. The results indicated that: 1) The average values of pH, EC and total salt content were 8.44, 5.13 mS·cm-1 and 21.66 g·kg-1, respectively, and the coefficient of variation ranged from 6.9% to 73.3%. The pH was weakly variable, while EC and total salt content were moderately variable. 2) Results of semivariogram analysis showed that the most fitting model for spatial variability of all three indexes was spherical model. The C0/(C0+C) ratios of three indexes ranged from 8.6% to 14.3%, which suggested the spatial variability of all indexes had a strong spatial autocorrelation, and the structural factors played a more important role. The variation range decreased in order of pH <total salt < EC. The Kriging interpolation showed that pH, EC and total salt content distributed in a striped pattern with good continuity. The pH value increased with increasing terrain slope, while EC and total salt content decreased. 3) In terms of vertical distribution, the salt aggregated on surface in the area with severe salinization. In the area with light salinization, the vertical distribution of salinity was firstly decreased and then increased. In general, the heterogeneity of soil salinization in the Mu Us Desert-Loess Plateau transition zone was influenced by climate, landscape, plant distribution, especially affected by geological conditions, topography and hydrogeological conditions. This study provided a theoretical basis for future land engineering and ecosystem restoration programs.

Climatology and seasonality of upper ocean salinity: a three-dimensional view from argo floats

Primarily due to the constraints of observation technologies (both field and satellite measurements), our understanding of ocean salinity is much less mature compared to ocean temperature. As a result, the characterizations of the two most important properties of the ocean are unfortunately out of step: the former is one generation behind the latter in terms of data availability and applicability. This situation has been substantially changed with the advent of the Argo floats which measure the two variables simultaneously on a global scale since early this century. The first decade of Argo-acquired salinity data are analyzed here in the context of climatology and seasonality, yielding the following main findings for the global upper oceans. First, the six well-defined “salty pools” observed around ±20° in each hemisphere of the Pacific, Atlantic and Indian Oceans are found to tilt westward vertically from the sea surface to about 600 m depth, forming six saline cores within the subsurface oceans. Second, while potential temperature climatology decreases monotonically to the bottom in most places of the ocean, the vertical distribution of salinity can be classified into two categories: A double-halocline type forming immediately above and below the local salinity maximum around 100–150 m depths in the tropical and subtropical oceans, and a single halocline type existing at about 100 m depth in the extratropical oceans. Third, in contrast to the midlatitude dominance for temperature, seasonal variability of salinity in the oceanic mixed layer has a clear tropical dominance. Meanwhile, it is found that a two-mode structure with annual and semiannual periodicities can effectively penetrate through the upper ocean into a depth of ~2000 m. Fourth, signature of Rossby waves is identified in the annual phase map of ocean salinity within 200–600 m depths in the tropical oceans, revealing a strongly co-varying nature of ocean temperature and salinity at specific depths. These results serve as significant contributions to improving our knowledge on the haline aspect of the ocean climate.

The Interplay Between Submesoscale Instabilities and Turbulence in the Surface Layer of the Bay of Bengal

The Air-Sea Interactions Regional Initiative (ASIRI) aims to understand vertical fluxes of momentum and heat across the surface layer in the Bay of Bengal. As the mesoscale and submesoscale eddies redistribute freshwater input over saline water of the bay, they influence the vertical distribution of salinity and thus impact air-sea fluxes. This study reports on numerical simulations performed to investigate processes that can lead to the observed vertical structure of stratification near the ocean surface. Processes are explored at multiple lateral scales, ranging from a few meters to tens of kilometers, to elucidate how the interplay among large-scale motion, submesoscale instabilities, and small-scale turbulent motion affects the surface layer.

Spatio-temporal distribution of chlorophyll-a in relation to physico-chemical parameters in coastal waters of the northwestern Bay of Bengal.

The present study focuses on understanding the long-term distribution of physico-chemical parameters and their influence on the distribution of chlorophyll-a (chl-a) at a coastal site in the northwestern Bay of Bengal. Chl-a showed large variability (0.12 to 10.05mgm(-3)) on a spatio-temporal scale during the study period. However, the distribution showed a similar pattern with marginal variability from March 2010 to February 2011 and March 2011 to February 2012. The vertical distribution of salinity, pH, total suspended matter (TSM) and chl-a showed systematic temporal variability. However, dissolved oxygen (DO) and nutrients (nitrite+nitrate, phosphate, silicate) did not show any significant spatio-temporal trend. Chl-a showed bimodal distribution on an annual scale, with the first peak appearing during the pre-monsoon period in March due to a seasonal phytoplankton bloom, whereas the second peak occurring during September as a result of nutrient loading from river influx due to monsoonal precipitation. Factor analysis revealed the association of low salinity and high nutrients with chl-a. This infers that the nutrients brought by the influx of river into the study area were fuelling the growth and abundance of phytoplankton. Cluster analysis resulted in two distinct clusters among all physico-chemical datasets, indicating the presence of two distinct areas separated by the 30 m isobath that were strongly influenced by physico-chemical characteristics associated with the seasonal monsoon.

Salinity minimum in the subsurface layers of the Japan Sea

Seasonal variability of vertical salinity distribution in the Japan Sea is considered. On the base of high accuracy data from the databases WODC-2013 (USA), JODC (Japan), and the databases of Far-Eastern State Hydrometeorological Institute and Pacific Oceanological Institute (Russia), several cases of salinity minimums are analyzed and interpreted taking into account seasonal variability of salinity profiles. High vertical homogeneity by salinity is noted for the Japan Sea waters, and the subsurface salinity minimum can be considered as a result of continuous changes of freshwater balance. It could be formed in the layers from the sea surface to 150-250 m as a temporary local extreme caused by prevalence of evaporation over precipitation on the sea surface in some seasons - that’s why it is observed seasonally. There is concluded that such conservative patterns as water masses are absent in the sea, at least in its active upper layers, but vertical salinity profiles are changing permanently under influence of changing freshwater fluxes, and their extremes appear or disappear in compliance with the dialectic laws.

The Temporal and Spatial Evolution of Saltwater Intrusion during Dry Season in the Yangtze River Estuary, China

Abstract. The saltwater intrusion in the Yangtze River Estuary is very frequent and complicated with a great effect on freshwater supply in Shanghai and nearby cities. By using the hydrologic data observed in dry season, the temporal and spatial variation of the saltwater intrusion in the Yangtze River Estuary were analyzed. The results show that the saltwater intrusion of the south branch is mainly induced by the saltwater spilling over from the north branch, which causes the Chenhang reservoir being plagued by saltwater intrusion during dry season. As the saltwater group from the north branch moving downward along the south branch, the longitudinal salinity distribution present a high-low-high shape during spring tide cycle, low-high-low-high shape during medium tide cycle and low-high shape during neap tide cycle along the south branch-south channel-south passage. Moreover, the north branch is controlled by high saline water with the increase of the salinity in the upstream reach in medium and spring tides, but this phenomenon is vanished in neap tide. In addition, the vertical distribution of salinity is more homogeneous in shoals than that in deep channels, which is induced by mixing degree in water column.