South Branch Research Articles

Influence of River Discharge on the Transport of the Saltwater Group from the North Branch in the Yangtze River Estuary.

The Yangtze River Estuary (YRE) is the largest estuary in China. Recently, due to the increase of extent and frequency, saltwater intrusion has received more and more attention. In this paper, with the adoption of hydrodynamic and salinity transport mode, quantitative research of the influence of river discharge to the North Branch (NB) of the Yangtze River on the saltwater group migration law is conducted. Tide and salinity data are used to validate the model effectively. In different paths, the changes in flow and the movement of the saltwater group are similar. The saltwater group starts to move downward from the sixth day. In the staged downward movement, the larger the runoff volume, the further the distance of the core of the saltwater group, and converges to around 90 km gradually. At different flow rates, the relationship between the average location of each waterway saltwater group core tide cycle and time is consistent with the Gompertz model, and its parameters had a nonlinear relationship with the flow rate. A function is constructed to calculate the length and time of the saltwater group migration. As the flow rate increases, the faster the core of the saltwater group reaches the entrance. The downwards movement takes 3–8 days. Quantitative research on the influence of the saltwater spilling from NB to the three major reservoirs in the South Branch (SB)is conducted. The simulation results are consistent with the function calculation. River discharge has a direct impact on saltwater transport and diffusion in the YRE.

Circulation characteristics of two cases of Sea-entering Tibetan Plateau Vortices causing obvious differences in China precipitation

By using the NCEP FNL, historical synoptic charts and the year books of Tibetan plateau vortex and shear Line, based on synoptic and diagnosis methods, the observation facts of the sea-entering Tibetan Plateau vortices (STPVs) from 1998 to 2018, (STPVs) from 1998 to 2018, the two southeast-path STPVs that made great differences in precipitation are comparatively analyzed. The results show that: (1) The would bring precipitation to the eastern coast of China, and further affecting Korean Peninsula, Japan and Russia. (2) The different circulation characteristics of large- and small-scale precipitation STPVs are as follows:there are strong north and south branch jets at 200hPa and the north branch jet extends to east-ward with the core moving to east, and the circulation is more stable at 500hPa to the north of 45°N in East Asia, and STPV induces low vortex in the lower atmosphere in large-scale precipiitation STPV process. The opposite situation is true for small-scale precipitation STPV process. As a result, there are rising motion areas with large range and strong strength in and near the large-scale precipitation STPV area in the middle and lower troposphere, where larger water vapor flux and strong water vapor flux convergence also exist.

Numerical analysis of sediment deposition in Yangtze river estuary: Insight from conceptual estuary models

Since the construction of the Deepwater Navigation Channel Project in Yangtze River Estuary 1998, it is extremely imperative to clarify the sediment dynamics in Yangtze River Estuary to reduce deposition risks in the channel. However, the sediment deposition mechanism has not been well understood. Therefore, four mechanisms of sediment deposition in Yangtze River Estuary were simulated and another one was analyzed through discussion in this research. First, a two-dimensional mathematical model of Yangtze River Estuary and four conceptual estuary models were established. Through the comparison of the models in the flow field and the sediment deposition, the characteristics of each mechanism were analyzed. The results indicated that the flow expansion, residual currents, riverbed thalweg orientation and local circulation played important roles respectively in different areas of the Yangtze River Estuary. Specifically, in the river mouth, the sediment deposition is mainly considered related to the flow expansion. While, in zones where riverine discharge and tide meet, the residual current is the primary cause. In the South Branch and the North Channel with interlaced shoals, the riverbed thalweg orientation is the major factor of the channel deposition. In the Deepwater Navigation Channel of the North Passage, the local circulation is the main cause. Finally, the sediment density current was discussed and concluded to be one of the causes leading to the sediment deposition in the North Passage. It was clear that the conceptual estuary models can be applied in explaining the mechanisms of the sediment deposition qualitatively.

Diel vertical migration of dominant planktonic crustaceans in the south branch of Yangtze Estuary, China

Zooplanktons are important food organisms of fishes, and their spatial and temporal distribution pattern has an important influence on the growth and reproduction of fishes in local habitats. The Yangtze River Estuary of China is rich in fishery resources, but the knowledge on the distribution pattern of zooplankton in this area is still very limited. The diel vertical migration (DVM) patterns and seasonal variations of the crustacean community, and their relationship with environmental factors were investigated in the south branch of the Yangtze Estuary, from June 2017 to May 2018. The results showed that the dispersion patterns of dominant crustacean taxa in the Yangtze Estuary were mostly aggregated. Migration amplitudes of crustacean were greater in spring and summer than in autumn and winter, and different migratory patterns occurred in different seasons. Sinocalanus dorrii, Schmackeria inopinus, Mesmackeria leuckarti, Bosmina longirostris, and B. fatalis, unlike S. forbesi, showed a significant DVM. The DVM patterns of crustaceans was possibly influenced by light dentisy, temperature, and total dissolved solids in the water column, and the fish predation effect; whereas, the nutrient concentration and pH were not supposed to be key factors.

Centurial Evolution of an Offshore Mud Deposition Area in the Changjiang (Yangtze) Estuary and Its Links to Environmental and Anthropogenic Activities

Large amounts of sediments originating from the Changjiang (Yangtze) River are deposited in the subaqueous delta and in the adjacent muddy area off the mouth and on the inner shelf of the East China Sea. The terrestrial sediments deposited in these areas not only contain information about the composition and environment of the source area, but they also record changes in anthropogenic activities. A sediment piston core (CJ0702) was extracted from the Changjiang subaqueous depocenter (31.00°N, 122.67°E) in a water depth of 22.0 m. The core was subsampled at 1–2 cm intervals and analyzed for grain size, clay mineralogy, and major element geochemistry. Results indicate a relatively high sediment accumulation rate of approximately 3.11 cmyr. These parameters exhibited only minor cyclical fluctuations in the core, which resulted from many factors. During the past 120 years, the Changjiang River-derived sediment is the primary source of sediment in the offshore mud area without evidence for the Yellow River-derived sediment increasing. After the trunk stream shifted from the North Branch to South Branch, the variations of proxies are controlled by the periodic fluctuation possibly linked to El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). In addition, anthropogenic heavy metal concentrations can be divided into three stages, which coincide well with economic development and environmental protection policies.

Impact of sea level rise on estuarine salt water intrusion–A numerical model study for Changjiang Estuarine

A 3D and high-resolution salinity transport numerical model of Changjiang Estuary with unstructured mesh was established using the MIKE3. The salinity transport model results were tested and verified by the observed data in Changjiang Estuary, the statistics of correlation coefficient are in good values. And then, the verified salinity transport model was used to study the impact of sea level rise on saltwater intrusion in the Changjiang Estuary. The results show that the entire North Branch was flooded with high saline water and a large amount of salt water spill over from the North Branch into the South Branch, which caused the South Branch with a high-low-high saddle-shaped distribution. With the rise of sea level, salt rocks such as the North Branch, the South Branch, and the North Channel moved upstream to varying degrees, strengthening the saltwater intrusion in the eastern Changjiang River. The high saline waters from North Branch spill over into South Branch also increased. The isohaline of North Branch South Branch and North Channel move to upstream, and move downstream in South Channel, North Passage and South Passage. The high salt water from the North Branch into the South Branch increased the salinity of the upper section of the South Branch.

Sea-level Rise Impacts on the Saline Water Intrusion and Stratification of the Yangtze Estuary

Chen, W.; Mao, C.; He, L., and Jiang, M., 2020. Sea-level rise impacts on the saline water intrusion and stratification of the Yangtze Estuary. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1395-1400. Coconut Creek (Florida), ISSN 0749-0208.Saline water intrusion is the movement of saline water into freshwater areas. The problem of saline water intrusion has been regarded as one of the most important issues in managing coastal zones, as it can significantly degrade drinking water and sediment flocculation. In this paper, a 3D numerical model of hydrodynamic and salinity transport of the Yangtze estuary was established based on MIKE3. This model was validated with the field measured tidal level, flow velocity, flow magnitude and salinity. The validated model was used to simulate the saline water intrusion caused by sea level rise (SLR) in the Yangtze estuary in the dry season. The responses of saline water intrusion to SLR in the Yangtze estuary were analyzed. Results indicate that: salinity in the upper reach of the North Branch, the South Branch, the North Channel, the South Channel, the North Passage and the South Passage increase due to SLR, especially the salinity of the South Branch entirely exceed 0.45 psu, however decreased significantly in the lower reach of the North Branch. This is induced by the increased flow split ratio of the North Branch due to SLR. The greater flood tidal current and flow split ratio of the North Branch due to SLR make stratification phenomenon of salinity increase with the Richardson number reaching 150 in the middle layer. For the South Passage, the bottom stratification phenomenon is weakened and the surface stratification phenomenon is enhanced, however the vertical trend is not apparent.

An Investigation on the Crustal Velocity Variations of the North Anatolian Fault Zone by a Dense Seismic Array

Aktif fay zonları boyunca asimetrik olarak dağılmış olan mikro çatlaklar bu zonlardaki depremlerin tekrarlı oluşumları nedeniyle meydana gelmektedir. Aynı bölgede sürekli tekrarlanan depremler, elastik olarak farklı olan malzemeleri ayırarak iki-malzemeli arayüzeyler meydana getirir ve deprem davranışını etkileyen önemli sonuçlar doğurur. Kuzey Anadolu Fay Zonu üzerinde kurulan DANA (Dense Array of Northern Anatolia) sismik ağı Kuzey Anadolu Fay Zonu’nun Sakarya ve Sapanca segmentleri üzerinde iki malzemeli arayüzeyin incelenmesi için elverişli veri sağlamaktadır. Bu çalışmanın amacı, yoğun sismik dizilim bulunan Kuzey Anadolu Fay Zonu’nun (KAFZ) batı ucunda Sakarya ve Sapanca segmentleri arasında, deprem dalgası çapraz ilişki analizleri kullanarak, iki malzemeli arayüzey geçişindeki hız değişimlerini belirlemektir. Araştırma kapsamında 2012-2013 yıllarında, çalışma alanında faaliyet gösteren DANA geçici sismik ağına ait 73 adet sismik istasyondan, 109 adet uzak deprem kaydı kullanılarak 50.000'den fazla dalga formu derlenmiştir. Uzak deprem dalgalarının, sismik kayıtçılara varışları arasındaki zaman farkları, fayın karşılıklı bölümlerinde kabuktaki hız kontrastını tespit etmek ve fark değerini ölçmek için kullanılmıştır. Elde edilen bulgular KAFZ kuzey kolunun kuzeybatısında düşük, kollar arası Armutlu-Ovacık bloğu altında yüksek hızlara işaret etmektedir. Referans kayıtçıların analizinde, hız oranlarında lokal değişimler hesaplanmış olsa da, bölge geneline bakıldığında KAFZ kuzey kolunun kuzeyi ile, yine KAFZ kuzey kolunun doğusu ve güney doğusu arasında görece büyük hız farkları elde edilmiştir. Sonuçlar, KAFZ kuzey ve güney kollarındaki hız değişimlerini ve genel tektonik ortamla ilişkilendirilen özellikleri ortaya koymaktadır.

An investigation of heat source effect of Tibetan Plateau on the wintertime India-Burma Trough

In this study, the heat source effect of the Tibetan Plateau (TP) on the India-Burma Trough (IBT) is investigated with multi-layer soil temperatures. Because the significantly positive correlation between the soil temperatures at 10 cm ( T soil −10 ) and the India-Burma Trough intensity index ( IBTI ) lasts from October to the following February, the T soil −10 of TP is selected as the heat source index (HSI). Our composite analysis showed that, when the HSI of TP in the cold season decreases, the subtropical jet moves downward. As a result, the south branch of the westerlies on the south side of the TP is enhanced and the IBT deepens. The upward motion in front of the trough is enhanced, resulting in convergence of a large amount of moisture and a steady vapor transport to Southwest and South China. Conversely, when the HSI strengthens, the subtropical jet moves upwards and the IBT weakens. Meanwhile, the northern branch of the westerlies intensifies, suppressing the moisture convergence and transportation in front of IBT. • The relationship between heat source index (HSI) of TP and India-Burma Trough (IBT) in cold season is investigated. • As HSI decreases, the IBT tends to be intensified due to the subtropical jet moving downward and southern branch of the westerlies strengthening. • Weak HSI in cold season can generally result in sufficient water vapor transportation and more precipitation over south and southwest China.

Analysis of critical river discharge for saltwater intrusion control in the upper South Branch of the Yangtze River Estuary

Saltwater intrusion in the estuary area threatens the use of freshwater resources. If river discharge increases to a critical value, then saltwater intrusion frequency and salinity level decreases. In this study, long-term river discharge and tidal range data in the Yangtze River Estuary (YRE) and salinity data obtained in the upper South Branch of the YRE were used to analyze the characteristics of different variables and the basic law of their interactions. Two methods, namely, the material analysis method and empirical models, were applied to determine the critical river discharge for saltwater intrusion control. Results are as follows: (1) the salinity might exceed the drinking water standard of China when the river discharge was less than 30,000 m3/s. Approximately 69% of salinity excessive days occurred when the river discharge was less than 15,000 m3/s; (2) the tidal range in the YRE roughly varied in sinusoidal pattern with a 15-day cycle length. Exponential relationship existed between daily salinity (chlorinity) and daily mean tidal range. Combining these two features with the cumulative frequency statistics of tidal ranges, it was showed that notable saltwater intrusion occurred when the tidal range was more than 2.7 m at Qinglonggang station. Moreover, the critical discharge was found to be slightly higher than 11,000 m3/s; (3) various of empirical models for salinity prediction could be chosen to calculate the critical discharge. The values obtained by different models were in the range of 11,000-12,000 m3/s; (4) the proposed critical discharge to reduce notable saltwater intrusion was 11,500 m3/s. After the Three Gorges Reservoir operation, the minimum river discharge into the YRE in 2008–2017 was below the critical discharge, thereby suggesting an increase in the minimum river discharge by reservoir regulation in drought periods.

Recent Spatio-Temporal Variations of Suspended Sediment Concentrations in the Yangtze Estuary

Water and sediment are two of the most essential elements in estuaries. Their product, suspended sediment concentration (SSC), is involved in hydrology, geomorphology and ecology. This study was focused on the spatial and temporal variations of SSC in the Yangtze Estuary under new situations after the closure of ~50,000 dams in the Yangtze basin, including the Three Gorges Dam (TGD) in 2003. It was found that the SSC first exhibited an increasing and then a decreasing trend longitudinally from Xuliujing Station to the outer estuary with the Turbidity Maximum Zone located in the mouth bar area. Vertically, the SSC in the bottom layers averaged 0.96 kg/m3, about 2.4 times larger than the surface layers (0.40 kg/m3). During spring tides, the SSCs were always higher than those in neap tides, which was fit for the cognition law. As for the seasonal variations in the North Branch and mouth bar area, the SSCs in the dry season were higher than those in the flood season, while in the upper reach of the South Branch and outer estuary, the seasonal variation of SSCs reversed. This phenomenon primarily reflected the competition of riverine sediment flux and local resuspended sediment flux by wind-induced waves. As for the interannual changes, the SSCs demonstrated overall fluctuant downward trends, determined by riverine sediment flux and influenced by waves. This study revealed the new situation of SSC and can be a reference for other related researches in the Yangtze Estuary.

Responses of river bed evolution to flow-sediment process changes after Three Gorges Project in middle Yangtze River: A case study of Yaojian reach

The Three Gorges Project (TGP) has changed the flow-sediment process in the middle Yangtze River. For navigation purposes, there is an urgent need to study the changes of the river regime over a long-term period and the shoal-channel evolution over different seasons since the completion of the TGP. Based on analysis of the measured data and the results of a two-dimensional mathematical model, the changes of the river regime and river bed evolution in the Yaojian reach downstream of the TGP were studied. Results show that a high sediment transport flux helps to keep the main flow in the North Branch, while a low sediment transport flux helps to keep the main flow in the South Branch. Thus, the main branch will not change in the near future because of the low sediment transport load. In this study, the flow-sediment process adjusted by the TGP was restored to the conditions before the TGP, and the river bed evolution under the adjusted and non-adjusted flow-sediment conditions was calculated. After the completion of the TGP, the reservoir storage accelerated the flood recession process and decreased the erosion by 11.9% under the flow-sediment conditions in 2010, and the deposition in the flood season decreased by 56.4%.

Clinical predictive value of short-term dynamic changes in platelet counts for prognosis of sepsis patients in intensive care unit: a retrospective cohort study in adults

To explore clinical predictive value of short-term dynamic changes in platelet counts (PLT) for prognosis of sepsis patients in intensive care unit (ICU). A retrospective cohort study was conducted. The patients aging 18 to 80 years old who were diagnosed by Sepsis-3 admitted to ICU of South Branch of Shanghai General Hospital from November 2015 to October 2018 were enrolled. According to whether the patients died within 28 days, they were divided into death and survival groups. General information and clinical baseline data [including disease severity score, infection biomarkers, PLT and organ function parameters (cardiac, liver, kidney, coagulation) and inflammatory cytokines] between the two groups were compared. Based on clinical indicators which had statistically significance, receiver operating characteristic (ROC) curve was drawn to predict the prognosis of the patients within 28 days. Then, risk factors of 28-day mortality of sepsis patients in ICU were screened by univariate and multivariate Logistic regression analysis. On the basis of multivariate Logistic regression analysis results, a multiparameter model was built, and the ROC curve was drawn to predict its prognosis within 28 days. A total of 220 sepsis patients were enrolled. Among them, 61 patients died and 159 patients survived within 28 days with a 28-day mortality of 27.7%. Compared with the survival group, the patients in the death group were senior in age, more likely to suffer from chronic cardiovascular, chronic kidney and immune system disease, had higher scores in acute physiologic and chronic health evaluation II (APACHE II) score, sequential organ failure assessment (SOFA) score, disseminated intravascular coagulation (DIC) score and less PLT on the 1st and 7th day, sustained a higher incidence of persistent thrombocytopenia (PLT were all < 100×109/L in the first week after ICU admission) or acquired thrombocytopenia (PLT ≥ 100×109/L on the day of ICU admission, but dropped over 50% during the first week after ICU admission), were subjected to higher procalcitonin (PCT) and interleukin-6 (IL-6) levels and endured worse organ function (cardiac, kidney, coagulation) with statistically significant differences. However, there was no significant difference in gender, disease type, infection sites, pathogens or liver function. The ROC curve analysis for the 28-day prognosis of sepsis illustrated that the three disease severity scores could predict the 28-day prognosis of sepsis in ICU, and the area under ROC curve (AUC) of SOFA score was the highest (AUC = 0.878). The AUC of PLT on the 7th day was higher than that on the 1st day (AUC: 0.862 vs. 0.674), and the AUC of other clinical indicators were all < 0.8. Univariate and multivariate Logistic regression analysis showed that SOFA score [odds ratio (OR) = 1.423, 95% confidence interval (95%CI) was 1.089-1.859, P = 0.010], troponin I (TnI; OR = 2.056, 95%CI was 1.057-3.999, P = 0.034), and persistent or acquired thrombocytopenia (OR = 13.028, 95%CI was 4.033-42.090, P < 0.001) were three independent risk factors for 28-day mortality of the sepsis patients in ICU. Based on the multivariate Logistic regression analysis results, a multiparameter model was built with SOFA score, TnI and persistent or acquired thrombocytopenia, which showed a AUC of 0.926 to predict the 28-day mortality of sepsis patients in ICU. When the optimum cut-off value was 0.398 in the model, the sensitivity was 76.8%, and the specificity was 92.8%. Persistent or acquired thrombocytopenia within the first week of hospitalization proves to have a relatively momentous clinical predictive value for prognosis of sepsis patients in ICU. Clinical intervention focusing on thrombocytopenia may become a new potential therapy for these sepsis patients.

Dynamics and spatial differentiation of dissolved copper load in the Yangtze estuary

Taking the Yangtze river estuary as the study area and based on the field measured data of the longest sequence from 2004 to 2018, analyzes the Dissolved Copper (DCu) concentration change process of six typical sections in the Yangtze river estuary in the past 15 years, namely, Xuliujing, Shidongkou, Nangang, Beigang, Qinglonggang and Qidonggang. The characteristics of the evolution trend of each section are quantitatively evaluated by the method of restandard range analysis. The spatial differentiation rules of DCu in the Yangtze river estuary at different stages were revealed and the correlation characteristics of each section load were calculated by Pearson coefficient. The results show that :(1) the evolution characteristics of DCu in the section of Xuliujing section are relatively complex, which can be divided into four stages. The average concentration of DCu in 15 years is about 3.52 μg/L, and the highest monthly average concentration is 17.8 μg/L.(2) due to the effect of regional sewage discharge, the load of DCu in the mouth section of the south branch stone is generally higher than that of the Nangang and Beigang sections, but the evolution trend of the three sections is basically similar. The oscillation amplitude of DCu concentration in Qidonggang section is the most significant. In 2007, the annual average value of DCu reached 30.3 μg/L, which is the highest annual average value in the existing measured data.(3) Hurst index of Nangang and Qidonggang reached 0.93 and 1.0 respectively, and the evolution trend of cross section DCu showed a strong persistence. The Hurst index of Qinglonggang section is 0.1515, which indicates that the section DCu has anti-persistence.(4) except Qidonggang, the DCu in the other five monitored sections all show significant positive correlation, among which the DCu concentration in Beigang and Qinglonggang have extremely similar variation rules. The main reason for this strong correlation should be related to the main driving weight factor of DCu load in the two sections. The research results have some reference value for prevention and control of heavy metal pollution in Yangtze estuary.

Risk factors of postoperative bleeding of endoscopic submucosal dissection for early gastrointestinal cancer

Objective To analysis the risk factors of postoperative bleeding of endoscopic submucosal dissection (ESD) for early gastrointestinal cancer. Methods A retrospective study was performed on the data of 430 patients (449 lesions) with early gastrointestinal cancer undergoing ESD in Fujian Provincial Hospital Digestive Endoscopic Center from June 2008 to February 2015 and in Fujian Provincial Hospital South Branch Digestive Endoscopic Center from May 2015 to April 2018. Patients with postoperative bleeding were compared with those without postoperative bleeding on the basis of general conditions, endoscopic performance, postoperative pathology and so on to analysis the risk factors for postoperative bleeding of ESD. Results Among the 430 cases (449 lesions)of early gastrointestinal cancer undergoing ESD, 16 cases (3.7%) had postoperative bleeding. According to whether the occurrence of postoperative hemorrhage, patients were divided into bleeding group (n=16) and not bleeding group (n=433). Univariate analysis suggested that whether had hypertension was statistically significant between the two groups (χ2=4.793, P=0.029), while patients age (t=0.465, P=0.642), gender (χ2=0.035, P=0.642), whether to have diabetes (χ2=0.647, P=0.421), whether to have coronary heart disease (P=1.000), lesion size (t=1.598, P=0.111), whether two or more lesions (P=1.000), lesion site (χ2=6.183, P=0.289), operation time (t=1.335, P=0.201), pathological grading (χ2=0.687, P=0.709), and lesion infiltration depth (χ2=0.134, P=0.714) were not statistically significant between the two groups. Logistic regression analysis showed that hypertension (OR=3.358, 95%CI: 1.227-9.186, P=0.018) was an independent risk factor of bleeding after ESD for early gastrointestinal cancer. Conclusion Hypertension is closely related to postoperative bleeding following ESD for early gastrointestinal cancer.Patients with hypertension are at a greater risk of bleeding after ESD. Key words: Risk factors; Early gastrointestinal cancer; Endoscopic submucosal dissection; Postoperative bleeding

Distributions of diatoms in surface sediments from the Chanthaburi coast, Gulf of Thailand, and correlations with environmental factors

This paper presents an analysis of diatoms collected from surface sediments in the Chanthaburi and Welu estuaries on the northern coast of the Gulf of Thailand. In total, 144 species are identified, representing 41 genera. Diatom abundance ranges from 645 to 24,979 valves/g, with an average of 7,215 valves/g. Diatoms primarily consist of common coastal species, warm water species and a few freshwater species. Additionally, Surirella tenera is identified as a unique freshwater species of the Welu River. Using cluster and redundancy analysis, we identified four diatom assemblages representing different environmental conditions. Diatom assemblages I and II are related to freshwater inputs from the Chanthaburi and Welu rivers. Assemblage III is closely related to nutrient concentrations and assemblage IV is representative of offshore waters from the Gulf of Thailand. The environmental factors controlling the distribution of diatoms are temperature, salinity, water depth and turbidity. The interior of the Welu Estuary was characterized by a brackish water environment strongly influenced by freshwater inputs to the south branch of the estuary and invasion of seawater into the north branch of the estuary. The Chanthaburi Estuary is a brackish water environment dominated by a single diatom assemblage. The main causes of differences in the distribution of diatoms between the Chanthaburi and Welu estuaries are runoff, estuary size, river width and nutrient concentrations.

Impacts of topography change on saltwater intrusion over the past decade in the Changjiang Estuary

Saltwater intrusion in estuaries is mainly controlled by tides and river discharge, as well as by topography and other factors. The Changjiang estuary has been seen a significant change in its topography from the data obtained in 2007 and 2017. In this study, a well-validated 3D numerical model was used to simulate and analyze the residual water and salt transport, water diversion ratio (WDR) in bifurcated channels and water resources in the Changjiang Estuary in 2007 and 2017. The comparisons of the model results showed that due to the North Branch becoming much shallower and narrower over the period from 2007 to 2017, the overall salinity in the North Branch decreased and the intensity of saltwater spillover (SSO) from the North Branch into the South Branch weakened. In the North Channel, the simulated residual or net transection water flux (NTWF) and WDR decreased during spring tides, resulting in increased saltwater intrusion. During neap tides, the saltwater intrusion was weakened despite the decreased NTWF and WDR because the water depth at the river mouth became shallower. The changes of topography during that period also resulted in changes of DWR, NTWF, salt transport across the tidal flats and dykes in the North Passage, South Passage and the South Channel, as well as overall dynamic mechanism. The results indicated that the salinity at the water intakes of the three reservoirs in the estuary slightly decreased, indicating that the time that reservoirs can take water from the estuary become longer in dry seasons. In the scenario of complete silt-up of the North Branch, the saltwater intrusion was weakened in the South Branch because of the disappearance of the SSO, which was favorable for the utilization of freshwater resources, but enhanced in the North Channel, North and South Passages. The overall influence from the topographic change over the period is that the saltwater intrusion is weakened in the North Branch, and enhanced during spring tides and weakened during neap tides in the North Channel, North and South Passages. Sediment accretion in the North Branch is favorable for utilization of freshwater resources.

Study on the Spillover of Sediment during Typical Tidal Processes in the Yangtze Estuary Using a High-Resolution Numerical Model

Because of special morphologies and complex runoff–tide interactions, the landward floodtide flows in Yangtze Estuary are observed to spill over from the North to the South Branches, carrying a lot of sediment. To quantitatively clarify the spillover problem, a two-dimensional numerical model using a high-resolution channel-refined unstructured grid is developed for the entire Yangtze Estuary from Datong to river mouths (620 km) and part of the East Sea. The developed model ensures a good description of the river-coast-ocean coupling, the irregular boundaries, and local river regimes in the Yangtze Estuary. In tests, the simulated histories of the tidal level, depth-averaged velocity, and sediment concentration agree well with field data. The spillover of sediment in the Yangtze Estuary is studied using the condition of a spring and a neap tide in dry seasons. For a representative cross-section in the upper reach of the North Branch (QLG), the difference of the cross-sectional sediment flux (CSSF) between floodtide and ebbtide durations is 43.85–11.26 × 104 t/day, accounting for 37.5–34.9% of the landward floodtide CSSF. The mechanics of sediment spillover in Yangtze Estuary are clarified in terms of a successive process comprising the source, transport, and drainage of the spillover sediment.

Morphodynamic couplings between the Biandan Shoal and Xinqiao Channel, Changjiang (Yangtze) Estuary

Channel-shoal systems (CSS) are some of the significant morphodynamic cells in estuaries, which provide immeasurable economic, ecological and environmental value. However, most CSS in mega-estuaries of the world are facing great challenges from serious risk of degradation due to intensive human activities and sea-level rise. Here, we focus on the tradeoff between the Biandan Shoal (BDS) and Xinqiao Channel (XQC), which is the largest CSS of the South Branch, Changjiang Estuary. The results show that the BDS area above the 5 m water depth had an observable increasing tendency with an interannual increasing rate of 1.43 km2/yr during 1996–2016. The corresponding XQC volume exhibited an obvious reduction trend with an annual decreasing rate of 3.79 × 106 m3/yr. Meanwhile, the BDS presented lateral and downward extension with more than 4.7 km of downward movement, while the XQC indicated shrinking with the width of the upper reaches decreasing by nearly half since 1998. Furthermore, the morphodynamic evolution of the BDS-XQC system during 1998–2016 could be divided into four stages: preflood stage with the joint extension of the BDS and XQC (1996–1998); conversion stage due to impacts from the extreme flood (1998–2000); development stage with obvious deposition throughout the system (2000–2009); stabilization stage with deposition on the high flats but no lateral expansion of the BDS, and continuous shrinkage of the XQC (2009–2016). The dynamic balance of the BDS-XQC system was mainly determined by the tradeoffs between the BDS and XQC, even though the occasional extreme hydrological events disrupted the coupling of the BDS-XQC. Meanwhile, the local channel blocked by the construction of the Dongfengxisha Reservoir induced a decrease in water discharge into the XQC, which was responsible for the recent XQC recession. In light of the impact of future climate change and increasing human interference in the anthropogenic era, fragile CSS distributed in estuaries should be holistically considered with policies to support sustainable integrated coastal zone management.

Energetic Electron Patterns in the New SLS5 Longitude System

AbstractEnergetic electron (110–300 keV) fluxes collected during the entire 13‐year Cassini mission are organized in the new Saturn longitude system (SLS5). This system is based on Saturn radio emissions, varies slowly in time and has a north and a south branch. When the fluxes are organized in SLS5 longitudes and magnetodisk coordinates, they display an m=1 wave pattern that is quasi‐linear in longitude‐range maps. These spiral patterns are easily recognized in energetic electrons and have positive slopes a few degrees of longitude per RS (1 RS =60,268 km), similar to that observed in both particles and magnetic fields earlier in the mission. The patterns are most prominent at elevations +2 RS (SLS5 north) or −2 RS (SLS5 south) relative to the magnetodisk center. The results indicate the persistence of this pattern for essentially half a Saturnian year, suggesting that this pattern is a quasi‐permanent feature of the magnetosphere, much the same as its plasma sheet or magnetopause.