scholarly journals Wind-driven stratification patterns and dissolved oxygen depletion off the Changjiang (Yangtze) Estuary

2020 ◽  
Vol 17 (10) ◽  
pp. 2875-2895
Author(s):  
Taavi Liblik ◽  
Yijing Wu ◽  
Daidu Fan ◽  
Dinghui Shang
Keyword(s):  
Dissolved Oxygen ◽  
Summer Monsoon ◽  
Changjiang Estuary ◽  
Wind Forcing ◽  
Coastal Current ◽  
The South ◽  
The Changjiang Estuary ◽  
Water Intrusion ◽  
The North ◽  
Hypoxic Area

Abstract. Multiple factors have been accused of triggering coastal hypoxia off the Changjiang Estuary, and their interactions lead to high yearly variation in hypoxia development time window and distribution extent. Two oceanographic cruises, conducted in July 2015 and August–September 2017, were complemented by river discharge, circulation simulation, remotely sensed wind, salinity and sea level anomaly data to study the dissolved oxygen (DO) depletion off the Changjiang Estuary from synoptic to interannual timescales. Intensification of the Chinese Coastal Current and Changjiang Diluted Water (CDW) spreading to the south together with coastal downwelling caused by the northerly wind was observed in the summer of 2015. This physical forcing led to a well-ventilated area in the north and a hypoxic area of 1.3×104 km2 in the south, while in 2017 the summer monsoon (southerly winds) induced offshore transport in the surface layer that caused a subsurface intrusion of Kuroshio-derived water to the shallower areas (<10 m depth) in the north and upwelling in the south. Wind-driven Ekman surface flow and reversal of the geostrophic current related to the upwelling compelled alteration of the Chinese Coastal Current. Consequently, intense hypoxia (DO down to 0.6 mg L−1) starting from 4 to 8 m depth connected to CDW and deep water intrusion in the north and coastal hypoxia linked to the upwelling in the south were observed in 2017. Distinct situations of stratification and DO distributions can be explained by wind forcing and concurrent features in surface and deep layer circulation, upwelling and downwelling events. Enhanced primary production in the upper layer of the CDW or the upwelled water determines the location and extent of DO depletion. Likewise, the pycnocline created by Kuroshio subsurface water intrusion is an essential precondition for hypoxia formation. Wind forcing largely controls the interannual change of hypoxic area location and extent. If the summer monsoon prevails, extensive hypoxia more likely occurs in the north. Hypoxia in the south occurs if the summer monsoon is considerably weaker than the long-term mean.

scholarly journals Wind-driven stratification patterns and dissolved oxygen depletion in the area off the Changjiang (Yangtze) Estuary

2019 ◽  
Author(s):  
Taavi Liblik ◽  
Yijing Wu ◽  
Daidu Fan
Keyword(s):  
Dissolved Oxygen ◽  
Subsurface Layer ◽  
River Mouth ◽  
Changjiang Estuary ◽  
Wind Forcing ◽  
Coastal Current ◽  
Strong Impact ◽  
The Changjiang Estuary ◽  
Low Do

Abstract. The area off the Changjiang Estuary is under strong impact of fresh water and anthropogenic nutrient load from the Changjiang River. The seasonal hypoxia in the area has variable location and range, but the decadal trend reveals expansion and intensification of the dissolved oxygen (DO) depletion. Two oceanographic cruises, conducted in summer 2015 and 2017, revealed very different stratification and DO conditions in the area. Strongly inclined oxycline well correlated with the thermocline in both years. Southerly wind caused reversal of the Chinese Coastal Current and as a result, spreading of the CDW (Changjiang Diluted Water) caused pronounced hypoxic zone in the area east and northeast of the river mouth in 2017. Hypoxic layer started right below the CDW layer at 5–8 m depth and extended down to bottom. Strong DO depletion was also observed in the shallow coastal slope in the southern part of the study area. High DO utilization there closely coincided with the interaction zone of the upwelling and fresher surface water. The stratification and hypoxia pattern observed in the area in 2017 is prevailing phenomena during summers if considering the long-term wind statistics. Northeasterly winds supported southward transport of the CDW before the survey in 2015. Consequently, low DO was found in the southern part of the study area while subsurface layer in the northern part was ventilated. Weaker than long-term average summer monsoon is required for the existence of such pattern. Importance of the wind forcing was confirmed by remotely sensed sea surface salinity fields and by circulation simulation. We suggest wind forcing, together with river run-off are likely main contributors of determining the synoptic, seasonal and inter-annual time scale variations of the extent and location of low DO areas off the Changjiang Estuary.

Numerical Analysis of Ebb Water Split Ratio of the South and North Branch in the Changjiang Estuary

2013 ◽  
Vol 807-809 ◽  
pp. 1624-1627
Author(s):  
Ji Zhong Yang ◽  
Jie Gu ◽  
Dan Qing Ma ◽  
Xiao Li Wang ◽  
Tian Hu ◽  
...  
Keyword(s):  
Spring Tide ◽  
Changjiang Estuary ◽  
The South ◽  
The Changjiang Estuary ◽  
Hydrodynamic Analysis ◽  
The North ◽  
Split Ratio ◽  
Calculation Results ◽  
Set Up ◽  
The One

The change of water split ratio has important impacts on the fluvial process, saltwater intrusion and navigation in estuary area. A 2D hydrodynamics numerical model of the Changjiang Estuary was set up using Delft3D-FLOW. The calculation results are consistent well with the real measured data, which indicates that the model can be used in hydrodynamic analysis. Simulation results show that the ebb water split ratio of the North Branch in the flood season is larger than that in the dry season, while the situation of the South Branch is opposite. Under the condition of different tidal types, the ebb water split ratio for the North Branch is maximum during the spring tide, and minimum during the neap tide, while the one during the middle tide takes the second place.

Analysis on Influences of Nanshatou Passage on the Deepwater Navigation Channel of the Changjiang Estuary

2012 ◽  
Vol 212-213 ◽  
pp. 221-224
Author(s):  
Jie Gu ◽  
Wei Chen ◽  
Xin Qin ◽  
Dan Qing Ma ◽  
Xiao Li Wang ◽  
...  
Keyword(s):  
Changjiang Estuary ◽  
Sediment Deposition ◽  
The Other ◽  
Flow Volume ◽  
Key Factors ◽  
The South ◽  
The Changjiang Estuary ◽  
Flow Discharge ◽  
The North ◽  
Navigation Channel

Based on the data of water depth in Nanshatou Passage, and the flow spilt ratio of the North Channel and the South Channel, the reasons for the sediment deposition in the Deepwater Navigation Channel of the Changjiang Estuary are explored. The sediment deposition in the Deepwater Navigation Channel of the Changjiang Estuary is affected by multi-factors, among these factors; the influences of the development of the Nanshatou Passage are significant. The development of the Nanshatou Passage leads to the increase of the ebb flow discharge and the southern bank of the South Channel scoured, the scoured sediment is carried by the ebb flow to the northern bank of the South Channel, and is silted in the entrance reach of the North Passage, which decreases the ebb flow volume entering into the Deepwater Navigation Channel. On the other hand, the Coriolis force and V-shaped diversion dike at the head of the Deepwater Navigation Channel are also key factors on effect of the Deepwater Navigation Channel.

scholarly journals Qualified temperature, salinity and dissolved oxygen climatologies in a changing Adriatic Sea

2014 ◽  
Vol 11 (1) ◽  
pp. 331-390
Author(s):  
M. Lipizer ◽  
E. Partescano ◽  
A. Rabitti ◽  
A. Giorgetti ◽  
A. Crise
Keyword(s):  
Dissolved Oxygen ◽  
Adriatic Sea ◽  
Eastern Mediterranean ◽  
Temporal Stability ◽  
The South ◽  
The North ◽  
Synthetic Temperature ◽  
Oxygen Utilisation ◽  
Oxygen Minimum

Abstract. An updated climatology, based on a comprehensive dataset (1911–2009) of temperature, salinity and dissolved oxygen, has been produced for the whole Adriatic Sea with the Variational Inverse Method using the DIVA software. Climatological maps were produced at 26 levels and validated with Ordinary Cross Validation and with real vs. synthetic Temperature–Salinity diagram intercomparison. The concept of Climatology–Observation Misfit (COM) has been introduced as an estimate of the physical variability associated with the climatological structures. In order to verify the temporal stability of the climatology, long-term variability has been investigated in the Mid Adriatic and the South Adriatic Pits, regarded as the most suitable records of possible long-term changes. Compared with previous climatologies, this study reveals a surface temperature rise (up to 2 °C), a clear deep dissolved oxygen minimum in the South Adriatic Gyre and a bottom summer oxygen minimum in the North Adriatic. Below 100 m all properties profoundly differ between the Middle and the South Adriatic. The South Adriatic Pit clearly shows the remote effects of the Eastern Mediterranean Transient, while no effect is observed in Middle Adriatic Pits. The deepest part of the South Adriatic seems now to be significantly saltier (+0.18 since the period 1911–1914, with an increase of +0.018 decade−1 since the late 1940s) and warmer (+0.54 °C since 1911–1914), even though a long-term temperature trend could not be statistically demonstrated. Conversely, the Middle Adriatic Pits present a long-term increase in apparent oxygen utilisation (+0.77 mL L−1 since 1911–1914, with a constant increase of +0.2 mL L−1 decade−1 after the 1970s).

scholarly journals Composition and predictive functional analysis of bacterial communities in the surface seawater of the Changjiang Estuary

2017 ◽  
Author(s):  
Dong-Mei Wu ◽  
Jian-Xin Wang ◽  
Xiao-Hui Liu ◽  
Ying-Ping Fan ◽  
Ran Jiang ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Microbial Communities ◽  
Bacterial Communities ◽  
High Throughput Sequencing ◽  
Carbon Fixation ◽  
Oxygen Demand ◽  
Environmental Parameters ◽  
Changjiang Estuary ◽  
Surface Seawater ◽  
The Changjiang Estuary

The objective of this study was to characterize the structure and function of microbial communities in surface seawater from the Changjiang Estuary and adjacent areas, China. Sample water was collected at 12 sites and environmental parameters were measured. Community structure was analyzed using high-throughput sequencing of 16S rDNA genes. Predictive metagenomic approach was used to predict the function of bacterial communities. Result showed that sample site A0102 had the highest bacterial abundance and diversity. The heatmap indicated that different samples could be clustered into six groups. Phylogenetic analysis showed that Proteobacteria was the predominant phylum in all samples, followed by Bacteroidetes and Actinobacteria. Alphaproteobacteria and Gammaproteobacteria were the dominant classes. The analysis of predictive metagenomic showed carbon fixation pathways in prokaryotes, nitrogen metabolism, carbon fixation in photosynthetic organisms, photosynthesis and polycyclic aromatic hydrocarbon degradation were enriched in all samples. Redundancy analysis (RDA) identified that dissolved oxygen (DO) and PO43– concentration had positive correlations with the bacterial communities while chemical oxygen demand (COD), dissolved oxygen (DO) and PO43– concentration were significantly associated with microbial functional diversity. This study adds to our knowledge of functional and taxonomic composition of microbial communities.

scholarly journals Impacts of the Qingcaosha Reservoir on saltwater intrusion in the Changjiang Estuary

2021 ◽  
Vol 4 (1) ◽  
pp. 17-35
Author(s):  
Zhangliang Ding ◽  
Jianrong Zhu ◽  
Hanghang Lyu
Keyword(s):  
Saltwater Intrusion ◽  
Neap Tide ◽  
Spring Tide ◽  
Changjiang Estuary ◽  
Water Diversion ◽  
The Changjiang Estuary ◽  
The North ◽  
Salinity Increase ◽  
Hydrodynamic Processes ◽  
Changxing Island

The massive Qingcaosha Reservoir (QCSR) is located in the Changjiang Estuary along the northwest coast of Changxing Island. The reservoir significantly narrowed the upper reaches of the North Channel and deepened the channel near the reservoir. These topographical changes inevitably influenced hydrodynamic processes and saltwater intrusion in the estuary. A well-validated model was employed to investigate the influence of the QCSR on saltwater intrusion in the Changjiang Estuary. The model results showed that the narrowed upper reaches of the North Channel decreased the water diversion ratio and thus increased salinity in the North Channel. During the moderate tide after neap tide, the salinity decreased at the water intake of the QCSR because saltwater intrusion was obstructed at flood slack at the surface, while the salinity increase during the moderate tide after spring tide was mainly due to the intensified saltwater intrusion during spring tide. The deepening of the channel near the QCSR resulted in an increased water diversion ratio, and the salinity in the Eastern Chongming Shoal decreased by more than 0.5 psu during spring tide; however, the saltwater intrusion was enhanced due to the strengthened baroclinic force, which is proportional to the water depth. During neap tide, the salinity in the entire North Channel decreased because of a 1.4% increase in the water diversion ratio of the North Channel and the relatively weak tide.

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