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.

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 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 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.

Temporal and spatial variations of three dimethylated sulfur compounds in the Changjiang Estuary and its adjacent area during summer and winter

2017 ◽  
Vol 14 (3) ◽  
pp. 160 ◽  
Author(s):  
Nan Gao ◽  
Gui-Peng Yang ◽  
Hong-Hai Zhang ◽  
Long Liu
Keyword(s):  
Atmospheric Chemistry ◽  
River Mouth ◽  
Primary Source ◽  
Sulfur Compounds ◽  
Changjiang Estuary ◽  
Oxidation Products ◽  
Adjacent Area ◽  
Aerosol Formation ◽  
The Changjiang Estuary ◽  
Chl A

Environmental contextDimethylsulfide is a biogeochemically important sulfur gas emitted from the oceans that can lead to aerosol formation, thereby affecting earth albedo and climate. Studies on the biogeochemistry of dimethylsulfide and its precursors and oxidation products in coastal waters can link the atmospheric chemistry of dimethylsulfide with the bioavailable organic sulfur pool in the oceans. The ensuing information is essential for understanding the biogeochemical dynamics of sulfur and its global cycles. AbstractThe spatiotemporal distribution patterns of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO) and chlorophyll a (Chl-a), as well as the oceanographic parameters influencing the concentrations of DMS, DMSP and DMSO, were measured in the Changjiang Estuary and its adjacent area during two cruises from 21 February to 10 March 2014 and from 10 to 22 July 2014. The concentrations of DMS and DMSP showed significant seasonal variation, i.e. higher values in summer than in winter. This result corresponded well with the seasonal change in Chl-a in the study area. The distribution of dissolved DMSO (DMSOd) decreased significantly with distance from shore, suggesting a primary source of terrestrial and riverine inputs. The seasonal variations of both DMSOd and particulate DMSO (DMSOp) were weaker than other sulfur compounds. Significant relationships were observed between DMS, particulate DMSP (DMSPp), DMSOp and Chl-a, suggesting that phytoplankton biomass plays an important role in controlling the distributions of DMS, DMSP and DMSO in the study area. The positive relationship between DMSPp and DMSOp suggested similar sources and cellular functions in algae, whereas the oxidation of DMS to DMSOd appeared to be a predominant source of DMSOd in winter in the area adjacent to the river mouth. The average sea-to-air fluxes of DMS in the Changjiang Estuary and its adjacent area were 0.37 and 1.70 µmol m–2 day–1 in winter and summer respectively; these values are much lower than those in other continental shelf seas.

Long-term changes in the Changjiang Estuary plankton community related to anthropogenic eutrophication

2010 ◽  
Vol 13 (1) ◽  
pp. 66-72 ◽  
Author(s):  
Yun Li ◽  
Daoji Li ◽  
Jingliang Tang ◽  
Yiming Wang ◽  
Zhigang Liu ◽  
...  
Keyword(s):  
Plankton Community ◽  
Changjiang Estuary ◽  
The Changjiang Estuary ◽  
Anthropogenic Eutrophication ◽  
Long Term Changes

scholarly journals Clarifying Water Column Respiration and Sedimentary Oxygen Respiration Under Oxygen Depletion Off the Changjiang Estuary and Adjacent East China Sea

2021 ◽  
Vol 7 ◽  
Author(s):  
Jun Zhou ◽  
Zhuo-Yi Zhu ◽  
Huan-Ting Hu ◽  
Gui-Ling Zhang ◽  
Qian-Qian Wang
Keyword(s):  
Dissolved Oxygen ◽  
Water Column ◽  
East China Sea ◽  
Oxygen Depletion ◽  
Changjiang Estuary ◽  
East China ◽  
The Changjiang Estuary ◽  
China Sea ◽  
Bottom Waters ◽  
Water Column Respiration

The Changjiang Estuary and its adjacent East China Sea are among the largest coastal hypoxic sites in the world. The oxygen depletion in the near-bottom waters (e.g., meters above the seabed) off the Changjiang Estuary is caused by water column respiration (WCR) and sedimentary oxygen respiration (SOR). It is essential to quantify the contributions of WCR and SOR to total apparent oxygen utilization (AOU) to understand the occurrence of hypoxia off the Changjiang Estuary. In this work, we analyzed the δ18O and O2/Ar values of marine dissolved gas samples collected during a field investigation in July 2018. We observed that the δ18O values of dissolved oxygen in near-bottom waters ranged from 1.039 to 8.457‰ (vs. air), generally higher than those of surface waters (−5.366 to 2.336‰). For all the sub-pycnocline samples, the δ18O values were negatively related to O2 concentrations (r2 = 0.97), indicating apparent fractionation of δ18O during oxygen depletion in the water column. Based on two independent isotope fractionation models that quantified the isotopic distillation of dissolved oxygen concentration and its δ18O, the mean contributions of WCR and SOR to total near-bottom AOU were calculated as 53 and 47%, respectively. Beneath the pycnocline, the WCR contribution to the total AOU varied from 24 to 69%, and the SOR contribution varied from 31 to 76%. The pooled samples beneath both the pycnocline and upper mixed layer indicated that WCR contributions (%) to total AOU increased with increasing AOU (μmol/L), whereas SOR% – AOU had the reverse trend. We propose that the WCR% and SOR% contributions to the total AOU of the sub-pycnocline waters are dynamic, not stationary, with changes in ambient environmental factors. Under hypoxic conditions, we observed that up to 70% of the total AOU was contributed by WCR, indicating that WCR is the major oxygen consumption mechanism under hypoxia; that is, WCR plays a vital role in driving the dissolved oxygen to become hypoxic off the Changjiang Estuary.

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