2023 Vol. 42, No. 9
Display Method:
2023, 42(9): 1-2.
Abstract:
2023, 42(9): 1-15.
doi: 10.1007/s13131-023-2159-9
Abstract:
To investigate the influence of asymmetric tidal mixing (ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M2 tidal flow, residual flow and suspended sediment concentration (SSC) are described. Model solutions are obtained in terms of tidally-averaged, and tidally-varying components (M2 and M4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River Estuary, where higher (or lower) eddy diffusivity was observed during flood (or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM (higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress (e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward (e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing (in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM, where sediment diffusivity is higher during the ebb.
To investigate the influence of asymmetric tidal mixing (ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M2 tidal flow, residual flow and suspended sediment concentration (SSC) are described. Model solutions are obtained in terms of tidally-averaged, and tidally-varying components (M2 and M4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varying eddy viscosity and time-varying eddy diffusivity of SSC. For the first time, an analytical solution for SSC variation driven by varying diffusivity could be derived. The model was applied to York River Estuary, where higher (or lower) eddy diffusivity was observed during flood (or ebb) in a previous study. The model results agreed well with the observation in both hydrodynamics and sediment dynamics. The vertical sediment distribution under the influence of ATM was analyzed in terms of the phase lag of the M2 component of SSC relative to tidal flow. The phase lag increases significantly in estuaries with typical ATM (higher diffusivity during flood and lower diffusivity during ebb) for the case of seaward-directed net bottom shear stress (e.g., strong river discharge). In contrary, the phase lag is reduced by ATM, if the tidally-averaged bottom shear stress is landward (e.g., strong horizontal density gradient). The dynamics of sediment transport was analyzed as a function of ATM phase lag to identify the time of highest sediment diffusivity, as well as a function of the residual flow, to evaluate the relative importance of seaward and landward residual flows. In estuaries with relative strong fresh water discharge or weak tidal forcing (in case of flood season or neap tide), the near bottom SSC could be higher during ebb than during flood, since the bottom shear stress is higher during ebb due to seaward residual flow. However, landward net sediment transport can be expected in these estuaries in case of a typical ATM, because higher diffusivity causes higher SSC and landward transport during the flood period, while both SSC and seaward transport could be lower during ebb. On the contrary, seaward sediment transport can be expected in estuaries with landward tidally mean bottom shear stress in case of a reverse ATM, where sediment diffusivity is higher during the ebb.
2023, 42(9): 16-26.
doi: 10.1007/s13131-022-2114-1
Abstract:
Submarine canyon is an important channel for long-distance sediment transport, and an important part of deep-water sedimentary system. The large-scale Rizhao Canyons have been discovered for the first time in 2015 in the continental slope area of the western South China Sea. Based on the interpretation and analysis of multi-beam bathymetry and two-dimensional multi-channel seismic data, the geology of the canyons has however not been studied yet. In this paper, the morphology and distribution characteristics of the canyon are carefully described, the sedimentary filling structure and its evolution process of the canyon are analyzed, and then its controlling factors are discussed. The results show that Rizhao Canyons group is a large slope restricted canyon group composed of one east−west west main and nine branch canyons extending to the south. The canyon was formed from the late Miocene to the Quaternary. The east−west main canyon is located in the transition zone between the northern terrace and the southern Zhongjiannan Slope, and it is mainly formed by the scouring and erosion of the material source from the west, approximately along the slope direction. Its development and evolution is mainly controlled by sediment supply and topographic conditions, the development of 9 branch canyons is mainly controlled by gravity flow and collapse from the east−west main canyon. This understanding result is a supplement to the study of “source-channel–sink” sedimentary system in the west of the South China Sea, and has important guiding significance for the study of marine geological hazards.
Submarine canyon is an important channel for long-distance sediment transport, and an important part of deep-water sedimentary system. The large-scale Rizhao Canyons have been discovered for the first time in 2015 in the continental slope area of the western South China Sea. Based on the interpretation and analysis of multi-beam bathymetry and two-dimensional multi-channel seismic data, the geology of the canyons has however not been studied yet. In this paper, the morphology and distribution characteristics of the canyon are carefully described, the sedimentary filling structure and its evolution process of the canyon are analyzed, and then its controlling factors are discussed. The results show that Rizhao Canyons group is a large slope restricted canyon group composed of one east−west west main and nine branch canyons extending to the south. The canyon was formed from the late Miocene to the Quaternary. The east−west main canyon is located in the transition zone between the northern terrace and the southern Zhongjiannan Slope, and it is mainly formed by the scouring and erosion of the material source from the west, approximately along the slope direction. Its development and evolution is mainly controlled by sediment supply and topographic conditions, the development of 9 branch canyons is mainly controlled by gravity flow and collapse from the east−west main canyon. This understanding result is a supplement to the study of “source-channel–sink” sedimentary system in the west of the South China Sea, and has important guiding significance for the study of marine geological hazards.
2023, 42(9): 27-43.
doi: 10.1007/s13131-022-2116-z
Abstract:
Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained: (1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies. (2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils. (3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir’s physical property when sea level slowly rises and improves the reservoir’s physical property when base level slowly falls.
Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained: (1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies. (2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils. (3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir’s physical property when sea level slowly rises and improves the reservoir’s physical property when base level slowly falls.
2023, 42(9): 44-52.
doi: 10.1007/s13131-023-2154-1
Abstract:
The devastating 2004 tsunamis that hit the southwestern coast of Thailand pose a serious threat to people along the coastal zone. A major aim for the tsunami hazard prediction is better prediction of the next tsunamis and their impacts. In this paper, we present the first implications of recent slope failure events of the Andaman outer shelf and upper slope based on a new detailed bathymetric data and subbottom profiler records acquired during two cruises of the MASS project in 2006 and 2007. Morphometric analysis reveals a variety of anomalous features, including: three large plateaus surrounded by moats, ruggedness and unevenness of slope morphology, and two translational submarine landslides. Two submarine landslides are studied from the detailed bathymetric data and subbottom profiler record covering the upper slope of the Andaman Sea shelf break within Thai exclusive economic zone. Maximum approximated volumes of both displaced masses are 4.8×107 m3 and 2.2×107 m3. Considering the data, there is no evidence that landslides have been the sources for tsunami hazard potential in recent geological time. These prerequisites will allow better study of slope failure events in the area. Further investigation is required to better understand obvious geotectonic phenomena.
The devastating 2004 tsunamis that hit the southwestern coast of Thailand pose a serious threat to people along the coastal zone. A major aim for the tsunami hazard prediction is better prediction of the next tsunamis and their impacts. In this paper, we present the first implications of recent slope failure events of the Andaman outer shelf and upper slope based on a new detailed bathymetric data and subbottom profiler records acquired during two cruises of the MASS project in 2006 and 2007. Morphometric analysis reveals a variety of anomalous features, including: three large plateaus surrounded by moats, ruggedness and unevenness of slope morphology, and two translational submarine landslides. Two submarine landslides are studied from the detailed bathymetric data and subbottom profiler record covering the upper slope of the Andaman Sea shelf break within Thai exclusive economic zone. Maximum approximated volumes of both displaced masses are 4.8×107 m3 and 2.2×107 m3. Considering the data, there is no evidence that landslides have been the sources for tsunami hazard potential in recent geological time. These prerequisites will allow better study of slope failure events in the area. Further investigation is required to better understand obvious geotectonic phenomena.
2023, 42(9): 53-61.
doi: 10.1007/s13131-023-2155-0
Abstract:
Past hydroclimatic conditions in southern China are poorly constrained owing to the lack of high-resolution marine-sediment records. In this study, we present high-resolution geochemical and grain-size records of marine sediments from the coastal shelf of the northern South China Sea to investigate regional hydrological variations. Results suggest a warm and humid climate during the interval 9 200–7 600 cal a BP, followed by a cold and dry climate from 7 600 cal a BP to 6 500 cal a BP, and progressive humidification during the period 6 500–6 200 cal a BP. A prominent hydrological anomaly occurred during 7 600–6 500 cal a BP. This abrupt event corresponds closely to tropical Pacific and interhemispheric temperature gradients, suggesting that moisture variations in southern China may have been driven by interhemispheric and zonal Pacific temperature gradients via modulation of the intensity and location of the West Pacific subtropical high.
Past hydroclimatic conditions in southern China are poorly constrained owing to the lack of high-resolution marine-sediment records. In this study, we present high-resolution geochemical and grain-size records of marine sediments from the coastal shelf of the northern South China Sea to investigate regional hydrological variations. Results suggest a warm and humid climate during the interval 9 200–7 600 cal a BP, followed by a cold and dry climate from 7 600 cal a BP to 6 500 cal a BP, and progressive humidification during the period 6 500–6 200 cal a BP. A prominent hydrological anomaly occurred during 7 600–6 500 cal a BP. This abrupt event corresponds closely to tropical Pacific and interhemispheric temperature gradients, suggesting that moisture variations in southern China may have been driven by interhemispheric and zonal Pacific temperature gradients via modulation of the intensity and location of the West Pacific subtropical high.
2023, 42(9): 62-70.
doi: 10.1007/s13131-023-2157-y
Abstract:
The Tianxiu hydrothermal field (TXHF) located on Carlsberg Ridge is one of the few active ultramafic-hosted venting systems known in the Indian Ocean. Despite numerous investigations, there is limited understanding of its sulfide structure morphology, and the factors controlling the formation of TXHF are poorly understood. In this study, we conducted detailed seafloor mapping using visual data obtained by dives using the human-occupied vehicle (HOV) Jiaolon g. The TXHF is found to be an active, off-axis, ultramafic-hosted, high-temperature hydrothermal area in which serpentine peridotite is exposed. Two main hydrothermal sites were identified, i.e., P and Y, both of which feature a complex of chimneys and beehive diffusers constituting a “chimney jungle” and isolated large steep-sided structures developed on flat-lying sulfide mounds. In addition, some sporadic inactive chimneys and outcrops of hydrothermal deposits were noted. The chimneys are rich in Fe and Zn sulfide, and lack the central fluid channel formed by focused high-temperature fluid flow. Hydrothermal venting at TXHF is likely related to low-angle detachment faults that focus and transport hydrothermal fluids away from a heat source along the valley wall. Our results complement and expand upon previous works concerning sulfide chimney morphology and their corresponding mineral paragenesis in ultramafic-hosted hydrothermal systems in the Indian Ocean and further our understanding of modern seafloor hydrothermal systems.
The Tianxiu hydrothermal field (TXHF) located on Carlsberg Ridge is one of the few active ultramafic-hosted venting systems known in the Indian Ocean. Despite numerous investigations, there is limited understanding of its sulfide structure morphology, and the factors controlling the formation of TXHF are poorly understood. In this study, we conducted detailed seafloor mapping using visual data obtained by dives using the human-occupied vehicle (HOV) Jiaolon g. The TXHF is found to be an active, off-axis, ultramafic-hosted, high-temperature hydrothermal area in which serpentine peridotite is exposed. Two main hydrothermal sites were identified, i.e., P and Y, both of which feature a complex of chimneys and beehive diffusers constituting a “chimney jungle” and isolated large steep-sided structures developed on flat-lying sulfide mounds. In addition, some sporadic inactive chimneys and outcrops of hydrothermal deposits were noted. The chimneys are rich in Fe and Zn sulfide, and lack the central fluid channel formed by focused high-temperature fluid flow. Hydrothermal venting at TXHF is likely related to low-angle detachment faults that focus and transport hydrothermal fluids away from a heat source along the valley wall. Our results complement and expand upon previous works concerning sulfide chimney morphology and their corresponding mineral paragenesis in ultramafic-hosted hydrothermal systems in the Indian Ocean and further our understanding of modern seafloor hydrothermal systems.
2023, 42(9): 71-78.
doi: 10.1007/s13131-023-2162-1
Abstract:
Sand waves in the Taiwan Shoal are characterized by two distinct spatial scales. Giant sand waves have a length of 2 kilometers with height between 5 m and 25 m, whilst small sand waves is less than 100-m long with height less than 5 m between giant sand wave peaks (crests). A series of five high-resolution multi-beam echo-sounding surveys between 2012 and 2020 in the middle of Taiwan Shoal indicated that artificial dredging on the giant sand waves had caused sand wave reform and evolution. Overall, the removal of giant sand waves significantly affected the migration of small sand waves adjacent to the dredging site, with the latter on both sides of the former appear to migrate towards the dredging pit. Moreover, in the dredging area, new sand waves emerged with wavelength much smaller than the original giant sand waves, while the convergent pattern of the small sand waves tends to store and form the giant sand waves, which might spread far beyond the survey period.
Sand waves in the Taiwan Shoal are characterized by two distinct spatial scales. Giant sand waves have a length of 2 kilometers with height between 5 m and 25 m, whilst small sand waves is less than 100-m long with height less than 5 m between giant sand wave peaks (crests). A series of five high-resolution multi-beam echo-sounding surveys between 2012 and 2020 in the middle of Taiwan Shoal indicated that artificial dredging on the giant sand waves had caused sand wave reform and evolution. Overall, the removal of giant sand waves significantly affected the migration of small sand waves adjacent to the dredging site, with the latter on both sides of the former appear to migrate towards the dredging pit. Moreover, in the dredging area, new sand waves emerged with wavelength much smaller than the original giant sand waves, while the convergent pattern of the small sand waves tends to store and form the giant sand waves, which might spread far beyond the survey period.
2023, 42(9): 79-89.
doi: 10.1007/s13131-022-2119-9
Abstract:
It is widely acknowledged that the distribution of macrobenthos is affected by salinity, but the degree of influence varies in different areas. To explore the distribution pattern of macrobenthic assemblages in the Hangzhou Bay, 12 stations were sampled to collect macrobenthos and the corresponding bottom water. Changes in the general characteristics of macrobenthos along the salinity gradient in the Hangzhou Bay and its adjacent waters were considered. Three dominant species were identified, including the polychaetes Sternaspis chinensis, the crustacea Oratosquilla oratoria and the echinoderm Ophiuroglypha kinbergi. And the macrobenthic assemblages showed a zonal distribution along with the salinity change. The correlation analyses showed that salinity, depth, temperature, suspended solids and dissolved oxygen had concurrent significant correlations with carnivorous group, Margalef species richness (d), Brillouin index (H) and Shannon-Wiener diversity index (H’). In light of the strong correlation between salinity and Changjiang River diluted water, which produces considerable disturbances by freshwater inflows, the deposition of suspended solids and the resuspension of seabed sediments, the combined environmental disturbances, instead of salinity alone, should be adopted to explain the zonation distribution pattern of macrobenthic assemblages.
It is widely acknowledged that the distribution of macrobenthos is affected by salinity, but the degree of influence varies in different areas. To explore the distribution pattern of macrobenthic assemblages in the Hangzhou Bay, 12 stations were sampled to collect macrobenthos and the corresponding bottom water. Changes in the general characteristics of macrobenthos along the salinity gradient in the Hangzhou Bay and its adjacent waters were considered. Three dominant species were identified, including the polychaetes Sternaspis chinensis, the crustacea Oratosquilla oratoria and the echinoderm Ophiuroglypha kinbergi. And the macrobenthic assemblages showed a zonal distribution along with the salinity change. The correlation analyses showed that salinity, depth, temperature, suspended solids and dissolved oxygen had concurrent significant correlations with carnivorous group, Margalef species richness (d), Brillouin index (H) and Shannon-Wiener diversity index (H’). In light of the strong correlation between salinity and Changjiang River diluted water, which produces considerable disturbances by freshwater inflows, the deposition of suspended solids and the resuspension of seabed sediments, the combined environmental disturbances, instead of salinity alone, should be adopted to explain the zonation distribution pattern of macrobenthic assemblages.
2023, 42(9): 90-100.
doi: 10.1007/s13131-023-2160-3
Abstract:
Prokaryotic diversity and community composition in the water column of eight stations (63 samples) around the Antarctic Peninsula of the Southern Ocean were investigated. Through pyrosequencing of the V3–V4 hypervariable regions of the 16S ribosomal RNA gene, we characterized 4 720 089 valid reads representing 48 188 operational taxonomic units (OTUs, 97% similarity). The community was dominated by the phyla Pseudomonadota (original name: Proteobacteria, 47%), Oxyphotobacteria (26%), and Bacteroidota (original name: Bacteroidetes, 18%), which comprised an average of 91% of the total OTUs in all samples. The prokaryotic community composition varied vertically within the water column. Water column prokaryotic communities exhibited a clear depth profile, with higher microbial richness and higher diversity observed with increasing water depth. Cluster analysis of the community composition of water column samples exhibited a similar trend with depth. Correlation with environmental factors suggested distinct variation in prokaryotic community composition with changes in depth, salinity, temperature and dissolved oxygen levels. Functional prediction showed presence of active nitrogen, sulphur and methane metabolic cycles along the vertical transect of the studied region. These results will improve our knowledge of prokaryotic diversity and community composition at different depth of water column for better understanding of the microbial ecology and nutrient cycles in Antarctic Peninsula region of the Southern Ocean.
Prokaryotic diversity and community composition in the water column of eight stations (63 samples) around the Antarctic Peninsula of the Southern Ocean were investigated. Through pyrosequencing of the V3–V4 hypervariable regions of the 16S ribosomal RNA gene, we characterized 4 720 089 valid reads representing 48 188 operational taxonomic units (OTUs, 97% similarity). The community was dominated by the phyla Pseudomonadota (original name: Proteobacteria, 47%), Oxyphotobacteria (26%), and Bacteroidota (original name: Bacteroidetes, 18%), which comprised an average of 91% of the total OTUs in all samples. The prokaryotic community composition varied vertically within the water column. Water column prokaryotic communities exhibited a clear depth profile, with higher microbial richness and higher diversity observed with increasing water depth. Cluster analysis of the community composition of water column samples exhibited a similar trend with depth. Correlation with environmental factors suggested distinct variation in prokaryotic community composition with changes in depth, salinity, temperature and dissolved oxygen levels. Functional prediction showed presence of active nitrogen, sulphur and methane metabolic cycles along the vertical transect of the studied region. These results will improve our knowledge of prokaryotic diversity and community composition at different depth of water column for better understanding of the microbial ecology and nutrient cycles in Antarctic Peninsula region of the Southern Ocean.
2023, 42(9): 101-112.
doi: 10.1007/s13131-023-2158-x
Abstract:
Green tidal algal Enteromorpha species complete their life cycles by the isomorphic alternation of generations. The provenance of green tide caused by them in the western Yellow Sea has been disputed. The cell reproduction derived from adult thallus was observed on E. clathrata collected from Shantou City, Guangdong Province in this study. Subsequently, it further found that E. proliferia collected from Qingdao City, Shandong Province and Qinhuangdao City, Hebei Province, produced reproductive cells by somatic cells of its early infantile thallus or branch. The latter is functionally similar to that the seedlings of red alga Porphyra yezoensis produce the monospores, and could exquisitely explain the ephemeral or opportunistic trait and environmental adaptation ability of Enteromorpha species. Changes in growth conditions may induce the two types of cell reproduction. They contribute to the bloom, and can effectively reveal the seasonally occurring large-scale and on-year and off-year phenomenon. The latter may have played a decisive role in its formation. This paper analyses the legal status of the species name, the type of generation during bloom, ephemeral traits, the role of microscopic propagule, the area of origin, on-year and off-year phenomenon, early warning and prevention and control of the species, and so on. On this basis, further study on the influence of environmental factors on cell reproduction of early infantile thalli or branches will achieve a positive effect for early warning and prevention and control of the green tidal algal bloom.
Green tidal algal Enteromorpha species complete their life cycles by the isomorphic alternation of generations. The provenance of green tide caused by them in the western Yellow Sea has been disputed. The cell reproduction derived from adult thallus was observed on E. clathrata collected from Shantou City, Guangdong Province in this study. Subsequently, it further found that E. proliferia collected from Qingdao City, Shandong Province and Qinhuangdao City, Hebei Province, produced reproductive cells by somatic cells of its early infantile thallus or branch. The latter is functionally similar to that the seedlings of red alga Porphyra yezoensis produce the monospores, and could exquisitely explain the ephemeral or opportunistic trait and environmental adaptation ability of Enteromorpha species. Changes in growth conditions may induce the two types of cell reproduction. They contribute to the bloom, and can effectively reveal the seasonally occurring large-scale and on-year and off-year phenomenon. The latter may have played a decisive role in its formation. This paper analyses the legal status of the species name, the type of generation during bloom, ephemeral traits, the role of microscopic propagule, the area of origin, on-year and off-year phenomenon, early warning and prevention and control of the species, and so on. On this basis, further study on the influence of environmental factors on cell reproduction of early infantile thalli or branches will achieve a positive effect for early warning and prevention and control of the green tidal algal bloom.
2023, 42(9): 113-124.
doi: 10.1007/s13131-023-2153-2
Abstract:
Microorganisms are fundamental for the functioning of marine ecosystems and are involved in the decomposition of organic matter, transformation of nutrients and circulation of biologically-important chemicals. Based on the complexity of the natural geographic characteristics of the Changjiang River Estuary, the geographic distribution of sedimentary microorganisms and the causes of this distribution are largely unexplored. In this work, the surface sediment samples from the adjacent sea area of the Changjiang River Estuary were collected. Their prokaryotic diversity was examined by high-throughput sequencing technology, and the environmental factors of the bacterial community were investigated. The results indicated that the distribution of prokaryotic communities in the sediments of the study areas showed obvious spatial heterogeneity. The sampling sequences divided the sample regions into three distinct clusters. Each geographic region had a unique community structure, although Proteobacteria, Bacteroidota, Desulfobacterota, Acidobacteriota, and Actinobacteriota all existed in these three branches. Canonical correspondence analysis demonstrated that prokaryotic diversity and community distribution were significantly correlated with the geographic location of sediment, seawater depth, and in particular, nutrient content (e.g., total phosphorus, total organic carbon and dissolved oxygen). Moreover, it was found for the first time that the metal ions obviously affected the composition and distribution of the prokaryotic community in this area. In general, this work provides new insights into the structural characteristics and driving factors of prokaryotic communities under the background of the ever-changing Changjiang River Estuary.
Microorganisms are fundamental for the functioning of marine ecosystems and are involved in the decomposition of organic matter, transformation of nutrients and circulation of biologically-important chemicals. Based on the complexity of the natural geographic characteristics of the Changjiang River Estuary, the geographic distribution of sedimentary microorganisms and the causes of this distribution are largely unexplored. In this work, the surface sediment samples from the adjacent sea area of the Changjiang River Estuary were collected. Their prokaryotic diversity was examined by high-throughput sequencing technology, and the environmental factors of the bacterial community were investigated. The results indicated that the distribution of prokaryotic communities in the sediments of the study areas showed obvious spatial heterogeneity. The sampling sequences divided the sample regions into three distinct clusters. Each geographic region had a unique community structure, although Proteobacteria, Bacteroidota, Desulfobacterota, Acidobacteriota, and Actinobacteriota all existed in these three branches. Canonical correspondence analysis demonstrated that prokaryotic diversity and community distribution were significantly correlated with the geographic location of sediment, seawater depth, and in particular, nutrient content (e.g., total phosphorus, total organic carbon and dissolved oxygen). Moreover, it was found for the first time that the metal ions obviously affected the composition and distribution of the prokaryotic community in this area. In general, this work provides new insights into the structural characteristics and driving factors of prokaryotic communities under the background of the ever-changing Changjiang River Estuary.
2023, 42(9): 125-131.
doi: 10.1007/s13131-022-2115-0
Abstract:
Quantitative evaluation of the copepod feeding process is critical for understanding the functioning of marine food webs, as this provides a major link between primary producers and higher trophic levels. In this study, a molecular protocol based on quantitative polymerase chain reaction (qPCR) targeting 18S rDNA was developed and used to investigate the feeding and digestion rates of the copepod Acartia erythraea in a laboratory experiment using microalgae Thalassiosira weissflogii, Prorocentrum shikokuense, and Alexandrium catenella as prey. Although offered an equal encounter rate based on biovolume, prey uptake varied substantially among the three algal species, with the ingestion rate (IR) and digestion rate (DR) of A. erythraea differing significantly (P< 0.001) based on both cell counting and qPCR detection.Acartia erythraea showed the highest IR (2.79 × 104 cells/(ind.·h)) and DR (2.43 × 104 cells/(ind.·h)) on T. weissflogii, and the lowest amounts of ingested P. shikokuense were detected. The highest assimilation rate (~90.64%, IR/DR) was observed in copepods fed with P. shikokuense. The qPCR method used here can help determine the digestion rate and assimilation rate of copepods by detecting cells remaining in the gut hence providing the possibility to examine trophic links involving key species in the marine ecosystem. Our results indicate that A. erythraea has diet-specific feeding performance in different processes, and a quantitative assessment of copepod feeding is needed to accurately determine its functional role in the energy and matter uptake from marine food webs.
Quantitative evaluation of the copepod feeding process is critical for understanding the functioning of marine food webs, as this provides a major link between primary producers and higher trophic levels. In this study, a molecular protocol based on quantitative polymerase chain reaction (qPCR) targeting 18S rDNA was developed and used to investigate the feeding and digestion rates of the copepod Acartia erythraea in a laboratory experiment using microalgae Thalassiosira weissflogii, Prorocentrum shikokuense, and Alexandrium catenella as prey. Although offered an equal encounter rate based on biovolume, prey uptake varied substantially among the three algal species, with the ingestion rate (IR) and digestion rate (DR) of A. erythraea differing significantly (P< 0.001) based on both cell counting and qPCR detection.Acartia erythraea showed the highest IR (2.79 × 104 cells/(ind.·h)) and DR (2.43 × 104 cells/(ind.·h)) on T. weissflogii, and the lowest amounts of ingested P. shikokuense were detected. The highest assimilation rate (~90.64%, IR/DR) was observed in copepods fed with P. shikokuense. The qPCR method used here can help determine the digestion rate and assimilation rate of copepods by detecting cells remaining in the gut hence providing the possibility to examine trophic links involving key species in the marine ecosystem. Our results indicate that A. erythraea has diet-specific feeding performance in different processes, and a quantitative assessment of copepod feeding is needed to accurately determine its functional role in the energy and matter uptake from marine food webs.
2023, 42(9): 132-144.
doi: 10.1007/s13131-022-2118-x
Abstract:
Channel dredging in estuaries increases water depth and subsequently impacts sediment dynamics and morphology. The Jiaojiang River Estuary is dredged frequently owing to heavy shipping demands. In this study, the effects of different dredging schemes on siltation were assessed through numerical modeling. The sediment model of the Jiaojiang River Estuary utilized an optimized bottom boundary layer model that considered the bed sediment grain size and fluid mud, and this model was calibrated using field data. Result reveal that channel dredging modifies the flow velocity inside and around the channel by changing the bathymetry; subsequently, this affects the residual current, bed stress, suspended sediment concentration, and sediment fluxes. Increasing the dredging depth and width increases the net sediment fluxes into the channel and dredging depth has a greater influence on the channel siltation thickness. When the dredging depth is 8.4 m or11.4 m, the average siltation thickness of the channel is 0.07 m or 0.15 m per mouth respectively. The parallel movement of the channel has small effects on the siltation volume during the simulation period. The sediment deposits in the channel primarily originates from the tidal flats, through bottom sediment fluxes. Vertical net circulation has a dominant impact on siltation because the difference of horizontal current of each layer on the longitudinal section of the channel increases, which intensifies the lateral sediment transport between the shoal and channel. The influence of vertical frictional dissipation on the lateral circulation at the feature points accounts for more than 50% before dredging, while the non-linear advective term is dominant after dredging. Tidal pumping mainly affects the longitudinal sediment fluxes in the channel. These results can be used for channel management and planning for similar estuaries worldwide.
Channel dredging in estuaries increases water depth and subsequently impacts sediment dynamics and morphology. The Jiaojiang River Estuary is dredged frequently owing to heavy shipping demands. In this study, the effects of different dredging schemes on siltation were assessed through numerical modeling. The sediment model of the Jiaojiang River Estuary utilized an optimized bottom boundary layer model that considered the bed sediment grain size and fluid mud, and this model was calibrated using field data. Result reveal that channel dredging modifies the flow velocity inside and around the channel by changing the bathymetry; subsequently, this affects the residual current, bed stress, suspended sediment concentration, and sediment fluxes. Increasing the dredging depth and width increases the net sediment fluxes into the channel and dredging depth has a greater influence on the channel siltation thickness. When the dredging depth is 8.4 m or11.4 m, the average siltation thickness of the channel is 0.07 m or 0.15 m per mouth respectively. The parallel movement of the channel has small effects on the siltation volume during the simulation period. The sediment deposits in the channel primarily originates from the tidal flats, through bottom sediment fluxes. Vertical net circulation has a dominant impact on siltation because the difference of horizontal current of each layer on the longitudinal section of the channel increases, which intensifies the lateral sediment transport between the shoal and channel. The influence of vertical frictional dissipation on the lateral circulation at the feature points accounts for more than 50% before dredging, while the non-linear advective term is dominant after dredging. Tidal pumping mainly affects the longitudinal sediment fluxes in the channel. These results can be used for channel management and planning for similar estuaries worldwide.
