With the combination of historical data, field observations and satellite remotely sensed images (Landsat TM/ ETM+ and CBERS), changes in Huanghe (Yellow) River estuary since 1996 when artificial Chahe distributary wa...With the combination of historical data, field observations and satellite remotely sensed images (Landsat TM/ ETM+ and CBERS), changes in Huanghe (Yellow) River estuary since 1996 when artificial Chahe distributary was built up were studied, mainly including water and sediment discharge from the river, tides, tidal currents, suspended sediment diffusion, coastline changes and seabed development. During following six and half years (up to the end of 2002), runoff and sediment loads into the river mouth declined dramatically. At the beginning of the re-routing, abundant sediment loads from the river filled up nearshore shallow water areas so that the newborn delta prograded quickly. With rapid decrease of sediment loads transported to the estuary, the delta retrograded. In 1997, subaerial tip of the abandoned delta receded 1.5km; its annual mean recession rate was about 150 m in following years. In addition, marine dynamic condition near the artificial outlet had also changed. Under the interaction of ocean and river flow, most of incoming sediment loads deposited in the vicin- ity of the outlet. Seabed erosion occurred at the subaqueous delta front. Between 1999 and 2002, erosion thick- ness averaged at 0.3 m in the subaqueous delta of 585.5 km2.展开更多
T he estuary and coast is an area where the land and the sea interact and a place in which human beings frequently move about so that understanding and controlling the change and development modes of the coastal landf...T he estuary and coast is an area where the land and the sea interact and a place in which human beings frequently move about so that understanding and controlling the change and development modes of the coastal landform plays a vital part in exploiting and protecting coastal resources. A model is the generalization and abstraction of objective things. This paper summarizes four methods for the landform development of the tidal shore and underwater delta, mainly discusses the model’s structural elements, and presents their specific application on the basis of the authors’ case study. With the application of the profile model, the dynamic change of coastal landform can be clearly seen by contrasting the different profiles of different years. Through the shrinking, expanding and transformation of the isobath, plane model is used to study the macro-change of the shoal and the coastal landform. Speed model is an efficient means to analyze the trend of erosion and deposition and the local change in a great area of the sea. Statistical survey model is a static analysis, which can be used to establish the relationship between the erosion and deposition of the shoal and the altitude and slope of survey spot.展开更多
We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblage...We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors.We used a multivariate analysis,including community ordination methods such as detrended correspondence analysis(DCA) and canonical correspondence analysis(CCA),and two-way indicator species analysis(TWINSPAN).We analyzed the biological community structure and environmental factors to determine their spatial distributions,temporal dynamics,and seasonal variations.Among the fish species,five exceeded 5% of the total abundance:Harpodon nehereus(42.82%),Benthosema pterotum(13.85%),Setipinna taty(11.64%),Thryssa kammalensis(9.17%) and Apogonichthys lineatus(6.49%).These were separated into four ecological assemblages:hypsithermal-saline,hypsithermal-brackish,hypothermal-brackish,and hypothermal-saline.We evaluated the degree of influence of environmental factors on the fish community.Our analyses suggested that environmental factors including water depth,salinity,turbidity,transparency,nutrient,and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas.Ecological and environmental factors changed temporally from 1998 to 2001,and drove the fish community succession.The environmental factors driving the fish community structure included bottom temperature,water depth,bottom and surface pH,surface total phosphorous,and bottom dissolved oxygen.This investigation was completed before completion of the Three Gorges Dam;therefore the results of this study provide an important foundation for evaluating the influence of the human activities.展开更多
The Changjiang(Yangtze)River estuary has been subject to a variety of anthropogenic pressures in recent decades.To assess the ecological health of the coastal benthic ecosystem adjacent to the estuary,three surveys we...The Changjiang(Yangtze)River estuary has been subject to a variety of anthropogenic pressures in recent decades.To assess the ecological health of the coastal benthic ecosystem adjacent to the estuary,three surveys were conducted in 2005,2009,and 2010.The AZTI's Marine Biotic Index(AMBI)and multivariate-AMBI(M-AMBI)were used to analyse the benthic ecological status of this coast.The AMBI indicate that the ecological status of the coast adjacent to the Changjiang River estuary was only slightly degraded in all 3 years.In contrast,the M-AMBI indicated that the ecological status was seriously degraded,a result that is most likely due to pollution and eutrophication induced by human activities.The assessment of the coast's ecological status by the AMBI was not in agreement with that of the M-AMBI at some stations because of lower biodiversity values at those sites.The analysis of the two indices integrated with abiotic parameters showed that the M-AMBI could be used as a suitable bio-indicator index to assess the benthic ecological status of the coast adjacent to the Changjiang River estuary.The reference conditions proposed for the coast of the Changjiang River estuary should be further evaluated in future studies.Designation of local species could also provide an important reference for Chinese waters.To improve the reliability of AMBI and M-AMBI,further research into the ecology of local species is required to understand their arrangement in ecological groups.展开更多
Surface sediment samples taken from the East China Sea off the Changjiang estuary are used as raw materials for phosphorus releasing experiment. It is found that after being thoroughly mixed with seawater for about 10...Surface sediment samples taken from the East China Sea off the Changjiang estuary are used as raw materials for phosphorus releasing experiment. It is found that after being thoroughly mixed with seawater for about 10 minutes, phosphorus released from the sediments reaches its maximum value. Adsorption kinetics can be fitted with both Elovich equation and two-constant rate equation. The releasing amount is closely related to the composition of the sediments. Phosphorus release from silty and muddy sediment is higher than from that dominated by sandy composition. For the desorption reaction, iron-phosphorus (Fe-P) is the most active one, with a releasing ratio higher than other phosphorus forms, followed by absorbed-phosphorus (Ad-P) and organic bound phosphorus (OP). All of them can be referred to as bio-available phosphorus. The results demonstrate that phosphorus in sediments can be released into seawater under suitable hydrodynamic conditions, and have a great impact on the nutrition state and primary productivity of marine biosphere.展开更多
Observations indicate an abnormal characteristic of saltwater intrusion in the upper Modaomen Waterway of the Pearl River Estuary,i.e.,the maximum salinity occurs during the neap tide or the coming moderate tide inste...Observations indicate an abnormal characteristic of saltwater intrusion in the upper Modaomen Waterway of the Pearl River Estuary,i.e.,the maximum salinity occurs during the neap tide or the coming moderate tide instead of during the spring tide.To explore the associated dynamic mechanisms,a high resolution three-dimensional numerical model was set up based on the Finite Volume Coastal Ocean Model(FVCOM),which covered the entire river network,the Pearl River Estuary,and the adjacent sea.Numerical experiments illustrated that the upper Modaomen Waterway is significantly influenced by the saltwater intrusion from the Hongwan Waterway,a narrow and shallow channel connecting the Modaomen Waterway to the sea.Specific topography,spring-neap tidal variation,local wind stress,and their interaction drive an up-estuary residual current in the Hongwan Waterway,which is much stronger during the neap tide than during the spring tide.As a result,more saltwater in the Hongwan Waterway is spilled over into the Modaomen Waterway during the neap tide or the coming moderate tide.This is the inherent dynamic mechanism why the saltwater intrusion in the upper Modaomen Waterway reaches its maximum during the neap tide or the coming moderate tide.Besides,we also found that the winter prevailing wind can pronouncedly enhance the saltwater intrusion in the Modaomen Waterway.展开更多
基金The work was supported by the National High-tech Research and Development Program of China (863 Program, No. AA633010-05) and key project of Natural Science Foundation of China (No. 50339050)
文摘With the combination of historical data, field observations and satellite remotely sensed images (Landsat TM/ ETM+ and CBERS), changes in Huanghe (Yellow) River estuary since 1996 when artificial Chahe distributary was built up were studied, mainly including water and sediment discharge from the river, tides, tidal currents, suspended sediment diffusion, coastline changes and seabed development. During following six and half years (up to the end of 2002), runoff and sediment loads into the river mouth declined dramatically. At the beginning of the re-routing, abundant sediment loads from the river filled up nearshore shallow water areas so that the newborn delta prograded quickly. With rapid decrease of sediment loads transported to the estuary, the delta retrograded. In 1997, subaerial tip of the abandoned delta receded 1.5km; its annual mean recession rate was about 150 m in following years. In addition, marine dynamic condition near the artificial outlet had also changed. Under the interaction of ocean and river flow, most of incoming sediment loads deposited in the vicin- ity of the outlet. Seabed erosion occurred at the subaqueous delta front. Between 1999 and 2002, erosion thick- ness averaged at 0.3 m in the subaqueous delta of 585.5 km2.
基金supported by the National Great Science Project(2002CB412407)the National Science Foundation(40076027).
文摘T he estuary and coast is an area where the land and the sea interact and a place in which human beings frequently move about so that understanding and controlling the change and development modes of the coastal landform plays a vital part in exploiting and protecting coastal resources. A model is the generalization and abstraction of objective things. This paper summarizes four methods for the landform development of the tidal shore and underwater delta, mainly discusses the model’s structural elements, and presents their specific application on the basis of the authors’ case study. With the application of the profile model, the dynamic change of coastal landform can be clearly seen by contrasting the different profiles of different years. Through the shrinking, expanding and transformation of the isobath, plane model is used to study the macro-change of the shoal and the coastal landform. Speed model is an efficient means to analyze the trend of erosion and deposition and the local change in a great area of the sea. Statistical survey model is a static analysis, which can be used to establish the relationship between the erosion and deposition of the shoal and the altitude and slope of survey spot.
基金Supported by the High Technology Research and Development Program of China (863 Program)(Nos 2006AA09Z180,2004AA639790)the National Natural Science Foundation of China (No 40106013)the National Basic Research Program of China (973 program)(No 2001CB409703)
文摘We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors.We used a multivariate analysis,including community ordination methods such as detrended correspondence analysis(DCA) and canonical correspondence analysis(CCA),and two-way indicator species analysis(TWINSPAN).We analyzed the biological community structure and environmental factors to determine their spatial distributions,temporal dynamics,and seasonal variations.Among the fish species,five exceeded 5% of the total abundance:Harpodon nehereus(42.82%),Benthosema pterotum(13.85%),Setipinna taty(11.64%),Thryssa kammalensis(9.17%) and Apogonichthys lineatus(6.49%).These were separated into four ecological assemblages:hypsithermal-saline,hypsithermal-brackish,hypothermal-brackish,and hypothermal-saline.We evaluated the degree of influence of environmental factors on the fish community.Our analyses suggested that environmental factors including water depth,salinity,turbidity,transparency,nutrient,and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas.Ecological and environmental factors changed temporally from 1998 to 2001,and drove the fish community succession.The environmental factors driving the fish community structure included bottom temperature,water depth,bottom and surface pH,surface total phosphorous,and bottom dissolved oxygen.This investigation was completed before completion of the Three Gorges Dam;therefore the results of this study provide an important foundation for evaluating the influence of the human activities.
基金Supported by the National Special Research Fund for Non-profit Sector(Environmental Protection)(No.2008467041)the National Natural Science Foundation of China(No.40976086)
文摘The Changjiang(Yangtze)River estuary has been subject to a variety of anthropogenic pressures in recent decades.To assess the ecological health of the coastal benthic ecosystem adjacent to the estuary,three surveys were conducted in 2005,2009,and 2010.The AZTI's Marine Biotic Index(AMBI)and multivariate-AMBI(M-AMBI)were used to analyse the benthic ecological status of this coast.The AMBI indicate that the ecological status of the coast adjacent to the Changjiang River estuary was only slightly degraded in all 3 years.In contrast,the M-AMBI indicated that the ecological status was seriously degraded,a result that is most likely due to pollution and eutrophication induced by human activities.The assessment of the coast's ecological status by the AMBI was not in agreement with that of the M-AMBI at some stations because of lower biodiversity values at those sites.The analysis of the two indices integrated with abiotic parameters showed that the M-AMBI could be used as a suitable bio-indicator index to assess the benthic ecological status of the coast adjacent to the Changjiang River estuary.The reference conditions proposed for the coast of the Changjiang River estuary should be further evaluated in future studies.Designation of local species could also provide an important reference for Chinese waters.To improve the reliability of AMBI and M-AMBI,further research into the ecology of local species is required to understand their arrangement in ecological groups.
文摘Surface sediment samples taken from the East China Sea off the Changjiang estuary are used as raw materials for phosphorus releasing experiment. It is found that after being thoroughly mixed with seawater for about 10 minutes, phosphorus released from the sediments reaches its maximum value. Adsorption kinetics can be fitted with both Elovich equation and two-constant rate equation. The releasing amount is closely related to the composition of the sediments. Phosphorus release from silty and muddy sediment is higher than from that dominated by sandy composition. For the desorption reaction, iron-phosphorus (Fe-P) is the most active one, with a releasing ratio higher than other phosphorus forms, followed by absorbed-phosphorus (Ad-P) and organic bound phosphorus (OP). All of them can be referred to as bio-available phosphorus. The results demonstrate that phosphorus in sediments can be released into seawater under suitable hydrodynamic conditions, and have a great impact on the nutrition state and primary productivity of marine biosphere.
基金supported by the "Creative Research Group" of National Natural Science Foundation of China (Grant No. 41021064)the National Basic Scientific Research Program of Global Change (Grant No.2010CB951201)Marine Special Program for Scientific Research on Public Causes (Grant No. 200705019)
文摘Observations indicate an abnormal characteristic of saltwater intrusion in the upper Modaomen Waterway of the Pearl River Estuary,i.e.,the maximum salinity occurs during the neap tide or the coming moderate tide instead of during the spring tide.To explore the associated dynamic mechanisms,a high resolution three-dimensional numerical model was set up based on the Finite Volume Coastal Ocean Model(FVCOM),which covered the entire river network,the Pearl River Estuary,and the adjacent sea.Numerical experiments illustrated that the upper Modaomen Waterway is significantly influenced by the saltwater intrusion from the Hongwan Waterway,a narrow and shallow channel connecting the Modaomen Waterway to the sea.Specific topography,spring-neap tidal variation,local wind stress,and their interaction drive an up-estuary residual current in the Hongwan Waterway,which is much stronger during the neap tide than during the spring tide.As a result,more saltwater in the Hongwan Waterway is spilled over into the Modaomen Waterway during the neap tide or the coming moderate tide.This is the inherent dynamic mechanism why the saltwater intrusion in the upper Modaomen Waterway reaches its maximum during the neap tide or the coming moderate tide.Besides,we also found that the winter prevailing wind can pronouncedly enhance the saltwater intrusion in the Modaomen Waterway.
