In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with ...In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with an oxygen minimum value of 1 mg/L.The extension of the dissolved oxygen deficiency extended to the 100m isobath in a southeastward direction along the bottom of the continental shelf of the East China Sea.During the last two decades,the minimum dissolved oxygen values in the low oxygen region of the Changjiang Estuary have decreased from 2.85 mg/L to 1 mg/L.In the hypoxic zone,the apparent oxygen utilization(AOU)was 5.8 mg/L and the total oxygen depletion approximately 1.59×10^(6) t.The strong halocline above the hypoxic zone,as a result of affluent water from the Changjiang,Taiwan Warm Current(TWC),and the high concentrations of particle organic carbon(POC)and nitrogen(PON)are the major factors causing the formation of the hypoxic zone.The POC:PON ratios and nutrient concentration distributions in the hypoxic zone suggest that the oxygen deficiency in the bottom water during the summer in the East China Sea off the Changjiang is the result of organic carbon production enhanced by nutrients from the Changjiang and fluvial organic matter input,followed by a shift in regeneration of nutrients in the East China Sea.展开更多
The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd(0) values gradually decrease downst...The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd(0) values gradually decrease downstream from -10.8 on average in the upper reaches to -12.3 in the lower reaches, whereas the 87Sr/86Sr ratios increase correspondingly, averaging 0.721899 and 0.725826 respectively in the upper and middle-lower reaches. The compositional variations primarily reflect the complex con- trols of provenance rocks, chemical weathering, and sediment characters between different catchments, among which the abnormal Sr-Nd isotopic compositions of the Yalong, Fujiang, Tuojiang and Yuanjiang rivers indicate the sediment provenance contributions from the Emeishan Basalt in the upper reaches and the old metamorphic and siliceous rocks in the middle-lower reaches. The Sr-Nd isotopic ratios of the Changjiang sediments can better reflect the average composition of weathered continental crust compared to other major rivers in the world because of the unique source rock types in the Changjiang drainage basin. The recognition of the Sr-Nd isotopic systematics of the Changjiang sediments will contribute to our understanding of the Changjiang evolution history and continental weathering processes during the Cenozoic, and also to reconstructing the paleoenvironmental changes in East China and the marginal seas.展开更多
Based on the data of high-resolution seismic profiles, an ancient river channel sys-tem of the last glaciation occurred along the Zhedong and Xihu depression in the southeast of Hupijiao rise. The distribution of the ...Based on the data of high-resolution seismic profiles, an ancient river channel sys-tem of the last glaciation occurred along the Zhedong and Xihu depression in the southeast of Hupijiao rise. The distribution of the channel fill system shows that the ancient Changjiang River went through the Changjiang depression into the low land plain of the outside continental shelf during the low sea level cycle of the last glaciation. The big channel fill into Okinawa Trough is not found due to the depletion of the river kinetic energy in the low land plain. The river discharge dispersal was of an important role to the dilution of the northern Okinawa Trough sea at that time. Six ancient river channel systems (A―F), which are main distributaries of ancient Changjiang in the East China Sea continental shelf during the last glaciation, may be buried off the modern Changjiang estuary. The distribution of these channels coincides with the zonal elevations in the sea floor.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
Due to its great strategic significance in integrating regional coordinated development and enhancing the rise of Central China, urban agglomeration in the middle reaches of Changjiang （Yangtze） River has attracted ...Due to its great strategic significance in integrating regional coordinated development and enhancing the rise of Central China, urban agglomeration in the middle reaches of Changjiang （Yangtze） River has attracted much attention from both theoretical and practical aspects. Such research into the area＇s economic network structure is beneficial for the formation of an urban- and regional-development strategy. This paper constructs an economic tie model based on a modified gravitation model. Subsequently, referring to social network analysis, the paper empirically studies the network density, network centrality, subgroups and structural holes of the middle reaches of Changjiang River＇s urban agglomeration economic network. The findings are fourfold： （1） an economic network of urban agglomeration in the middle reaches of Changjiang River has been formed, and economic ties between the cities in this network are comparatively dense; （2） the urban agglomeration in the middle reaches of Changjiang River can be divided into four significant subgroups, with each subgroup having its own obvious economic communications, while there is less economic-behavioral heterogeneity among subgroups - this is especially true for the two subgroups that exist in the Poyang Lake Ecological Economic Zone; （3） an economy pattern driven by the central cities of Wuhan, Changsha and Nanchang has emerged in the urban agglomeration of the middle reaches of Changjiang River, while these three capital cities have exerted great radiation abilities to their surrounding cities, the latter are less able to absorb resources from the former （4） the Wuhan Metropolitan Areas and the Poyang Lake Ecological Economic Zone have more structural holes than the Ring of Changsha, Zhuzhou and the Xiangtan City Clusters, meaning that cities at the periphery of these two areas are easily constrained by central cities. The Ring of Changsha, Zhuzhou and the Xiangtan City Clusters have fewer structural holes; thus, the cities in this area wil展开更多
The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazite...The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazites in the Quaternary, indicating a great change of their provenance. The first presence horizon of monazites younger than 25 Ma is just above the Matruyama/Gauss boundary (~2.58 Ma), whch is exactly when uplift of the Tibetan Plateau began to influence deposition in the East China Sea. Variations in contents of monazites younger than 25 Ma can be divided into two sections. The Early-Middle Pleistocene with less <25 Ma monazites corresponds with rapid uplift of the Tibetan Plateau, and the Late Pleistocene with more <25 Ma monazites parallels the peak uplift of the Tibetan Plateau. This study demonstrates that chemical dating of monazites in the river-mouth strata is a useful method to explore changes of river drainage basins, and deconvolute multistage tectonic and magmatic activity histories in the provenance areas.展开更多
The objective of this study is to analyze soil physical and chemical properties,soil comprehensive functions and impact factors after different years of reclamation.Based on the survey data taken from 216 soil samplin...The objective of this study is to analyze soil physical and chemical properties,soil comprehensive functions and impact factors after different years of reclamation.Based on the survey data taken from 216 soil sampling points in the Fengxian Reclamation Area of the Changjiang (Yangtze) River Estuary,China in April 2009 and remotely sensed TM data in 2006,while by virtue of multivariate analysis of variance (MANOVA),geo-statistical analysis (GA),prin-cipal component analysis (PCA) and canonical correspondence analysis (CCA),it was concluded that:1) With the in-crease in reclamation time,soil moisture,soil salinity,soil electric conductivity and soil particle size tended to decline,yet soil organic matter tended to increase.Soil available phosphorous tended to increase in the early reclamation period,yet it tended to decline after about 49 years of reclamation.Soil nitrate nitrogen,soil ammonia nitrogen and pH changed slightly in different reclamation years.Soil physical and chemical properties reached a steady state after about 30 years of reclamation.2) According to the results of PCA analysis,the weighted value (0.97 in total) that represents soil nutrient factors (soil nitrate nitrogen,soil organic matter,soil available phosphorous,soil ammonia nitrogen,pH and soil particle size) were higher than the weighted value (0.48 in total) of soil limiting factors (soil salinity,soil elec-tric conductivity and soil moisture).The higher the F value is,the better the soil quality is.3) Different land use types play different roles in the soil function maturity process,with farmlands providing the best contribution.4) Soil physi-cal and chemical properties in the reclamation area were mainly influenced by reclamation time,and then by land use types.The correlation (0.1905) of the composite index of soil function (F) with reclamation time was greater than that with land use types (-0.1161).展开更多
We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and th...We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and their interactions on WDR using the improved version of three-dimensional numerical model ECOM. Using data for annual mean wind speed and river discharge during January, we determined that the flood, ebb, net WDR values in the North Branch of the estuary were 3.48%, 1.68%,-4.06% during spring tide, and 4.82%, 2.34%,-2.79% during neap tide, respectively. Negative net WDR values denote the transport of water from the North Branch into the South Branch. Using the same data, the corresponding ratios were 50.09%, 50.92%, 54.97%, and 52.33%, 50.15%, 43.86% in the North Channel and 38.56%, 44.78%, 103.96%, and 36.92%, 43.17%, 60.97% in the North Passage, respectively. When northerly wind speed increased, landward Ekman transport was enhanced in the North Branch, increasing the flood WDR, while the ebb WDR declined and the net WDR exhibited a significant decrease. Similarly, in the North Channel, the flood WDR is increased, the ebb WDR reduced, and the net WDR showed a marked decrease. In the North Passage, the flood WDR also increased while the ebb and net WDR declined. As the river discharge increased, the flood and ebb WDR of the North Branch increased slightly and the net WDR increased markedly. In the North Channel the flood and ebb WDR changed very slightly, while the net WDR declined during spring tides and increased during neap tides. The WDR in the North Passage changed slightly during flood and ebb tides while the net WDR showed a marked increase. The WDR values of different bifurcations and the responses to northerly wind, river discharge, and tide are discussed in comparison with variations in river topography, horizontal wind-induced circulation, and tidal-induced residual current.展开更多
Sandwaves in the Changjiang estuary were measured with a shallow sediment profiler and an echosounder from 1978 to 1988. The data, together with grain size and bedform of sediment indicates that the bedload movement b...Sandwaves in the Changjiang estuary were measured with a shallow sediment profiler and an echosounder from 1978 to 1988. The data, together with grain size and bedform of sediment indicates that the bedload movement by rolling and saltation is of great significance to sediment transport and is the principal factor responsible for sandwave and sandbody development in the estuary. The sandwaves were found well-developed, which is related to the tidal range and the velocity of ebb current. However, the further growth is restricted by strong flood current prevailing in the estuary. Because of the significant bedload, the sandbodies shift obviously and frequently, and sometimes the exchange of position occurs between the sandbodies and tidal channels. As a result, ships are regularly forced to change their navigation course.展开更多
On the basis of data collected in the summer of 2006 from 27 sampling stations in the Changjiang Estuary and its adjacent waters, the ecological characteristics of macrobenthos and the relationship between the macrobe...On the basis of data collected in the summer of 2006 from 27 sampling stations in the Changjiang Estuary and its adjacent waters, the ecological characteristics of macrobenthos and the relationship between the macrobenthos and the environmental factors were studied using hierarchical cluster and non-metric multidimensional scaling （MDS）. The biomass, abundance, Shannon -Wiener＇s and Margalef＇ s indices of the macrobenthos were presented. The results showed that a total of 253 macrobenthic species were found in the research region, and most of them belong to mollusks and polychaetes. The dominant species were Cossurella dimorpha, Eocylichna cylindrella, Episiphon kiaochowwanense, Nassarius semiplicatus, Ocstergrenia variabilis and Sternaspis scutata. The average abundance of the macrobenthos was （313. 15 ±233.4） ind./m^2, and the average biomass was （ 15. 2 ± 11.2 ）g/m^2. The distribution patterns of the abundance and biomass of the macrobenthos were similar. The abundance and biomass in the area close to the estuary were lower than those from the area more distant to the estuary; the central part of the research region had higher abundance and biomass than other parts of the research region. In accordance with the results, four macrobenthic communities with distinct spatial differences were identified. The low abundance and biomass in the area close to the estuary should be caused by the high sedimentation rate. The statistical analysis indicated that the depth is the most important factor affecting the distribution of macrobenthos.展开更多
Rock weathering plays an important role in studying the long-term carbon cycles and global climatic change. According to the statistics analysis, the Huanghe (Yellow) River water chemistry was mainly controlled by eva...Rock weathering plays an important role in studying the long-term carbon cycles and global climatic change. According to the statistics analysis, the Huanghe (Yellow) River water chemistry was mainly controlled by evaporite and carbonate weathering, which were responsible for over 90% of total dissolved ions. As compared with the Huanghe River basin, dissolved load of the Changjiang (Yangtze) River was mainly originated from the carbonate dissolution. The chemical weathering rates were estimated to be 39.29t/(km(2).a) and 61.58t/(km(2).a) by deducting the HCO3- derived from atmosphere in the Huanghe River and Changjiang River watersheds, respectively. The CO2 consumption rates by rock weathering were calculated to be 120.84 x 10(3)mol/km(2) and 452.46 x 10(3)mol/km(2) annually in the two basins, respectively. The total CO2 consumption of the two basins amounted to 918.51 x 10(9)mol/a, accounting for 3.83% of the world gross. In contrast to other world watersheds, the stronger evaporite reaction and infirm silicate weathering can explain such feature that CO2 consumption rates were lower than a global average, suggesting that the sequential weathering may be go on in the two Chinese drainage basins.展开更多
Based on the results of water sample measurements of nutrient concentrations at th e Datong Station of the Changjiang River from 1998 to 1999, combined w ith historical data of water quality, seasonal variations of nu...Based on the results of water sample measurements of nutrient concentrations at th e Datong Station of the Changjiang River from 1998 to 1999, combined w ith historical data of water quality, seasonal variations of nutrient concentrations and nutrient transports are discussed.The following results have been obtained: (1) the fluxes of the nitrate nitrogen, ammonium nitrogen and nitrite nitrogen increased by time-series from 1962 to 1990 , even if runoff volume had a little variation; (2) the concentrations and fluxes of the dissolved inorganic nitrogen (DIN) and dissolved in organic phosphorus (DIP) increased notably with time, but those of the dissolved silicon (DSI) decreased pronouncedly; and (3) the concentration s and fluxes changed synchronously with time between the Datong Station a nd the Changjiang Estuary.展开更多
基金This study was made under the auspices of the National Key Basic Research Program of the Ministry of Science and Technology,P.R.China(Grant No.G1999043705)and the Shanghai Priority Academic Discipline.
文摘In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with an oxygen minimum value of 1 mg/L.The extension of the dissolved oxygen deficiency extended to the 100m isobath in a southeastward direction along the bottom of the continental shelf of the East China Sea.During the last two decades,the minimum dissolved oxygen values in the low oxygen region of the Changjiang Estuary have decreased from 2.85 mg/L to 1 mg/L.In the hypoxic zone,the apparent oxygen utilization(AOU)was 5.8 mg/L and the total oxygen depletion approximately 1.59×10^(6) t.The strong halocline above the hypoxic zone,as a result of affluent water from the Changjiang,Taiwan Warm Current(TWC),and the high concentrations of particle organic carbon(POC)and nitrogen(PON)are the major factors causing the formation of the hypoxic zone.The POC:PON ratios and nutrient concentration distributions in the hypoxic zone suggest that the oxygen deficiency in the bottom water during the summer in the East China Sea off the Changjiang is the result of organic carbon production enhanced by nutrients from the Changjiang and fluvial organic matter input,followed by a shift in regeneration of nutrients in the East China Sea.
基金National Natural Science Foundation of China (Grant No. 40476029) Shanghai Rising-Star Program (Grant No. 04QMX1430)
文摘The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd(0) values gradually decrease downstream from -10.8 on average in the upper reaches to -12.3 in the lower reaches, whereas the 87Sr/86Sr ratios increase correspondingly, averaging 0.721899 and 0.725826 respectively in the upper and middle-lower reaches. The compositional variations primarily reflect the complex con- trols of provenance rocks, chemical weathering, and sediment characters between different catchments, among which the abnormal Sr-Nd isotopic compositions of the Yalong, Fujiang, Tuojiang and Yuanjiang rivers indicate the sediment provenance contributions from the Emeishan Basalt in the upper reaches and the old metamorphic and siliceous rocks in the middle-lower reaches. The Sr-Nd isotopic ratios of the Changjiang sediments can better reflect the average composition of weathered continental crust compared to other major rivers in the world because of the unique source rock types in the Changjiang drainage basin. The recognition of the Sr-Nd isotopic systematics of the Changjiang sediments will contribute to our understanding of the Changjiang evolution history and continental weathering processes during the Cenozoic, and also to reconstructing the paleoenvironmental changes in East China and the marginal seas.
基金This work was supported by the National“973”Project(Grant No.2002CB412408)the Nat ional Natural Science Foundation of China(Grant Nos.90211022 and 49976013).
文摘Based on the data of high-resolution seismic profiles, an ancient river channel sys-tem of the last glaciation occurred along the Zhedong and Xihu depression in the southeast of Hupijiao rise. The distribution of the channel fill system shows that the ancient Changjiang River went through the Changjiang depression into the low land plain of the outside continental shelf during the low sea level cycle of the last glaciation. The big channel fill into Okinawa Trough is not found due to the depletion of the river kinetic energy in the low land plain. The river discharge dispersal was of an important role to the dilution of the northern Okinawa Trough sea at that time. Six ancient river channel systems (A―F), which are main distributaries of ancient Changjiang in the East China Sea continental shelf during the last glaciation, may be buried off the modern Changjiang estuary. The distribution of these channels coincides with the zonal elevations in the sea floor.
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National Natural Science Foundation of China, No.41371182 Key Project of Hunan Social Science Foundation, No. 12ZDB01 Entrusting Project of Hunan Social Science Foundation Base, No. 12JD 12
文摘Due to its great strategic significance in integrating regional coordinated development and enhancing the rise of Central China, urban agglomeration in the middle reaches of Changjiang （Yangtze） River has attracted much attention from both theoretical and practical aspects. Such research into the area＇s economic network structure is beneficial for the formation of an urban- and regional-development strategy. This paper constructs an economic tie model based on a modified gravitation model. Subsequently, referring to social network analysis, the paper empirically studies the network density, network centrality, subgroups and structural holes of the middle reaches of Changjiang River＇s urban agglomeration economic network. The findings are fourfold： （1） an economic network of urban agglomeration in the middle reaches of Changjiang River has been formed, and economic ties between the cities in this network are comparatively dense; （2） the urban agglomeration in the middle reaches of Changjiang River can be divided into four significant subgroups, with each subgroup having its own obvious economic communications, while there is less economic-behavioral heterogeneity among subgroups - this is especially true for the two subgroups that exist in the Poyang Lake Ecological Economic Zone; （3） an economy pattern driven by the central cities of Wuhan, Changsha and Nanchang has emerged in the urban agglomeration of the middle reaches of Changjiang River, while these three capital cities have exerted great radiation abilities to their surrounding cities, the latter are less able to absorb resources from the former （4） the Wuhan Metropolitan Areas and the Poyang Lake Ecological Economic Zone have more structural holes than the Ring of Changsha, Zhuzhou and the Xiangtan City Clusters, meaning that cities at the periphery of these two areas are easily constrained by central cities. The Ring of Changsha, Zhuzhou and the Xiangtan City Clusters have fewer structural holes; thus, the cities in this area wil
基金supported by the National Natural Science Foundation of China(Grant Nos.40176022,40276018 and 40476028).
文摘The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazites in the Quaternary, indicating a great change of their provenance. The first presence horizon of monazites younger than 25 Ma is just above the Matruyama/Gauss boundary (~2.58 Ma), whch is exactly when uplift of the Tibetan Plateau began to influence deposition in the East China Sea. Variations in contents of monazites younger than 25 Ma can be divided into two sections. The Early-Middle Pleistocene with less <25 Ma monazites corresponds with rapid uplift of the Tibetan Plateau, and the Late Pleistocene with more <25 Ma monazites parallels the peak uplift of the Tibetan Plateau. This study demonstrates that chemical dating of monazites in the river-mouth strata is a useful method to explore changes of river drainage basins, and deconvolute multistage tectonic and magmatic activity histories in the provenance areas.
基金Under the auspices of Ministry of Education,China (No.108148)State Key Laboratory of Urban and Regional Ecology (No.SKLURE2010-2-2)+2 种基金National Basic Research Program of China (No.2010CB951203)Key Research Program of Shanghai Science & Technology (No.08231200700,08231200702)111 Project,Ministry of Education,China (No.B08022)
文摘The objective of this study is to analyze soil physical and chemical properties,soil comprehensive functions and impact factors after different years of reclamation.Based on the survey data taken from 216 soil sampling points in the Fengxian Reclamation Area of the Changjiang (Yangtze) River Estuary,China in April 2009 and remotely sensed TM data in 2006,while by virtue of multivariate analysis of variance (MANOVA),geo-statistical analysis (GA),prin-cipal component analysis (PCA) and canonical correspondence analysis (CCA),it was concluded that:1) With the in-crease in reclamation time,soil moisture,soil salinity,soil electric conductivity and soil particle size tended to decline,yet soil organic matter tended to increase.Soil available phosphorous tended to increase in the early reclamation period,yet it tended to decline after about 49 years of reclamation.Soil nitrate nitrogen,soil ammonia nitrogen and pH changed slightly in different reclamation years.Soil physical and chemical properties reached a steady state after about 30 years of reclamation.2) According to the results of PCA analysis,the weighted value (0.97 in total) that represents soil nutrient factors (soil nitrate nitrogen,soil organic matter,soil available phosphorous,soil ammonia nitrogen,pH and soil particle size) were higher than the weighted value (0.48 in total) of soil limiting factors (soil salinity,soil elec-tric conductivity and soil moisture).The higher the F value is,the better the soil quality is.3) Different land use types play different roles in the soil function maturity process,with farmlands providing the best contribution.4) Soil physi-cal and chemical properties in the reclamation area were mainly influenced by reclamation time,and then by land use types.The correlation (0.1905) of the composite index of soil function (F) with reclamation time was greater than that with land use types (-0.1161).
基金Supported by the Funds for Creative Research Groups of China (No. 40721004)the National Natural Science Foundation of China (Nos. 40776012, 40976056)the Special Funds of the State Key Laboratory of Estuarine and Coastal Research (No. 2008KYYW03)
文摘We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and their interactions on WDR using the improved version of three-dimensional numerical model ECOM. Using data for annual mean wind speed and river discharge during January, we determined that the flood, ebb, net WDR values in the North Branch of the estuary were 3.48%, 1.68%,-4.06% during spring tide, and 4.82%, 2.34%,-2.79% during neap tide, respectively. Negative net WDR values denote the transport of water from the North Branch into the South Branch. Using the same data, the corresponding ratios were 50.09%, 50.92%, 54.97%, and 52.33%, 50.15%, 43.86% in the North Channel and 38.56%, 44.78%, 103.96%, and 36.92%, 43.17%, 60.97% in the North Passage, respectively. When northerly wind speed increased, landward Ekman transport was enhanced in the North Branch, increasing the flood WDR, while the ebb WDR declined and the net WDR exhibited a significant decrease. Similarly, in the North Channel, the flood WDR is increased, the ebb WDR reduced, and the net WDR showed a marked decrease. In the North Passage, the flood WDR also increased while the ebb and net WDR declined. As the river discharge increased, the flood and ebb WDR of the North Branch increased slightly and the net WDR increased markedly. In the North Channel the flood and ebb WDR changed very slightly, while the net WDR declined during spring tides and increased during neap tides. The WDR in the North Passage changed slightly during flood and ebb tides while the net WDR showed a marked increase. The WDR values of different bifurcations and the responses to northerly wind, river discharge, and tide are discussed in comparison with variations in river topography, horizontal wind-induced circulation, and tidal-induced residual current.
文摘Sandwaves in the Changjiang estuary were measured with a shallow sediment profiler and an echosounder from 1978 to 1988. The data, together with grain size and bedform of sediment indicates that the bedload movement by rolling and saltation is of great significance to sediment transport and is the principal factor responsible for sandwave and sandbody development in the estuary. The sandwaves were found well-developed, which is related to the tidal range and the velocity of ebb current. However, the further growth is restricted by strong flood current prevailing in the estuary. Because of the significant bedload, the sandbodies shift obviously and frequently, and sometimes the exchange of position occurs between the sandbodies and tidal channels. As a result, ships are regularly forced to change their navigation course.
文摘On the basis of data collected in the summer of 2006 from 27 sampling stations in the Changjiang Estuary and its adjacent waters, the ecological characteristics of macrobenthos and the relationship between the macrobenthos and the environmental factors were studied using hierarchical cluster and non-metric multidimensional scaling （MDS）. The biomass, abundance, Shannon -Wiener＇s and Margalef＇ s indices of the macrobenthos were presented. The results showed that a total of 253 macrobenthic species were found in the research region, and most of them belong to mollusks and polychaetes. The dominant species were Cossurella dimorpha, Eocylichna cylindrella, Episiphon kiaochowwanense, Nassarius semiplicatus, Ocstergrenia variabilis and Sternaspis scutata. The average abundance of the macrobenthos was （313. 15 ±233.4） ind./m^2, and the average biomass was （ 15. 2 ± 11.2 ）g/m^2. The distribution patterns of the abundance and biomass of the macrobenthos were similar. The abundance and biomass in the area close to the estuary were lower than those from the area more distant to the estuary; the central part of the research region had higher abundance and biomass than other parts of the research region. In accordance with the results, four macrobenthic communities with distinct spatial differences were identified. The low abundance and biomass in the area close to the estuary should be caused by the high sedimentation rate. The statistical analysis indicated that the depth is the most important factor affecting the distribution of macrobenthos.
基金Undertheauspicesof Ministry of Science and Technology Project of China (No. G1999043075)
文摘Rock weathering plays an important role in studying the long-term carbon cycles and global climatic change. According to the statistics analysis, the Huanghe (Yellow) River water chemistry was mainly controlled by evaporite and carbonate weathering, which were responsible for over 90% of total dissolved ions. As compared with the Huanghe River basin, dissolved load of the Changjiang (Yangtze) River was mainly originated from the carbonate dissolution. The chemical weathering rates were estimated to be 39.29t/(km(2).a) and 61.58t/(km(2).a) by deducting the HCO3- derived from atmosphere in the Huanghe River and Changjiang River watersheds, respectively. The CO2 consumption rates by rock weathering were calculated to be 120.84 x 10(3)mol/km(2) and 452.46 x 10(3)mol/km(2) annually in the two basins, respectively. The total CO2 consumption of the two basins amounted to 918.51 x 10(9)mol/a, accounting for 3.83% of the world gross. In contrast to other world watersheds, the stronger evaporite reaction and infirm silicate weathering can explain such feature that CO2 consumption rates were lower than a global average, suggesting that the sequential weathering may be go on in the two Chinese drainage basins.
基金National Natural Science Foundation of China,No.39790110
文摘Based on the results of water sample measurements of nutrient concentrations at th e Datong Station of the Changjiang River from 1998 to 1999, combined w ith historical data of water quality, seasonal variations of nutrient concentrations and nutrient transports are discussed.The following results have been obtained: (1) the fluxes of the nitrate nitrogen, ammonium nitrogen and nitrite nitrogen increased by time-series from 1962 to 1990 , even if runoff volume had a little variation; (2) the concentrations and fluxes of the dissolved inorganic nitrogen (DIN) and dissolved in organic phosphorus (DIP) increased notably with time, but those of the dissolved silicon (DSI) decreased pronouncedly; and (3) the concentration s and fluxes changed synchronously with time between the Datong Station a nd the Changjiang Estuary.
