Phytoplankton cell density, biomass, chl-α concentration and their seasonal fluctuations at five stations in the channel between Dongting Lake and the Changjiang （Yangtze） River were studied from May 1995 to Decemb...Phytoplankton cell density, biomass, chl-α concentration and their seasonal fluctuations at five stations in the channel between Dongting Lake and the Changjiang （Yangtze） River were studied from May 1995 to December 1997. The seasonal fluctuations had two peaks in a year in general. The annual patterns of total cell density and biomass indicated that diatoms contributed more than 70 percent of the total biomass （except from June to October） during the investigation period. Twenty-one dominant species contributed about 60--80 percent of the biomass in various months. The cell density, biomass and seasonal fluctuation were similar at Stations 1-4, but at Station 5 connected directly with the Changjiang River, the annual mean values （127.34×10^4cells/L and 0.46 mg/L in 1996, 41.98×10^4ceUs/L and 0.2 mg/L in 1997 respectively） were lower than those （ 195.92× 10^4 cells/L and 0.5 mg/L in 1996, 132.96 ×10^4 cells/L and 0.57 mg/L in 1997 respectively） at Station 1-4; and the curve of the seasonal fluctuation sometimes did not coincide with those at Stations 1-4. Based on criteria for evaluating trophic status, the dominant species, annual average cell density values of 114.86× 10^4-179.57× 10^4 cells/L, biomass of 0.48-0.5 mg/L, chl-αconcentration of 0.42-0.51 μg/L respectively recorded at five stations in 1996 and 1997, and values associated with the physico-chemical properties of the waterbody indicated that the water in the channel could be characterized as oligo-mesotrophic.展开更多
Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and...Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.展开更多
With the enhanced warming and acidification of global ocean, whether and to what extent the naturally-weathered flu- vial sediment into the sea can release elements and thus influence the geochemical process and ecosy...With the enhanced warming and acidification of global ocean, whether and to what extent the naturally-weathered flu- vial sediment into the sea can release elements and thus influence the geochemical process and ecosystem of global ocean remain to be resolved. In this contribution, an experimental study was carried out to examine the release rates of major elements （Ca, K, Mg and AI） from the surface sediments in the Changjiang （Yangtze River） Estuary under the pH values of 4.0, 6.0 and 7.0. The two stud- ied sediments consist primarily of quartz, plagioclase, calcite and clay minerals, with the BET （Brunauer, Emmett and Teller） surface areas of 61.7m2g-1 and 23.1 m2g-1. Major elements of Ca, K, Mg and A1 show different release rates under different solution pH values. With the decreasing solution pH, the release rates of Ca and K increase obviously, while the release rates of Mg and A1 in- crease with the initial solution pH varying from 6.0 to 7.0. The different release rates of these elements are closely related to the original mineral composition of the sediments and the reaction kinetics. Based on the experimental observation, quartz and clay min- erals that have low dissolution rates may dominate the major element release to the aqueous phase. This study reveals that the en- hancing ocean acidification could cause considerable release of major elements from natural terrigenous sediments into the ambient marine environment, which has to be considered carefully in the future study on global change.展开更多
As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental condi...As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates.However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood.A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin.The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C.The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected.By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic.The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately -2‰ to the extremely high value of 8‰ within a period of about 5 Ma.The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around -6‰ to the maximum near 4‰).The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates.This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic.The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.展开更多
With rapid industrialization and agricultural modernization in the past two decades, the Yangtze Delta Region in China has been one of the regions in the world most influenced by human activity. How has the economic d...With rapid industrialization and agricultural modernization in the past two decades, the Yangtze Delta Region in China has been one of the regions in the world most influenced by human activity. How has the economic development impacted on ecosystem, environment, agriculture and regional climate in this region ？ What are the mechanisms of the interactive processes and feedbacks？ What will be the future changes under different development scenarlos？ These are questions of critical importance to sustain the rate of social and economic development. A Major Project, The Physical-Chemical Processes in the Lower Atmosphere and Their Interaction with the Ecological System over Yangtze Delta, as one of the Ninth Five-Year Major Programs （1996-2000） funded by the National Natural Science Foundation of China, NSFC, just focused on those questions. Under the leadership of Prof. Zhou Xiuji, academician of the Chinese Academy of Sciences this project has made significant achievements and great progress in answering the above questions.展开更多
基金Project 39670155 and 39430101 supported by NSFC.
文摘Phytoplankton cell density, biomass, chl-α concentration and their seasonal fluctuations at five stations in the channel between Dongting Lake and the Changjiang （Yangtze） River were studied from May 1995 to December 1997. The seasonal fluctuations had two peaks in a year in general. The annual patterns of total cell density and biomass indicated that diatoms contributed more than 70 percent of the total biomass （except from June to October） during the investigation period. Twenty-one dominant species contributed about 60--80 percent of the biomass in various months. The cell density, biomass and seasonal fluctuation were similar at Stations 1-4, but at Station 5 connected directly with the Changjiang River, the annual mean values （127.34×10^4cells/L and 0.46 mg/L in 1996, 41.98×10^4ceUs/L and 0.2 mg/L in 1997 respectively） were lower than those （ 195.92× 10^4 cells/L and 0.5 mg/L in 1996, 132.96 ×10^4 cells/L and 0.57 mg/L in 1997 respectively） at Station 1-4; and the curve of the seasonal fluctuation sometimes did not coincide with those at Stations 1-4. Based on criteria for evaluating trophic status, the dominant species, annual average cell density values of 114.86× 10^4-179.57× 10^4 cells/L, biomass of 0.48-0.5 mg/L, chl-αconcentration of 0.42-0.51 μg/L respectively recorded at five stations in 1996 and 1997, and values associated with the physico-chemical properties of the waterbody indicated that the water in the channel could be characterized as oligo-mesotrophic.
基金The work is supported by the National Natural Science Foundation of China(Grant Nos.430100203 and 49801018)the Foundation for University Key Teachers by the Ministry of Education of China.
文摘Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.
基金supported by research funds awarded by the National Natural Science Foundation of China (Grant Nos. 41225020 and 41376049)Continental Shelf Drilling Program (Grant No. GZH201100202)China Geologic Survey (Grant No. GZH201100203)
文摘With the enhanced warming and acidification of global ocean, whether and to what extent the naturally-weathered flu- vial sediment into the sea can release elements and thus influence the geochemical process and ecosystem of global ocean remain to be resolved. In this contribution, an experimental study was carried out to examine the release rates of major elements （Ca, K, Mg and AI） from the surface sediments in the Changjiang （Yangtze River） Estuary under the pH values of 4.0, 6.0 and 7.0. The two stud- ied sediments consist primarily of quartz, plagioclase, calcite and clay minerals, with the BET （Brunauer, Emmett and Teller） surface areas of 61.7m2g-1 and 23.1 m2g-1. Major elements of Ca, K, Mg and A1 show different release rates under different solution pH values. With the decreasing solution pH, the release rates of Ca and K increase obviously, while the release rates of Mg and A1 in- crease with the initial solution pH varying from 6.0 to 7.0. The different release rates of these elements are closely related to the original mineral composition of the sediments and the reaction kinetics. Based on the experimental observation, quartz and clay min- erals that have low dissolution rates may dominate the major element release to the aqueous phase. This study reveals that the en- hancing ocean acidification could cause considerable release of major elements from natural terrigenous sediments into the ambient marine environment, which has to be considered carefully in the future study on global change.
基金supported by National Natural Science Foundation of China(Grant Nos.40839908,41172099)
文摘As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates.However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood.A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin.The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C.The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected.By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic.The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately -2‰ to the extremely high value of 8‰ within a period of about 5 Ma.The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around -6‰ to the maximum near 4‰).The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates.This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic.The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.
文摘With rapid industrialization and agricultural modernization in the past two decades, the Yangtze Delta Region in China has been one of the regions in the world most influenced by human activity. How has the economic development impacted on ecosystem, environment, agriculture and regional climate in this region ？ What are the mechanisms of the interactive processes and feedbacks？ What will be the future changes under different development scenarlos？ These are questions of critical importance to sustain the rate of social and economic development. A Major Project, The Physical-Chemical Processes in the Lower Atmosphere and Their Interaction with the Ecological System over Yangtze Delta, as one of the Ninth Five-Year Major Programs （1996-2000） funded by the National Natural Science Foundation of China, NSFC, just focused on those questions. Under the leadership of Prof. Zhou Xiuji, academician of the Chinese Academy of Sciences this project has made significant achievements and great progress in answering the above questions.
