Poyang Lake is the largest freshwater lake in China, and it has a seasonal flooding cycle that significantly changes the water level every year. The aim of this paper was to explain how these hydrological changes infl...Poyang Lake is the largest freshwater lake in China, and it has a seasonal flooding cycle that significantly changes the water level every year. The aim of this paper was to explain how these hydrological changes influence diatom populations in Poyang Lake. The yearly hydrological cycle can be divided into 4 phases: low water-level phase, increasing water-level phase, high water-level phase and decreasing waterlevel phase. Variations in the abundance of planktonic diatoms were studied using quarterly monitoring data collected from January 2009 to October 2013. Generally, diatoms were dominant in Poyang Lake and accounted for more than 50% of the total phytoplankton biomass except in July 2009(26%) and January 2012(35%). Aulacoseira granulata and Surirella robusta were the predominant species in all four phases, and they accounted for 25.02% to 56.89% and 5.07% to 14.78% of the total phytoplankton biomass, respectively. A redundancy analysis(RDA) showed that changes in physico-chemical parameter were related to the water level, and changes in diatom biomass were related to nitrite levels and p H. These results indicate that changes in environmental parameters related to both seasonal variations and water-level fluctuations caused variations in diatom biomass and community composition in Poyang Lake. Furthermore, extreme hydrological events can have different influences on the diatom community composition in the main channel and lentic regions. This research provides data on the diatom variations in Poyang Lake and will be useful for establishing biological indicators of environmental change and protecting Poyang Lake in the future.展开更多
Clay fraction contents distribution in the Senegal River estuary after the building of the anti-salt Diama dam has shown that upstream sediments are very muddy. Clay fraction content is as high as 60 % of sediments in...Clay fraction contents distribution in the Senegal River estuary after the building of the anti-salt Diama dam has shown that upstream sediments are very muddy. Clay fraction content is as high as 60 % of sediments in the middle of the channel with a pronounced downstream decreasing trend on the banks comparing to the contents in the middle of the channel. Towards the river mouth, the fine fraction tends to disappear leading to a shelly sand sediment type essentially. During low water period, clay fraction contents increase particularly at the vicinity of the dam reservoir. In the estuarine reach, downstream the dam, this increasing trend during the low water stage is particularly marked in the middle of the channel. The clay mineral assemblage shows that kaolinite and smectite are the main components, whereas interlayered illite-smectite and illite are minor constituents. The upstream-downstream profile shows a decrease in kaolinite content although it remains the dominant constituent. Floating clay minerals （smectite and illite-smectite） concentrate rather in the middle of the channel and on the right bank where the water depth is higher. According to seasonal variations, the distribution of these clay minerals often follows the concentration of the entire clay fraction; their contents increase during low water stage period. This hydrodynamics sorting of floating minerals, evident in the up-dam zone, tends to disappear in the eastern reach between Diama dam and the mouth. Clay minerals assemblage shows, through the time, a rather homogeneous composition which does not seem to be altered by the seasonal fluctuations.展开更多
基金Supported by the National Basic Research Program of China(973)(No.2012CB417005)the National Natural Science Foundation of China(No.41301088)the Jiangsu Planned Projects for Postdoctoral Research Funds(No.1401158C)
文摘Poyang Lake is the largest freshwater lake in China, and it has a seasonal flooding cycle that significantly changes the water level every year. The aim of this paper was to explain how these hydrological changes influence diatom populations in Poyang Lake. The yearly hydrological cycle can be divided into 4 phases: low water-level phase, increasing water-level phase, high water-level phase and decreasing waterlevel phase. Variations in the abundance of planktonic diatoms were studied using quarterly monitoring data collected from January 2009 to October 2013. Generally, diatoms were dominant in Poyang Lake and accounted for more than 50% of the total phytoplankton biomass except in July 2009(26%) and January 2012(35%). Aulacoseira granulata and Surirella robusta were the predominant species in all four phases, and they accounted for 25.02% to 56.89% and 5.07% to 14.78% of the total phytoplankton biomass, respectively. A redundancy analysis(RDA) showed that changes in physico-chemical parameter were related to the water level, and changes in diatom biomass were related to nitrite levels and p H. These results indicate that changes in environmental parameters related to both seasonal variations and water-level fluctuations caused variations in diatom biomass and community composition in Poyang Lake. Furthermore, extreme hydrological events can have different influences on the diatom community composition in the main channel and lentic regions. This research provides data on the diatom variations in Poyang Lake and will be useful for establishing biological indicators of environmental change and protecting Poyang Lake in the future.
文摘Clay fraction contents distribution in the Senegal River estuary after the building of the anti-salt Diama dam has shown that upstream sediments are very muddy. Clay fraction content is as high as 60 % of sediments in the middle of the channel with a pronounced downstream decreasing trend on the banks comparing to the contents in the middle of the channel. Towards the river mouth, the fine fraction tends to disappear leading to a shelly sand sediment type essentially. During low water period, clay fraction contents increase particularly at the vicinity of the dam reservoir. In the estuarine reach, downstream the dam, this increasing trend during the low water stage is particularly marked in the middle of the channel. The clay mineral assemblage shows that kaolinite and smectite are the main components, whereas interlayered illite-smectite and illite are minor constituents. The upstream-downstream profile shows a decrease in kaolinite content although it remains the dominant constituent. Floating clay minerals （smectite and illite-smectite） concentrate rather in the middle of the channel and on the right bank where the water depth is higher. According to seasonal variations, the distribution of these clay minerals often follows the concentration of the entire clay fraction; their contents increase during low water stage period. This hydrodynamics sorting of floating minerals, evident in the up-dam zone, tends to disappear in the eastern reach between Diama dam and the mouth. Clay minerals assemblage shows, through the time, a rather homogeneous composition which does not seem to be altered by the seasonal fluctuations.
