The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity character...The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.展开更多
A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and sever...A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and several environmental factors were monitored along a 20-m stretch at each of four sites, at intervals of approximately three months （one sampling per season）. Several stream conditions were relatively constant over the sampling period （pH, maximum width and maximum depth）, whereas others exhibited a distinct seasonal pattern （water temperature and specific conductance）, and some fluctuated with no discernable seasonal pattern （current velocity and dissolved oxygen）. Forty-two species of macroalgae were found, with a predominance of Chlorophyta （26 species, 61.9%）. Rhodophyts and Charophyta represented the smallest proportion （1 species each, 2.38%）. Six macroalgae species were the most widespread, occurring in all four sampling sites. Twelve species were found at only one site each. In terms of seasonality, eight species occurred throughout the year, whereas 16 species were found in only one season each. The macroalgal community at Xin＇an Spring was species rich relative to other streams. Species richness per sampling site was negatively correlated with pH. Principal component analysis revealed that no single variable had much influence on the macroalgal seasonal dynamics. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also shows that macroalgae in different locations have significant reproductive isolation.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51539007,51479128 and 51609160)the National Key Research and Development Program of China(Grant No.2016YFC0402302).
文摘The aquatic plants are often found in natural rivers,and they affect the channel flow structure significantly.To study the effects of the vegetation density a(the frontal area per volume)on the flow velocity characteristics,rigid bamboo circular cylinders are chosen as the model emergent vegetation.In the experiments,the density of the vegetation takes various values while all other flow parameters are kept constant.A 3-D acoustic Doppler velocimeter(ADV)is used to measure the local flow velocities for different vegetation densities.The results show that the existence of the vegetation patch leads to an increase of the depth-averaged velocity on the right and left sides behind the vegetation patch,and it increases monotonically with the vegetation density.For different vegetation densities,the lateral distribution of the stream-wise velocity behind the vegetation patch follows approximately an S-shaped profile when a≤60 m-1,and a logarithmic profile if a>60 m-1.The vertical distribution of the stream-wise velocity along the channel varies with the vegetation density and also follows an S-shaped distribution in a certain range,with the locations and the ranges being affected by the vegetation density.
文摘A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and several environmental factors were monitored along a 20-m stretch at each of four sites, at intervals of approximately three months （one sampling per season）. Several stream conditions were relatively constant over the sampling period （pH, maximum width and maximum depth）, whereas others exhibited a distinct seasonal pattern （water temperature and specific conductance）, and some fluctuated with no discernable seasonal pattern （current velocity and dissolved oxygen）. Forty-two species of macroalgae were found, with a predominance of Chlorophyta （26 species, 61.9%）. Rhodophyts and Charophyta represented the smallest proportion （1 species each, 2.38%）. Six macroalgae species were the most widespread, occurring in all four sampling sites. Twelve species were found at only one site each. In terms of seasonality, eight species occurred throughout the year, whereas 16 species were found in only one season each. The macroalgal community at Xin＇an Spring was species rich relative to other streams. Species richness per sampling site was negatively correlated with pH. Principal component analysis revealed that no single variable had much influence on the macroalgal seasonal dynamics. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also shows that macroalgae in different locations have significant reproductive isolation.
