Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in th...Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in the middle of Yangtze River since 2003.The objective of this study was to understand the effects of altered hydrological regime on the trophic structure of fish food web along the hydrological gradient in the TGD.Methods:Fish samples were collected from an upstream,a midstream and a downstream site of the Yangtze River upstream of the TGD in May and September of 2004.Muscle tissue of each fish species was determined for stable isotopic compositions(δ^(13)C and δ^(15)N)which were used to calculate isotope-based Bayesian community-wide trophic metrics.Results:Stable isotope trophic niche analysis reveals reduced utilization of basal resource and trophic niche space at the midstream and downstream sites.By contrast,community trophic diversity and species redundancy were higher at the downstream than the upstream and midstream,likely as the result of reduced the spectrum of basal resources.These findings suggested that the negative impacts on the overall trophic niche space from reduced flow,increased water depth and stagnancy occurred only one year after the completion of the TGD.Conclusions:Altered hydrological regimes posed multiple impacts to the aquatic food web.Reduced flow and increased water depth within TGD has posed initial effects to the fish community trophic structure.Further collections ana analysis of ecological data to compare the fish trophic structure revealed in this study are needed to assess the long-term impacts of TGD on fish community structure and resources utilization.展开更多
Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Chan...Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Changjiang River, the channel immediately downstream of the Three Gorges Dam(TGD), are assessed based on remote sensing images between 2000 and 2016. It can be found that the entire area of sandbars reduces drastically by 19.23% from 149.04 km~2 in 2003 to 120.38 km~2 in 2016, accompanied with an increase in water surface width. Owing to differences in sediment grain size and anti-erosion capacity, sandbar area in the upstream sandy gravel reach(Yichang-Dabujie) and downstream sandy reach(Dabujie-Chenglingji) respectively decreases by 45.94%(from 20.79 km~2 to 11.24 km~2) and 14.93%(from 128.30 km~2 to 109.14 km~2). Furtherly, morphological evolutions of sandbars are affected by channel type: in straight-microbend channel, mid-channel sandbars exhibit downstream moving while maintaining the basic profile; in meandering channel, point sandbars show erosion and deposition in convex and concave bank respectively, with mid-channel sandbars distributing sporadically; in bending-branching channel, point sandbars experience erosion and move downstream while mid-channel sandbars show erosion in the head part along with retreating outline. We document that the primary mechanism of sandbars shrinkages along the Yichang-Chenglingji Reach can be attributed to TGD induced suspended sediment concentration decreasing and increasing in unsaturation of sediment carrying capacity. Additionally, channel type can affect the morphological evolution of sandbars. Along the Yichang-Chenglingji Reach, sandbars in straight-microbend channel are more affected by water flow than that in bending-branching channel.展开更多
基金supported by two NSFCs(Grant Nos.51179094 and 30700091)supported by a NSFC(Grant No.41376158)。
文摘Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in the middle of Yangtze River since 2003.The objective of this study was to understand the effects of altered hydrological regime on the trophic structure of fish food web along the hydrological gradient in the TGD.Methods:Fish samples were collected from an upstream,a midstream and a downstream site of the Yangtze River upstream of the TGD in May and September of 2004.Muscle tissue of each fish species was determined for stable isotopic compositions(δ^(13)C and δ^(15)N)which were used to calculate isotope-based Bayesian community-wide trophic metrics.Results:Stable isotope trophic niche analysis reveals reduced utilization of basal resource and trophic niche space at the midstream and downstream sites.By contrast,community trophic diversity and species redundancy were higher at the downstream than the upstream and midstream,likely as the result of reduced the spectrum of basal resources.These findings suggested that the negative impacts on the overall trophic niche space from reduced flow,increased water depth and stagnancy occurred only one year after the completion of the TGD.Conclusions:Altered hydrological regimes posed multiple impacts to the aquatic food web.Reduced flow and increased water depth within TGD has posed initial effects to the fish community trophic structure.Further collections ana analysis of ecological data to compare the fish trophic structure revealed in this study are needed to assess the long-term impacts of TGD on fish community structure and resources utilization.
基金National Natural Science Foundation of China,No.41576087National Science Foundation for Young Scientists of China,No.41706093Fund of the Key Laboratory of Coastal Science and Engineering,Beibu Gulf,Guangxi,No.2016ZZD01
文摘Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Changjiang River, the channel immediately downstream of the Three Gorges Dam(TGD), are assessed based on remote sensing images between 2000 and 2016. It can be found that the entire area of sandbars reduces drastically by 19.23% from 149.04 km~2 in 2003 to 120.38 km~2 in 2016, accompanied with an increase in water surface width. Owing to differences in sediment grain size and anti-erosion capacity, sandbar area in the upstream sandy gravel reach(Yichang-Dabujie) and downstream sandy reach(Dabujie-Chenglingji) respectively decreases by 45.94%(from 20.79 km~2 to 11.24 km~2) and 14.93%(from 128.30 km~2 to 109.14 km~2). Furtherly, morphological evolutions of sandbars are affected by channel type: in straight-microbend channel, mid-channel sandbars exhibit downstream moving while maintaining the basic profile; in meandering channel, point sandbars show erosion and deposition in convex and concave bank respectively, with mid-channel sandbars distributing sporadically; in bending-branching channel, point sandbars experience erosion and move downstream while mid-channel sandbars show erosion in the head part along with retreating outline. We document that the primary mechanism of sandbars shrinkages along the Yichang-Chenglingji Reach can be attributed to TGD induced suspended sediment concentration decreasing and increasing in unsaturation of sediment carrying capacity. Additionally, channel type can affect the morphological evolution of sandbars. Along the Yichang-Chenglingji Reach, sandbars in straight-microbend channel are more affected by water flow than that in bending-branching channel.
