The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that incl...The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.展开更多
珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效...珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效应对悬沙浓度分布与输运通量的影响。采用控制实验,研究有无斜压作用时悬沙浓度分布的变化;分析有无斜压作用时的泥沙输运通量与海底冲淤的变化情况,结果表明有斜压作用时悬浮泥沙的输运路径、通量均与无斜压时不同,伶仃洋的悬沙除向西口外输运外,还随着河口羽流的扩展向西南方向输运。有斜压作用时在伶仃洋的西南端及下游的西南沿岸均有明显的海底淤积,而无斜压作用时泥沙淤积主要发生于伶仃洋的西口附近及磨刀门口外落潮射流末端。利用悬沙输运方程进行诊断分析,揭示了斜压作用导致悬沙浓度分布与输运通量变化的动力机制,表明斜压作用虽然减小了底切应力与垂向混合系数,但由于增大的海底泥沙可侵蚀量及垂向悬沙梯度,悬沙输运方程中的再悬浮量与垂向混合通量要比无斜压时要大。本研究对河口区的悬沙输运过程与机理分析具有一定的指导意义。展开更多
Hydrologic process,turbidity,suspended particles matters(SPM),major cations and TOC concentrations during two storm events in late April 2008 were monitored at Jiangjia Spring which is the outlet of Qingmuguan undergr...Hydrologic process,turbidity,suspended particles matters(SPM),major cations and TOC concentrations during two storm events in late April 2008 were monitored at Jiangjia Spring which is the outlet of Qingmuguan underground river system.Scanning electron microscopy(SEM) and energy disperse spectroscopy(EDS) analyses of SPM were展开更多
含沙量预测对流域泥沙治理、水沙调控以及水质与水环境管理等具有重要意义。长江上游地区幅员广阔,支流众多,水沙来源复杂,对准确预测三峡入库含沙量过程构成了挑战。针对长江上游区间降雨和干支流来水来沙对寸滩站含沙量产生不同程度...含沙量预测对流域泥沙治理、水沙调控以及水质与水环境管理等具有重要意义。长江上游地区幅员广阔,支流众多,水沙来源复杂,对准确预测三峡入库含沙量过程构成了挑战。针对长江上游区间降雨和干支流来水来沙对寸滩站含沙量产生不同程度的影响,提出了一种基于随机森林(Random Forest,RF)与长短时记忆(Long Short Term Memory,LSTM)神经网络结合的日含沙量预测深度学习模型RF-LSTM。首先,该模型利用RF算法筛选出与寸滩站日含沙量相关性强的水沙因子,然后将这些因子作为LSTM神经网络的输入变量,进一步识别出优选水沙因子与寸滩含沙量之间的映射关系,最后以长江上游向家坝至寸滩区间为研究区域,应用该模型对不同预见期下的寸滩站汛期日含沙量进行了预测,结果表明:与LSTM模型相比,RF-LSTM模型能较好地考虑预测因子对含沙量影响的滞后效应,且有效捕获与寸滩站日含沙量相关性强的特征,四种预见期下其在预测精度和性能方面均有较好表现,其中无预见期和预见期1 d时两种模型预测精度均较高,验证期的纳什效率系数均大于0.82,无预见期下RF-LSTM模型的纳什效率系数可达到0.91,相应的均方根误差和平均绝对误差分别较LSTM模型降低了13%和8%,且两种预见期下RF-LSTM模型可以较为准确捕获沙峰及峰现时间;当预见期增加至2 d和3 d时两种模型精度均有明显下降,但RF-LSTM模型计算精度仍优于LSTM模型。研究结果可为长江上游含沙量预测提供参考。展开更多
基金Supported by the Financial from the U.S.Army Corps of Engineers-Lower Mississippi Valley Division,Vicksburg,Mississippi,U.S.A.
文摘The lower Mississippi River(LMR) has been heavily modified for multiple human purposes such as navigation, flood control, and bank stabilization. However, the LMR simultaneously supports a diverse fish fauna that includes recreational and commercial fisheries. Due to river training and diversion structures constructed during the past 80 years, the historic characteristics of the LMR have been drastically altered and have likely influenced fishes and fisheries in the system. One common restoration measure used throughout the LMR has been to "notch" wing-dike structures that close secondary(side) river channels. Dike notching allows year-round flows through secondary channels, which enhances habitat diversity and promotes biological productivity at the ecosystem scale. Although notching is presumed good for LMR fishes and other biota, few studies have examined its effects on fish assemblages. In this study, fish assemblages were sampled at seven LMR secondary channels spanning from river kilometer(rkm) 628(Louisiana-Mississippi, U.S.A.) upstream to rkm 1504(Missouri-Kentucky, U.S.A.). Four secondary channels were termed "permanent"(i.e.,with notched dikes) while three secondary channels were termed "temporary"(i.e., without notched dikes).Fishes were sampled by boat-mounted electrofishing conducted during falling and low stages from1995—1997. Fish assemblages differed between permanent and temporary secondary channels, and varied somewhat between falling and low stages. Gizzard shad(Dorosoma cepedianum), threadfin shad(D. petenense), and white bass(Morone chrysops) demonstrated consistent preferences for low-current conditions associated with temporary secondary channels. Conversely, blue catfish(Ictalurus furcatus), flathead catfish(Pylodictis olivaris), and freshwater drum(Aplodinotus grunniens) were more associated with permanent secondary channels. Future restoration strategies in the LMR should consider dike notching and resultant maintenance of permanent secondary channels in selected river reaches. However, temporary secondary channels also contain unique fish species, and also appear to be important sites of riverine primary production. Restoration strategies should consider a balance of both secondary channel types, which should support the greatest biodiversity for the LMR ecosystem.
文摘珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效应对悬沙浓度分布与输运通量的影响。采用控制实验,研究有无斜压作用时悬沙浓度分布的变化;分析有无斜压作用时的泥沙输运通量与海底冲淤的变化情况,结果表明有斜压作用时悬浮泥沙的输运路径、通量均与无斜压时不同,伶仃洋的悬沙除向西口外输运外,还随着河口羽流的扩展向西南方向输运。有斜压作用时在伶仃洋的西南端及下游的西南沿岸均有明显的海底淤积,而无斜压作用时泥沙淤积主要发生于伶仃洋的西口附近及磨刀门口外落潮射流末端。利用悬沙输运方程进行诊断分析,揭示了斜压作用导致悬沙浓度分布与输运通量变化的动力机制,表明斜压作用虽然减小了底切应力与垂向混合系数,但由于增大的海底泥沙可侵蚀量及垂向悬沙梯度,悬沙输运方程中的再悬浮量与垂向混合通量要比无斜压时要大。本研究对河口区的悬沙输运过程与机理分析具有一定的指导意义。
文摘Hydrologic process,turbidity,suspended particles matters(SPM),major cations and TOC concentrations during two storm events in late April 2008 were monitored at Jiangjia Spring which is the outlet of Qingmuguan underground river system.Scanning electron microscopy(SEM) and energy disperse spectroscopy(EDS) analyses of SPM were
文摘含沙量预测对流域泥沙治理、水沙调控以及水质与水环境管理等具有重要意义。长江上游地区幅员广阔,支流众多,水沙来源复杂,对准确预测三峡入库含沙量过程构成了挑战。针对长江上游区间降雨和干支流来水来沙对寸滩站含沙量产生不同程度的影响,提出了一种基于随机森林(Random Forest,RF)与长短时记忆(Long Short Term Memory,LSTM)神经网络结合的日含沙量预测深度学习模型RF-LSTM。首先,该模型利用RF算法筛选出与寸滩站日含沙量相关性强的水沙因子,然后将这些因子作为LSTM神经网络的输入变量,进一步识别出优选水沙因子与寸滩含沙量之间的映射关系,最后以长江上游向家坝至寸滩区间为研究区域,应用该模型对不同预见期下的寸滩站汛期日含沙量进行了预测,结果表明:与LSTM模型相比,RF-LSTM模型能较好地考虑预测因子对含沙量影响的滞后效应,且有效捕获与寸滩站日含沙量相关性强的特征,四种预见期下其在预测精度和性能方面均有较好表现,其中无预见期和预见期1 d时两种模型预测精度均较高,验证期的纳什效率系数均大于0.82,无预见期下RF-LSTM模型的纳什效率系数可达到0.91,相应的均方根误差和平均绝对误差分别较LSTM模型降低了13%和8%,且两种预见期下RF-LSTM模型可以较为准确捕获沙峰及峰现时间;当预见期增加至2 d和3 d时两种模型精度均有明显下降,但RF-LSTM模型计算精度仍优于LSTM模型。研究结果可为长江上游含沙量预测提供参考。
