Abstract
Hydrologic regime plays a major role in structuring biotic diversity within river ecosystems by controlling key habitat conditions within the river channel and floodplain. Daily flow records from seven hydrological stations and the range of variability approach were utilized to investigate the variability and spatial pattern of the hydrologic alterations induced by the construction of the Three Gorges Dam (TGD) in the middle and lower reaches of the Yangtze River, China. Results show that the impoundment of the TGD disturbed the hydrologic regime downstream and directly affected the streamflow variations. The rate of changes and the annual extreme conditions were more affected by the TGD, particularly the low-flow relevant parameters. The alterations in the hydrologic regime were mainly caused by the TGD storing water during early autumn and releasing water during winter and spring. The effects on spatial patterns decreased as the distance from the dam increased, which was mainly attributed to the inflows from large tributaries along the Yangtze River as well as the interaction with the two largest natural lakes (i.e., Dongting Lake and Poyang Lake). These hydrologic alterations not only break the natural balance of eco-flow regimes but also result in undesirable ecological effects, particularly in terms of habitat availability for the fish community.
Highlights
Natural flow regime is extremely important in sustaining river environments and aquatic ecosystems and has been widely adopted as a paradigm for ecological integrity conservation and restoration; it is well recognized by river scientists, stream ecologists, and water resource managers [1,2,3,4,5]
The results show that the low-flow relevant parameters were more affected by the construction of the Three Gorges Dam (TGD) than the high-flow relevant indicators, because low flows often occurred in dry seasons and the TGD mainly released water to facilitate irrigation during these seasons
The construction and operation of the TGD, aiming to control flood and generate electricity, have inevitably caused significantly hydrological alterations, which severely change the balance of natural flow regime and result in undesirable ecological effects
Summary
Natural flow regime is extremely important in sustaining river environments and aquatic ecosystems and has been widely adopted as a paradigm for ecological integrity conservation and restoration; it is well recognized by river scientists, stream ecologists, and water resource managers [1,2,3,4,5]. Building dams for flood control and hydroelectric generation can alter the downstream hydrologic regime by affecting the total runoff quantity, water quality, and duration of extreme runoff, thereby resulting in hydrologic fragmentation both longitudinally and laterally [10]. Hydrologic regime may affect the distribution and availability of riverine habitat conditions, with potentially adverse consequences on the structure and persistence of aquatic communities [11]
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