Impacts of Dam Operation on Vegetation Dynamics of Mid-Channel Bars in the Mid-Lower Yangtze River, China

Abstract

Vegetation dynamics on mid-channel bars (MCBs) is essential for supporting ecosystem functions and associated services in river systems, especially in dammed large rivers. Generally, there are two possible changing patterns that vegetation of MCBs downstream a dam would experience. On one hand, the vegetation area may shrink because of a decrease in the MCB area in the post-dam period, which has been observed in many rivers around the world. On the other hand, the MCB vegetation area may expand because flood disturbances would be weakened by dam operation. However, little evidence has been reported to clarify such confusion. Therefore, vegetation dynamics of MCBs in the mid-lower Yangtze River downstream the Three Gorges Dam (TGD; the world’s largest dam) is selected as a case study to address the issue. Using long-term (1987–2017) Landsat archive images, this study reveals the spatiotemporal variations of vegetation area change intensities (VACIs; indicated by dynamic trends) on MCBs in the mid-lower Yangtze River. Results show that an overall VACI in the post-dam period (2003–2017) is about three times faster than that in the pre-dam period (1987–2002). In other words, the rate of vegetation colonization accelerated after the TGD operation began in 2003. Moreover, the VACIs in the post-dam period are size dependent, where large size MCBs are likely to gain higher VACIs: Small-sized MCBs (0.33 km2/yr), medium-sized MCBs (1.23 km2/yr), large-sized MCBs (1.49 km2/yr). In addition, VACIs of individual MCBs in the post-dam period are distance dependent, where the further a MCB was from the TGD, the higher the VACI. It is also suggested that the weakened flood disturbances in the post-dam could explain the rapid vegetation growth and colonization. This work is not only beneficial for managing and protecting MCBs downstream the TGD after its operation, but is also helpful in understanding vegetation dynamics of MCBs in other dammed river systems around the world.

Comprehensive Environmental Flows Assessment for Multi‐Guilds in the Riparian Habitats of the Yangtze River

“…In the middle reaches of the Yangtze River, the annual life stages for fish include the larval and juvenile, and for hygrophytes include the germination and dormant stages (Lin et al., 2016; Liu et al., 2018; Yin et al., 2013; Zhou et al., 2021). The EFs for hygrophytes do not need to be considered in their dormant stage.…”

Dune Development Dominates Flow Resistance Increase in a Large Dammed River

“…Here, the surface bed is composed of medium‐fine sand with a D 50 ≈ 0.23 mm. The majority of the riverbanks in the alluvial reaches consist of modern fluvial deposits with a typical two‐layer structure consisting of a non‐cohesive, medium‐fine sand lower layer with a thickness of up to 30 m and a cohesive, silty clay or loam upper layer with a thickness of a few meters (Hu et al., 2023; Xia et al., 2014).…”