Acceleration of vegetation dynamics in hydrologically connected wetlands caused by dam operation

Abstract

The dynamic responses of wetlands to upstream water conservancy projects are becoming increasingly crucial for watershed management. Poyang Lake is a dynamic wetland system of critical ecological importance and connected with the Yangtze river. However, in the context of disturbed water regime in Poyang Lake resulting from human activities and climate change, the responses of vegetation dynamics to the Three Gorges Dam (TGD) have not been investigated. We addressed this knowledge gap by using daily water level data and Landsat images from 1987 to 2018. Landsat images were acquired between October and December to ensure similar phenological conditions. Object-oriented Artificial Neural Network Regression for wetland classification was developed based on abundant training and validation samples. Interactions between vegetation coverage and water regimes pre and post the operation of the TGD were compared using classification and regression trees and the random forest model. Since the implementation of the TGD in 2003, Poyang Lake has become drier, especially during the dry season. A more rapid plant growth rate was observed post TGD (44.74 km 2 year −1) compared to that of the entire study period (12.9 km 2 year −1). Average water level for the antecedent 20 days most significantly affected vegetation before 2003, whereas average water level for the antecedent 5 or 10 days was more important after 2003. The impoundment of the TGD after the flood season accelerated the drawdown processes of Poyang Lake, and the rapidly exposed wetlands accelerated vegetation expansion during the dry seasons, resulting in shrinkage and degradation of the lake area. This study deepens our knowledge of the influences of newly developed dams on lakes and rivers.

Influences of increasing water release of the Three Gorges Reservoir during dry season on water regimes of downstream lake

“…The study of Lin et al (2023) found that the area of wetland vegetation in Poyang Lake has increased to a certain extent and expanded to the centre of the lake since 2000. Moreover, Zheng et al (2021) compared the vegetation coverage of Poyang Lake wetland before and after the operation of the TGR, and found that the vegetation growth rate accelerated after 2003. Han et al (2018) revealed that the area of Carex cinerascens , Phalaris arundinacea ‐ Polygonum hydropiper and Phragmites australis ‐ Triarrhena lutarioriparia communities in Poyang Lake wetland had an obvious increasing trend from 2000 to 2014.…”

Influence of Terrestrial Water Storage on Flood Potential Index in the Yangtze River Basin, China

“…In the past, there have been many flood events in the YRB, causing serious loss to life and property (e.g., Figure 2) [34]. The flood disaster situation in the YRB has been alleviated only by the construction of the Three Gorges Dam [35]. This study divides the YRB into 12 sub-basins according to the classification criteria of the Ministry of Water Resources of the People's Republic of China (e.g., Figure 1 and Table 1).…”

“…In the past, there have been many flood events in the YRB, causing serious loss to life and property (e.g., Figure 2) [34]. The flood disaster situation in the YRB has been alleviated only by the construction of the Three Gorges Dam [35]. Taihu Lake Rivers Basin TLRB…”

Growing impacts of low-flow events on vegetation dynamics in hydrologically connected wetlands downstream Yangtze River Basin after the operation of the Three Gorges Dam

“…The Three Gorges Dam (TGD) in the upstream of the Yangtze River is the world's largest dam and remains one of the most controversial projects in China. Previous studies showed that TGD operation, which began in 2003, has significantly changed the hydrological rhythm downstream (Zhang et al, 2015;Wang et al, 2019;Peng et al, 2020;Zheng et al, 2021). For example, Zhang et al (2015) found that the waterflow from downstream lakes connected to the Yangtze River has increased by 57 billion m 3 as compared with that during pre-TGD period.…”