1、J.Geogr.Sci.2023,33(4):885-904 DOI:https:/doi.org/10.1007/s11442-023-2111-0 2023 Science Press Springer-Verlag 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 WANG Dandan1,LIU Yi
2、ng1,*ZHENG Lilin2,3,LI Dahui4 1.Nanjing Institute of Environmental Sciences,Ministry of Ecology and Environment,Nanjing 210042,China;2.Key Laboratory of Geographic Information Science(Ministry of Education),School of Geographic Sciences,East China Normal University,Shanghai 200241,China;3.Key Labora
3、tory of Watershed Geographic Sciences,Nanjing Institute of Geography and Limnology,CAS,Nanjing 210008,China;4.School of Geospatial Engineering and Science,Sun Yat-Sen University,Zhuhai 519082,Guangdong,China Abstract:Wetland vegetation is intimately related to floodplain inundations,which can be ser
4、iously affected by dam operation.Poyang Lake is the largest floodplain wetland in China and naturally connected with the Yangtze River and the Three Gorges Dam(TGD)upstream.To understand the potential impacts of TGD on Poyang Lake wetlands,we collected remote sensing imagery acquired during dry seas
5、on from 1987 to 2020 and extracted vegetation coverage data in the Ganjiang Northern-branch Delta(GND)and the Ganjiang South-ern-branch Delta(GSD),using the Object-oriented Artificial Neural Network Regression.Principal components analysis,correlation analysis,and the random forest model were used t
6、o explore the interactions between vegetation extent in the two deltas and 33 hydrological variables regarding magnitude,duration,timing,and variation.The implementation of the TGD advanced and extended the low-flow periods in Poyang Lake.Vegetation coverage in the GND and GSD increased at the rates
7、 of 0.39 and 0.22 km2/year,respectively.The res-ervoir storage at the end of September accelerated the runoff recession in the GND and the GSD,making low-flow events more influential for vegetation dynamics and shortening the response time of vegetation to the water regime.This study provides an imp
8、ortant reference for evaluating the impacts of dam engineering on downstream wetlands.Keywords:vegetation coverage;water level fluctuation;Three Gorges Dam;Poyang Lake Received:2022-03-11 Accepted:2022-11-30 Foundation:Open Research Fund of State Key Laboratory of Information Engineering in Surveyin
9、g,Mapping and Re-mote Sensing,Wuhan University(20R01)and East China Normal University Excellent Doctoral Students Academic Innovation Ability Improvement Plan Project,No.YBNLTS2021-028 Author:Wang Dandan(1978),PhD,specialized in environmental science,hydrology and watershed management.E-mail:*Corres
10、ponding author:Zheng Lilin(1994),PhD,specialized in remote sensing and hydrology.E-mail: 886 Journal of Geographical Sciences 1 Introduction Wetlands link terrestrial and aquatic habitats.Despite occupying only about 4%6%of the Earths surface(Kentula,2000),wetlands play an essential role in maintain
11、ing the ecological balance,providing nutrients,and ensuring productivity(Nicholls,2004;Mu et al.,2020).As vegetation coverage is a sensitive and critical feature of wetlands and reflects hydrological processes(Casanova et al.,2000;Maihemuti et al.,2020),monitoring the long-term vegeta-tion dynamics
12、can help quantify the effects of hydrological events on wetlands.The wetlands landscape is formed as a result of the long-term adaptation to hydrological processes and other natural factors(Zedler et al.,2005).However,the establishment of dams destroys the ecological equilibrium between vegetation a
13、nd hydrological processes.Globally,by 2020,about 58,713 dams have been built,of which 40%are located in China(Jiang et al.,2019).Although dams are used for flood control,electricity generation,and shipping(Nils-son et al.,2005),their negative environmental impacts are considerable.According to pre-v
14、ious studies,the operation of large dams can substantially alter downstream hydrological processes(Alizadeh-Choobari et al.,2016;Cheng et al.,2018;Jiang et al.,2019).For ex-ample,dam operation in the Amazon remarkably altered the frequency,duration,and change rates of high-flow events(Ely et al.,202
15、0).After the first damming of the Tocantins River(eastern Amazon),more than half of the river floodplains were no longer inundated by floods,and the hydroperiod decreased by 15 days(Swanson et al.,2021).The Three Gorges Dam(TGD)in the upstream of the Yangtze River is the worlds largest dam and remai
16、ns 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 m3 as compared with that during pre-TGD period.In addition,as to the TGD frequently rises the water level ahead of the