Dynamic Coupling Relationship Between Hydrological Rhythm And Wetland Landscape In Poyang Lake Based On GIS

Hydrological process is the most basic process in wetland ecosystem.As the main phenomenon of hydrological process,the amplitude and frequency of water level fluctuation are the most important factors affecting the composition and function of wetland species.In recent years,due to climate change and human disturbance(such as water conservancy projects,sand mining),the phenomena of frequent low water level,early dry season and prolonged low water level appeared in Poyang Lake,which changed the inherent hydrological rhythm of the wetland in Poyang Lake.The study on the influence of hydrological change on Poyang Lake wetland can provide theoretical basis for wetland protection and management.However,the current research on the impact of water level changes on Poyang Lake wetland is limited in both time and space scales.Based on this,this study used long-term and large-scale hydrological data and remote sensing data to analyze Poyang Lake.This study mainly includes three parts:(1)By analyzing the observed water level data of Xingzi Station in Poyang Lake from 1980 to 2016,the water regime characteristics of Poyang Lake in the past 30 years are studied;(2)Based on remote sensing and geographic information system technology,118 Landsat images of Poyang Lake in recent 30 years were selected for interpretation.Nine different landscape types and their areas of Poyang Lake were classified and extracted.The changes of landscape area and seasonal changes of vegetation landscape at different time stages were analyzed;(3)The relationship between water level change and wetland vegetation was studied by using two types of water level fluctuation variables constructed by hydrological process and interpreted vegetation landscape data.The main results are follows: 1.Water regime characteristics of Poyang Lake in the past 30 years(1)Since 1980s,the water regime of Poyang Lake has shown different characteristics after the Three Gorges Dam.Since 2003,the overall water level of Poyang Lake has been lower than that before.Specifically,The water regime of Poyang Lake during the flood season is "high water is not high",the recession period is accelerated,and the dry season is advanced.(2)Through cluster analysis of lake water level process in different years,it can be divided into six types: high water type,normal water level fluctuation type,prolonged flood period,advanced recession period type,low high water level type and frequent fluctuation type,which can provide an important understanding of water level characteristics for future generations to study Poyang Lake.2.Landscape change of Poyang Lake Wetland(1)The total area of vegetation in Poyang Lake(including sparse grasslands,dense grasslands and tall grasslands)showed an increasing trend,among which the area of sparse grasslands showed a significant increasing trend(p < 0.05),and there was no significant change in the area of dense grasslands.The area of tall grasslands decreased significantly(p < 0.05).(2)Water area and vegetation area have significant influence after the Three Gorges Project.For the area of water,the area of deep water decreased significantly(p=0.012),the area of shallow water decreased significantly(p=0.032)and the very shallow water increased significantly in flood season(p=0.018)and recession season(p=0.001);for vegetation,the area of sparse grasslands increased significantly in the dry season(p=0.003)and the flood season(p=0.002),while that of tall grasslands decreased significantly in the dry season(p=0.033),but increased significantly in the flood season(p=0.026),and the area of dense grasslands did not change significantly before and after the dam.3.Effect of water level change on wetland vegetation in Poyang LakeBased on the correlation and regression analysis of water level fluctuation(WLF)variables(including 13 non-cumulative variables and 14 cumulative variables,with four time-scales of day,month,season and year)and three types of vegetation(sparse grassland,dense grassland and high grassland),it is found that:(1)For the WLF without cumulative effect,seasonal time scale WLF has significant effect on three vegetation types,and annual scale WLF is only related to sparse grassland.(2)For the WLF of cumulative effect,the time scales of cumulative hydrological effect on three vegetation are different: the longest cumulative time scale(annual scale)in dense grassland,the second is sparse grassland(seasonal time scale),and the last is the shortest cumulative time scale(30 days time scale)in high grassland.(3)The lag effect of water level fluctuation exists,and the cumulative effect of water level fluctuation should also be considered in the study of water level fluctuation.