Response Characteristics Of Wetland Ecological Landscape To Low Dry Water Level In Poyang Lake

Poyang lake is the largest freshwater lake in China,and also an important international migratory bird.In recent decades,the low water level of poyang lake has been extended,and the extreme dry water level has been innovated low and the hydrological situation has changed significantly.Low in the low water level,under the influence of poyang lake wetland landscape pattern change is quietly,mainly reflects in:water area was decreased year by year,grass continent area expands unceasingly,as the habitat of birds such as land and water bottomland transition zone height down,etc.Paper using the landscape ecology,statistics,remote sensing,GIS and hydrodynamic simulation methods,such as system integration "hydrological cycle driven-ecological landscape pattern change-winter migratory birds habitat landscape evolution,of the coupling relationship between the three,the poyang lake wetland ecological landscape pattern for nearly 30 years to study and analysis of low response characteristics of the low water level,formed the following conclusions:(1)The index system of low dry water level which affects the change of vegetation landscape in Poyang lake wetland was constructed,and the optimum time of flooding for different vegetation groups was identified.By analysis,and the grass continent area of correlation factors from big to small in turn is:high water down days(MaxDay),40 to 50 days before the average water level(D50),an average of 70 days before the water level(W70),average 60 days before(W60),an average of 80 days before the water level(W80),an average of 90 days before the water level(W90).Among them,MaxDay and average water level of the first 40-50 days(D50)are two important factors that influence the change of the area of grassland in dry water period.High water down days(MaxDay)maximum correlation with grass continent area and at the same time,when the planetesimals 40 to 50 days before the average water level(D50)within the scope of 9.5 to 11 m,grass continent area of growth is slow,at about 1000 km2,after the D50 break through the water,grass continent area changed significantly,it shows the influence D50 grass continent area and wetland vegetation growth important level.In addition,according to the ecological threshold theory,gaussian model was used to analyze the response characteristics of different vegetation groups to the length of flooded water.Of carex flooded formation of the optimum length is 110-190 days,Yi grass formation for 170-235 days,smartweed grass formation is 195-260 days,the reeds in the formation of 100-150 days,the south national formation for 70-115 days,other grasses formation for 30-100 days,other sedge formation is 125-175 days.At the same time,the distribution of different vegetation groups in different altitudes was identified.(2)Preliminarily quantified the water level range of the ecological landscape div-ersity of poyang lake wetland.The landscape pattern of wetland is also changed periodically with the periodic change of lake water level.From the perspective of landscape diversity,the star water level 9.58m and 14.52m play an important role in the wetland landscape diversity of poyang lake.According to the correlation analysis of wetland landscape index and star water level,the landscape diversity was highest when the star water level was 9.58m.When the level of the star was fluctuating between 9.58m and 14.52m,the diversity of landscape in Poyang lake was not significant.When the planetesimals level in 14.52 to 15.55 m,landscape diversity rapid decline,reduced the degree of separation between different landscape patches,relevance,the water level fluctuation range has significant effects to the poyang lake wetland landscape diversity;When the star water level>15.55m,the diversity of landscape reaches the minimum and remains unchanged.(3)The response law of wetland ecological landscape to water level in ecologcally sensitive areas was revealed.In Poyang lake national nature reserve,the vegetation of clam lake under the influence of low dry water level,the vegetation distribution elevation range expanded,gradually spread to the lake heart,and the lake swamping speed was accelerated.Duchang migratory birds reserve under the condition of low water of different levels:the planetesimals standing low water(water level under 10m),serious water shortage,water level below 8 m)and special low water(water)under 6 m,much treasure protected areas are most affected.When the star water level is above 12m,the area of duchang reserve covers more than 90%.Poyang lake and the Yangtze river hydrological conditions continue to evolve in the future,under the trend of further duchang nature reserve flooded bottomland length will further cut short,see reserve dashanzi dominant species from carex formation in turn into other sedge formation,reeds,south and other grasses formation,the national treasure son reserve advantage cultivation was from smartweed grass formation gradually transformed into Yi grass formation,carex formation,other sedge national formation,formation of reeds,south of formation and other grasses formation.However,duchang migratory birds reserve smartweed son grass as the main food source of wild goose quantity is numerous,the stupa child protection zones of vegetation and drought in the future to transfer may cause goose class foraging habitat shrinking,affect duchang migratory birds reserve wild goose class number(4)The water level maintenance mechanism based on the wintering migratory birds to protect the habitat landscape was preliminarily established.Paper through the establishment of wintering birds foraging habitat and the lake water level response relationship,identify the wintering birds of different stages of wintering habitat landscape and water level relationship,to get the following understanding:winter migratory birds in the end of October to early November in phase,the lake water level should be kept under 11 m,in the mid to late December bird population has reached the peak,the lake water level should be maintained within the scope of 7.6 to 8 m can maximize the migratory birds foraging habitat area.