| East Dongting Lake owns abundant wetland vegetation species, which providesfood, habitat and spawning grounds for fish and other aquatic animals. And EastDongting Lake is also an important stopover in migration route for East Asia migratorybirds, where there are many national endangered animals inhabit, such as Chinesesturgeon, White sturgeon, Finless porpoise, White-flag dolphin and so on. The wetlandvegetation of East Dongting Lake is of important ecological and economic benefits.After operating the Three Gorges Project, the drainage amount of the sedimentsignificantly reduces, the Water flow come under adjustment at the same time so thatdrainage of process changes; the alteration the Three Gorges Project causes in theriver-lake relation is bound to affect the growth and succession of the vegetation inEast Dongting Lake. the spatial distribution pattern and dynamics of the Wetlandvegetation and its biomass can reflect the influence of environment on differentvegetation’s survival and growth, and also illustrate and instruct different vegetation’secological adaptability in East Dongting Lake, also can predict the influence ofhydrological changes caused by Three Gorges Project’s operation at the same time.Based on "3s" technology, this study uses HJ-1A/1B satellite date in2010toextract wetland vegetation of East Dongting Lake. Then, it synthesizes year’smaximum and average value of the Enhanced Vegetation Index (EVI) based on thesame period’s MODIS13data production, and analyzes vegetation’s spatial distributionand its biomass by combining elevation figure of East Dongting Lake. After that, itproves the most appropriate growth area of reeds and moss grasses that provides thebasis for the protection and exploitation of East Dongting Lake’s resources. It showsthat the nonvegetated area is generally under23m for elevation, and moss grasses growbetween23m and27m, and most of the reeds grow above27m and near the waters,but both moss grasses and reeds exist from26m to27m for elevation, and shelter forests grow in more than30m for elevation; the EVI value of shelter forests and reedsis larger in maximum and average value than moss grasses, and far greater than thenonvegetated area; the EVI value of reeds increases with the rise of elevation, andreaches to maximum in the area near the waters and in high relief; the EVI value ofmoss grasses in the regions of low elevation is smaller in maximum and average valuethan other areas, especially in average value, whose variation tendency is very obvious,which proves that long water flooded time in the regions of low elevation is harmful tothe growth of moss grasses. Results show that, vegetation’s spatial distribution and itsbiomass in East Dongting Lake has great correlation with elevation and waterenvironment; reeds grow well in the area above27m elevation and near waters; mossgrasses are suit to grow in the regions under26m or27m and above23m elevation.Finally, through analyzing vegetation growth and succession model of EastDongting Lake before the three gorges project operating, and on the basis of previousstudies about spatial distribution and adaptability analysis of vegetation and its biomassin East Dongting Lake wetland, this study discusses the influence of the changes ofriver-lake relation caused by three gorges project operating on vegetation growth andsuccession in East Dongting Lake from the factors of sediment deposition and thechange of water level and water hydrology. The results show that: in the factor ofsediment deposition, after The operating Three Gorges Reservoir, sediment fromYangtze river into Dongting Lake has significantly reduced, that greatly eases thesedimentation and atrophy of Dongting Lake; Sediment deposition speed and modedetermines the evolution trend of wetland vegetation, but the sedimentation reductiondoes not affect existing vegetation’s growth for the time being, It is mainly to play therole of slowing rise speed of bottomland so that positive succession rate in EastDongting Lake slows down. In addition, in the aspect of water level and water yieldchanging, because of the Three Gorges Project’s adjust action in water storage,water-level fluctuation amplitude in East Dongting Lake decreases during every year,that is mainly in favor of reeds’ growth in lower elevation, whose biomass begins to increase, but reeds’ biomass in the high elevation relatively reduced because of notgetting enough water, and gradually replaced by shelter forest. But in the long run,Three Gorges Project’s operating Changed the original natural state of water andsediment conditions, Flushing in downstream of the dam is aggravated, so that waterlevel of the downstream river channel declines and water yield into the Denting Lake isgreatly reduced, water yield, lake area and the average water depth in dongting lake,come up corresponding changing. Besides, plant community in different elevation areaown different sensitive degree to the changes, that Will make advantage varieties, reedsand moss grasses, develop faster and take over living space from submerged vegetation.At the same time, it is advantageous to propagate and invest new habitat for the plantsgrowing in high relief and owning poor water resistance ability such as poplar, so thatit will break the original succession model and the existing pattern of vegetationcommunity. |
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