| The reservoir hydro-fluctuation belt is a kind of special seasonal wetland ecological system and has the dual attributes of land and water, which has become the focus of research in recent years. The vegetation of reservoir hydro-fluctuation belt is an important part of the reservoir hydro-fluctuation belt ecosystem and its succession will take a dramatic ecological impact. Therefore, study the suitable mechanism and temporal and spatial succession pattern of the reservoir hydro-fluctuation belt wetland vegetation from two aspects of internal mechanism and macroscopic characterization, which has the important meaning and value for keep the balance of the reservoir hydro-fluctuation belt ecosystem, maintaining the ecological function of the reservoir hydro-fluctuation belt ecosystem, and protecting the ecological environment of the reservoir hydro-fluctuation belt ecosystem.In this paper, taking the wetland ecology and ecological hydrology as theoretical basis, using remote sensing and GIS technology, selecting Guanting Reservoir where the hydro-fluctuation belt habitat degradation seriously as the study area, collecting the remote sensing images during1987-2013in the study area which include3high resolution remote sensing images (SPOT-5and ZY-3) and medium-resolution remote sensing images (Landsat ETM+, Landsat TM and Landsat8OLI), and combined with the ground measured data. Firstly, based on the long time series of Landsat satellite data and the historical hydrological data of Guanting Reservoir; the remote sensing change detection and GIS spatial analysis technology were used to discriminate the stability of the Guanting Reservoir shore, the coverage and partition of Guanting Reservoir hydro-fluctuation belt reasonably. Secondly, based on the moderate, high resolution satellite images and the ground measured hyperspectral data; the different classification systems were made for the different spatial resolution data; and the object-oriented classification, back propagation artificial neural network (BP-ANN) and Fisher linear discriminant analysis were made use of to extract the wetland vegetation of the hydro-fluctuation belt. Then, based on the5wetland vegetation spatial distribution maps of hydro-fluctuation belt extracted from the medium-resolution Landsat images and the partition data of hydro-fluctuation belt; the analysis methods of landscape pattern and CA-Markov were used to reveal the temporal and spatial succession pattern of wetland vegetation with different partitions of hydro-fluctuation belt, and predicted the future spatial distribution pattern of wetland vegetation with different partition of hydro-fluctuation belt. Finally, based on the ground measured hyperspectral data, water quality data and laboratory biochemical parameter data; the mathematical statistics method and the species distribution statistical model (GAM) combined with spatial distribution prediction module (GRASP) were used to analyze the suitable mechanism of wetland vegetation. The principal conclusions of this paper are as follows:a) The high slope stability shore, soothing slope stability shore and soothing slope deposit shore were mainly3shore types of the Guanting Reservoir. The water area of Guanting Reservoir first increased and then decreased during1987-2013, which had the maximum water area in1996(113.12km2) and minimum water area in2007(32.49km2), the overall atrophy of water body in Guanting Reservoir was more serious. According to overlay analysis, the hydro-fluctuation belt of Guanting Reservoir was divided into long-term outcrop region and frequent flooding region. The total coverage of Guanting Reservoir hydro-fluctuation belt was also determined reasonably. The area of long-term outcrop region, frequent flooding region and Guanting Reservoir hydro-fluctuation belt were42.06km2,46.19km2and88.25km2, respectively.b) The average overall classification accuracy of5Landsat series images was84.86%and the Kappa coefficient was0.81. The average overall classification accuracy of3high resolution images was86.67%and the Kappa coefficient was0.86. The extraction results were ideal. Making use of the selected8spectral characteristic variables to typical wetland vegetation identification, the total classification accuracy of BP-ANN and Fisher linear discriminant analysis were85.5%and87.98%respectively. The classification results were also ideal.c) With the water area shrinking, The submerged plant, emerged plant, hygrophilous plant and mesophyte plant presented degeneration obviously in long-term outcrop region from the recent30years; while the halophilous plant and cultivated land presented expansion obviously. The cultivated land landscape became the dominant landscape type of long-term outcrop region; it had continuous spatial distribution and large area. The halophilous plant became the second dominant landscape type of long-term outcrop region. Compared with the long-term outcrop region, water in the frequent flooding region was relative enough, so submerged plant, emerged plant, hygrophilous plant and mesophyte plant did not present the trend of degeneration; instead, they presented a certain degree of expansion. In addition, the enough water greatly inhibited the growth and distribution of the halophilous plant and cultivated land, the halophilous plant and cultivated land did not become the dominant landscape types of the frequent flooding region. The CA-Markov model was used to simulate the spatial distribution pattern of wetland vegetation in the Guanting Reservoir hydro-fluctuation belt based on the2007and2013data. The predicted results show that the wetland vegetation will still present degradation trend in the long-term outcrop region and the ecological environment will further deteriorated; the wetland vegetation will not present degradation trend obviously in the frequent flooding region and the ecological environment will still good. Based on the temporal and spatial analysis results with different partition of Guanting Reservoir hydro-fluctuation belt, succession analysis results with different partition of Guanting Reservoir hydro-fluctuation belt and the CA-Markov prediction result, combined with the transfer direction distribution map of wetland vegetation in different partition of Guanting Reservoir hydro-fluctuation belt, the temporal and spatial succession pattern of long-term outcrop region was inhibitory succession, the temporal and spatial succession pattern of frequent flooding region was inhibitory succession and promotive succession.d) The reflectance spectrum of submerged plant was special because of the influence of water body, suspended solid in water, etc. The reflectance spectra of the other five plant ecological types were similar. The WP_r, Dr, WP_g, Rg,510nm and675nm absorption feature parameters had certain differences. The response models of water content and chlorophyll content to spectral feature parameters of typical wetland vegetation were established respectively. The response model of water content was y=-9.462х2-2.671х+0.608(х was the yellow edge area, SDy) and y=0.219e1.010x (х was SRWI) respectively, the response model of chlorophyll content was y=20.89х-18.45(x was ND (565,735)). According to Cross Validation examination, the response models have achieved the satisfactory test results. Finally, take the aquatic plant for example to analyze the suitable mechanism between the species distribution and environmental factors. The6environmental factors which had the effect to the spatial distribution of the submerged plant and emerged plant were selected in advance; CHLa, TP and distowater were the main factors that influence the spatial distribution of the submerged plant and emerged plant, but the response between the spatial distribution and the environmental factors (CHLa, TP and distowater) had certain differences. The submerged plant were generally distributed where the CHLa and TP were lower and distowater was larger, the emerged plant were generally distributed where the CHLa and TP were higher and distowater was smaller. |
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