Distribution And Degradation Factors Analysis Of Wetlands In Qomolangma National Nature Reserve

In this paper, MODIS, DEM, field data collected in Qomolangma Nature Reserve were used to identify and analyze the spatial distribution of wetlands, analyzing the characteristics of wetlands seasonal variation from 2000 to 2007, the changing reasons of wetlands were analyzed in the perspective of climate changing and human activities.Because the accuracy was low when single MODIS vegetation indict was used(Wang et al.,2006), so several parameters were adopted to distinguish wetlands in this paper. In this paper, we used the data of MOD09A1 and MOD13Q1datasets of MODIS data covered Qomolangma National Nature Reserve of 2008, 1:50,000 Digital Elevation Model, and field data collected in September 2008. Synthesized EVI (enhanced vegetation index), MSAVI (modified soil adjusted vegetation index), LSWI (land surface water index) altitude, and slope data to analysized the characteristics of wetlands in spatial-temporal distribution in Qomolangma National Nature Reserve. The results show that: Firstly, The wetland types of Qomolangma National Nature Reserve were mainly riverine and lacustrine and swamp meadow wetlands which distributed from the altitude 4100m to 4700m where the slope less than or equal to 4 degree. The wetlands'area accounts for the total reserve area 11.3% form June to September in wet season. Secondly, lacustrine wetlands were mainly distributed in PeikuCuo plateau basin in core zones of protected area, LangqiangCuo in experiment zones, the DuobuzhaCuo plateau region in the east of Dingjie County. Riverine and swamp meadow wetlands are mainly distributed in the lacustrine plains or flood plains between PeikuCuo and LangqiangCuo, as well as broad and rift valley and basin with intensive stream network located in central and northern of the reserve. Thirdly, slope and altitude are key factors which impacted the distribution characteristics of wetlands in Qomolangma National Nature Reserve and they are important parameters to identify the range pattern of wetlands.After the anglicizing the areas of wetlands in wet season and dry season from 2000 to 2008 ,the result show that the wetlands area in wet season were changing less, and there were Increasing trend. The wetlands areas were 3782.4km2 in 2000, accounted for 11.2% of protected areas, the wetlands areas were 3822.4km2 in 2007, accounted for 11.2% of protected areas. It seems the wetlands are stable in wet season but not stable in dry season during 2000 to 2008.Due to the intensity storms taken place in winter of 2005 and 2008, wetlands covered by snow results to abnormal analysis results when using vegetation indexes which were mainly based on vegetation information. Hence, wet season should be chosen when analyzing interannual variability of wetlands in Qomolangma Nature Reserve.For the purpose of studying the seasonal changes characteristics of wetlands, wetland distribution and climate factors in the precipitation, annual temperature, annual sunshine duration of raster image were overlaid, at last protected area of wetland will be divided into three separate regions, in the region of minimum annual precipitation, maximum sunshine hours, maximum evaporation, vegetation coverage is low, lake-type were mainly brackish to saltwater lakes, with more typical characteristics of inland lakes, rainfall can not afford the needing of wetlands, water supplies in the region mainly iceberg melt water, hence the seasonal wetlands of the region greatest affected by the changing of snowmelt; in the regions of annual precipitation, mean annual temperature, annual sunshine hours are in the middle of the three regional areas , marsh and swamp meadow mainly in such regions, rainfall in the region focused on May to September, there were almost no other significant precipitation other months, high evaporation throughout the year, glacier melt water were mainly the source of wetlands in the region. Seasonal changes in wetlands were impacted, but snow and ice melt water were still dominant; for the most annual precipitation, annual sunshine hours, the shortest of the region, the seasonal effects of precipitation were most important. because of the precipitation were more concentrated, seasonal precipitation in the area of rivers and lakes wetlands is obvious, but for inland salt lake such as Duobuzha lake, the greater impact is melting ice and snow.In order to studying the annual changing of wetlands in Qomolangma Nature Reserve, first of all, the method of linear trend were used form 2000 to 2007 to analyze the changes in wet season. The results showed that: wetland area was rising at the speed of 5.38km2 per year from 2000 to 2007,sig = 0.05. Then EVI data from 2000 to 2007 were used, using the method of linear regression slope. The area of degraded wetland distribution and the influencing factors were studied. The results showed that during the period from 2000 to 2007, the wetlands of Qomolangma Nature Reserve were degraded; the degradation area were about 782.6km2,which was calculated by ArcGIS, accounting for the 20.47% of total area of wetlands, the better area were 13.9km2, accounting for the 0.36% of total study area of wetlands. To verify the accuracy of analytical results, author to investigate the reason in September 2008 in the field. We found that three regions have different degrees of wetland degradation in the field.In this paper the gray relational grade was used in order to solve the problem where the wetland area increase at the speed of 5.38km2 per year, but the wetlands depredated area account for 20.47% of the total wetlands area. Climatic factors of annual mean temperature, annual total precipitation, average relative humidity, annual pan evaporation and sunshine daily hours in wet season were used to analyze the relation between wetlands area and climate data. The results show that: the increasing in sunshine hours and temperature will accelerate the evaporation of surface water of wetlands, the annual pan evaporation changing has a direct reflection, but the increasing in temperature and sunshine hours also intensified the process of melting glaciers, some studies have shown that the glaciers were accelerating melting in recent years, glacial lakes area is rising. As the melted water of glacier is one of the important sources of wetlands, thus the wetlands area may be increase. But the area are becoming more and more drought from 2000 to 2007 which can be reflected directly from the changing of annual precipitation and daily mean relative humidity; but to the wetlands which from seasonal precipitation as the water source, because of increasing evaporation, reduction of precipitation and evaporation of moisture, so the wetlands can not be timely supplemented by water with low vegetation cover in the region, wetland vegetation are greater restrictions of water vegetation type, vegetation productivity of annual fluctuations are more fluently, stability are poor, and alpine vegetation in the bad environment will rapidly degraded, so wetlands are likely to degraded in such climate.In addition, in order to analyze the impact of human activities, population, year-end total number of livestock and cultivated area were used to discuss human activities on the changing of the wetlands. Qomolangma Nature Reserve as poorer areas in Tibet, crop and animal husbandry as the only local source of income. The region of wetlands were mainly in the pilot protected areas, protection efforts are limited, and many wetlands distributed in the region with gentler slopes, less water and pasture conditions are especially suitable for grazing. Because of poverty, local people have to explore the limit resources. The normal growth of wetland vegetation was destructed because of the overgrazing. Many wetland plants lost reproductive capacity and grass was destroyed. Under the impacting of soil microbes in aerobic propagation lead soil nutrients to be destroyed, resulting in changing in plant species and the degradation of wetland vegetation. In addition, the forming age of soil is young and thin with poor structure and low soil fertility. In most areas of wetland vegetation cover is low, soils are extremely sandy, and lakes were mainly inland lakes. Due to the climate changing dryer, temperatures rising faster, resulting in lower water fallow, without timely supply of glacier melt water, could easily lead to back lakes with salt-rich product, then resulting in the lakeside area of soil salinization, and finally formed degradation of lacustrine wetlands.