| Napahai, lying between 99037'~99043'E and 27049'~27055'N at 3,260 m above sea level, in the middle part of Hengduan Mountain, northwestern Yunnan is a unique and seasonal marsh wetland. Distributing on ancient planation surface produced in Tertiary period, Napahai was formed by faultage sinking and has developed on limestone rocks. Scattering over the plateau like other lakes but without connecting watercourse with others, Napahai has relatively a small area and is beneficial to develop its own endemic species but this also brings the fragility and instability to the ecosystem. Moreover, situated in the upstream of the Yangtze River, Napahai plays an important role in adjusting the water flow and the water level of the downstreams. Also, it is an important pastureland that supports local people's daily life and provides a habitat for rare and endangered species. However, there have been few studies on such wetlands. Affected by karstification and human disturbances, the primary swamp in Napahai has been drained off, which causes retrogressive ecological succession to change from the primary swamp into swampy meadow, meadow and reclaimed wetland. Given the noninterference of primary swamp that could be an experimental control, we have selected swampy meadow, meadow and reclaimed wetland as the experiment sites to study the impacts of human disturbances on the ecological environment of Napahai. A two-year longterm study was carried out by applying In-situ technique to analyzing the temporal-spatial changes of swamp plant and soil chemical properties, and also the response to the changes of soil microbes and enzyme activities in the localization plots from four different wetland types according to seasonal variation and human activities, such as drainage, pasturing, tourism and reclamation. Further more, forest soil properties and plant compositions on the sides of Napahai basin are studied in the same way for us to understand the affection of forest ecosystem on wetland. The two-year study on the soil degradation process of Napahai Wetland has shown that In-situ is a simple and efficient method used in the conditions of plateau climate for dynamic position-setting study, especially for N cycling study. The research findings are: As human activities aggravated, the amount of organic carbon and total nitrogen declined by 22.92%~69.64% and 30.63%~58.67%, respectively. The available nutrients spatially decomposed from primary swamp to swampy meadow, meadow and reclaimed wetland. The descending range of hydrolysable N is 23.70%~57.92%, of available P is 16.43%~17.20% and of available K is 53.62%~61.45%. There is also a significant change of soil microbes. The fungus, the actinomyces and the bacteria in primary swamp soil are 0.75×103 ·g-1, 2.50×103 ·g-1 and 17.33×105 ·g-1 but they are increased to 9.04~21.38×103 ·g-1, 34.56~48.75×103 ·g-1 and 34.89~49.44×105 ·g-1, respectively resulted in the human active of drainage. The increasing regularity of microbes in Napahai wetland soil is of swampy meadow > meadow > reclaimed wetland. In the composition of microbes, a bacterium, accounting for 98% of microbes'total, is very important in Napahai ecosystem. The soil enzyme activities alternation shows the same trends as the changes of soil microbes when human interferences aggravated. The lowest soil enzyme activities are in the soil of primary swamp too. The urease, invertase and protease account for 65.69%, 41.00% and 18.64% of those in swampy meadow soil, respectively. Because of human disturbances, the soil enzyme activities are increased to the highest in the reclaimed wetland and followed in swampy meadow and meadow. The increasing rate of soil enzyme activities is of urease > invertase > protease implying that urease is the most sensitive enzyme in Napahai ecosystem and would be a representative of soil degradation. The alternation range of catalase is only 0.22~0.24 (0.1mol·L-1 KMnO4 ml·g-1), but the highest is in the soil of meadow and followed is in the reclaimed wetland, which shows the changes of aridity affected by human disturbances. The alternation of plants, soil nutrients, soil microbes and enzyme activities in Napahai wetland ecosystem has also shown the seasonal variation regularity. The soil nutrientsin forest ecosystem around Napahai basin are rich. Soil organic matter reaches the range of 81.26~110.27 g ·kg-1 and total N reaches 1.59~2.72 g ·kg-1. The amount of mineral N and surface soil loss caused by forest destruction on Napahai Wetland has reached 6,755.83 t ·a-1 and 6.1×104 m3 ·a-1, respectively, which has affected the material flow and substance sediment in wetland ecosystem. The loss of the function of soil ecosystem in Napahai has resulted in the alternation of aquatic plant types, the decline of biodiversity and the disappearing of endemic species in the area. Analyzing the causes of wetland environment deterioration, it has been shown that wetland shrinking, soil subsidence and regressive ecological succession of marsh are affected by both nature and human beings. Limestone rock has provided the background of deterioration. The karstification, tectonic movement and warming temperature have prepared the conditions for the deterioration of Napahai ecosystem. But the human interferences are the main factor that degrades the ecological environment of Napahai wetland. Destroying the vegetation, converting swamp to cultivated land, overgrazing and unordered touring-these four factors have rendered the natural possibilities into cruel reality and have aggravated the deterioration of Napahai wetland environment.
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