| Recently,due to the combined impact of global climate change and human activities,human improper development and utilization of resources has obstructed the ecological environment in grassland seriously.The degradation and salinization of grassland,soil erosion and desertification along with climate warming and drying are increasing.Meanwhile,wetland in grassland suffers too.The effect of the pressure of human excessive production activities and social economic development on wetland has been gradually revealed.The degradation of grassland wetland has become a crucial challenge to the sustainable development of grassland ecological environment.The management,conservation and restoration of grassland wetland have become a popular and difficult point in current wetland research.Taking the Hulun Buir Grassland wetland as a research area,using the combined method of ground monitoring and remote sensing,this paper explores the development pattern of prairie wetlands over time and space in recent three decades with computer and artificial visual interpretation of remote sensing image to extract wetland water body,and analyses the influence factors of grassland wetland degradation according to the characteristic of regional natural environment and social economic conditions.To observe the response of wetland sediment to the greenhouse effect,an artificial device simulating greenhouse effect is designed and constructed;to measure the physical characteristics and activity of hydrolase in the sediment,the temperature of the identified wetland sediment is changed by alternative environmental conditions,to reveal the biogeochemical cycling process of wetland soil and the related varying pattern of hydrolase activity under the condition of warming effect.The main research results are as follows:(1)The proportion of large(>10 hm2),medium(1-10 hm2)and small(<1 hm2)lake wetlands in grassland is basically maintained at 1:2:7,but the number of grassland lake wetlands shows a decreasing trend.Lake water area in grassland shows a shrinking trend,the total water area of grassland lakes has decreased by 39.8 percent in the past 30 years.On the whole,the number and area of wetlands decreased significantly.(2)The order of the number of lake wetlands over various cities and counties is as follows:Xin Barag Zuoqi>Xin Barag Youqi>Chenbaerhu Qi>Ewenk Autonomous Qi>Hailar District>Manzhouli,with the proportion of 39.86%,30.67%,13.41%,8.95%,3.87%,3.24%,respectively.Lake wetlands are mainly distributed in the Xin Barag Zuoqi and Xin Barag Youqi,the number of lake wetlands in these two banners accounts for about 70%of the whole Hulun Buir grassland lake wetland,the average proportion of large,medium and small lake wetlands in different elevation ranges is 86:11:3.(3)The three variables that farmland irrigated area,mining output and annual stock of livestock were contributed the most to the variation of lakes wetlands in the study area,with the contribution rates by 46.0%,26.0%and 16.8%respectively.Furthermore,natural factors are the direct causes of the shrinking grassland wetland area,but human interference is the most important factor affecting wetland degradation.(4)The growth rate of the total organic carbon content of the warming treatment was higher than that of the control group;the total nitrogen and total phosphorus content of the sediment of the permanently flooded wetland was significantly higher than that of the inter-annual and seasonal flooded wetland.The urease activities between inter-annual flooded wetland and seasonal flooded wetland have no significant differences.(5)The total organic carbon content of sediment in different flooded periods varies greatly,but the change of total organic carbon and total nitrogen content is not significant month to month.The total organic carbon has a significantly positive correlation with the total phosphorus content,a-1,4-glycosidase enzymes,L-leucine aminopeptidase activity,and the correlation coefficient were 0.485,0.330,0.246 respectively.(6)The descending sequence of average activity of 7 hydrolases in the research zone is:AP>LAP>?X>?G>aG>NAG>CBH,and the values were 29.287,16.164,2.036,1.122,1.096,0.951,0.420 nmol g-1·h-1,respectively.The activity of acid phosphatase indicated a small change month to month,in the meantime the differences of enzyme activity between the other six hydrolases were significant;the biogeochemical characteristics and hydrolase enzyme activities of sediment were significantly affected by environmental temperature variation.To sum up,the results of this study reveals the temporal and spatial dynamic distribution rules of Hulun Buir Grassland,including river wetland and lake wetland in different elevation ranges and different counties and urban areas in recent 30 years,and calculates the contribution rate and proportion of natural driving force and human driving force that affect the change of wetlands.The biogeochemical characteristics and hydrolytic enzyme activities of wetland sediment with different flooded periods are quantitatively identified and revealed under the conditions of artificial warming and natural environment warming. |
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