干旱区生态环境知识资源中心(Arid): 宁南半干旱地区农田和草地生态系统能量通量的季节变化

Arid

	宁南半干旱地区农田和草地生态系统能量通量的季节变化
其他题名	Seasonal differences of energy fluxes among crop and grass ecosystems in semiarid region of southern Ningxia
	张晓煜; 王连喜; 袁海燕
来源期刊	生态学报
ISSN	1000-0933
出版年	2005
卷号	25 期号:9 页码:2333-2340
中文摘要	根据2002-2003年宁南山区不同下垫面小气候考察资料，用能量平衡法计算了不同下垫面不同季节的感热、潜热通量。分析结果表明：（1）宁南半干旱地区夏季农田和草地的净辐射峰值可达到700W／m^2以上，土壤热通量的值比净辐射小1个量级。同类下垫面净辐射通量日积分值夏季＞春季＞秋季＞冬季。（2）宁南半干旱山区感热输送强度以典型草地的最大，其次是禁牧草地，稀树草地的最小。春季各类下垫面地表热量平衡以感热输送为主。在春、夏、秋季的晴天，感热通量日积分值为正，冬季为负。（3）农田在夏、秋季、冬季水汽输送大于各类草地的，其次是稀树草地的，典型草地向上的水汽输送量是最小的。夏季白天农田beta在0．2～0．7，稀树草地beta为0．2～1．0，能量输送以潜热为主。禁牧草地beta为0．2～9．2，典型草地为1．5～13．1，能量输送以感热为主。（4）宁南半干旱地区宜退耕，发展典型草原，在水分充足的山地背阴坡少量发展稀树草地。
英文摘要	Human activities have dramatically influenced terrestrial ecosystems through altering the surface energy balance in the atmosphere land interactions. Understanding the surface energy balance in various vegetation surfaces and ecosystems is essential for evaluating the impacts of management activities on the succession of natural andanthropogenic ecosystems. In the semiarid region in Southern Ningxia of China, expanding agricultural and overgrazing grasslands has resulted in degradation of natural grass ecosystems. Recently, a management policy-crop-to grassland conversion has been practiced in this area to prevent deterioration of ecological processes. To understand the effects of this management activity on ecological processes, we examined microclimate and energy fluxes in four types of ecosystems, including typical grassland （TG）, which are grasslands with regular grazing, grazing-forbidden grassland （GFG）, which are grasslands without grazing, semiarid savanna （SS）, which are grasslands with sparse trees, and cropland （CL）. The objectives of this study were to （1） examine microclimate differences in the four crop and grassland ecosystems; （2） quantify each component of surface energy balance （i. e. , net radiation, soil heat flux, sensible heat flux, and latent heat flux） in different ecosystem types and seasons; and （3） evaluate the benefits of crop-to-grassland conversion in semiarid agricultural area. This studv was conducted in Haiyuan County, Ningxia Hui Autonomous Region, China, located between 1528-2600 m elevation within 36°02′4-36°-27′ 54＂N, 105°32′42-105°37′36＂E. All microclimatic measurements were collected manually or automatically once an hour during Spring （April 17-26, 2001）, Summer （July 13-22, 2001）, Fall （October 15-24, 2001）, and Winter （January 15-24, 2002）. We measured net radiation （B） at 1.5 height and soil heat flux （Qs） at 5cm depth. We also measured air temperature, relative humidity, and wind speed at 0.5, 1.0, 1.5, and 2.0m in height above the ground. Using those measurements and Energy Balance method （B=H＋LE-Qs）, we calculated sensible heat flux （H） and latent heat flux （LE）. Bowen Ratio （B=H/LE,） was also computed to evaluate the features of heat and water vapor transportation in the four types of ecosystems. Our results indicated that the magnitudes and diurnal patterns of net radiation, soil heat flux, sensible heat flux, and latent heat flux were significantly different among typical grassland, grazing-forbidden grassland, semiarid savanna, and cropland in four typical seasons： Net radiation had regular diurnal patterns in all seasons. Positive net radiation occurred during the daytime （7：00-18：00） with maximum up to 700 W/m^2（12：00-14：00）, while negative net radiation displayed at night with minimum less than 100 W/m^2. The highest daily accumulated net radiation occurred in the summer, and the lowest occurred in the winter. In the spring, daily accumulated net radiation was larger than that in the fall. Comparing daily accumulated net radiation among the four types of ecosystems, we found that semiarid savanna had relatively larger daily accumulated net radiation in the spring and fall seasons and smaller daily accumulated net radiation in the summer than the other three types cropland experienced the highest daily accumulated net radiation during the summer. Daily accumulated net radiation in typical grassland and semiarid savanna was negative during winter. Soil heat flux was ten times less than net radiation. It indicated that up to 90% of net radiation was allocated to sensible and latent heat flux （i.e. , H and LE） rather than soil heat flux. However, the seasonal patterns of soil heat flux determined daily and annual increase and decrease in soil temperature. For example, in the spring, soil heat flux （90 W/m^2） was used to heat soil surface in the daytime and resulted in an increase in soil temperature; soil heat flux （30 W/m^2） escaped from soil surface during the nighttime and resulted in decrease in soil temperature. Soil heat flux showed a general seasonal pattern, which showed the largest in the spring. the second largest in the summer, and the smallest in the winter. In the four ecosystem types, typical grassland and grazing-for bidden grassland had similar diurnal patterns of soil heat flux. Semiarid savanna had smaller values than typical grassland during the nighttime because this type of ecosystem was dominant in the shaded slopes. It suggested that semiarid savanna experienced less soil temperature fluctuation ina day or in seasons than the other three types of ecosystem. Comparing the fluctuation of soil heat flux, we found that the maximum of soil heat flux in the summer and fall （30-50 W/m^2） was significantly lower than that in the spring （90 W/m^2）. During the winter, heat was transported from the soil surface, resulting in a decrease in soil temperature. Sensible heat flux showed typical diurnal patterns that had been reported in other semiarid and arid area. Sensible heat flux was positive during the daytime but negative during the nighttime. This feature of sensible heat flux significantly differed from the patterns observed in moist climatic zones, which might have lower positive value or remain negative all day long. Apparently, moisture conditions controlled the magnitudes and diurnal patterns of sensible heat flux. Because there was significant variation among the four types of ecosystems, a variety of patterns of sensible heat flux appearecl. In the spring, sensible heat flux was the most important part of surface energy budget and differed in different ecosystem types. For example, sensible heat flux was 70%-95% of net radiation in typical grassland and 40%-60% in grazing-forbidden grassland and semiarid savanna. In the summer, sensible heat flux was still the major distribution of net radiation. In typical grassland, 60%-80% of net radiation was contributed to sensible heat flux. and less than 50% of net radiation was contributed to sensible heat flux in other types of ecosystems. In the fall, the maximum of sensible heat flux occurred at 381 w/m^2 in typical grassland, and cropland had the lowest peak value of sensible heat flux （128 W/m^2） in the four types of ecosystems. In the winter, there was a strong diurnal pattern in typical grassland, but it was not observable in other ecosystem types. Latent heat flux indicated that the features of water vapor transport were significantly different in the four ecosystem types. Compared with the other three types of grasslands, cropland had the greatest upward water vapor transport in the summer, fall, and winter. The lowest upward water vapor transport occurred in typical grassland. In the daytime of spring, because semiarid savanna received the most net radiation of the ecosystem types and also had relatively sufficient water supplement for evapotranspiration, upward water transport was the greatest in the four ecosystem types with the maximum 283 w/m^2 in a day and daily accumulated value 3.5 w/m^2.
中文关键词	感热 ; 潜热 ; 土壤热通量 ; 退耕还草 ; 能量平衡法 ; 草地 ; 农田
英文关键词	heat flux latent flux soil heat flux crop-to-grassland conversion energy balance method grassland cropland
类型	Article
语种	中文
国家	中国
收录类别	CSCD
WOS类目	Environmental Sciences & Ecology
WOS研究方向	Environmental Sciences & Ecology ; Plant Sciences
CSCD记录号	CSCD:2180425
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/206547
作者单位	张晓煜, 宁夏气象防灾减灾重点实验室, 宁夏气象防灾减灾重点实验室, 银川, 宁夏 750002, 中国.; 王连喜, 宁夏气象防灾减灾重点实验室, 宁夏气象防灾减灾重点实验室, 银川, 宁夏 750002, 中国.; 袁海燕, 宁夏气象防灾减灾重点实验室, 宁夏气象防灾减灾重点实验室, 银川, 宁夏 750002, 中国.
推荐引用方式 GB/T 7714	张晓煜,王连喜,袁海燕. 宁南半干旱地区农田和草地生态系统能量通量的季节变化[J],2005,25(9):2333-2340.
APA	张晓煜,王连喜,&袁海燕.(2005).宁南半干旱地区农田和草地生态系统能量通量的季节变化.生态学报,25(9),2333-2340.
MLA	张晓煜,et al."宁南半干旱地区农田和草地生态系统能量通量的季节变化".生态学报 25.9(2005):2333-2340.