A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado
A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado
复制标题
DOI：
10.1007/s10533-009-9325-9
复制
发表时间：
2009-08-01
期刊：
影响因子：
4
通讯作者：
Ackerman, Todd
中科院分区：
文献类型：
--
作者：
Blanken, Peter D.;Williams, Mark W.;Ackerman, Todd
科罗拉多州 Niwot Ridge 附近高海拔（海拔 3,480 m）高山苔原上表面能量平衡和二氧化碳交换的涡流协方差测量与 2007 年 6 月 9 日至 2008 年 7 月 3 日两个夏天和一个冬天对邻近亚高山森林进行的同步测量进行了比较。高山地点的表面能量平衡闭合率在冬季和夏季分别平均为 71% 和 91%，由于测量地点的风速高、湍流通量足迹短以及相对平坦的山脊顶部位置。与森林地区相比，高山地区全年温度较低，相对湿度较高，水平风速较高，尤其是在冬季。高山地区（夏季和冬季、白天和夜间）的风向持续为下坡，而森林地区夏季白天常见上坡风。森林地区的潜热通量和感热通量始终较大，夏季差异最大。高山站点 CO(2) 的水平平流通量在夏季夜间平均占净生态系统交换 (NEE) 的 6%（夏季白天为 5%），并且相对于高风速、相对平坦的站点和站点上风向的 CO(2) 来源弱而言，CO(2) 的水平平流通量较小。使用三种方法计算高山东北东风的强度和日变化；涡协方差、摩擦速度滤波器以及平流和存储计算得出了类似的结果。高山地区净 CO(2) 吸收（负 NEE）期间为 100 天，净吸收量为 16 g C m(-2)，而森林地区为 208 天，净吸收量为 108 g C m(-2)，净吸收开始时间与气温达到 +10A 摄氏度一致。高山地区冬季呼吸损失为 164 g C m(-2)。 271 天，而森林地点 175 天的净损失为 52 g C m(-2)，净损失的开始时间与每个地点的气温达到 -10A 摄氏度同时发生。
Eddy covariance measurements of the surface energy balance and carbon dioxide exchange above high-elevation (3,480 m above sea level) alpine tundra located near Niwot Ridge, Colorado, were compared to simultaneous measurements made over an adjacent subalpine forest over two summers and one winter, from June 9, 2007 to July 3, 2008. The surface energy balance closure at the alpine site averaged 71 and 91%, winter and summer, respectively, due to the high wind speeds, short turbulent flux footprint, and relatively flat ridge-top location of the measurement site. Throughout the year, the alpine site was cooler with higher relative humidity, and had a higher horizontal wind speed, especially in winter, compared to the forest site. Wind direction was persistently downslope at the alpine site (summer and winter, day and night), whereas upslope winds were common at the forest site during summer daytime periods. The latent and sensible heat fluxes were consistently larger in magnitude at the forest site, with the largest differences during summer. The horizontal advective flux of CO(2) at the alpine site averaged 6% of the net ecosystem exchange (NEE) during summer nights (5% during summer daytime), and was small in relation to the high wind speeds, relatively flat site, and weak sources of CO(2) upwind of the site. The magnitudes and diurnal behavior of the alpine NEE calculated using three methods; eddy-covariance, friction velocity filter, and with advection and storage calculations, gave similar results. The period of net CO(2) uptake (negative NEE) was 100 days at the alpine site with a net uptake of 16 g C m(-2), compared to 208 days at the forest site with a net uptake of 108 g C m(-2), with initiation of net uptake coinciding with air temperatures reaching +10A degrees C. Winter respiration loss at the alpine site was 164 g C m(-2) over 271 days, compared to 52 g C m(-2) over 175 days at the forest site, with the initiation of net loss coinciding with air temperatures reaching -10A degrees C at each site.