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Surface fluxes and water balance of spatially varying vegetation within a small mountainous headwater catchment

机译：山区小源流域内空间变化植被的表面通量和水平衡

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Precipitation variability and complex topography often create a mosaic of vegetation communities in mountainous headwater catchments, creating a challenge for measuring and interpreting energy and mass fluxes. Understanding the role of these communities in modulating energy, water and carbon fluxes is critical to quantifying the variability in energy, carbon, and water balances across landscapes. The focus of this paper was: (1) to demonstrate the utility of eddy covariance (EC) systems in estimating the evapotranspiration component of the water balance of complex headwater mountain catchments; and (2) to compare and contrast the seasonal surface energy and carbon fluxes across a headwater catchment characterized by large variability in precipitation and vegetation cover. Eddy covariance systems were used to measure surface fluxes over sagebrush (Artemesia arbuscula and Artemesia tridentada vaseyana), aspen (Populus tremuloides) and the understory of grasses and forbs beneath the aspen canopy. Peak leaf area index of the sagebrush, aspen, and aspen understory was 0.77, 1.35, and 1.20, respectively. The sagebrush and aspen canopies were subject to similar meteorological forces, while the understory of the aspen was sheltered from the wind. Missing periods of measured data were common and made it necessary to extrapolate measured fluxes to the missing periods using a combination of measured and simulated data. Estimated cumulative evapotranspiratation from the sagebrush, aspen trees, and aspen understory were 384 mm, 314 mm and 185 mm. A water balance of the catchment indicated that of the 699 mm of areal average precipitation, 421 mm was lost to evapotranspiration, and 254 mm of streamflow was measured from the catchment; water balance closure for the catchment was within 22 mm. Fluxes of latent heat and carbon for all sites were minimal through the winter. Growing season fluxes of latent heat and carbon were consistently higher above the aspen canopy than from the other sites. While growing season carbon fluxes were very similar for the sagebrush and aspen understory, latent heat fluxes for the sagebrush were consistently higher, likely because it is more exposed to the wind. Sensible heat flux from the aspen tended to be slightly less than the sagebrush site during the growing season when the leaves were actively transpiring, but exceeded that from the sagebrush in May, September and October when the net radiation was not offset by evaporative cooling in the aspen. Results from this study demonstrate the utility of EC systems in closing the water balance of headwater mountain catchments and illustrate the influence of vegetation on the spatial variability of surface fluxes across mountainous rangeland landscapes.
机译：降水多变性和复杂的地形常常在山头水源流域造成植被群落的镶嵌，这给测量和解释能量和质量通量带来了挑战。了解这些社区在调节能量，水和碳通量中的作用对于量化景观中能量，碳和水平衡的可变性至关重要。本文的重点是：（1）证明涡度协方差（EC）系统在估算复杂水源山集水区水量平衡的蒸散量中的作用; （2）比较并对比整个降水量和植被覆盖率变化较大的源头流域的季节性表面能和碳通量。涡度协方差系统用于测量鼠尾草（ Artemesia arbuscula 和 Artemesia tridentada vaseyana ），白杨（ Populus tremuloides ）和林下的表面通量白杨树冠下的草和草。鼠尾草，白杨和白杨林下叶的峰面积指数分别为0.77、1.35和1.20。鼠尾草和白杨树冠受到类似的气象作用，而白杨树的下层却被风挡住了。测量数据的丢失周期很普遍，因此有必要使用测量数据和模拟数据的组合将测量通量外推到丢失周期。估计从鼠尾草，白杨树和白杨林下的累积蒸散量分别为384 mm，314 mm和185 mm。流域的水平衡表明，在699 mm的平均面积降水中，有421 mm的蒸散量损失了，从该流域测得的流量为254 mm。集水区的水量平衡关闭在22毫米以内。整个冬季，所有场所的潜热通量和碳通量最小。生长季节的潜热和碳通量一直高于白杨树冠，高于其他地方。尽管鼠尾草和白杨林下生长期的碳通量非常相似，但鼠尾草的潜热通量始终较高，这可能是因为它更容易受到风的影响。在生长季节，当叶子活跃地蒸腾时，来自白杨的感热通量往往略小于鼠尾草的部位，但超过了五月，九月和十月的鼠尾草的感热通量，此时净辐射不能被植物中的蒸发冷却所抵消。白杨。这项研究的结果证明了EC系统在关闭上游水源流域水平衡方面的实用性，并说明了植被对山区牧场景观中地表通量的空间变异性的影响。

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