Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone
Soil water stable isotopes reveal evaporation dynamics at the soil–plant–atmosphere interface of the critical zone
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DOI：
10.5194/hess-21-3839-2017
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发表时间：
2017-07
影响因子：
6.3
通讯作者：
M. Sprenger;D. Tetzlaff;C. Soulsby
中科院分区：
文献类型：
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作者：
M. Sprenger;D. Tetzlaff;C. Soulsby
抽象的。了解植被对上层土壤水分储存和通量的影响，对于评估气候和土地利用变化的后果至关重要。我们在四个植被不同的地点(樟子松和石南)每隔5厘米对表层20厘米的沼泽化土壤进行采样。和Erica Sp))和方面。这些地点位于苏格兰高地布伦特兰燃烧长期试验性集水区内，那里是一个低能量、潮湿的环境。2015年9月至2016年9月期间进行了11次采样，以捕捉同位素动态的季节性变化。用直接平衡法分析了土壤样品的孔隙水的同位素组成(δ2H和δ18O)。我们的结果表明，尽管北纬地区的潜在蒸发率很低，但与全年的降水输入相比，表层土壤中的土壤水分是动态分馏的。这种分级信号在上部15厘米内减弱，导致顶部5厘米与土壤深度15-20厘米处的土壤等渗分异。石南林下土壤和樟子松下土壤的分级信号有显著差异，后者更为明显。但同样，这种差异在土壤表层15厘米范围内变小。表层土壤重同位素的富集具有季节滞后性，表明土壤分馏信号与土壤蒸发在春/秋季节的增减之间存在滞后。根据土壤水分同位素的动态富集度，我们估算出石南松和樟子松下土壤的蒸发损失分别约为土壤入渗水量的5%和10%。在时间(每月)和深度(5厘米间隔)上的高采样频率显示，土壤水的同位素组成具有很高的时间和空间变异性，当使用稳定同位素作为示踪剂来评估临界区内的植物吸水模式或将其应用于校准示踪剂辅助的水文模型时，这可能是至关重要的。
Abstract. Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn long-term experimental catchment in the Scottish Highlands, a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analyzed for their isotopic composition (δ2H and δ18O) with the direct-equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15–20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers to assess plant water uptake patterns within the critical zone or applying them to calibrate tracer-aided hydrological models either at the plot to the catchment scale.