In situ measurements of soil and vadose zone water isotopes reveal water storage and fluxes in semi-aird ecosystems

These data are from the following publication: Oerter, E. J., & Bowen, G. (2017). In situ monitoring of H and O stable isotopes in soil water reveals ecohydrologic dynamics in managed soil systems. Ecohydrology, 10(4). Abstract: The water cycle in urban and hydrologically-managed settings is subject to perturbations that are dynamic on small spatial and temporal scales, the effects of which may be especially profound in soils. We deploy a membrane inlet-based laser spectroscopy system in conjunction with soil moisture sensors to monitor soil water dynamics and H and O stable isotope ratios (δ H and δ18O values) in a seasonally irrigated urban landscaped garden soil over the course of 9 months between the cessation of irrigation in the autumn and the onset of irrigation through the summer. We find that soil water δ2H and δ18O values predominately reflect seasonal precipitation and irrigation inputs. A comparison of total soil water by cryogenic extraction and mobile soil water measured by in situ water vapor probes, reveals that initial infiltration events after long periods of soil drying (the autumn season in this case) emplace water into the soil matrix that is not easily replaced by, or mixed with, successive pulses of infiltrating soil water. Tree stem xylem water H and O stable isotope composition did not match that of available water sources. These findings suggest that partitioning of soil water into mobile and immobile “pools” and resulting ecohydrologic separation may occur in engineered and hydrologically-managed soils and not be limited to natural settings. The laser spectroscopy method detailed here has potential to yield insights in a variety of Critical Zone and vadose zone studies, potential that is heightened by the simplicity and portability of the system.本数据集源自以下发表文献： Oerter, E. J. 与 Bowen, G. (2017). 《土壤水中氢、氧稳定同位素的原位监测揭示调控型土壤系统的生态水文动态》，《生态水文学》（Ecohydrology），第10卷第4期。 摘要： 城市及水文调控场景下的水循环会受到小尺度时空动态扰动的影响，此类扰动的效应在土壤环境中尤为显著。我们采用基于膜进气口的激光光谱系统，结合土壤湿度传感器，在一处季节性灌溉的城市景观花园土壤中开展了为期9个月的监测，监测周期覆盖秋季停止灌溉至夏季重新灌溉的完整时段，同步监测土壤水动态以及氢（H）、氧（O）稳定同位素（stable isotope）比值（δ²H与δ¹⁸O值）。 研究发现，土壤水的δ²H与δ¹⁸O值主要反映了季节性降水与灌溉输入的同位素特征。通过对比低温萃取（cryogenic extraction）法获取的总土壤水与原位水汽探针测得的移动态土壤水，我们发现：在长期土壤干燥期（本研究中为秋季）后的初始入渗事件中，进入土壤基质的水分难以被后续的入渗土壤水脉冲替代或混合。树木茎干木质部水（xylem water）的氢、氧稳定同位素组成与可利用水源的同位素组成并不匹配。 上述研究结果表明，土壤水可被划分为移动态与固定态“库”，由此产生的生态水文分离现象可能存在于人工构建与水文调控的土壤系统中，而非仅局限于自然环境。本文详述的激光光谱方法在各类关键带（Critical Zone）与包气带（vadose zone）相关研究中均具备提供关键科学见解的潜力，而该系统兼具简便性与便携性，进一步提升了这一应用前景。