The δ²H and δ¹⁸O values (isotope values) of porewater in soils have been used as natural tracers in many research disciplines. Conventional methods to determine the isotope values of porewater require extraction of water from the soil. To extract soil porewater cryogenic vacuum distillation is a commonly used technique. Based on extraction techniques porewater can be considered to be composed of ‘extractable’ and ‘non-extractable’ two components. Based on the goal of most studies, porewater consists of ‘active’ and ‘inactive’ two components, of which only the active part is of interest. Because different porewater components are interrelated through isotope exchange, in principle the conventional distillation technique cannot extract the active porewater without changing its original isotopic composition, regardless of whether recovery of the active porewater is complete or not. Thus, using the isotope results determined on the extracted water to represent the active porewater in soil may lead to variable results. Here, we describe a new distillation strategy for extraction of porewater for determining active porewater isotope values. The extraction uses a lower extraction temperature that is comparable to natural conditions. The isotope values are determined on the extracted water corresponding to different recoveries resulted from multi-step extraction. The final results of the active porewater can be derived indirectly from the multi-step extraction. This study demonstrates that in some cases the conventional one-step extraction technique may not be capable for accurate determination of isotope values of the active porewater. The multi-step extraction technique described in this paper can be used to give more reliable results. Multi-step extraction is similar to direct equilibration methods in that it determines the porewater component which plays an active part in the water cycle, regardless of whether extraction of the porewater is complete or not. Multi-step extraction method could provide an alternative approach to direct equilibration methods in some special cases, or provide a way to test the reliability of other methods for the determination of δ²H and δ¹⁸O values of soil porewater.

的δ ² H和δ ¹⁸土壤中孔隙水的O值（同位素值）已在许多研究领域中用作天然示踪剂。确定孔隙水同位素值的常规方法需要从土壤中提取水。提取土壤孔隙水的低温真空蒸馏是一种常用的技术。基于提取技术，孔隙水可以被认为是由“可提取的”和“不可提取的”两个组成。基于大多数研究的目标，孔隙水由“活跃”和“非活跃”两个部分组成，只有活跃部分受到关注。由于不同的孔隙水成分通过同位素交换而相互关联，因此原则上常规蒸馏技术无法在不改变其原始同位素组成的情况下提取出活性孔隙水，无论活性孔隙水的回收是否完成。因此，使用在提取水上确定的同位素结果来代表土壤中的活性孔隙水可能会导致结果变化。在这里，我们描述了一种用于提取孔隙水以确定活性孔隙水同位素值的新蒸馏策略。提取使用的提取温度较低，可与自然条件相比。在提取水上确定同位素值，该值对应于多步提取所产生的不同回收率。活性孔隙水的最终结果可以间接地从多步提取中得出。这项研究表明，在某些情况下，常规的一步提取技术可能无法准确确定活性孔隙水的同位素值。本文所述的多步提取技术可用于提供更可靠的结果。多步萃取类似于直接平衡法，因为它决定了在水循环中起着重要作用的孔隙水成分，而与孔隙水的萃取是否完成无关。多步提取方法可以为某些特殊情况下的直接平衡方法提供替代方法，或者提供一种方法来测试其他方法测定δ的可靠性² H和δ ^18个土壤孔隙水的O值。