氘氧同位素是示踪水循环的有效工具，过往研究中地下水中的同位素值被假定为继承自降水源中的相应值，并将其计算为等同于降水的同位素平均值。然而有研究发现，地下水的δ¹⁸O（δ¹⁸O_g）并不总是与降水的平均δ¹⁸O（δ¹⁸O_p）一致。造成这种不一致的原因仍有争议。含水层内部特征（如地下水埋藏深度和土壤质地）和外部降水特征（如降雨强度和持续时间）都可能使同位素变异性明显降低，进而导致降水与地下水之间存在偏差。然而，对于这些因素中哪一个起着决定性作用，目前尚缺乏明确的量化分析。本研究利用季风区不同土壤质地和埋藏深度的十个地中蒸渗仪土柱，获取了该实验场地内降水和地下水的新稳定同位素数据，以研究降水向地下水传递同位素信号的控制因素。实验在两次强降水事件（日降水量超过10毫米）期间和之后，以事件间采样间隔（30分钟）采集数据。研究结果表明：

（1）介质类型不同，出流及同位素表现不同。下渗能力更强、水位埋深较浅的介质在出流强度历时上会更多地接近降水强度特征，出流表现为更加明显的峰值和较早的峰现时间，出流衰减快，稳定同位素受降水影响也更大。相比之下，渗透性较弱的介质对降水的响应更为缓慢，出流量峰值较低，峰现时间滞后较长。

（2）降水特征（如降雨强度和持续时间）对降水到地下水的出流和同位素变化具有重要影响。暴雨事件对包气带的影响较大，导致出流峰值明显，但峰现时间存在滞后，这反映了水分通过土壤从地表转移到地下水位需要一定时间。相比之下，小降水事件则像是一个缓慢的向下压力，降水缓慢入渗，出流均匀，水量几乎即进即出。在暴雨条件下，不同介质的出流特征差异比小降水条件下更大，对土壤水同位素的改变也更为显著。这表明极端降水事件已成为影响地下水入渗过程的一个重要且不可控的新因素，需要在未来的水文地质研究中给予特别关注。同位素变化与出流变化不同步。具体而言，强降雨时，特别是在地下水位大于0.5m米的蒸渗仪中，有明显的出流滞后现象，而在早期入渗阶段观测到的同位素变化最大。降水的同位素下降趋势在地下水中有所减弱，只有在地下水位为0.5m和1.0m的砂砾石蒸渗仪以及地下水位为0.5m的黄土质黏砂蒸渗仪中观察到δ¹⁸O_g振幅与出流量之间的正相关关系。

（3）地下水位埋深对入渗过程和同位素组成也有重要影响。研究发现，随着深度的增加，同一介质的渗透能力逐渐减弱。冗余分析表明，降水量是影响流出量变化的最主要因素（~51%，p<0.05），水位埋深是影响同位素时间变化的关键因素（~52%，p <0.05）。这些结果与主成分分析结果的聚类一致。因此，水位波动作为地下水同位素变化的重要因素，在地下水古气候研究中应得到特别关注。

（4）在4个蒸渗仪中观测到土壤水分与强降雨事件分量的混合，混合比例f_P在10%~50%范围内变化，表明强降雨对土壤的有效补给。与当地大气水线平行的样品强调了土壤蒸发。据估计，砂砾石和黄土质黏砂的补给速率分别为400毫米/年和100毫米/年，这表明水分在黏土中的停留时间较长。蒸发导致的¹⁸O富集在地下水古气候研究中不可忽视，并且进一步证实了强降水事件对于地下水同位素组成的影响。

综上，本文通过对降水和地下水水量及稳定同位素进行分析比较，强调大降水事件对地下水补给的重要影响，讨论了介质、地下水水位埋深等对降水到地下水的补给过程及同位素信号传递的影响。建议在古气候研究中使用地下水同位素时，必须重点考虑到强降雨事件、地下水水位的历史波动以及蒸发引起的扭曲等附加限制。

Deuterium-oxygen isotopes are an effective tool for tracing the water cycle, the isotopic values in groundwater are assumed to be inherited from the corresponding values in the source precipitation. and calculated to equal the isotopic mean value of precipitation in the previous studies.  However, several studies have observed that groundwater δ¹⁸O (δ¹⁸O_g) is not always in accordance with the average δ¹⁸O of precipitation (δ¹⁸O_p). The cause of this inconsistency is still the subject of debate. Significant reduced isotopic variability and potential deviations from precipitation to groundwater because of the aquifer itself (e.g., groundwater buried depths and soil texture) and external precipitation characteristics (e.g., rainfall intensity and duration) have been poorly quantified in terms of identifying the dominant factors.  In this study, new stable isotope data for precipitation and groundwater from an experimental site using ten soil cylinders of different soil textures and burial depths in a monsoon region were presented to investigate the controls on the transmission of isotopic signals from precipitation to groundwater. We collected data at inter-event sampling intervals (30 min) during and after two heavy precipitation events (daily amounts higher than 10 mm). The results of the study show that:

(1) The outflow and isotope performance of different media types are diverse. The medium with stronger infiltration capacity and shallower groundwater table is closer to the precipitation intensity in the outflow intensity, and the outflow shows more obvious peaks and earlier peak appearance time, and the outflow decays quickly, and the stable isotopes are more affected by the precipitation. In contrast, a less permeable medium responds more slowly to precipitation, with a lower peak outflow and a longer lag in peak occurrence time.

(2) Precipitation characteristics (e.g., rainfall intensity and duration) are significant for the outflow and isotopic changes from P to G. Heavy rainfall events have a greater impact on the vadose zone, resulting in a pronounced peak outflow. The lag of peak occurrence, indicates that it takes time for moisture to move from the surface to the groundwater table through the soil. In contrast, a small precipitation event acts like a slow downward pressure, with slow infiltration of precipitation and uniform outflow, with the amount of water entering and exiting almost instantaneously. Under heavy rainfall conditions, the differences in outflow characteristics of different media are greater than under light rainfall, and the changes in soil water isotopes are more significant. This suggests that extreme precipitation events have become an important and uncontrollable new factor affecting the groundwater infiltration process, which requires special attention in future hydrogeologic studies. The isotopic variations were not synchronized with the outflow changes. Specifically, there were evident outflow lags in response to heavy rainfall, especially in the lysimeters with GBDs deeper than 0.5 m, while the greatest isotopic variation was observed in the early infiltrating stage. The descending isotopic trends of precipitation were weakened in groundwater with the only positive relationships between the amplitude of δ18Og and outflow being observed at the gravel sand lysimeters with GBDs of 0.5 m and 1.0 m and the loess clay lysimeters with a GBD of 0.5 m.

(3) The groundwater table also has an important effect on the infiltration process and isotopic composition. Redundancy analysis indicated that precipitation amount was the most important contributor to the outflow variation (~ 51%, p < 0.05), while groundwater buried depth was the key factor for isotopic temporal variation (~ 52%, p < 0.05). These results concurred with the clustering of principal component analysis results. Therefore, water level fluctuations, as an important factor in groundwater isotope variations, should receive special attention in groundwater paleoclimate studies.

(4) The mixing of soil water and heavy rainfall event components was observed in four lysimeters with mixing proportions f_P varying in the range of 10% ~ 50%, indicating the effective recharge from heavy rainfall. Soil evaporation was highlighted with samples located parallel to the local meteoric water line. A recharge rate of 400 mm/yr and 100 mm/yr was estimated for the gravel sand and loess clay sand, indicating a longer residence time in clayey soils. ¹⁸O enrichment due to evaporation should not be neglected in paleoclimate studies, and that the effect of heavy rainfall events on the isotopic compositions of groundwater has been further demonstrated.

In summary, the present study emphasizes the important impact of heavy precipitation events on groundwater recharge by analyzing and comparing precipitation and groundwater volumes and stable isotopes, and discusses the effects of medium, depth of groundwater table burial, etc., on the recharge process and isotope signaling from precipitation to groundwater. It is recommended that the use of groundwater isotopes in paleoclimate studies must focus on the additional constraints of intense rainfall events, historical fluctuations in groundwater levels, and distortions introduced by evaporation.