通过长期监测推进对临界区自电位特征的定量理解
Advancing quantitative understanding of self-potential signatures in the critical zone through long-term monitoring
摘要：
自然电位（SP）法是一种被动地球物理技术，它可以提供有关包气带中的水和离子通量的见解。目前禁止其在定量包气带水文常规使用的主要障碍是叠加的信号所产生的各种源机制，难以预测的电极极化效应，取决于电极的设计和年龄，以及水饱和度，孔隙水化学，粘土含量和温度在电极附近。我们提出了一个独特的长期SP监测实验，重点是在丹麦HOBE水文观测站在包气带不同深度采集的前四年的数据。使用国家的最先进的SP理论结合流动和运输模拟，我们试图复制观察到的数据，并提出观察到的差异的原因。在监测的头六个月期间，预测总体上是令人满意的，此后观测数据的模式和幅度都发生了急剧变化。我们的主要观察结果是（1）预测的SP幅度对有效过量电荷如何与水饱和度成比例非常敏感，这意味着需要继续研究以建立非饱和条件下电动现象的更准确模型，（2）电极极化的显着变化发生在一年的时间尺度上的最浅电极，这表明电极效应不能被忽略，在未来的监测研究中应考虑明确的电极模型，以及（3）需要多速率传质和反应输运模型来更好地预测盐度和孔隙水电导率。我们希望刺激其他研究人员测试新的SP建模方法和解释策略对这些数据，使SP和免费的数据时间序列。
英文摘要：
The self-potential (SP) method is a passive geophysical technique, which may offer insights about water and ionic fluxes in the vadose zone. The main obstacles presently prohibiting its routine use in quantitative vadose zone hydrology are the superposition of signals arising from various source mechanisms, difficult-to-predict electrode polarization effects that depend on electrode design and age, as well as water saturation, pore water chemistry, clay content, and temperature in the immediate vicinity of the electrodes. We present a unique long-term SP monitoring experiment focusing on the first four years of data acquired at different depths in the vadose zone within the HOBE hydrological observatory in Denmark. Using state-of-the-art SP theory combined with flow and transport simulations, we attempt to replicate the observed data and suggest reasons for observed discrepancies. The predictions are overall satisfactory during the first six months of monitoring after which both the patterns and magnitudes of the observed data change drastically. Our main observations are (1) that predicted SP magnitudes are strongly sensitive to how the effective excess charge scales with water saturation implying that continued research is needed to build more accurate models of electrokinetic phenomena in unsaturated conditions, (2) that significant changes in electrode polarization occur in the shallowest electrodes at time scales of a year, suggesting that electrode effects cannot be ignored and that explicit electrode modeling should be considered in future monitoring studies, and (3) that multi-rate mass transfer and reactive transport modeling are needed to better predict salinity and pore water conductivity. We hope to stimulate other researchers to test new SP modeling approaches and interpretation strategies against these data by making the SP and complimentary data time-series available.
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