Integrative application of geoelectrical methods for the characterization of preferential flow and reactive transport in the vadose soil zone

优先流现象普遍存在于非饱和地下环境中，并对水平衡、移动的物质输送和微生物活动产生多重影响。对这种现象进行量化和建模仍然很困难，可以通过地球物理方法大大改进。本提案的目的是通过层析地电方法的优先流的表征及其对土壤芯反应性运输的影响。在时变和非饱和介质中，地球物理数据解释通常不是唯一的。例如，渗透水、从土壤中释放离子以及由于微生物活动而产生碳酸盐导致土壤核心的电导率较大。这种非唯一性将通过电阻率、激发极化和自电位测量的组合来减少。这些方法将被应用在一个受控的实验室环境中，因为它是假设的非唯一性，可以进一步减少通过适当选择的边界条件和示踪剂。为了能够表征对地球物理变量（如电导率）的影响的一个过程，有必要实现其余影响过程的稳态条件。这可以例如通过在稳态和瞬态状态之间改变流量或通过施加具有不同化学性质的输入溶液（例如抑制或激发微生物活性的溶液）来完成。在该项目中，地球物理方法将得到频域反射仪探头、张力计和多室吸盘等蒸渗仪技术的支持。拟议的项目是创新的，因为它适用于几个地电方法同时在一个不饱和的，非均质土芯结合时变，但控制流边界条件。

Preferential flow phenomena are ubiquitous in unsaturated subsurface environments and have multiple influences on water balance, transport of mobile substances and microbial activity. Quantification and modelling of such phenomena is still difficult and could be greatly improved by geophysical methods. The aim of this proposal is the characterization of preferential flow and its impact on reactive transport in a soil core by means of tomographic geoelectrical methods. In a time variable and unsaturated medium geophysical data interpretation is usually not unique. For instance, infiltrating water, release of ions from the soil and production of carbonates due to microbial activity result in a larger electrical conductivity of the soil core. This non-uniqueness will be reduced by a combination of electrical resistivity, induced polarization and self potential measurements. These methods will be applied in a controlled laboratory environment, because it is assumed that the non-uniqueness can furthermore be reduced by an appropriate selection of boundary conditions and tracers. To be able to characterize one process of influence on a geophysical variable like electrical conductivity, it is necessary to achieve steady state conditions for the remaining processes of influence. This can be done, for example, by varying the flow between steady state and transient regime or with the application of input solutions with different chemical properties, for example solutions, which either inhibit or provoke microbial activity. In this project, the geophysical methods will be supported by lysimeter techniques like frequency domain reflectometry (FDR) probes, tensiometers and a multi-compartment suction plate. The proposed project is innovative as it applies several geoelectrical methods simultaneously in an unsaturated, heterogeneous soil core in combination with time variable but controlled flow boundary conditions.