Near surface halogen (F, Cl, Br, I) cycle

卤素在自然界中无处不在；较重的卤素(氯、溴和碘)通常被认为是土壤和地壳上部岩石中涉及流体的过程中的惰性示踪剂。然而，越来越多的证据表明，这可能不是真的，而且卤素记录了低温环境中的各种流体来源、反应和沉淀过程。这些过程是由镁铝榴石类矿物(PYGM)记录下来的，它是由铅矿石(如方铅矿)在wt.%水平上含有卤素的表生风化而形成的。这些矿物至今仍在近地表流体作用过程中形成，并记录了参与其在环境条件下形成的近地表流体的卤素特征(例如F/Cl、BrCl值、I/C值)。在项目的第一个资助期，卤素在两个土壤剖面的不同深度层和地表水(降水、土壤溶液、小溪水和平坦水域)中的行为进行了调查。此外，由于吸附对近地表卤素循环有重要影响，我们已经开始研究卤素在不同粘土矿物组分上的吸附过程。为了完成这个项目，我们的目标是表征卤素在PYGM和不同组成的流体之间的分配。因此，计划1.进行一系列实验，并确定新沉淀的俾格玛晶体中的卤素浓度以及从晶体中沉淀出来的相应流体中的卤素浓度；2.完成从土壤剖面分离出的粘土部分中的卤素浓度的测定。有了这个全面的数据集，我们将能够开发一个详细的模型，用于卤素在地表附近的分布、动员和重要的保留过程，并可能将PYGM用作低温流体监测器。

Halogens are omnipresent in nature; the heavier halogens (Cl, Br and I) are commonly regarded as inert tracers in fluid-involving processes in soils and upper crustal rocks. There is, however, increasing evidence that this may not be true and that the halogens record various fluid sources, reactions and precipitation processes in low-temperature environments. These processes are recorded by pyromorphite-group minerals (PyGM), which form by the supergene weathering of Pb ores (e. g., galena) incorporating halogens at the wt.% level. These minerals still form today during near-surface fluid-mediated processes and record the halogen characteristics (e.g., F/Cl, Br/Cl, I/C ratios) of near surface fluids that are involved in their formation at ambient conditions.During the first funding period of the project, the halogen incorporation into PyGM, the behavior of halogens (F, Cl, Br, I) in different depth layers of two soil profiles and in surface waters (precipitation, soil solutions, creek waters and adit waters) was investigated. Furthermore, since adsorption has a major influence on the near surface halogen cycle, we already started to investigate adsorption processes of halogens on different clay mineral fractions. To finish up this project we aim to characterize halogen partitioning between PyGM and fluids of different composition. It is therefore planned 1. to perform a series of experiments and to determine halogen concentrations in freshly precipitated PyGM crystals and in the corresponding fluid from which the crystals precipitated and 2. to finish the determination of halogen concentrations in separated clay fractions from the soil profiles. With this comprehensive data set we will be able to develop a detailed model for halogen distribution, mobilization and important retention processes close to the surface, with a possible application of PyGM as low-temperature fluid monitor.