Effects of Redox Oscillations on Soil Clay Mineralogy and Colloid Dynamics

动态氧化还原条件是土壤中微生物活性和矿物质反应性的主要决定因素，但污染物、养分和碳动态的生物地球化学模型描述得很差。在湿地和高地系统中，由于水分含量和地下水位以及相关的生物氧气生产和需求的变化，氧化还原条件可能在每天、每周或季节性的基础上迅速变化；经常导致明显的氧化还原不平衡。水文流动条件的时间动态可以产生明显的土壤氧化还原梯度，影响矿物（转化）的形成和反应性，从而影响主要元素和微量元素的循环。然而，交替氧化还原条件对矿物学变化的影响以及作为“元素穿梭”的胶体物质在土壤中的动力学作用仍然知之甚少。因此，本研究计划的目的是评估(1)矿物学对土壤中波动氧化还原条件的响应，重点是铁（III）氧化物和层状硅酸盐矿物学，以及(2)多次氧化还原振荡期间胶体形成和组成的动力学。该计划的研究将提高我们对与氧化还原诱导的矿物形成、转化和溶解反应有关的基本土壤形成过程的认识，以及在土壤饱和循环期间控制主要和微量元素的土壤-地下水转移的过程。因此，它将有助于更好地了解由于气候变化，预计中欧若干地区将出现不同时期的土壤湿润和干燥。

Dynamic redox conditions are a major determinant of microbial activity and mineral reactivity in soils, but are poorly described by biogeochemical models of contaminant, nutrient, and carbon dynamics. In wetland and upland systems, redox conditions may change rapidly on a daily, weekly or seasonal basis due to changing moisture contents and water-table levels and associated biological oxygen production and demand; frequently resulting in distinct redox disequilibria. The temporal dynamics of hydrologic flow conditions can create pronounced soil redox gradients influencing mineral (trans)formation and reactivity and thus major and trace element cycling. However, the effect of alternating redox conditions on mineralogical changes and the dynamics of colloidal matter acting as "element shuttle" in soil are still poorly understood. Therefore, the aim of this research proposal is to assess (1) mineralogical responses to fluctuating redox conditions in soils, focusing on Fe(III)-oxide and phyllosilicate mineralogy, and (2) the dynamics of colloid formation and composition during multiple redox oscillations. The panned research will improve our knowledge on basic soil-forming processes linked to redox-induced mineral formation, transformation, and dissolution reactions, as well as processes controlling the soil-groundwater transfer of major and trace elements during recurring periods of soil saturation. It will thus contribute to a better understanding of soil responses to more distinct periods of soil wetting and drying expected in several Central European regions as a consequence of climate change.