The impact of light on microbial iron(II) oxidation in freshwater sediments.

生物地球化学铁循环是影响沉积物中一系列环境相关过程的重要反应网络。铁（II）氧化细菌和铁（III）还原细菌在很大程度上控制铁的周转和（不）动员。在经典的观点的沉积地球化学铁循环铁（II）-氧化细菌喂养的铁（II）通量，起源于微生物铁（III）还原，通常位于更深的氧化还原分层沉积物的区域。虽然研究了开放的水域系统，铁（III）的光还原过程和随之而来的铁（II）的供应到目前为止一直被忽视的沉积系统。在拟议的研究中，我们假设，铁（III）光还原提供额外的铁（II）作为基板的铁（II）-氧化社区在顶部阳光照射层的沉积物-在一个区域，目前的特点是由氧化过程和铁（III）的形成。沿着这些路线，我们将测量光和地球化学参数（氧，溶解铁（II），H2 O2和pH值）与微传感器和铁（III）矿物学（穆斯堡尔和酸提取）在高空间和时间分辨率的照明淡水沉积物芯的功能。除此之外，我们还将研究天然有机物如何驱动铁（III）光还原和铁（II）在沉积系统中用于微生物氧化的可用性。此外，活性氧物种将被检测为曝气的功能，并将评估其对铁（II）的稳定性和可用性的影响。拟议的研究项目将打开大门，到目前为止被忽视的反应机制，并走向我们目前的理解的地球化学铁循环和相关的基板通量在沉积物中的氧化还原梯度的修正。

Biogeochemical iron cycling has been recognized as an important reaction network that affects a series of environmentally relevant processes in sediments. Iron(II)-oxidizing and iron(III)-reducing bacteria control to large extent the turnover and the (im)mobilization of iron. In the classical view of the sedimentary biogeochemical iron cycle iron(II)-oxidizing bacteria are fed by an iron(II) flux that originates from the zone of microbial iron(III) reduction, typically located in deeper depth of redox stratified sediments. Although studied for open water systems, the process of iron(III) photoreduction and the consequent provision of iron(II) has so far been neglected for sedimentary systems. In the proposed study, we hypothesize that iron(III) photoreduction provides additional iron(II) as substrate for the iron(II)-oxidizing community in the top sunlit layers of sediments – in a zone that is currently characterized by the oxidative processes and the formation of iron(III). Along these lines we will measure light and geochemical parameters (oxygen, dissolved iron(II), H2O2 and pH) with microsensors and iron(III) mineralogy (Mössbauer and acid extraction) on high spatial and temporal resolution as a function of illumination in freshwater sediment cores. In addition to that we will examine how natural organic matter drives iron(III) photoreduction and the availability of iron(II) for microbial oxidation in sedimentary systems. Furthermore, reactive oxygen species will be detected as a function of aeration and their effect on the stability and availability of iron(II) for microbial oxidation will be assessed. The proposed research project will open doors towards a so far neglected reaction mechanisms and heads towards revision of our current understanding of the biogeochemical iron cycle and related substrate fluxes across redox gradients in sediments.