Interactions between flow hydrodynamics and biofilm attributes and functioning in streams

生物膜是水生生态系统的重要组成部分，受光照、放牧、资源可利用性、水化学和水流条件等多种因素的控制。天然山地溪流呈现出从巨石到沙粒等小颗粒沉积物的非均质河床，从而引发了高时空变异性的流场。在这里，流体动力学成为塑造生物膜形态（如生物量和结构）的主导因素，一方面通过阻力控制生物膜群落组成，另一方面通过传质过程控制资源供应。目前关于流体动力学和生物膜属性之间相互作用的知识是基于一些理想化的案例研究，缺乏与河流生态系统功能后果的联系，例如氮吸收。以往的研究都局限于水槽实验，无法完全还原自然溪流高度复杂的流场。在一种新的方法中，我们的目标是将河床异质性的详细调查和流场的相关发展与生物膜特性和氮吸收的后果联系起来。为了避免中间环境研究的伪影，我们将在现场和中间环境中进行实验和测量，从而提供真实的溪流尺度结果和详细的传质基本过程的水槽研究的优势。此外，我们不仅将整合河流斑块尺度的结果，还将整合生物膜在河流河段尺度上的作用。这项高度跨学科的研究将提供对不同流量条件下生物膜氮吸收的机制理解，从而扩展目前对山区河流中整个河流生态系统过程调节的认识。

Biofilms constitute an integral part of aquatic ecosystems and are controlled by many factors such as light, grazing, resource availability, water chemistry and flow conditions. Natural mountainous streams exhibit a heterogeneous river bed ranging from boulders to small sediment grains like sand and thus provoking high spatio-temporal variability of the flow field. Here, flow hydrodynamics become a dominant factor shaping biofilm morphology such as biomass and architecture and controlling biofilm community composition through drag forces on the one side and supply of resources through mass transfer processes on the other. Current knowledge of the interactions between flow hydrodynamics and biofilm attributes is based on a few idealized case studies and is lacking a link to the consequences for stream ecosystem functioning like, e.g., nitrogen uptake. Previous studies have been restricted to flume experiments where the highly complex flow field of natural streams can not be reconstructed to the full extent. In a novel approach we are aiming at linking detailed investigations on river bed heterogeneity and associated development of flow fields to biofilm characteristics and the consequences for nitrogen uptake. In order to avoid artefacts of mesocosm studies we will conduct experiments and measurements in both, field and mesocosm environments, thereby providing the advantages of real stream scale results and detailed flume studies on basic processes of mass transfer. Furthermore, we will integrate not only results from the river patch scale but also the role of biofilms on the river reach scale. This highly interdisciplinary research will provide mechanistic understanding of nitrogen uptake of biofilms under varying flow conditions and will thereby extend current knowledge on the regulation of whole stream ecosystems processes in mountainous streams.