Mechanisms and consequences of vertical light-nutrient competition between benthic and pelagic primary producers in running-water systems

在水生系统中，初级生产严重依赖于光和营养物的垂直分布，这尤其影响到中上层和底栖藻类的竞争。远洋藻类可以遮蔽底栖藻类，而底栖藻类反过来又可以拦截从沉积物或深海带到远洋栖息地的营养通量。在流水系统中，光和养分的垂直分布按纵向梯度变化。随着光-养分利用率的变化，藻类的碳-养分化学计量也发生了变化，这通常与食草动物的食物质量有关。本研究的目的是通过实验分析营养供应途径和特征纵向变化的影响——即：光和营养供应的大小，以及远洋种群的补充和平流——对远洋和底栖初级生产者及其碳-营养化学计量的相互作用的影响。实验将首先在没有食草动物的情况下进行，第二年在该地区典型的优势食草动物中进行，以检查藻类群落对食草动物的影响，以及食草动物对这些群落的影响。研究结果将有助于了解基本的生态机制和过程，也将有助于评估人为压力的影响，如污水处理厂的地表流入与农业环境中通过潜流途径扩散的源有关，并将与理论和应用生态学和环境管理领域特别相关。

In aquatic systems primary production critically depends on the vertical distribution of light and nutrients which particularly influences the competition of pelagic and benthic algae. Pelagic algae can shade benthic algae which, in turn, can intercept the nutrient flux from the sediment or hyporheic zone to the pelagic habitat. In running water systems the vertical distribution of light and nutrients changes in a longitudinal gradient. With changing light-to-nutrient availability also algal carbon-to-nutrient stoichiometry changes which usually is correlated with food quality for herbivores. The aim of this study is to experimentally analyse the influence of pathways of nutrient supply and characteristic longitudinal shifts - which are: magnitude of light and nutrient supply, and recruitment and advection of pelagic populations - on the interaction of pelagic and benthic primary producers and their carbon-to-nutrient stoichiometry. The experiments will be first carried out without grazers and in a second year with site-typical dominant herbivores to examine the effect of the algal communities on the grazers, but also the effect of the grazers on these communities. The results will provide an understanding of fundamental ecological mechanisms and processes and will also help to evaluate the impact of anthropogenic pressures like surface influx from sewage treatment plants in relation to diffuse sources in agricultural environments via hyporheic pathways and would be of particular relevance for the fields of theoretical and applied ecology and environmental management.