Functional assessment of lotic ecosystems
Developing a functional approach to assess and ultimately to manage freshwater ecosystems is one of the overarching aims of the integrated project “Healthy aquatic ecosystems”. The study of food webs is the central approach to address this research aim due to its strong focus on relevant ecosystem functions such as productivity or organic matter processing. Our aim is to evaluate the suitability of various indicators of ecosystem functioning in terms of their response to stressors such as eutrophication, hydromorphological degradation and toxicants. Based on this, we develop a hierarchy of stressors by quantifying the relative strength of impacts of the various stressors for ecosystem functioning. Much of this work is conducted in the Holtemme River, a 3rd order river that is located in the TERENO area. The river is natural in the upstream reach but highly impacted due to channelization and riparian clearcutting in urban and agricultural areas in the downstream reach. Moreover, the river receives substantial inputs of nutrients as well as a large range of urban chemicals from two waste water treatment facilities and from tributaries draining agricultural areas. With this longitudinal increase of human stressors, the Holtemme River is a typical example of a multiple stressed ecosystem.