Benthic macroinvertebrates and multiple stressors : quantification of the effects of multiple stressors in field, laboratory and model settings

Organisms are always exposed to several simultaneously operating stressors in nature. It appears that the combined effects of multiple stressors cannot be understood as a simple product of their individual effects. To understand how multiple stressors affect the composition and functioning of ecosystems it is necessary to know their quantitative contributions but also to explore their interactions. The central theme of this thesis is the quantification of the combined effects of multiple stressors on benthic aquatic macroinvertebrates and their communities. The statistical analyses of data sets in this thesis demonstrate that effects of multiple stressors in field situation can be quantified and that the benthic macroinvertebrate communities are affected by micropollutants. Furthermore, the modeling and laboratory studies show that the type of interaction between stressors can be analyzed and also that the effect of a certain stressor depends on the impact of all other stressors. Energy budgets and scope for growth seem powerful tools for improving the knowledge on the distribution and abundance of organisms. Finally, this thesis provides a foundation for differentiated standard setting.