Combined effects of chemical and natural stressors on Daphnia magna in a context of global change: extrapolating from short-term experiments on individuals to long-term effects at the population level

Abstract

The exponentially increasing human population and the associated rise in chemical and nutrient input through ongoing urban, industrial and agricultural activity have exerted substantial pressure on aquatic ecosystems. The research conducted in the context of this PhD dissertation is situated in the field of ecotoxicology, which is concerned with investigating how individuals, populations, communities, and ecosystems respond to chemical stress. As such, ecotoxicology underpins many important legal frameworks related to environmental protection, such as ecological risk assessment (ERA) and the setting of environmental quality standards (EQS) for chemicals. Typically, the effects of single substances have been tested by means of laboratory toxicity tests, on a few (more or less relevant) model test species. There is however a pressing need to evaluate the combined effects of stressors, as research suggests that mixtures at No-Observed-Effect-Concentration (NOEC) levels of individual substances may cause adverse effects when they are combined. With global climate change projections, co-occurrences of natural and chemical stressors are only predicted to increase. The aim of the PhD thesis was to investigate the combined effects of metals (copper and zinc) with additional stressors (harmful algal blooms and global warming) at different organization levels (individual vs. population), and time-scales (short term vs. long term) on the freshwater zooplankton Daphnia magna