The working group „Ecotoxicology and Environment“ hosts a state-of-the-art outdoor freshwater stream mesocosm facility for ecological and environmental research. It consists of in total 16 independent concrete channels (length = 45 m; width = 0.4 m; average water depth = 0.26 m). In order to simulate stream conditions, water flow can be maintained either in a flow-through mode or in recirculation mode via pumps usually using flow rates of 1 and up to 3 L/s, respectively. The stream channels are supplied by tap water which can optionally pass a pre-aging step in a 230 m3 storage reservoir (Elsaesser et al. 2013).

The stream channels can be equipped with sieved topsoil, artificial sediment (e.g. according to OECD standards) or natural sediments. In order to provide habitats for aquatic invertebrates or to study chemical retention e.g. of pesticides, the channels can be equipped with submerged (e.g. Elodea canadensis, Elodea nuttallii, Myriophyllum spicatum), helophyte (e.g. Berula erecta) or emergent macrophyte species. Invertebrate communities can be established typically covering major functional feeding groups and trophic levels (e.g. shredders, grazers and predators). Hereby, invertebrates may be chosen according to their intrinsic sensitivity to the specific mode of action of the test substance.

Realistic or worst case exposure events with pesticides, expected to be representative for edge-of-field streams, can be reproduced in the mesocosms using standardized exposure scenarios with durations in the range of ≤ 1 to ≥ 24 hours. These exposure scenarios can be used to perform a multitude of test approaches in the field of environmental fate and effect assessment of e.g. pesticides, biocides and nanomaterials.

Generally, the stream mesocosms are suitable for short- and long-term experiments lasting between few weeks and several years to assess changes of stream components (invertebrates and macrophytes) over the whole growing season and whole reproduction circles of long-lived invertebrate species (e.g. uni- or semivoltine merolimnic insect species). It was already used in various research projects to assess the environmental fate of pesticides (e.g. Stang et al. 2014), the environmental impacts of herbicide or insecticide exposure (Wieczorek et al. in press; Wieczorek et al. submitted), or to study aquatic-terrestrial subsidies by means of stable isotope analysis (Wieczorek et al. 2015).