In situ bioassays with macrophytes in aquatic mesocosm studies
In higher-tier ecotoxicological testing of plant protection products, outdoor mesocosm ponds serve as models for aquatic ecosystems. Guidance documents recommend adding macrophytes to the ponds since they are one of the key species for herbicide testing and they are also thought to increase the diversity of the biocoenosis in the model systems. However, macrophyte growth and species composition are difficult to control in such ponds and often result in high variability between replicates. Due to this low reproducibility, quantification of toxic effects on water plants in mesocosms is usually very difficult. Moreover, the ponds are often dominated by few or only one fast growing macrophyte species. For the above-mentioned reasons, an in-situ bioassay with water plants was developed and tested for its use in mesocosm ponds. Several water plant species were planted in pots, hooked onto the walls of the ponds using pot holders. This enabled regular brief removal of the pots for observations and measurements of toxic effects on the plants, and restricted the plants to growth within the pots.
This approach of macrophyte in situ bioassays within a mesocosm study has been proven and has several advantages: Firstly, performing toxicity testing with several macrophytes species simultaneously under more realistic conditions than can be simulated in the laboratory. Secondly, to include macrophytes as important structural and functional components in mesocosms while limiting their dominance of the model ecosystem, thereby reducing their potential to mask effects on other sensitive parameters.
Up to now we have used the following plants in mesocosm studies: Lemna minor, Myriophyllum spicatum, Potamogeton lucens, Elodea canadensis, Glyceria maxima, Sparganium erectum, Ceratophyllum demersum and Chara globularis.
At present, we are investigating the impact of submerged macrophytes on phytoplankton, periphyton and metaphyton by nutrient limitation, allelopathic inhibition and competition in aquatic mesocosms (research study).
Classen S, Hammers-Wirtz M, Strauss T (2010): Effects of the seasonal development of macrophytes on other primary producers in aquatic mesocosms. Poster presentation, 20th SETAC- Europe Annual Meeting 23-27 May 2010, Seville, Spain.
Strauss T, Hammers-Wirtz M, Classen S, Memmert U (2007): In-situ bioassay with macrophytes in mesocosm pond studies. Poster presentation, 17th SETAC- Europe Annual Meeting 20-24 May 2007, Porto, Portugal.