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(79-06) The variability of different sized and designed mesocosms in relation to biotic and abiotic parameters. Rengers, C.*,1, Kroos, M.1, Ebke, K.-P.1, Schnöder, F.1, Vogel, F.1, 1 Covance Laboratories GmbH, Münster, Germany ABSTRACT- The use of mesocosms to observe ecotoxicological effects is inter alia limited by the variability of the used model ecosystem. Three different desinged pond systems (each three replicats, 9 ponds) were monitored during five month for Zooplankton, Macrozoobeenthos, Phytoplankton and physicochemical parameters of the water. The follwing systems were used to evaluate the variability: a concrete 36000 L pond was established as an outer basin for stainless steel cylinders used as enclosures (about 1000L water volume), ponds each consisting of an outer concrete container (10 cm thickness) and an inner stainless steel container (2 mm thickness). Three of them "mixed" by a special designed intermixing system and three of them established unmodified over five month. All systems contain water, sediment and macrophyts taken from natural sources natural and correspond to oligotrophic and mesotrophic natural ponds. It could be demonstrated that within the three described systems/designs special organisms (e.g. Baetids, Cladocera, Algae) and physicochemical characteristics show different development of variability. Interaction of populations between ponds (e.g. emerging insects), live cycle and structure (e.g. macrophyts) of the systems are main components of regulation/deregulation concerning the intermixing/design. It is therefore concluded that the design of the mesocosms for ecotoxicological tests has to be considered to the specific aspects in the risk assessment of the respective test substance. Key words: mesocosm, ecosystem variability, delayed fluorescence |
