|
(031) How representative are mesocosms of natural pond ecosystems? Tattersfield, Lisa1, Biggs, Jeremy 2, Maund, Steve1, Pickervance, Julie1, Whitfield, Mericia2, Williams, Penny2, 1 2 ABSTRACT- Outdoor aquatic microcosms are an established tool for higher-tier risk assessment of agrochemicals. Such studies enable the determination of effects under more realistic exposure conditions and can permit effects identified in lower tiers of testing to be put in ecological context. While consensus on experimental techniques is now reasonably well-developed, evaluation and interpretation of the ecological relevance of microcosm data remains an area of discussion. One aspect of this is to what degree microcosms are representative of natural systems (HARAP, 1999). We compared macroinvertebrate and macrophyte assemblages, in two sets of experimental outdoor microcosms (cylindrical ponds: 1.25 m wide x 1.25 m deep; rectangular ponds 4.5 m long x 1 m wide incorporating 3 depths of 0.1, 0.3 and 0.7 m) to assemblages found in natural ponds in Britain. The cylindrical microcosms supported macroinvertebrate assemblages with no uncommon species and significantly fewer species of Coleoptera, Hemiptera and Trichoptera because of the lack of a littoral zone. The cylindrical microcosms supported no marginal wetland plants but their submerged and floating plant assemblages were similar in community type and species-richness to natural ponds. The rectangular microcosms incorporated greater habitat heterogeneity and correspondingly, were found to be closer analogues of natural ponds. Incorporation of a shallow zone and grassy margins in the rectangular microcosms enhanced the numbers of Coleoptera, Hemiptera and Trichoptera which prefer shallow, littoral habitat. Design modifications, depending upon the objectives of the study, and with consideration of system variability and statistical robustness, are discussed. Key words: Microcosm, Aquatic, Higher tier risk assessment, Natural ponds |
