Minimum Detectable Difference (MDD) in model ecosystems with different experimental designs

• Autor(a) principal: Leal, Daniela Alexandra Mendes
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/124289
• topic: Domínio/Área Científica::Engenharia e Tecnologia::Engenharia do Ambiente

Ecotoxicological testing of chemicals have traditionally focused on the bioassay approach, where the ecotoxicity of a compound is evaluated on only a single species at the time in the laboratory. However, natural ecosystems are must more complex and include species interactions and the influence of ambient environmental factors. On the other hand, the evaluation of the toxic effects in the field has the disadvantage that this complexity hampers the interpretation of the correlations of treatment-related effects of individual stressors, and it is very hard to find a non-polluted field site. Model ecosystems, also referred to as microcosms and mesocosms, are experimental ecosystems that are constructed with components of natural ecosystems. This experimental design allows the evaluation of the correlations of treatment-related effects (when compared to field trials) with a higher ecological realism (when compared with laboratory bioassay tests). Thus, the model ecosystems have often been used to evaluate how the natural ecosystems function and how the exposure to toxic elements or potentially toxic elements influences ecosystem structure and functioning. The Minimum Detectable Difference (MDD) is the minimum difference between the control and treatments with a compound under study that must exist to be statistically significant. This indicator was developed in order to provide a measure for the statistical power of microcosms and mesocosms experiments. However, few MDD calculations on model ecosystem studies have been made so far. Therefore, the aim of this thesis work was to evaluate the influence of the experimental design of the previously conducted microcosms and mesocosms experiments on their MDD values. The method presented in the Aquatic Guidance document for pesticides was used to calculate and compare MDD values from model ecosystem studies previously conducted with the same pesticide (the insecticide chlorpyrifos) in the Netherlands and Thailand. MDD values reported in previously published papers dealing with model ecosystems were also procured and compared. From these calculated and compiled MDD values, several factors that potentially increase or decrease the MDD values were identified. Several directions for future research based on the study findings are provided in the last section of this thesis.