Indicators For The Assessment of Thresholds And Points of Non-Return


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Ecological indicators are used increasingly to assess the conditions and/or status of ecosystems. Historically, the first approach was to develop indices based on a particular species or components, e.g. macrophytes, zooplankton, etc. In general, such indices are not broad enough to reflect the complexity of the ecosystem, as they do not include information at the structural, functional and system levels. To cope with these aspects new indices have been develop (for recent reviews see Rapport, 1995; Jørgensen et al., 2005) that try to synthesyze information at all ecosystem levels. In this project we are interested in evaluating indicators in terms of their potential to detect thresholds and point of non-return in coastal ecosystem. Analyses have so far been mainly carried out using:

- Specific species or ratio between species. For example, vegetation cover and submerged versus floating plant biomassess (Scheffer and Carpenter, 2003);
- Concentrations of chemical compounds. Total phosphorous (TP) is one of the most used indicators for threshold detection, see Scheffer and Carpenter (2003) and Qian et al. (2003). Oxygen has also been proposed by Jørgensen (1997) to account for pollution in rivers and by Turner and Rabalais (1994) in the Gulf of Mexico. Dose-response curves used in toxicology are based on contaminant concentrations (e.g. Klepper and Bedaux, 1997; Brock et al., 2004);
- Biodiversity indices. Carpenter (1996) suggested the existence of a threshold between ecosystem function and biodiversity, but he did not provide experimental evidence.

This report aims at providing a comprehensive overview of indicators with applicability to the assessment of thresholds of ecosystem integrity in coastal ecosystems. A preliminary screening has been performed and indicators suited for identification of thresholds have been described. The selected indicators have been divided into seven levels according to the classification presented in Jørgensen et al. (2005). The emphasis has been placed on these indicators that we believe will be able to detect thresholds and points of non-return due to eutrophication as well as contaminants effects, i.e. toxicity and bioaccumulation in the food chain, which are two of the main focuses of the project. No attempt has been made for covering the economic and social aspects.

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