Complexity and emergent properties in aquatic ecosystems: predictability of ecosystem responses

1. The paper explores the predictability of ecological conditions in aquatic systems and of their responses to catchment management schemes, in which the hydrological and material loads can be accurately and precisely quantified. Linkages between catchment hydrology and impacts on water quality are considered. 2. New approaches to modelling the complex biological behaviour of recipient systems are briefly reviewed. The case is made for simulating emergent outcomes based on the adaptive strategies and dynamic behaviours of species attempting to meet their material demands within the supportive capacities furnished by local environments. This ‘bottom-up’ approach is justified by the fact that ecosystems are the sum of their smallest components; their behaviour is the aggregate of the activities of individuals. 3. A framework model template founded upon the emergent properties of high-performing organisms is developed within the context of exergy fluxes and their deployment and against axes representing the resource-carrying capacity versus the energy (photosynthetic and chemical) available to process it. 4. Some worked examples of simulated emergence in lakes are given, using the phytoplankton-community model, PROTECH, to demonstrate the acuity of predictions of the responses to quite subtle variations in biologically active solutes and suspensoids to simulated communities of the pelagic