Modelling Biological Processes in the Aquatic Environment

Based on some of the most recent contributions to the field of biological modelling within the frame of ecosystems analysis, some aspects of modelling eco-physiological processes in the aquatic environment are discussed. First, a few rather general comments are made on the predictive capabilities of complex ecosystems models, and the related need to use more realistic and causal descriptions for various complex biological processes. Following this, some ideas and formulations, guided by the above principles, are compiled and discussed. The use of more realistic representations of biological processes, including time-varying parameters, is advocated, and several approaches are compared. Key factors such as temperature, light or nutrients are considered with regard to the basic biological internal control mechanism of adaptation. The inclusion of adaptation phenomena in the representation of, for example, effects of temperature, light dependency of primary production, or nutrient uptake kinetics, is described on different levels of mechanistic detail and complexity, and as a holistic feature. This is also an attempt to reduce dimensionality in complex models by increasing the realism in the description of functionally heterogeneous lumped compartments and thus avoiding separate detailed descriptions of their major component elements. In addition to the adaptation in single-species populations, the problem of community adaptation in multi-species populations, represented in most ecosystem models by lumped variables and averaged parameters, is considered in relation to environmental fluctuations and environmental uncertainty. A concept of environmental tracking is proposed, represented by the relation of parameter values to their governing input variables and state variables, as a major adaptive strategy for biotic systems