Analysis of a system response and effects of acidification on a freshwater ecosystem

Abstract: Natural processes occurring in the environment have been studied from an-cient times. Because of their complexity, their behaviour is complicated to predict. Modelling reality is an integral part of most of the research and analy-sis of complex systems. There is awareness that there is often a need to accept models whose properties differ significantly from those in the system that is modelled. Acceptance of this state is a direct result of the need to conduct some research, when implementation of a real-time system is too expensive, too difficult or too dangerous and often quite impossible. Acidification of aquatic ecosystems is considered one of the major interna-tional issues connected to environmental threat in Europe. Many lakes in Scandinavia suffer from chronic acidity – a state in which water has a con-stant low pH level. Freshwater acidification is a common problem in areas of high sulphur and nitrogen deposition as atmospheric pollution is the major cause of acid rain that leads to acidification. These substances reach surface water not only from rain but also via run-off from the entire catchment. How-ever, run-off might be neutralized due to buffering characteristics of the soil, i.e. containing base character compounds. In Sweden, acidic run-off from the catchment relates to the areas where subsoil is developed on acid granite bed-rock. Because acid rain is correlated with climate change and atmospheric pollution, it becomes a very complex system where not all of the factors are known. The primary aim of this study was to develop a computer model that allows one to foresee the long-term effects of the system behaviour to the deposition of acidifying compounds built in Powersim environment. Also the influence and effects of lake liming were modelled.