Causes, historical development, effects and future challenges of a common environmental problem: Eutrophication

The impact of the presence of us humans as well as our activities to nature has led to over-exploitation of natural resources and to dramatic changes in land-use including the use of artificial fertilizers contributes to the deterioration of the natural environment. The population density, industrial processes and the use of fertilizers are the main causes for the eutrophication of river systems, estuaries and seas. There are several ways to determine the actual nutrient levels back to the 1950s, back to 1900 or even back to 1800. Available data indicate that the natural background concentrations of nutrients (pristine conditions or the period prior to the widespread use of artificial fertilizers and detergents) were dramatically lower than today. Available time series on chemical and biological data collected from different parts of the world show the (sometimes tremendous) increase in nutrient levels and the related productivity. The same time series, however, also show the decreases in values when measures were taken to reduce the nutrient emissions. Investigations of different systems all over the world show that nearly every system responses differently to eutrophication. Especially physical boundary conditions play an important role in the manifestation of the ultimate effect of local eutrophication. Apart from the physical boundary conditions also the transformation and retention of nutrients in estuarine and coastal systems contribute to system specific responses. Depending on all these different conditions, site specific responses with even site specific problems may occur. The challenge of this millennium is to really reach a balance between nature and mankind including its population size. A beneficial step in this discussion is assessing criteria to reduce eutrophication back to a level acceptable to both humans and nature.