Drainage basin nutrient inputs and eutrophication: an integrated approach

Abstract

Eutrophication is an increase in primary production due to increased nutrient supply and its consequences. In its widest sense eutrophication means any increase of nutrient availability that increases primary production. Frequently, however, eutrophication is understood exclusively as the consequence of nutrient input by anthropogenic activities. The primary consequence of eutrophication in aquatic environments is an enhancement of algal productivity and accumulation of algal biomass. Secondary consequences are changes in community structure of plankton and benthos. Man-induced eutrophication or changes in biodiversity are nothing new: they are a well-known consequence of human culture. Eutrophication phenomena accompanied all human settlements. Even in the early days of mankind human activities resulted in ecosystem changes. Several large animals such as the mammoth survived the glacial periods, but not the last one. It has been suggested that Neolithic hunters decimated this species to extinction. Similar suggestions have also been made regarding other large mammals that did not continue to exist after the last glacial. The main sewage canal in the city of Rome, ‘cloaca’, has given rise to a number of expression regarding sewage pathways in numerous languages. Since classical and medieval times there have been ‘clean-ups’ of unsanitary, plague-ridden cities. Eutrophication is thus the oldest environmental problem of human civilization and not a recent phenomenon. However, with the significant increase of human population over recent decades, eutrophication has developed from a more or less local to a global issue. Due to changes in human living conditions and the declining number of people employed in agriculture, the population in the coastal zone increases steadily. The nutrient concentration increases continually from small streams over rivers and larger lakes to the estuaries. The consequences of this, such as discoloured waters, ‘rotten’ bottom water, odour and reduced fishing yields are obvious to even a casual observer. The combined effect of increasing human population and movement to the coastal zone, the environmental pressure on rivers, estuaries and shelf regions results in an ever-increasing pressure on the entire coastal zone (Figure 1). Consequently, eutrophication turns into an escalating global phenomenon as long as the human population increases. Homo sapiens has thus a vital impacton nature that is part of its culture. As a consequence of that we have to distinguish between natural and cultural eutrophication. In most of this text the term eutrophication stands for cultural eutrophication.