Eutrophication and derivative concepts. Origins, compatibility and unresolved issues

Eutrophication of lakes, as one of the most challenging global environmental problems for more than half a century has been addressed by a vast number of publications. Issues hitherto not considered or treated superficially have been discussed here. They concern: i. breakthrough phases in the 100-year period of development of the Eutrophication Concept (EC) and, ii. concepts and theories derived from EC and their complementarity in terms of assumptions and terminology. The paper traces the history of perception of the primary factors responsible for lake eutrophication. It presents the evolution of the approach to the problem, initially focusing on point and then non-point external sources of pollution, supplemented with internal nutrient supply, bottom-up and top-down regulation, with increasing emphasis on the role of interactions in the food web. The article addresses the justification of the Lake Aging Concept (LAC), assuming an inevitable increase in the trophic status during the development of a lake, and unjustly identifying eutrophication with progressing disappearance of lakes in a geologically-relevant timescale. It also discusses the assumptions of the Theory of Alternative Stable States (TASS) and discrepancies between EC and TASS regarding the application of different terminology in reference to the same phenomena and lake classifications.