The International Symposium on Trophic Relationships in Inland Waters, held from 1st-4th September 1987, at the Balaton Limnological Research Institute of the Hungarian Academy of Sciences, Tihany (Hungary), was intended to give an insight into current research on limnology of inland waters. The meeting was organized on the occasion of the 60th anniversary of the Institute in order to promote the exchange of ideas and discussion of new results. Papers presented during the Symposium dealt with four main topics: (1) Interactions of inorganic nutrients, primary producers and bacteria, (2) Interactions between primary and secondary producers, (3) Trophic relationships between plankton and fish, (4) Studies on complex trophic systems. Participants from 18 countries presented 40 oral lectures and 15 posters, that reviewed the structure and functioning of inland water ecosystems from different aspects. Since in such functioning nutrients are main forcing factors, the pathways of nutrients., as well as trophic connections, are widely studied nowadays. The IX papers of these proceedings thus present a series of different approaches to the main results of current limnological research in this very important field. The structure of these proceedings was somewhat altered when papers were ranked into three main groups: (1) Long-term changes, (2) Annual and seasonal cycles and (3) Short-term changes and pilot scale operations. The sequence of papers within these groups follows the four main subjects discussed during the Symposium.

The idea of convening an international workshop on hypertrophic ecosystems originated during the 20th S.I.L. Congress in Copenhagen. A group of about 30 delegates met there in an informal gathering to discuss the specific problems of lakes which have reached a noxious stage of eutrophication. This ad hoc group realized its own specific identity within the limnological community and suggested the organization of a specialized future meeting on hypertrophic ecosystems. After two years of preparatory work, the workshop was fmally held in Vaxjo, Sweden, between September 10 and 14, 1979, on the premises of the University campus. The Institute of Limnology, University of Lund (Professor Sven Bjork), undertook the task of host and organizer. The City ofVaxjo and the University of Lund co-sponsored the event, which was held under the auspices and patronage of the Societas Internationalis Limnologiae. The objective of the workshop was to seek better understanding of highly-eutrophic, disturbed and unstable aquatic ecosystems (lakes, reservoirs and ponds developing noxious algal and bacterial blooms, fluctuating in their water quality on a daily and seasonal scale, producing gases, off-flavor and toxic substances, experiencing periodic anoxia and massive fish kills, etc.), Le., systems requiring corrective measures and new concepts for their solution beyond those generally accepted for 'normal' eutrophic systems.