Hypertrophic Ecosystems

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.

Session 1: Definition, characterization and causes of hypertrophy.- The summer limnology of Lake Waahi, New Zealand.- Identification of different phosphorous forms and their role in the eutrophication process of Lake Balaton.- Metalimnetic gradient and phosphorus loss from the epilimnion in stratified eutrophic lakes.- The influence of sediments on changed phosphorus loading to hypertrophic L. Glumsø.- The cyanobacterium Microcystis aeruginosa kg. and the nitrogen cycle of the hypertrophic Lake Brielle (The Netherlands).- Comparison of hypertrophy on a seasonal scale in Dutch inland waters.- Control of undesirable algae and induction of algal successions in hypertrophic lake ecosystems.- Occurrence of Oscillatoria agardhii and some related species, a survey.- The influence of periodicity in light conditions, as determined by the trophic state of the water, on the growth of the green algae Scenedesmus protruberans and the cyanobacterium Oscillatoria agardhii.- The role of microlayers in controlling phytoplankton productivity.- Short-term load-response relationships in shallow, polluted lakes.- The importance of trophic-level interactions to the abundance and species composition of algae in lakes.- Vegetation changes in the nutrient-rich shallow Lake Hjälstaviken.- N2-fixing cyanobacteria; why they do not become dominant in Dutch, hypertrophic lakes.- Session 2: Stability of hypertrophic ecosystems and causes of hypertrophy.- Nirate overdose: effects and consequences.- A chemical model to describe nutrient dynamics in lakes.- Changes in the respiration and anaerobic nutrient regeneration during the transition phase of reservoir development.- Modelling carbon and phosphorus in a small hypertrophic North German lake.- An algal bloom model as a tool to simulate management measures.- Phosphorus stability in a hypereutrophic lake.- Structural and functional quantification in a series of Hungarian hypertrophic shallow lakes.- Muddy odour in fish from hypertrophic waters.- The importance of hydrologic factors on the relative eutrophic impacts of point and non-point pollution in a reservoir.- Environmental constraints on Anabaena N2- and CO2-fixation: effects of hyperoxia and phosphate depletion on blooms and chemostat cultures.- Toxicity fluctuations and factors determining them.- Stability and multiple steady states of hypereutrophic ecosystems.- Session 3: Foodchain properties, productivity and utilization of hypertrophic ecosystems.- On the role of soil in the maintenance of fish ponds’ fertility.- Fish as a factor controlling water quality in ponds.- The role of fishery management in counteracting eutrophication.- Fish production in some hypertrophic ecosystems in South India.- Session 4: Rehabilitation.- Enrichment and recovery of a Malaysian reservoir.- Lake treatment with hydrogen peroxide.- Characterization of the recovery processes in hypertrophic lakes in terms of actual (lake water) and potential (algal assay) chloropically.- Morphometrically conditioned eutrophy and its amelioration in some British Columbia lakes.- Hartbeespoort Dam - a case study of a hypertrophic, warm, monomictic impoundment.- Cascade reservoirs as a method for improving the trophic state downstream.- Concluding Remarks.- Summaries and Abstracts.- The effect of pig manure and mineral fertilization on a eutrophic lake ecosystem.- Hypertrophy in slow flowing rivers.- CO2-uptake as a measure of bacterial production.- Response of shallow hypertrophic lakes to reduced nutrient loading.- Fish as a regulator of structure and function in eutrophic lake ecosystems.- Algenbekämpfung durch Zusatz von Kalk und Dolomithydrat.- Possible triggering mechanisms for the collapse of Aphanizomenon-flos-aquae blooms.- Self-purification and respiration in polysaprobic area of natural flowing waters receiving raw domestic sewage.- Short-circuit metabolism in highly eutrophic lakes - relationship between primary production and decomposition rates.- Heterotrophic functions in the freshwater carbon cycle.- Effects of temperature and temperature-nutrient interactions on phytoplankton growth.- Natural and induced sediment rehabilitation in hypertrophic lakes.- Aspects of biological competition between Stigeoclonium tenue and Cladophora glomerata, two filamentous green algae, characteristic of eutrophic waters.- Seasonal succession and standing crop determinations of the epiphytic algae in two hypertrophic lakes.- Nitrogen transformations in artificial loaded limnocorrals.- Zur quantitativen Bestimmung der potentielle Bioproduktion in aquatischen Ökosystemen mittels Algentest.