are considered quantitatively and qualitatively and within awiderangeofspatialand time scales. The hydrological studies in the interdisciplinary The present hydrological situation in the area workgroup WQL (Water Quality research Loos is the result of a complex sequence of events of drecht lakes) on restoration of the Loosdrecht natural and man-made origin. The present distri Lakes have been carried from 1982-1988 (Kal bution of nutrients in the water systems of the et al. , 1984; Engelen & Kal, 1985; Kal, 1986). The area can be understood only when the hydrolog aim of the study was to provide an integrated ical history is traced back. One has to start at the description of the abiotic part of the water sys beginning of the Holocene period and to follow tems and its contribution to thefunctioningofthe up closely the increasing interference of man. aquatic ecosystems in the Loosdrecht Lakes (En Overthelastcenturies and decades man has been gelen, 1986). changing the flow systems around the lakes by Theresults hadto servethefollowingpurposes: digging peat, draining lakes, extracting ground water, maintaining fixed surface water levels in General framework. The integrated hydrological polders and transferring water from adjacent riv studies had to provide a general frame of refer ers and canals to supply the lakes to maintain ence for the other project participants represent their water levels.

Zusammenfassung
Proceedings of a Conference held in Amsterdam, The Netherlands, 18-19 April, 1991

Inhalt
one: Aspects of water quality research in Loosdrecht lakes.- Working group Water Quality Research Loosdrecht Lakes: its history, structure, research programme, and some results.- The state of the environment of the Loosdrecht lakes.- The hydrology of the Loosdrecht lakes area.- Phosphorus in the sediment of the Loosdrecht lakes and its implications for lake restoration perspectives.- Coupling of phytoplankton and detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands).- Dynamics of phytoplankton detritus in a shallow, eutrophic lake (Lake Loosdrecht, The Netherlands).- The dynamics and role of limnetic zooplankton in Loosdrecht lakes (The Netherlands).- P-load, phytoplankton, zooplankton and fish stock in Loosdrecht Lake and Tjeukemeer: confounding effects of predation and food availability.- Restoration and resilience to recovery of the Lake Loosdrecht ecosystem in relation to its phosphorus flow.- Multivariate analysis of the plankton communities in the Loosdrecht lakes: relationship with the chemical and physical environment.- A mathematical model of the phosphorus cycle in Lake Loosdrecht and simulation of additional measures.- Remote sensing as a tool for assessing water quality in Loosdrecht lakes.- Water quality research in the Loosdrecht lakes: proposals for the follow-up restoration measures.- The significance of the Loosdrecht lakes research project for eutrophication policy in the Netherlands.- Water quality research in Loosdrecht lakes: the salient features.- Publications of the workgroup WQL (Water Quality Research Loosdrecht Lakes) 1983 - present.- two: Eutrophication research in The Netherlands, with emphasis on additional measures.- The influence of flushing on nutrient dynamics, composition and densities of algae and transparency in Veluwemeer, The Netherlands.- Lake restoration with and without dredging of phosphorus-enriched upper sediment layers.- Fixation of phosphorus in lake sediments using iron(III)chloride: experiences, expectations extended abstract).- Fisheries management as an additional lake restoration measure: biomanipulation scaling-up problems.- The effects of dredging and fish stocking on the trophic status of shallow, peaty ditches.- Eutrophication control strategies for three shallow Vecht lakes in the province of North Holland.- Restoration of fen ecosystems in the Vecht River plain: cost-benefit analysis of hydrological alternatives.- Phosphorus eutrophication in the SW Frisian lake district. 1. Monitoring and assessment of a dynamic mass balance model.- Phosphorus eutrophication in the SW Frisian lake district. 2. Phosphorus balances and simulation of reduction scenarios.- Three: Europhication control in The Netherlands.- Restoration and recovery of shallow eutropic lake ecosystems in The Netherlands: epilogue.