DECREASED PHOSPHORUS LOADING CHANGES PHYTOPLANKTON COMPOSITION AND BIOMASS IN THE STOCKHOLM ARCHIPELAGO
The Stockholm archipelago has been used as a receiver for waste water for several decades. During 1968-73 the waste water treatment was improved, after which the phosphorus load significantly decreased. Since 1970 concentrations of nitrogen, phosphorus and other hydrographical parameters were measured along the eutrophication gradient from Stockholm. Quantification of cyanobacteria and chlorophyll a were also carried out. The improved waste water treatment resulted m a strong reduction in the total P concentrations in the surface water of the archipelago, e.g. from 170 to 40 μg/l as a mean during June-September in the area south of Lidingö. There is also an obvious decrease in the phosphate concentration but an increase in mineral nitrogen. The inorganic mean N/P ratio (June-September) has increased from 1/1 to 20-40/1 and phosphorus has replaced nitrogen as the most limiting nutrient throughout the entire archipelago within about 50 km from Stockholm. “Complete abstract not presented.”