Nutrient limitation in relation to phytoplankton carotenoid/chiorophyll a ratios in freshwater mesocosms |
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| Authors: | Schituter Louise; Riemann Bo; Sondergaard Morten |
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| Institution: | The International Agency for 14 Determination, VKI Water Quality Institute Agern Allé 11, DK-2970 Hørsholm, Denmark
1Present address: National Environmental Research Institute, Department of Marine Ecology and Microbiology PO Box 358, DK-4000 Roskilde
2Freshwater Biological Laboratory, University of Copenhagen Helsingørsgade 51, DK-3400 Hillerød, Denmark |
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| Abstract: | The 480/665 nm absorption ratio for pigment extracts was evaluatedas an indicator of nutrient limitation using freshwater planktoncommunities and a mesocosm approach. The mesocosm design wasused to create various nutrient regimes for the phytoplanktoncommunities, and nutrient limitation was detected by means ofgrowth response assays (14 fixation and pigment increase followingaddition of nutrients) and the 480/665 ratio. Results from fourperiods in 1993 and one period in 1994 showed that high 480/665ratios (indicative of nutrient limitation) were only found atchlorophyll a concentrations <20 µg I–1, wherenutrient limitation was not detected. Periods with potentialnutrient limitation exhibited low 480/665 ratios. Consequently,the absolute values of the 480/665 ratio could not be used topredict nutrient limitation. However, when nutrients were addedto nutrient- limited phytoplankton communities in growth responseassays, the ratio decreased, indicating that the 480/665 ratiocan be used as a relative index to detect nutrient limitationin bioassays. |
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