Temporal discontinuity of nutrient limitation in plankton communities |
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| Authors: | John-Mark Davies Weston H Nowlin Blake Matthews Asit Mazumder |
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| Institution: | (1) Water and Watershed Research, Department of Biology, University of Victoria, P.O. Box 3020, Stn. CSC, Victoria, BC, V8N 3N5, Canada;(2) Saskatchewan Watershed Authority, #101-108 Research Drive, Saskatoon, SK, S7K 2H6, Canada;(3) Department of Biology, Aquatic Station, Texas State University, 601 University Drive, San Marcos, TX 78666, USA;(4) Department of Aquatic Ecology, Eawag, Seestrasse 79, 6047 Kastanienbaum, Switzerland |
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| Abstract: | Ideas on how various measures of nutrient limitation relate to plankton biomass and species composition are re-examined. While
long-term and multi-lake studies typically focus on determining overall biomass, seasonal studies are more focused toward
understanding species composition. We use physiological assays to assess short-term nutrient deficiency of nitrogen and phosphorus
in two moderately fertile lakes. While biomass in the lakes was considered to ultimately be limited by total phosphorus, nutrient
assays were variable in time. Nutrient ratios (TN:TP, PN:PP, PC:PP and PC:PN) did not predict short-term deficiencies, notably
that nitrogen deficiency occurred in these phosphorus-limited lakes. In one of our study lakes, there was a relaxation of
phosphorus deficiency despite phosphate concentrations occurring below traditional detection limits. Following this period,
there was an autumn bloom of Aphanizomenon flos-aquae. This relationship corresponds with other studies that have found A. flos-aquae to be a poor competitor for phosphorus. In contrast, phosphorus deficiency remained high prior to the autumn diatom bloom
in our other study lake. Deficiency measures remain an excellent means of assessing physiological status of plankton communities
and provide greater insight into species compositional changes, especially when other potential indicators like dissolved
nutrient concentrations are inconclusive. Regardless of the nutrient limitation indicator used for a given study, it is critical
to consider the appropriate scale of the measure. |
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