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Effects of Fertilization and Planktivorous Fish (Yellow Perch) Predation on Size Distribution of Particulate Phosphorus and Assimilated Phosphate: Large Enclosure Experiments

A. Mazumder, D. J. McQueen, W. D. Taylor and D. R. S. Lean
Limnology and Oceanography
Vol. 33, No. 3 (May, 1988), pp. 421-430
Stable URL: http://www.jstor.org/stable/2837015
Page Count: 10
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Effects of Fertilization and Planktivorous Fish (Yellow Perch) Predation on Size Distribution of Particulate Phosphorus and Assimilated Phosphate: Large Enclosure Experiments
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Abstract

Nutrients, planktivorous fish (1 + yellow perch), or both were added to eight large enclosures in a 2 × 2 factorial design. The size distributions of particulate phosphorus (PP) and assimilated 32 PO4 3- and PO4 3- turnover times were determined from June through August by filter fractionation. The amount of $PP>200 \mu m$ (mesoplankton) increased with fertilization and decreased with addition of fish, but the amount of PP in nanoplankton (3-20 μ m) and large picoplankton (1-3 μ m) showed opposite results. Fertilization and addition of fish had interacting effects on the PP in microplankton (20-200 μ m). Microplankton phosphorus was higher with fish in unfertilized enclosures and lower with fish in fertilized enclosures. Slopes estimated from the relationship between the proportion of PP retained and the logarithm of filter size were used to characterize the size spectra of plankton and were lower with fertilization and steeper with addition of fish. They were negatively correlated with PO4 3- turnover time, reflecting that plankton communities dominated by small cells were more nutrient limited. The slope parameter was also significantly correlated with water clarity (Secchi depth) and algal biomass (Chl a), but particle size distribution contributed to water clarity independent of biomass or pigment concentration. This slope parameter can be used as a convenient indicator of plankton size spectra and trophic interactions in freshwater ecosystems.

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