Temporal and vertical dynamics of phytoplankton net growth in Castle Lake, California |
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Authors: | Huovinen P; Brett M; Goldman C |
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Institution: | Department of Environmental Science and Policy, University of California, Davis, CA 95616, USA; Present address: University of Jyvaskyla, Department of Biological and Environmental Science, PO Box 35, FIN-40351 Jyvaskyla, Finland; Present address: Department of Civil and Environmental Engineering, University of Washington, Box 352700, Seattle, WA 98195, USA |
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Abstract: | The impact of nutrient additions, zooplankton grazing and light intensity
on phytoplankton net growth with depth and season was studied with five
microcosm experiments in meso-oligotrophic, subalpine Castle Lake,
California, during the period of summer stratification in June-September
1994. The incubations (4 day) were performed at 5 m intervals from the
surface to the bottom using natural phytoplankton and zooplankton
assemblages, with enrichments of phosphorus and nitrogen. The phytoplankton
community was only limited by nutrients in the upper 5 m (epilimnion), as
indicated by change in chlorophyll concentration. Nutrient enrichments had
the greatest effect on the phytoplankton net growth in June and July. High
light inhibited the phytoplankton net growth at the surface. Low light
intensities limited phytoplankton at 20 m and below, and at the end of the
growing season already around 10-15 m. A deep chlorophyll maximum in the
hypolimnion in June-August was not limited by either light or nutrients.
The results showed variation in grazers' impact on phytoplankton. These
results suggest the importance of nutrient limitation only in the
epilimnion with light inhibition at the surface, light limitation in the
hypolimnion, and varying impact of zooplankton grazing in influencing the
development of the phytoplankton in Castle Lake.
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