Nutrient enrichment experiments in three central Florida lakes of different trophic states |
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Authors: | Bruce C Cowell Clinton J Dawes |
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Affiliation: | (1) Department of Biology, University of South Florida, 33620 Tampa, Florida, USA |
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Abstract: | Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic
states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated
in situ in clear polyethylene bags for 3 to 6 days. The 25 factorial design employed two levels (ambient and enriched) of each of five nutrients NH4
+, PO
inf4
sup3−
, Fe− -EDTA, SiO
inf3
sup2−
and a cation (Ca2+ or K+) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the
eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll
a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative
effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions
were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible
for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors
and predictive models. |
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Keywords: | chlorophyll a phytoplankton nutrient enrichment seasonal variation subtropical lakes |
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