Reduction of Cladophora Biomass and Tissue Phosphorus in Lake Ontario, 1972–83

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Abstract
Cladophora biomass and tissue phosphorus concentrations at seven sites in Lake Ontario have decreased from 1972 to 1983 in response to phosphorus control programs introduced in the early 1970's. Biomass and tissue phosphorus were significantly different between 1972 and 1982–83 (ANOVA, P < 0.001) but not significantly different between 1982 and 1983. The lakewide average tissue phosphorus was 0.49% in 1972 but by 1982 and 1983 had dropped to 0.26 and 0.20%, respectively, on an ash-free dry weight basis. Tissue phosphorus concentrations did not limit growth in 1972 but in 1983 had begun to limit growth. Model-predicted net production for a 6-wk sampling period in 1983 was 1.7 times greater in the western end of the lake than at a remote site in eastern Lake Ontario due to higher soluble reactive phosphorus concentrations.
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