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The effects of nitrogen/ phosphorus ratios on the prediction of chlorophyll in phosphorus-limited lakes in Central Ontario

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Title: The effects of nitrogen/ phosphorus ratios on the prediction of chlorophyll in phosphorus-limited lakes in Central Ontario
Author: Dillon, P. J.; Reid, R. A.; Molot, Lewis A.
Abstract: The response of mean annual ice-free chlorophyll a in 15 stratified, P-limited oligotrophic and mesotrophic lakes in central Ontario to changes in mean epilimnetic total phosphorus (TP) within a lake was highly variable between years during the period 1976 to 1987. The linear regression coefficient of determination, R2, using all annual means was only 0.36 (n = 172 lake-years) and within-lake regressions revealed mostly random associations between chlorophyll a and TP, suggesting fluctuations about steady state levels. Nevertheless, by using the long-term average of annual means for each lake, a bivariate linear regression model was developed relating the long-term, average response of chlorophyll a to the long-term, average TP concentration in these lakes (R2 = 0.78). Annual variation could not be explained by changes in TN/TP. R2 increased slightly from 0.78 to 0.82 with TN/TP as a second independent variable using long-term averages but remained at 0.78 with 1/TP as a second variable. Re-analysis of published data excluding lakes which were not P-limited showed that TN/TP is of little or no benefit as an independent variable. A minimum of 6 consecutive years of sampling was required to avoid anomalously poor fits (defined as R2 < 0.6) for this set of lakes. Therefore, chlorophyll a/TP regression models should be viewed as steady state models with an inherent inability to predict annual variation.
URI: http://hdl.handle.net/10214/15771
Date: 1991
Rights: Queen's Printer for Ontario, Crown Copyright, Non-Commercial Use Permitted
Rights Holder: Queen's Printer for Ontario


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