Use of sedimentary pigments to infer past phosphorus concentration in lakes |
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| Authors: | Piero Guilizzoni Aldo Marchetto Andrea Lami Stefano Gerli Simona Musazzi |
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| Institution: | (1) CNR-Istituto per lo Studio degli Ecosistemi, Largo Tonolli 50, 28922 Verbania Pallanza, Italy |
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| Abstract: | We propose a palaeolimnological method for inferring past total phosphorus (TP) concentrations in lake water from spectrophotometrically-measured
sedimentary pigments, particularly total carotenoids (TC). Our approach is based on a highly significant statistical correlation
(P < 0.0001) between pigment concentrations (total carotenoids) in the surface sediment of 28 Italian lakes (subalpine, large,
deep, shallow, volcanic) and TP concentrations measured in these lakes at overturn when the core was collected. A transfer
function was developed from this “training” set, and used to estimate past TP concentrations from pigment concentrations in
sediment cores. The results generally agreed with TP values as measured by long-term water quality monitoring programs. Contrasting
results were obtained by a comparison with diatom-inferred TP. While the diatom model showed a tendency to overestimate TP
values higher than 100 μg l−1, the pigment model correctly estimated TP in lakes when TP was <100 μg l−1, but not when lakes were rich in macrophytes. In fact, lakes with extensive populations of aquatic submersed macrophytes
and epiphytes are outliers in terms of the TC versus TP relationship. The root mean square error of prediction of the pigment
model is lower than those derived from certain diatom—based inference models. The predicted and residual values are not related
to the estimated values and their average is not statistically different from zero. Errors were estimated via a ‘leave-one-out’
re-sampling technique. The proposed method permits rapid and relatively inexpensive determination of reference trophic conditions. |
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