A diatom-based inference model for autumn epilimnetic total phosphorus concentration and its application to a presently eutrophic boreal lake |
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Authors: | Tommi Kauppila Teppo Moisio Veli-Pekka Salonen |
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Affiliation: | (1) Department of Geology, University of Turku, FIN-20014 Turku, Finland;(2) Geological Survey of Finland, P.O. Box 96, FIN-02151 Espoo, Finland;(3) Golder Associates Oy, Ruosilankuja 3E, 00390 Helsinki, Finland |
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Abstract: | A diatom transfer function to infer epilimnetic total phosphorus (TP) concentration was derived using surface sediment diatom data from 68 medium-sized (10–1000 ha) lakes in Southern Finland. Publicly available monitoring records were used in lake selection to avoid gradients caused by pH and humic substances. Constrained and partially constrained ordinations indicated that TP was an important variable influencing diatom assemblages. A long floristic gradient in relation to TP was also apparent and therefore an inference model was developed for TP using unimodal-based regression and calibration methods. The final model included 61 lakes with epilimnetic TP concentrations between 3 and 89 g P l–1, measured during the autumnal circulation period. It has a jackknifed-estimated root mean squared error of prediction of 0.16 log g P l–1, a maximum bias of 0.28 log g P l–1, and an r2jack of 0.76.The model was tested in the presently eutrophic Lake Valkjärvi (epilimnetic [TP] 60–85 g P l–1), located in Southern Finland. It successfully predicted the measured autumnal epilimnetic TP concentration for the past twenty years and the changes in inferred [TP] reflected disturbances known to have occurred before that time. The diatom-based inferences show that Lake Valkjärvi was oligo-mesotrophic as late as the 1930's and has become eutrophic because of nutrient inputs from agriculture and, especially, municipalities. However, epilimnetic TP concentration has not increased further. |
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Keywords: | diatoms weighted averaging total phosphorus inference model Finland |
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