Oligotrophication outweighs effects of global warming in a large,deep, stratified lake ecosystem |
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Authors: | H. B. STICH ALEXANDER BRINKER |
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Affiliation: | 1. Institute for Lake Research – State Institute for Environment, Measurement and Nature Conservation of Baden‐Württemberg, Argenweg 50/1, 88085 Langenargen, Germany;2. Fisheries Research Station of Baden‐Württemberg, Argenweg 50/1, 88085 Langenargen, Germany |
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Abstract: | Between 1951 and 1979, total phosphorous concentrations in Lake Constance increased from 7 to 87 μg L?1. Following wastewater treatment, phosphorus levels were brought under control, returning to 7.6 μg L?1 by spring 2007. The biological and chemical data from 1980 to 2004 were first modelled by seasonal time series analyses and then used to create a general model. Excluding collinear variables allowed the data set to be condensed to six variables that could be fitted into a general linear model that explained ~75% of the observed annual variation in chlorophyll a. A clear seasonal influence was apparent, with chlorophyll a tracking trends in temperature and the progress of spring. A nonseasonal influence was also observed in the interaction of two biological components, the proportion of phytoplankton biomass available to Daphnia (i.e. the percentage of ingestible size <30 μm) and the grazing intensity. In combination, these biotic variables had a negative impact on chlorophyll a levels. In contrast, the concentration of soluble reactive phosphorus (SRP) correlated positively with chlorophyll a. The effect of SRP showed a significant seasonal component, as it was more abundant in spring than at other times of year. In general, the model predicts a negative exponential response of chlorophyll a to further depletion of SRP in Lake Constance, while the temperature trends predicted by current global warming scenarios will result in a moderate increase in productivity. Data from 2005 to 2007 were used to verify the model. The modelled chlorophyll a values were nonbiased and showed a close match to the measured values (r2: 75%). Thus the applicability, reliability, and informative value of the model for pelagic Lake Constance was confirmed. The approach might easily be applied to other waters. |
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Keywords: | chlorophyll climate change Daphnia grazing lake management oligotrophication phosphor time series modelling |
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