Disentangling the effects of climate change and reoligotrophication on primary production in a large lake

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1007/s00027-022-00910-2. This is version 1 of this Preprint.

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Authors

Shubham Krishna, Hugo Nicolás Ulloa , Emile Barbe, Alfred Wüest

Abstract

Climate change and reduction in nutrient loads have significant effects on primary production and phytoplankton growth dynamics. Since in the last few decades in many regions, nutrients in lakes were reduced simultaneously as the climate changed. Yet, it remains unclear which of the two has impacted primary production the most. In this study, we couple the General Ocean Turbulence Model with the Ecological Regional Ocean Model to disentangle the effects of climate change and reoligotrophication on primary production (PP) in Lake Geneva, Switzerland-France. We apply a data assimilation method to calibrate the model with the observations from the past (1981-1990) and validate it against the in-situ data from the present decade (2011-2019). Both decades represent different climate conditions and trophic states of the lake.
We show that the model is skilful to reproduce assimilated and unassimilated observations from both periods. According to our results, the effect of reoligotrophication on PP is marginally higher than that of warming, leading to a net decrease in primary production by 10% from the past to the present. The areal phosphorus supply in Lake Geneva, in spite of a decrease by 70%, is still characteristic of a meso-to-eutrophic ecosystem. This points towards an incomplete reoligotrophication of the lake. The effects of future climate change on winter mixing and PP dynamics have also been studied. Although there would be a significant reduction in deep mixing, the autotrophic production in Lake Geneva is expected to increase by 20% by the end of 21st century, largely due to stimulation in biomass build-up of temperature-dependent algae (e.g. dinoflagellates and cyanobacteria).
Considering our results to represent other large temperate lakes with similar trophic status and water residence time as Lake Geneva, future climate scenarios are expected to bring back symptoms of eutrophication.

DOI

https://doi.org/10.31223/X5RH25

Subjects

Earth Sciences, Ecology and Evolutionary Biology, Environmental Sciences

Keywords

eutrophication, oligotrophication, global-warming, climate change, carbon fixation, phytoplankton, mixin, trophic-status, nutrient-supply

Dates

Published: 2022-11-17 12:37

Last Updated: 2022-11-17 17:37

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
The observations analysed in this study are available at https://si-ola.inrae.fr. The model data is available on request to the corresponding author.

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