Bimodality and alternative equilibria do not help explain long-term patterns in shallow lake chlorophyll-a

Thomas A. Davidson, Carl D. Sayer, Erik Jeppesen, Martin Søndergaard, Torben L. Lauridsen, Liselotte S. Johansson, Ambroise Baker, Daniel Graeber

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Abstract

Since its inception, the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider range of ecological and socioecological systems. The theory posits the existence of two alternative stable states or equilibria, which in shallow lakes are characterised by either clear water with abundant plants or turbid water where phytoplankton dominate. Here, we used data simulations and real-world data sets from Denmark and north-eastern USA (902 lakes in total) to examine the relationship between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentrations across a range of timescales. The data simulations demonstrated that three diagnostic tests could reliably identify the presence or absence of alternative equilibria. The real-world data accorded with data simulations where alternative equilibria were absent. Crucially, it was only as the temporal scale of observation increased (>3 years) that a predictable linear relationship between nutrient concentration and chlorophyll-a was evident. Thus, when a longer term perspective is taken, the notion of alternative equilibria is not required to explain the response of chlorophyll-a to nutrient enrichment which questions the utility of the theory for explaining shallow lake response to, and recovery from, eutrophication.

Original languageEnglish
Article number398
JournalNature Communications
Volume14
Issue number1
DOIs
Publication statusPublished - 25 Jan 2023

Bibliographical note

Funding Information:
C.D.S. and T.A.D. would like to thank June and Derek Sayer for extraordinary support over many years. The authors of this work have been supported by a number of projects over the elephantine gestation period of this manuscript. These include support from the Poul Due Jensen Fonden, Danmarks Frie Forskningsfond Natur og Univers project GREENLAKES (No. 9040-00195B) and the UFM-funded project LTER_DK for Long Term Ecosystem Research in Denmark. In addition, support was provided by The European Union’s Horizon 2020 research and innovation programmes under grant agreement No 869296—The PONDERFUL Project”, TREICLAKE under grant agreement No 951963, and the AQUACOSM project and by the European Commission EU H2020-INFRAIA-project (No. 731065) and AQUACOSM plus (No. 871081). E.J. was also supported by the TÜBITAK outstanding researcher programme 2232 (project 118C250) and AnaEE, Denmark. The work of D.G. was funded by the Fourth Period of Programme-oriented Funding, Helmholtz Association of German Research Centres, Research Field Earth and Environment.

Publisher Copyright:
© 2023, The Author(s).

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