Warming-induced release of benthic nutrients in mountain lakes: an incubation experiment

Mountain lakes are generally extremely oligotrophic, which limits the production of aquatic biomass and gives them the crystal-clear waters that make them popular tourist destinations. Recently, stakeholders involved in the French Lacs Sentinelles network (https://www.lacs-sentinelles.org) have observed a proliferation of benthic algae in the littoral zones of high-altitude lakes. These observations echo recent studies documenting a proliferation of benthic algae in many oligotrophic lakes around the world, whether located in lowlands or in mountains^1,2. Among the various hypotheses proposed to explain this phenomenon, the interaction between the pronounced warming of high-altitude lakes and nutrients’ cycling is to date the most likely explanation yet to be tested^3,4.  Here, we test whether the increasing temperature of littoral zones in mountain lakes can trigger the release of nutrients contained in sediments to the water column. In spring 2025, littoral sediment cores were collected before ice melt in two mountain lakes (one forested, one proglacial) in the French Alps and brought back to the lab. The cores were then either submitted to increasing temperatures in a ~2-week incubation experiment (n=4, treatment group) or kept cold (n=4, control group) and were analyzed for the chemical composition of the overlying water at regular intervals. Increasing temperature induced a significant release of sediment ammonium to the overlying water for the forested lake, but not for the proglacial lake. Both lakes exhibited similarly decreasing nitrate concentration with warming, but no significant evolution of phosphate was measured. Analysis of the temperature sensitivity (Q10) of sediment microbial respiration revealed a significant temperature influence for the forested lake (Q10=2) but not for the proglacial lake (Q10≤1). These preliminary results highlight the potential importance of temperature as a driver of nutrient cycling in littoral sediments of mountain lakes. 1.         Vadeboncoeur, Y. et al. Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide. BioScience 71, 1011–1027 (2021). 2.         Oleksy, I. A., Baron, J. S., Leavitt, P. R. & Spaulding, S. A. Nutrients and warming interact to force mountain lakes into unprecedented ecological states. Proc. R. Soc. B. 287, 20200304 (2020). 3.         Oleksy, I. A., Baron, J. S. & Beck, W. S. Nutrients and warming alter mountain lake benthic algal structure and function. Freshwater Science 40, 88–102 (2021). 4.         Hampton, S. E. et al. Warming-induced changes in benthic redox as a potential driver of increasing benthic algal blooms in high-elevation lakes. Limnology and Oceanography Letters 9, 1–6 (2024).

Presentation Preference: No Preference

Primary Presenter: Ilann Bourgeois, USMB (ilann.bourgeois@univ-smb.fr)

Authors:

Ilann Bourgeois, USMB  (ilann.bourgeois@univ-smb.fr)

Romane Bernard--Coquard, USMB  (romane.bernard-coquard@laposte.net)

Maria Page, USMB  (maria.page@univ-smb.fr)

Florent Arthaud, OFB  (florent.arthaud@univ-smb.fr)

Jeremy Puissant, CNRS  (jeremy.puissant@univ-grenoble-alpes.fr)

Cindy Arnoldi, UGA  (cindy.arnoldi@univ-grenoble-alpes.fr)

Marine Souchier, USMB  (marine.souchier@univ-smb.fr)

Jean-Christophe Clément, USMB  (jean-christophe.clement@univ-smb.fr)