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Aquatic plant dynamic and fishes over the last 1800 years in the Lake Aiguebelette (Northern French Alps)
Abstract
Watersheds of large peri-alpine lakes have undergone substantial demographic and urban developments (leading to the release of waste waters, containing nitrates and phosphates), as well as agricultural activities intensification (use of fertilizers) during the 20th century. The seasonal fluctuations of their water levels is often reduced and controlled to generate hydroelectric power or to reduce flooded areas. Furthermore, these lakes host fishing activities, often for commercial purpose. These pressures, combined with global warming, significantly impacted the aquatic ecosystems especially through the eutrophication process and modifications of the trophic web.
In order to understand such limnological changes, several peri-alpine lakes are monitored for several decades. However, this instrumental monitoring does not allow the assessment of the ecosystem state before the anthropisation acceleration. Lake sediment cores represent relevant archives to fill this gap. Geochemical analyses and biotic remains preserved in lake sediments can be used to reconstruct the past long-term trajectories of aquatic ecosystems.
However, up to now, palaeoecological studies undertaken on lake sediments were only focused on phytoplankton, zooplankton, chironomids or microbial communities, but nor on aquatic plant community, nor on fishes. For fishes, this lack is explained by the absence (or rare presence) of fossils preserved in the sediments and for aquatic plants by a limited detection by pollen analyses. Environmental DNA preserved in the sediment offers a unique opportunity to address these challenges.
In this paper, the DNA metabarcoding approach is used to identify past aquatic plants and fishes living over the last 1800 years in the Lake Aiguebelette (390 m a.s.l., 5.45 km 2 lake surface area, 70 km 2catchment area, 73m deep). The most significant result is the evidence of interactions between aquatic plants and fishes. Roach, a fish species which has a preference for aquatic grass habitats, appears from 1000 years AD, i.e. when the diversity and biomass of aquatic plants highly increase. This change also corresponds to the development of mesotrophic conditions due to the intensification of the livestock farming.
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Messager Erwan, Giguet-Covex Charline, Doyen Elise, Etienne David, Gielly Ludovic, Sabatier Pierre, Banjan Mathilde, Develle Anne-Lise, Didier Julien, Poulenard Jérôme, Julien Andréa, Arnaud Fabien. Two Millennia of Complexity and Variability in a Perialpine Socioecological System (Savoie, France): The Contribution of Palynology and sedaDNA Analysis. Frontiers in Ecology and Evolution. Vol. 10:2022. Frontiers Media SA. [Cross Ref]