Cécile Figus

Françoise Chalié

Christine Paillès

Sandrine Conrod

Marta Garcia Molina

Frédéric Guiter

Jean-Charles Mazur

Laurence Vidal

Reconstruction of limnological and environmental variations in the lake Lauzet (Southern Alps) during the last 3 centuries : contribution of diatoms

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Alpine lakes are particularly sensitive to climatic and environmental variations (Cartier et al., 2015): the study of lake sedimentary records allows to reconstruct the evolution of the lake and its catchment area.

Diatoms are micro-algae that are sensitive to variations in the physico-chemical parameters of the water. Combined with a very short residence time, this capacity enables diatoms to be very good bioindicators.

A sediment core was taken from the Lake Lauzet (890 m altitude), in the Alpes de Haute-Provence (PACA, France). This lake of glacial origin is located downstream of sentinel lakes: those are preserved from anthropic pressures, and has a sedimentary ll of over 15 m in depth. However, at the Lake Lauzet, numerous developments of the lake and his catchment area have taken place since 1702.

The DURANSED project, started in 2019, has enabled the coring of the lake (mastercore Lau19). Other cores and samples were taken by OSU Pythéas students.

Context:

Objectives:

-Reconstruct the limnological and environmental variations of the lake.

-Show the impact of Humans on the lake and is catchment area during the last three centuries.

-Show that diatoms are good bioindicators of the Actual variations of the physico-chemical parameters of the lake, and of the impact of Humans; but also of past environmental variations.

Results and interpretations:

Results of the Actual samples study:

-47 species dertermined and counted -2 dominant species :

  Pantocsekiella delica- tula (Hustedt) Kiss & Ács and Staurosira lap- ponica Lange-Bertalot -Rare cysts of chrysophytes -pH between 8 and 9 Notes and interpretations: -Actual dominant species identical to those in fossil Zone 1b : the species living in and around the lake are well deposited in the sediment -Dominant species are neutrophilic and alkaliphilic, which corresponds to the pH of the lake (8 to 9) -Diatoms and mineral indicators show numerous anthropic pressures Conclusion: -The self-ecology of the species translates well the characteristics of the environment on the present, and can be used on the fossil to reconstruct the past environment -Anthropic pressure detected by both diatoms and mineralogical indicators (XRF) -Since the 2000s, improvement of the ecological state of the lake: possible awareness on the preservation of the environment? Perspectives: -More dating at the base of the core -Pollen analysis (watershed plant colonization, aquatic plants) -Temporal resolution: more accurate analyses -Application of transfer functions to quantify past pH and trophy -Coring of a longer slice of sediment, and therefore time 2020 P l a n k t o n i c T y c h o p l a n k t o n i c B e n t h i c E p i p h y t i y s o p h y t e s O l i g o t r o p h i c t o m e s o t r o p h i c M e s o t r o p h i c M e s o t r o p h i c t o e u t r o p h i c E u t r o p h i c T r o p h y -t o l e r a n t U n k n o w n t r o p h y O l i g o t r o p h i

  Reconstruction of limnological and environmental variations in the lake Lauzet (Southern Alps), during the last 3 centuries: contribution of diatoms Cécile Figus 1 , Françoise Chalié 1 , Christine Paillès 1 , Sandrine Conrod 1 , Marta Garcia 1 , Frédéric Guiter 2 , Jean-Charles Mazur 1 & Laurence Vidal 1 1 Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE), Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France Europôle Méditerranéen de l'Arbois, BP 80, 13545 Aix-en-Provence cedex 4, France 2 Institut Méditerranéen de Biodiversité et d'Ecologie Marine et Continentale (IMBE), Aix Marseille Univ, Avignon Université, CNRS, IRD, Aix en Provence, France

			Diatom sampling
			Core drilling:
			Lau19 (2019)
			Lau4 (2018)
			3% 2%
		20%
			43%
		29%
			3%
	6%	4%
	12%
	3%
			Achnanthidium minutissimum
			Cyclotella distinguenda
		76%	Pantocsekiella delicatula Pseudostaurosira bardii
			Staurosira lapponica
			Others
			10 µm	10 µm

PACA