Freshwater ecosystems produce, degrade, store and exchange carbon with the atmosphere1,2,3. Many freshwater lakes are supersaturated in CO2 with respect to the atmosphere that makes them a significant source of atmospheric carbon. Degradation of organic C can be further mediated by anaerobic processes, such as in lake sediments, including methanogenesis, which contribute to the emission of methane (CH4) and CO2 to the atmosphere. Numerical process-based lake models can be used to simulate both the organic and inorganic pools of carbon in lakes and can document exchanges with atmosphere. One dimensional models have been widely implemented over the last years4–6, but most of these models are calibrated and validated against very few years of instrumental data, potentially limiting the robustness in long-term reconstructions and preventing inclusion of future scenarios. To analysis the long-term variability and the effects of climate change on inorganic carbon and methane flux of deep hard-water lakes, the successful candidate will rely on the Aquatic Ecodynamics model (AED; aed_carbon module) and on pluri-decadal series of limnological data collected by the French Observatoire des LAcs (OLA). Eventually, model simulations will be further constrained with published paleolimnological records of oxygen conditions7,8 and primary productivity for the past 300 years. Altogether, the 1D model approach will help at quantifying trends in CO2 CH4 flux in perialpine lakes over the period 1850-2100. The project will seek ultimately to transfer knowledge from model simulations to lake managers to anticipate future changes in perialpine lakes geochemical conditions as well as in services that depend on it.

Expected results:
1. Lake model simulating CO2 and CH4 dynamics for a deep perialpine lake
2. Model calibration and validation with comprehensive measurements of sediment and/or water column CO2 concentration.
3. Improved validation of 1D model approaches with long-term limnological data and paleolimnological records
4. Recommendations for lake managers

Host institution:
The INRAE CARRTEL Center, Technolac, Bourget du lac, France, is a leading limnological institute with a large, diverse and welcoming community of researchers, students, and support staff. CARRTEL contributes to the understanding of how human and climate change affect fundamental resources and ecological functions within lake systems and their watersheds, and how this affects ecosystem services like food, drinking water, biodiversity, maintenance of aquatic fauna and flora, water flow regulation, transfer and sequestration of nutrient or pollutants. CARRTEL has two locations: Technolac campus near Lake Bourget (URL), and a limnological station near Lake Geneva. At the institution level, various in-house technical groups will support the project. In Technolac, the project will be supported by shared analytical platforms, with computing facilities including a shared storage capacity raid and the MUST High Performance Computer cluster. The successeful candidate will be fully integrated into the institute, and benefit from full participation in various interactions facilitated by seminar programs, discussion groups and lab meetings, as well as monthly interdisciplinary keynotes given by high-profile researchers.

Specific requirements
• Technical Skills required: Good programming skills in typical scientific programming languages (e.g., Python, R, etc.). Willingness to face complex modelling problems. Ability with mathematics and statistics are essential. Basic knowledge about physical and/or biogeochemical processes affecting water systems.
• Proficiency in the English language is desires, as well as good communication skills, both oral and written.

Conditions
Funder: French National Agency of Research (ANR)
Duration: Fulltime employment contract for 6 months
Deadline for application: December 15, 2021
Start of contract: January/February 2022
Supervisors: Dr Jean-Philippe JENNY (INRAE), Dr Emilie Lyautey (USMB), Dr Brigitte Vinçon-Leite (LEESU)

Enquires
For additional information on this project, please contact Dr Jean-Philippe JENNY
[email protected]

References
1. Cole, J. J. et al. Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget. Ecosystems 10, 172–185 (2007).
2. Abril, G. & Borges, A. V. Ideas and perspectives: Carbon leaks from flooded land: do we need to replumb the inland water active pipe? Biogeosciences 16, 769–784 (2019).
3. Tranvik, L. J. et al. Lakes and reservoirs as regulators of carbon cycling and climate. Limnology and Oceanography 54, 2298–2314 (2009).
4. Bruce, L. C. et al. A multi-lake comparative analysis of the General Lake Model (GLM): Stress-testing across a global observatory network. Environmental Modelling & Software 102, 274–291 (2018).
5. Shatwell, T., Thiery, W. & Kirillin, G. Future projections of temperature and mixing regime of European temperate lakes. Hydrology and Earth System Sciences 23, 1533–1551 (2019).
6. Snortheim, C. A. et al. Meteorological drivers of hypolimnetic anoxia in a eutrophic, north temperate lake. Ecological Modelling 343, 39–53 (2017).
7. Jenny, J.-P. et al. Inherited hypoxia: A new challenge for reoligotrophicated lakes under global warming : Holocene hypoxia dynamics in large lakes. Global Biogeochemical Cycles 28, 1413–1423 (2014).
8. Jenny, J.-P. et al. Urban point sources of nutrients were the leading cause for the historical spread of hypoxia across European lakes. PNAS 113, 12655–12660 (2016).

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