Daily O2 and CO2 metabolism in Lake Geneva

Phosphorous levels have declined drastically in Lake Geneva since the 1980’s, but the resulting temporal trends in primary production (PP) and biomass development remain difficult to explain. To obtain a better understanding of the driving forces behind the PP development, it is necessary to resolve PP dynamics during a variety of meteorological and environmental conditions. However, the standard long-term monitoring of Lake Geneva is typically restricted to sampling only once or twice per month and during fairly stable weather.
To improve the temporal resolution of PP estimates as well as the rate of decay of biomass in the water column, we deployed a suite of oxygen (O2) and carbon dioxide (CO2) sensors in Lake Geneva. When algae photosynthesize – a light dependent process – during the day, they consume CO2 from the surrounding water and release O2 as a waste product. All other organisms, in contrast, consume O2 and respire CO2 when oxidizing biomass. The countering processes leave a significant diel pattern in O2 and CO2:
Thus, when the resulting dynamics in these two gases are well resolved, it is possible to infer rates of the gross PP (GPP), community respiration (CR), and net ecosystem production (NEP = GPP – R) at the daily scale.
Since October 2018, we monitor O2 and CO2 at high frequency and along with other environmental variables (water temperature, light, chlorophyll-a and pH) in Lake Geneva. Our multi parameter setup covers the upper 30 m of the water column and is located within the protective circle of the LéXPLORE platform, where this in-situ monitoring is complemented by additional sampling and experimental work within the primary production project.