Published in:
Biogeosciences, 15 (2018) 7, Seite 2021-2032
Language:
English
DOI:
10.5194/bg-15-2021-2018
ISSN:
1726-4189
Origination:
Footnote:
Description:
Abstract. Lakes are important actors in biogeochemical cycles and a powerful naturalsource of CO2. However, they are not yet fully integrated in carbon globalbudgets, and the carbon cycle in the water is still poorly understood. Infreshwater ecosystems, productivity studies have usually been carried outwith traditional methods (bottle incubations, 14C technique), which areimprecise and have a poor temporal resolution. Consequently, our ability toquantify and predict the net ecosystem productivity (NEP) is limited: theestimates are prone to errors and the NEP cannot be parameterised fromenvironmental variables. Here we expand the testing of a free-water methodbased on the direct measurement of the CO2 concentration in the water. Theapproach was first proposed in 2008, but was tested on a very short data set(3 days) under specific conditions (autumn turnover); despite showingpromising results, this method has been neglected by the scientificcommunity. We tested the method under different conditions (summerstratification, typical summer conditions for boreal dark-water lakes) and ona much longer data set (40 days), and quantitatively validated it comparingour data and productivity models. We were able to evaluate the NEP with ahigh temporal resolution (minutes) and found a very good agreement (R2≥0.71) with the models. We also estimated the parameters of theproductivity–irradiance (PI) curves that allow the calculation of the NEPfrom irradiance and water temperature. Overall, our work shows that theapproach is suitable for productivity studies under a wider range ofconditions, and is an important step towards developing this method so thatit becomes more widely used.