A new method to estimate planktonic oxygen metabolism using high‐frequency sensor measurements in mesocosm experiments and considering daytime and nighttime respirations

Abstract

Understanding how aquatic ecosystems respond to perturbations has emerged as a crucial way to predict the future of these ecosystems and to assess their capacity to produce oxygen and store atmospheric carbon. In this context, in situ mesocosm experiments are a useful approach for simulating disturbances and observing changes in planktonic communities over time and under controlled conditions. Within mesocosm experiments, the estimation of fundamental parameters such as gross primary production (GPP), net community production (NCP), and respiration (R) allows the evaluation of planktonic metabolic responses to a perturbation. The continuous estimation of these metabolic parameters in real time and at high frequency is made possible by employing noninvasive automated sensors in the water column. However, some uncertainties and methodological questions about the estimation of daytime respiration remain to be addressed for this method, and notably to address the fact that respiration could be significantly higher during the day than during the night. In this study, data from two in situ mesocosm experiments performed in fall and spring in a coastal Mediterranean area were used to develop a new method of estimating daytime respiration, and in turn daily GPP, R, and NCP, by considering the maximum instantaneous R, and that takes into account the variability of the coupling between day-night and dissolved oxygen cycles. This new method was compared with the Winkler incubation technique and with another existing method. Results showed that using this existing method, daytime R was significantly underestimated relative to estimates obtained with the newly proposed method.

Functional Stability of a Coastal Mediterranean Plankton Community During an Experimental Marine Heatwave

“…The calibrated DO data were then corrected using temperature and salinity data obtained from the water temperature probes and the conductivity sensor, respectively, following the procedure of Bittig et al (2018). To ensure high-quality oxygen data, daily oxygen concentrations were also measured using the Winkler method to correct the sensor data (Soulié et al, 2021). The entire calibration and correction procedures are detailed in Soulié et al (2021).…”

“…To ensure high-quality oxygen data, daily oxygen concentrations were also measured using the Winkler method to correct the sensor data (Soulié et al, 2021). The entire calibration and correction procedures are detailed in Soulié et al (2021).…”

“…Gross primary production, respiration, and net community production were estimated using the high-frequency DO sensor data with a method based on the classical free-water diel oxygen technique (Odum and Odum, 1955). This technique was specially developed for mesocosm experiments and considered variability in daytime and nighttime respiration, and in the coupling between day-night and DO cycles (Soulié et al, 2021). Table 1 lists the equations used in the study.…”

“…5. In this equation, O 2 t represents the instantaneous change in DO concentration, F is the physical oxygen exchange between the water and the atmosphere, and A encompasses all other physical and chemical phenomena that could affect the DO concentration in the considered system; the parameter A was considered null in the present study as well as in most other investigations (Staehr et al, 2010;Soulié et al, 2021). Then, the calculation needs to be performed in two important steps.…”

“…In the case of gently mixed mesocosms, as in the present study, Z mix can be considered equal to the water column length of the mesocosms. The piston velocity k was adopted from the literature values provided in the study by Soulié et al (2021). This parameter is determined using water viscosity and O 2 solubility, which are affected by the water temperature and salinity.…”