Approche discriminante de contributions de différents échelons microplanctoniques aux mesures globales d'ETS dans des échantillons de mer. b. Bacteria

Discriminating approach of various microplanktonic-stage contributions to whole electron transport system (ETS) measurements in sea-water sampless. b. Bacateria Data obtained from cultures of natural bacterial populations were applied to various water samples in order to determine both the phytoplanktonic and bacterial contributions to whole ETS water-sample measurements. The bacterial part was estimated both by cell enumerations and HPLC muramic-acid measurements and the phytoplankton contribution by enumeration and chlorophyll levels. An appropriate first-order equation is adequate to low carbon content samples but must be corrested for highly organic loaded samples in order to obtain a better adjustment between the sum of the “estimated” phytoplanktonic and bacterial ETS and the really-measured ETS concentrations in the water samples.     

Production de CO2 à l'interface air-mer. Une approche par l'étude des phénomènes respiratoires dans la microcouche de surface. CO2 Production at the Sea-Air Interface. An Approach by the Study of Respiratory Processes in Surface Microlayer

Sea-surface microlayer and underlaying water samples were collected in the Bay of Marseilles (France) in order to study respiratory activity of microneuston and its possible influence on respiratory CO₂ production. Three methods were tested: Biochemical Oxygen Demand (BOD) as an estimation of community respiration, Electron Transport System activity (ETS) and ¹⁴C-Glucose uptake monitored by ¹⁴C-CO₂ liberation. BOD and ETS data clearly showed enhanced respiratory activities (up to 310 μl O₂/l/h) in surface-films as compared to underlaying waters; moreover the slope of the linear regression between these data led to R/ETS value of 0.689 and provides evidence for the presence of an important heterotrophic fraction within the microneuston. Though ¹⁴C-Glucose measurements showed only a slight trend for higher total activity (incorporation + respiration) in surface microlayers, significant enhancement of relative ¹⁴C-CO₂ production giving rise to CO₂ diffusion across air-water interface was observed.