Microorganisms' activity and energy fluxes in Lake Varese (Italy): a field method

Microorganisms are fundamental components of energy fluxes in aquatic ecosystems. Interest in plankton production and respiration has recently stimulated exploration of the use of electron transfer system (ETS) activity in oceanography and limnology. If we consider microorganism production (MP) and microorganism respiration (MR), due to aerobic and anaerobic metabolism, microorganism growth efficiency can be defined as MGE = MP/(MP + MR). In order to calculate MGE, we measured independently the two components of ETS (photosynthesis electron transfer system activity (PETS) and respiration electron transfer system activity (RETS)) during an annual cycle using a portable biosensor microorganisms amperometric detector system (MiDAS) on the site. MGE was calculated in samples collected from the photic and aphotic zones and the superficial sediment and ranged between 0.60 and 0.45 and dropped to 0.15 at the end of the summer. This substantial decrease is probably due to the prevalence of the anaerobic-heterotrophic metabolism after a pronounced state of anoxia during the summer algal bloom.