The present work was dedicated to the development of a lab-on-chip microsystem for the monitoring of microalgal photosynthetic activity. Thanks to integrated electrochemical microcells, dissolved oxygen O2 concentrations due to photosynthetic microalgal activity were measured in a continuous way and oxygen production rates of microalgae cultures were finally determined in the frame of artificial night/day cycles. Application was performed by studying the physiological metabolisms of the green microalga Chlamydomonas reinhardtii. First, the different growth dynamics of microalgal cultures were characterized, enabling the determination of the induction, "exponential growth", "declining growth rate" and stationary phases. Then, the influences of carbon-based nutrients, such as sodium bicarbonate HCO3Na and methanol CH3OH, as well as of pollutants, such as silver nitrate AgNO3, were studied, evidencing contradictory behaviors according to the competition between nutritional properties, toxicity effects and acclimation phenomena. This paves the way to the development of analysis microsystems for the understanding of microalgal metabolisms as well as for the improvement of microalgae growth processes and associated industrial production.