Size-dependent variation in the oxygen consumption rate of organic particles

Abstract

Traditionally, the oxygen consumption rates of organic particles in aquatic environments have remained largely unexplored due to measurement difficulties, and the factors controlling these rates are unknown. In this study, we aimed to elucidate the primary carriers of oxygen consumption by fractionating organic particles in water by size and culturing them under in-situ light and temperature conditions. Measurements conducted in Lake Biwa revealed that the fraction of particles larger than 1.2 µm exhibited respiration rates close to the total, whereas organic particles smaller than 1.2 µm contributed minimally to respiration. On the other hand, it is generally known that dissolved organic particles are more prevalent. These results suggest that dissolved particles are stable, and organic particles larger than 1.2 µm are the controlling factors for oxygen consumption in aquatic environments. Furthermore, it was found that particles larger than 1.2 µm have shorter lifespans, indicating that events causing their descent could directly lead to the formation of hypoxic water masses.