Abstract
The production of reactive oxygen species (ROS) in surface waters is important for the biogeochemical cycling of carbon. ROS are powerful oxidants that include hydroxyl radical (HO), hydroperoxyl radical (HO2), superoxide (O2-), and hydrogen peroxide (H2O2). In particular, H2O2 is a long-lived compound (with a maximum of 60 h), which makes it detectable. The main source of natural H2O2 production is the photochemical reaction with dissolved organic matter (DOM). The quality of DOM, including molecular size, humification, and aromaticity, is a key factor that can influence abiotic H2O2 production. More humified and aromatic DOM appears to be a better substrate for photochemical H2O2 production. To a lesser extent, constant amounts of H2O2 can be released by microorganisms such as bacteria, fungi, and phytoplankton. All lifeforms produce intracellular ROS, and both ROS and H2O2 could be released outside of the cells (extracellular production). The natural variation in H2O2 concentration can be related to several physiological and environmental factors such as cell density, growth phase, temperature, and irradiance. In addition, over the past decade, the use of H2O2 as an algicide has proven to be superior to other methods of controlling algae. It offers several advantages, including selectively suppressing harmful cyanobacterial blooms and their toxins. It is crucial to gain a better understanding of the appropriate concentration of H2O2 because excessive amounts can pose a threat to aquatic ecosystems. The main factors influencing the natural variation of H2O2 are summarized in this chapter.