Occurrence, fate and effects of reactive oxygen and nitrogen species on biogeochemical cycles in aquatic ecosystems

Abstract

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are increasingly recognised as playing significant roles in modulating redox conditions and biogeochemical cycles across a broad range of aquatic ecosystems. This chapter aims to synthesise current understanding of the occurrence, formation pathways, and environmental fate of major ROS (superoxide, hydrogen peroxide, hydroxyl radical, and singlet oxygen) and RNS (nitric oxide, nitrogen dioxide, and peroxynitrite) in natural aquatic ecosystems. It highlights the key abiotic and biotic processes responsible for their generation and consumption, including photochemical reactions, microbial activity, redox transformations at oxic-anoxic interfaces, and partitioning to and from the gas phase. The balance of these processes determines steady-state concentrations and lifetimes of ROS and RNS in natural aquatic systems, which in turn influence the redox speciation and biogeochemical cycling of carbon, trace metals, and a range of other elements. Despite advances in recent decades, significant knowledge gaps remain in our understanding of ROS and RNS dynamics, particularly in groundwaters, the deep ocean, and atmospheric waters. Addressing these gaps is critical to fully understand the role of ROS and RNS in elemental cycling and quantify their potential influence in aquatic ecosystems.