Natural levels of hydrogen peroxide (H2O2) in deep clear South temperate lakes: Field and laboratory evidence of photo- and biotic production

Hydrogen peroxide (H2O2) is a ubiquitous reactive oxygen species (ROS) in aquatic systems and is produced mainly in surface water by the interaction of ultraviolet radiation (UVR) and natural dissolved organic carbon (DOC). Andean Patagonian lakes are ultraoligotrophic, clear systems with extended photic zones (similar to 40 m), and are exposed to challenging UVR levels due to their lati-altitudinal situation and extremely low DOC levels. This investigation describes the seasonal levels of H2O2 in relation to DOC quality in the water column of lakes Moreno East (ME) and Moreno West (MW), two deep (ca. 100 m), ultraoligotrophic, low-DOC (<0.7 mg L-1) systems of Andean Patagonia. H2O2 concentrations recorded in the lakes were below 60 nM, ranging from similar to 3 to similar to 60 nM in Lake ME and from similar to 5 to similar to 35 nM in Lake MW. Inmost of the samples of both lakes, the H2O2 levels were higher in the photic zone (surface to 30-40 m) than the aphotic zone (from 30-40 m to 90-100m), particularly in summer samples. Laboratory experiments evaluated the abiotic (photochemical) and biotic (microbial) production of H2O2 in seasonal (summer, autumn) samples which varied DOM quality due to lake(ME, MW) and depth (photic and aphotic lake layers) provenance. Abiotic and biotic production of H2O2 attained higher levels in summer samples from the photic zones of both lakes. Humic DOM from deep layers (particularly from summer samples) was more susceptible to both photo- and bio-degradation than DOM from upper lake layers, which was characterized by stronger signs of degradation and progress in diagenesis. (C) 2020 Elsevier B.V. All rights reserved.