Characterization and photodegradation of dissolved organic matter (DOM) from a tropical lake and its dominant primary producer, the cyanobacteria Microcystis aeruginosa

Author(s)

Bittar, Thais B. ; Stubbins, Aron ; Vieira, Armando A. H. ; Mopper, Kenneth

• Document type: Journal article
• Source: MARINE CHEMISTRY; v. 177, p. 13-pg., 2015-12-20.

Abstract

This study investigates optical and high-resolution molecular signatures and photochemical degradation of DOM from the Barra Bonita Reservoir (BB-DOM), a tropical eutrophic lake, as well as from its dominant phytoplankton species, the cyanobacteria Microcystis aeruginosa (Microcystis-DOM). Consistent with a predominantly autotrophic source, BB-DOM and Microcystis-DOM exhibited high protein-like fluorescence and contained a large number of aliphatics. Microcystis-DOM was enriched in peptide-like formulae, while BB-DOM had higher chromophoric and fluorescent DOM (CDOM and FDOM) and was enriched in moderately unsaturated formulae, indicating additions of terrigenous DOM and/or in situ processing of autochthonous material in the lake. Consistent with its higher CDOM content, BB-DOM was more photoreactive than Microcystis-DOM. For both types of DOM, photodegradation resulted in loss of CDOM, FDOM, moderately unsaturated structures, high O/C and low H/C formulae, and preservation of aliphatics. The majority of photoproducts of 0.5 d irradiation were subsequently removed by day 7, and photoproducts represented a minor fraction of the photo-irradiated DOM. For BB-DOM, molecular formula photolability increased with increasing aromaticity index values, while for Microcystis-DOM, molecular formula photolability increased with molecular mass. Photodegradation increased the proportion of molecular formulae containing N (CHO + N) in BB-DOM, while the molecular mass and the proportion of CHO + N formulae decreased upon photo-irradiation of Microcystis-DOM. In concert, these molecular shifts due to photodegradation decreased the diversity of and increased the similarity between BB-DOM and Microcystis-DOM, suggesting the selective pressure exerted by photochemistry selects for the survival of similar compounds in both samples. (C) 2015 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 05/57213-0 - Effect of solar radiation on the bioavailability of dissolved organic matter (DOM) produced by Microcystis aeruginosa
• Grantee: Thais Beraldo Bittar
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 05/51263-5 - Fate of dissolved organic matter released by Cyanobacteria in an eutrophic reservoir (Tietê River): studies of processes
• Grantee: Armando Augusto Henriques Vieira
• Support Opportunities: Research Projects - Thematic Grants