Active DNRA and denitrification in oxic hypereutrophic waters. (15th April 2021)

• Record Type: Journal Article
• Authors: Broman, Elias; Zilius, Mindaugas; Samuiloviene, Aurelija; Vybernaite-Lubiene, Irma; Politi, Tobia; Klawonn, Isabell; Voss, Maren; Nascimento, Francisco J.A.; Bonaglia, Stefano
• Is Part Of: Water research. Volume 194(2021)
• Publication Date: 2021-04-15
• Subjects: Cyanobacteria -- Estuarine ecosystem -- Eutrophication -- Metagenome -- Nitrogen cycling -- Nutrients; Corg Organic carbon -- DIN Dissolved inorganic nitrogen -- DIP Dissolved inorganic phosphorus -- DNRA Dissimilatory nitrate reduction to ammonium -- DON Dissolved organic nitrogen -- GeTMM Gene length corrected trimmed mean of M-values -- POC Particulate organic carbon -- PON Particulate organic nitrogen -- RT-qPCR Quantitative reverse transcription PCR -- TDN Total dissolved nitrogen -- TN Total nitrogen; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2021.116954
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: DNRA was the main nitrate reduction process in the water. Denitrification was also detected in the water, but was predominant in the sediment. These processes were likely occurring in low-oxygen niches related to cyanobacteria. DNRA recycles n and may be a cause of hypereutrophication. Abstract: Since the start of synthetic fertilizer production more than a hundred years ago, the coastal ocean has been exposed to increasing nutrient loading, which has led to eutrophication and extensive algal blooms. Such hypereutrophic waters might harbor anaerobic nitrogen (N) cycling processes due to low-oxygen microniches associated with abundant organic particles, but studies on nitrate reduction in coastal pelagic environments are scarce. Here, we report on 15 N isotope-labeling experiments, metagenome, and RT-qPCR data from a large hypereutrophic lagoon indicating that dissimilatory nitrate reduction to ammonium (DNRA) and denitrification were active processes, even though the bulk water was fully oxygenated (> 224 µM O2 ). DNRA in the bottom water corresponded to 83% of whole-ecosystem DNRA (water + sediment), while denitrification was predominant in the sediment. Microbial taxa important for DNRA according to the metagenomic data were dominated by Bacteroidetes (genus Parabacteroides ) and Proteobacteria (genus Wolinella ), while denitrification was mainly associated with proteobacterial genera Pseudomonas, Achromobacter, and Brucella . The metagenomic and microscopy data suggest that these anaerobic processes were likely occurring in low-oxygen microniches related to extensive growth of filamentous cyanobacteria, including diazotrophic Dolichospermum and non-diazotrophic Planktothrix . By summing the total nitrate fluxes through DNRA and denitrification, it results that DNRA retains approximately one fifth (19%) of the fixed N that goes through the nitrate pool. This is noteworthy as DNRA represents thus a very important recycling mechanism for fixed N, which sustains algal proliferation and leads to further enhancement of eutrophication in these endangered ecosystems. Graphical abstract: Image, graphical abstract