| Title |
Active DNRA and denitrification in oxic hypereutrophic waters |
| Authors |
Broman, Elias ; Zilius, Mindaugas ; Samuiloviene, Aurelija ; Vybernaite-Lubiene, Irma ; Politi, Tobia ; Klawonn, Isabell ; Voss, Maren ; Nascimento, Francisco J.A ; Bonaglia, Stefano |
| DOI |
10.1016/j.watres.2021.116954 |
| Full Text |
|
| Is Part of |
Water research.. Oxford : Pergamon-Elsevier Science. 2021, vol. 194, art. no. 116954, p. 1-13.. ISSN 0043-1354. eISSN 1879-2448 |
| Keywords [eng] |
cyanobacteria ; estuarine ecosystem ; eutrophication ; metagenome ; nitrogen cycling ; nutrients |
| Abstract [eng] |
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 harbour 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 15N isotope-labelling 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 (NO3 −) fluxes through DNRA and denitrification, it results that DNRA retains approximately one fifth (19 %) of the fixed N that goes through the NO3 − 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. |
| Published |
Oxford : Pergamon-Elsevier Science |
| Type |
Journal article |
| Language |
English |
| Publication date |
2021 |
| CC license |
|
