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Carbon amendment stimulates benthic nitrogen cycling during the bioremediation of particulate aquaculture waste

Lookup NU author(s): Georgina Robinson, Dr Gary Caldwell, Professor Selina Stead

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

The treatment of organic wastes remains one of the key sustainability challenges facing the growing global aquaculture industry. Bioremediation systems based on coupled bioturbation―microbial processing offer a promising route for waste management. We present, for the first time, a combined biogeochemical-molecular analysis of the short-term performance of one such system that is designed to receive nitrogen-rich particulate aquaculture wastes. Using sea cucumbers (Holothuria scabra) as a model bioturbator we provide evidence that adjusting the waste C:N from 5:1 to 20:1 promoted a shift in nitrogen cycling pathways towards the dissimilatory nitrate reduction to ammonium (DNRA), resulting in net NH₄⁺ efflux from the sediment. The carbon amended treatment exhibited an overall net N₂ uptake whereas the control receiving only aquaculture waste exhibited net N₂ production, suggesting that carbon supplementation enhanced nitrogen fixation. The higher NH₄⁺ efflux and N₂ uptake was further supported by metagenome predictions that indicate organic carbon addition stimulated DNRA over denitrification. These findings indicate that carbon addition may potentially result in greater retention of nitrogen within the system, however longer-term trials are necessary to determine whether this nitrogen retention is translated into improved sea cucumber biomass yields. Whether this truly constitutes a remediation process is open for debate as there remains the risk that any increased nitrogen retention may be temporary, with any subsequent release potentially raising the eutrophication risk. Longer and larger-scale trials are required before this approach may be validated with the complexities of the in-system nitrogen cycle being fully understood.

Publication metadata

Author(s): Robinson G, MacTavish T, Savage C, Caldwell GS, Jones CLW, Probyn T, Eyre BD, Stead SM

Publication type: Article

Publication status: Published

Journal: Biogeosciences

Year: 2018

Volume: 15

Issue: 6

Pages: 1863–1878

Online publication date: 29/03/2018

Acceptance date: 11/01/2018

Date deposited: 29/03/2018

ISSN (print): 1726-4170

ISSN (electronic): 1726-4189

Publisher: European Geosciences Union

URL: https://doi.org/10.5194/bg-15-1863-2018

DOI: 10.5194/bg-15-1863-2018

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