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Marine Ecology Progress Series

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MEPS 392:17-32 (2009)  -  DOI:

Effects of organic perturbation on marine sediment betaproteobacterial ammonia oxidizers and on benthic nitrogen biogeochemistry

A. Bissett1,2,6,*, P. L. M. Cook3, C. Macleod4, J. P. Bowman2, C. Burke1,5

1School of Aquaculture, Launceston, Australia and 2School of Agricultural Science, University of Tasmania, Hobart, Tasmania 7001, Australia
3Water Studies Centre, Monash University, Clayton, Victoria 3800, Australia
4Tasmanian Aquaculture and Fisheries Institute (TAFI), Marine Research Laboratories, Nubeena Crescent, Taroona, Tasmania 7053, Australia
5National Centre for Marine Conservation and Resource Sustainability (NCMCRS), Australian Maritime College, University of Tasmania, Hobart, Tasmania 7001, Australia
6Present address: CSIRO Plant Industry, GPO Box 1600, Canberra, ACT, 2601 Australia

ABSTRACT: The failure of denitrification to remove nitrogen build-up from aquatic systems is often attributed to sediment chemical conditions inhibiting nitrification and therefore the supply of suitable substrates to be denitrified. We investigated the effects of organic fish farm pollution on nitrogen-cycle dynamics and betaproteobacterial ammonia-oxidizing bacteria (β-AOB) community structure to elucidate the potential role of the nitrifier community on nitrogen biogeochemistry in marine sediments. Porewater nitrogen concentrations, denitrification rates, β-AOB 16S rDNA gene quantification, denaturing gradient gel electrophoresis (DGGE) community fingerprints and infaunal counts were determined in samples collected from beneath fish cages and at adjacent, non-impacted control sites. The study was conducted over 2 full, 1 yr production cycles. Although nitrogen cycling was significantly altered beneath cages, changes appeared to result from a reduction in the proportion of ammonia nitrified rather than from inhibition of nitrification per se. DGGE revealed β-AOB communities shifted rapidly and remained diverse at both cage and reference sites. Quantitative PCR (qPCR) showed β-AOB numbers did not decline in absolute terms but did decline as a proportion of the total bacterial community at cage sites and at the end of the stocking periods. Sediment infaunal community analysis showed significant effects of organic loading and indicated more bioirrigation at impacted sites. Despite the induction of conditions thought to be detrimental to nitrification and to β-AOB (low oxygen, reduced sediments, low pH, and high sulphide concentrations), these communities remained diverse and apparently viable, perhaps a result of heavy sediment bioirrigation. However, despite the increase in denitrification, nitrogen left the sediment predominantly as ammonia, thus producing potential point sources of eutrophication.

KEY WORDS: Eutrophication · Nitrification · Denitrification · Sediment · Ammonia-oxidising bacteria

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Cite this article as: Bissett A, Cook PLM, Macleod C, Bowman JP, Burke C (2009) Effects of organic perturbation on marine sediment betaproteobacterial ammonia oxidizers and on benthic nitrogen biogeochemistry. Mar Ecol Prog Ser 392:17-32.

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