Abstract
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 614:35-50 (2019) - DOI: https://doi.org/10.3354/meps12901 Diazotroph activity in surface Narragansett Bay sediments in summer is stimulated by hypoxia and organic matter delivery R. F. Spinette1,2, S. M. Brown1,3, A. L. Ehrlich1,4, G. Puggioni5, C. Deacutis6, B. D. Jenkins1,2,* 1Department of Cell and Molecular Biology, University of Rhode Island, Kingston, Rhode Island 02881, USA 2Graduate School of Oceanography, Narragansett, Rhode Island 02882, USA 3Sailors for the Sea, Newport, Rhode Island 02840, USA 4Sema4, Branford, Connecticut 06405, USA 5Department of Computer Science and Statistics, University of Rhode Island, Kingston, Rhode Island 02881, USA 6Rhode Island Department of Environmental Management, Providence, Rhode Island 02908, USA *Corresponding author: bjenkins@uri.edu ABSTRACT: Bacteria that carry out many processes of the nitrogen cycle inhabit estuarine sediments. Denitrification is known to be a dominant process causing estuarine sediments to behave as net nitrogen sinks. However, measurements of nitrogen fluxes in the sediments of Narragansett Bay, Rhode Island, USA, have at times revealed high rates of net nitrogen (N2) fixation. Whereas changes in primary production, in magnitude and phenology, within Narragansett Bay have been identified as possible causes for these changes in nitrogen cycling within the benthos, a factor that has not been examined thus far is seasonal hypoxia. Since anaerobic diazotrophs figure so prominently within the sediments of Narragansett Bay, we hypothesized that dissolved oxygen concentrations in the bottom waters affect their activity. In order to explore this relationship, we measured the activity of diazotrophs in the surface sediments of 3 study areas during the summers of 2013 and 2014 using the acetylene reduction assay. We explored the effects of several water quality parameters on nitrogenase activity including, among others, dissolved oxygen and chlorophyll concentrations. Our measurements of nitrogenase activity were generally low, ranging between 2 and 5 nmol ethylene g-1 d-1 but spiked to 16 nmol ethylene g-1 d-1 at an area experiencing severe hypoxia in July 2013. Our data suggest that diazotrophy in estuarine sediments is enhanced when the benthos experiences very low dissolved oxygen in conjunction with recent influxes of autochthonous organic matter. Experiments with sediment core incubations conducted in the laboratory support our hypothesis that low dissolved oxygen and organic matter additions promote N2 fixation. KEY WORDS: N2 fixation · Diazotrophy · Hypoxia · Estuary · Sediments Full text in pdf format Supplementary material PreviousNextCite this article as: Spinette RF, Brown SM, Ehrlich AL, Puggioni G, Deacutis C, Jenkins BD (2019) Diazotroph activity in surface Narragansett Bay sediments in summer is stimulated by hypoxia and organic matter delivery. Mar Ecol Prog Ser 614:35-50. https://doi.org/10.3354/meps12901 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 614. Online publication date: April 04, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.
Highlights
Estuaries, residing at the interface of freshwater systems and oceans, are attractive habitats for human populations
The Providence River estuary and Greenwich Bay are prone to seasonal hypoxia in July and August
Greenwich Bay was the site of a large fish kill in 2003, which was later attributed to severe hypoxia (RIDEM 2003)
Summary
Estuaries, residing at the interface of freshwater systems and oceans, are attractive habitats for human populations. Hypoxic conditions occur at depth when dissolved oxygen is depleted faster (by bacterial respiration) than it can be replenished. These conditions are typically established when water temperatures are high and surface waters are stratified leading to high rates of biological activity and elevated primary production in the surface water. Greatest hypoxic expression is found in the upper third of the estuary, where the major rivers enter and the major wastewater effluents discharge. These conditions generate a clear gradient of chlorophyll, surface salinity, and hypoxia in Narragansett Bay (Oviatt et al 2017)
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