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  • 1
    ISSN: 1573-515X
    Keywords: amino acids ; ammonium production ; coastal marine sediments ; anoxic ; sulfate reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In sediment slurry experiments with anoxic marine sediments collected in Cape Lookout Bight, NC, and a site in mid-Chesapeake Bay, the rates of sulfate reduction and ammonium production decrease with increasing dilution of sediment with oxygen-free sea-water. The effect of sediment dilution on the rates of these processes can be described by a simple mathematical relationship, and when these rates are corrected for sediment dilution they yield values which agree well with direct measurements of these processes. In sediment slurry studies of amino acid utilization in Cape Lookout Bight sediments, the fermentative decarboxylation of glutamic acid (to γ-aminobutyric acid) or aspartic acid (to alanine or β-alanine) did not occur when either of these amino acids were added to Cape Lookout Bight slurries. The addition of glutamic acid did however lead to a small (∼1) transient build-up of β-aminoglutaric acid. Measured rates of glutamic acid uptake in these slurries also decreased with increasing sediment dilution. Molybdate inhibition experiments demonstrated that dissolved free amino acids represent 1–3% of the carbon sources/electron donors used for sulfate reduction in Cape Lookout Bight sediments. The direct oxidation of amino acids by sulfate reducing bacteria also accounts for 13–20% of the total ammonium produced. Glutamic acid, alanine, β-aminoglutaric acid, aspartic acid and asparagine are the major amino acids oxidized by sulfate reducing bacteria in Cape Lookout Bight sediments.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. H., Sutherland, K., Wankel, S. D., Burdige, D. J., & Zimmerman, R. C. Ebullition of oxygen from seagrasses under supersaturated conditions. Limnology and Oceanography, (2019), doi:10.1002/lno.11299.
    Description: Gas ebullition from aquatic systems to the atmosphere represents a potentially important fraction of primary production that goes unquantified by measurements of dissolved gas concentrations. Although gas ebullition from photosynthetic surfaces has often been observed, it is rarely quantified. The resulting underestimation of photosynthetic activity may significantly bias the determination of ecosystem trophic status and estimated rates of biogeochemical cycling from in situ measures of dissolved oxygen. Here, we quantified gas ebullition rates in Zostera marina meadows in Virginia, U.S.A. using simple funnel traps and analyzed the oxygen concentration and isotopic composition of the captured gas. Maximum hourly rates of oxygen ebullition (3.0 mmol oxygen m−2 h−1) were observed during the coincidence of high irradiance and low tides, particularly in the afternoon when oxygen and temperature maxima occurred. The daily ebullition fluxes (up to 11 mmol oxygen m−2 d−1) were roughly equivalent to net primary production rates determined from dissolved oxygen measurements indicating that bubble ebullition can represent a major component of primary production that is not commonly included in ecosystem‐scale estimates. Oxygen content comprised 20–40% of the captured bubble gas volume and correlated negatively with its δ18O values, consistent with a predominance of mixing between the higher δ18O of atmospheric oxygen in equilibrium with seawater and the lower δ18O of oxygen derived from photosynthesis. Thus, future studies interested in the metabolism of highly productive, shallow water ecosystems, and particularly those measuring in situ oxygen flux, should not ignore the bubble formation and ebullition processes described here.
    Description: Two anonymous reviewers provided thoughtful contributions that improved this manuscript. We thank Miraflor Santos, Victoria Hill, David Ruble, Jeremy Bleakney, and Brian Collister for assistance in the field and the staff of the Anheuser‐Busch Coastal Research Center for logistical support. This work was supported by NSF OCE grants 1633951 (to MHL) and 1635403 (to RCZ and DJB), NASA Fellowship NESSF NNX15AR62H (to KS), and a fellowship from the Hansewissenschaftskolleg (Institute for Advanced Studies; to SDW).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Long, M. H., Rheuban, J. E., McCorkle, D. C., Burdige, D. J., & Zimmerman, R. C. Closing the oxygen mass balance in shallow coastal ecosystems. Limnology and Oceanography, 64(6), (2019): 2694-2708, doi: 10.1002/lno.11248.
    Description: The oxygen concentration in marine ecosystems is influenced by production and consumption in the water column and fluxes across both the atmosphere–water and benthic–water boundaries. Each of these fluxes has the potential to be significant in shallow ecosystems due to high fluxes and low water volumes. This study evaluated the contributions of these three fluxes to the oxygen budget in two contrasting ecosystems, a Zostera marina (eelgrass) meadow in Virginia, U.S.A., and a coral reef in Bermuda. Benthic oxygen fluxes were evaluated by eddy covariance. Water column oxygen production and consumption were measured using an automated water incubation system. Atmosphere–water oxygen fluxes were estimated by parameterizations based on wind speed or turbulent kinetic energy dissipation rates. We observed significant contributions of both benthic fluxes and water column processes to the oxygen mass balance, despite the often‐assumed dominance of the benthic communities. Water column rates accounted for 45% and 58% of the total oxygen rate, and benthic fluxes accounted for 23% and 39% of the total oxygen rate in the shallow (~ 1.5 m) eelgrass meadow and deeper (~ 7.5 m) reef site, respectively. Atmosphere–water fluxes were a minor component at the deeper reef site (3%) but a major component at the shallow eelgrass meadow (32%), driven by diel changes in the sign and strength of atmosphere–water gradient. When summed, the measured benthic, atmosphere–water, and water column rates predicted, with 85–90% confidence, the observed time rate of change of oxygen in the water column and provided an accurate, high temporal resolution closure of the oxygen mass balance.
    Description: This work was substantially improved by comments from two anonymous reviewers. We thank Victoria Hill, David Ruble, Jeremy Bleakney, and Brian Collister for assistance in the field and the staff of the Bermuda Institute of Ocean Sciences and the Anheuser‐Busch Coastal Research Center for logistical support. This work was supported by NSF OCE grants 1657727 (to M.H.L. and D.C.M.), 1635403 (to R.C.Z. and D.J.B.), and 1633951 (to M.H.L.).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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