Marine & Environmental Sciences Faculty Articles


Enigmatic Marine Ecosystem Metabolism Measured by Direct Diel ΣCO2 and O2 Flux in Conjunction with DOC Release and Uptake

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Marine Biology







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In an attempt to evaluate ΣCO2 changes as an index of net ecosystem metabolism, ΣCO2 and dissolved organic carbon (DOC) by infrared (IR) analysis and O2 by the Winkler method were followed over 12 diel cycles in a salt marsh, a simulated estuarine ecosystem, and the mixed layer of the northwestern Caribbean Sea. Each ecosystem exhibited replicable diel cycles, net production during the photoperiod, and a significant inverse correlation between ΣCO2 and O2 changes. Daily rates of system production and respiration calculated from ΣCO2, however, exceeded those from O2 by 1.5 to 3.5 fold in nearshore waters and by 2 to 6 fold in the open ocean. Net total system apparent production based on O2 and ΣCO2, respectively, were 2 345 and 3 604 mg C m-3d-1 for the salt marsh, 348 and 625 mg C m-3d-1 for the estuarine ecosystem, and 53 and 306 mg C m-3d-1 for the oceanic ecosystem, both parameters exceeding 14C data in the literature for similar environments by one to two orders of magnitude. The IR ΣCO2 productivity estimates are compatible with the diel cycles in DOC. In the marsh and Caribbean Sea, maxinium DOC concentrations were usually observed in the evening following a gradual accumulation during the photoperiod, while minimal values occurred in the early morning. In all ecosystems the average net release of DOC lagged CO2 uptake and O2 production and represented 22.7 and 43.3% of the carbon fixed as estimated from CO2 uptake and O2 production, respectively. If the consistently higher ΣCO2 measurements are not a systematic error nor due to atmospheric diffusion, then diel variation in O2 and CO2 may not always be quantitatively coupled due in part to habitat-dependent factors such as the nonphotosynthetic incorporation of CO2 and chemosynthetic removal of O2.


©Springer-Verlag 1981

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NSF grant #s:OCE-7681779, OCE-7826388; EPA Grant:R-80-607-202



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