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Aquatic Microbial Ecology

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AME 58:117-126 (2010)  -  DOI:

Stoichiometry of dissolved organic matter and the kinetics of its microbial degradation in a coastal upwelling system

Christian Lønborg1,2,*, Xosé A. Álvarez-Salgado1, Sandra Martínez-García3, Axel E. J. Miller2, Eva Teira3

1CSIC, Instituto de Investigacións Mariñas, Eduardo Cabello 6, 36208 Vigo, Spain
2Scottish Association for Marine Science, Oban, Argyll PA37 1QA, UK
3Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo,36200 Vigo, Spain

ABSTRACT: The degradation of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) collected in the coastal upwelling system of the Ría de Vigo (NW Iberian Peninsula) was assessed following the time-course of DOC, DON and DOP concentrations in laboratory incubations. Initial concentrations varied from 73 to 94 µM for DOC, 4.5 to 7.2 µM for DON and 0.12 to 0.32 µM for DOP. The bioavailable fraction (BDOM) represented 17 ± 6% (average ± SE) of DOC, 38 ± 6% of DON and 65 ± 9% of DOP. BDOM was significantly correlated with temperature (R2 > 0.3, p < 0.05) and chlorophyll a (R2 > 0.5, p < 0.05), indicating that the differences in DOM bioavailability were associated with the seasonal variations in plankton biomass and activity. The C:N:P stoichiometry of BDOM, 111 (±38):18 (±6):1, was not significantly different from the Redfield ratio (106:16:1), pointing to a phytoplankton origin of BDOM. Accordingly, exponential rate constants of BDOM suggest that this pool is very labile. Despite the reduced flushing times of the Ría de Vigo, from 3 to 8 d, as much as 70 ± 13% of BDOC (average ± SD), 81 ± 8% of BDON and 88 ± 5% of BDOP are mineralized within the embayment. The remaining C-rich BDOM is exported to the adjacent oligotrophic waters, suggesting that the offshore transport of labile DOM must be accounted for when considering the carbon balance of ocean surface waters adjacent to productive coastal areas.

KEY WORDS: DOM · Bioavailability · Degradation · Stoichiometry · Biochemical composition · Coastal upwelling

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Cite this article as: Lønborg C, Álvarez-Salgado XA, Martínez-García S, Miller AEJ, Teira E (2010) Stoichiometry of dissolved organic matter and the kinetics of its microbial degradation in a coastal upwelling system. Aquat Microb Ecol 58:117-126.

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