Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

• Published in: Marine chemistry Vol. 113; no. 3; pp. 219 - 226
• Main Authors: Lønborg, Christian, Davidson, Keith, Álvarez–Salgado, Xosé A., Miller, Axel E.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20.02.2009; Elsevier
• Subjects: Bacteria; Bioavailability; DOM; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Geochemistry; Marine; Mineralization; Mineralogy; Physical and chemical properties of sea water; Physics of the oceans; Refractory; Silicates; Stoichiometry; Water geochemistry; United Kingdom; Scotland; Great Britain; Europe; Western Europe; ANE, British Isles, Scotland; Refractory; Stoichiometry; DOM; Bioavailability; Mineralization; sea water; experimental studies; stoichiometry; springs; nitrogen; testing; concentration; cycles; degradation; mineralization; correlation; hydrochemistry; standard samples; organic materials; temperature; residence time; export; seasonal variations; dissolved organic carbon
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/j.marchem.2009.02.003

The bioavailability and bacterial degradation rates of dissolved organic matter (DOM) were determined over a seasonal cycle in Loch Creran (Scotland) by measuring the decrease in dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) concentrations during long-term laboratory incubations (150 days) at a constant temperature of 14 °C. The experiments showed that bioavailable DOC (BDOC) accounted for 29 ± 11% of DOC (average ± SD), bioavailable DON (BDON) for 52 ± 11% of DON and bioavailable DOP (BDOP) for 88 ± 8% of DOP. The seasonal variations in DOM concentrations were mainly due to the bioavailable fraction. BDOP was degraded at a rate of 12 ± 4% d – 1 (average ± SD) while the degradation rates of BDOC and BDON were 7 ± 2% d – 1 and 9 ± 2% d – 1 respectively, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentration and degradation rate of DOM suggested that the higher the concentration the faster DOM would be degraded. On average, 77 ± 9% of BDOP, 62 ± 14% of BDON and 49 ± 19% of BDOC were mineralized during the residence time of water in Loch Creran, showing that this coastal area exported C-rich DOM to the adjacent Firth of Lorne. Four additional degradation experiments testing the effect of varying temperature on bioavailability and degradation rates of DOM were also conducted throughout the seasonal cycle (summer, autumn, winter and spring). Apart from the standard incubations at 14 °C, additional studies at 8 °C and 18 °C were also conducted. Bioavailability did not change with temperature, but degradation rates were stimulated by increased temperature, with a Q 10 of 2.6 ± 1.1 for DOC and 2.5 ± 0.7 for DON (average ± SD).