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. 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) and the degradation rates of BDON and BDOC were 78 ± 18 % and 58 ± 17 % slower than for BDOP, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentrations and degradations rates of DOM suggested that with higher 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

ASLO Aquatic Scicences Meeting, 25-30 January 2009, Nice (France)

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