Assessing the microbial bioavailability and degradation rate constants of dissolved organic matter by fluorescence spectroscopy in the coastal upwelling system of the Ría de Vigo

Abstract

15The time course of colored dissolved organic matter (CDOM) absorption and 16 fluorescence were monitored during 50 to 70 days of laboratory incubations with water 17 collected in the coastal upwelling system of the Ría de Vigo (NW Iberian Peninsula) under 18 contrasting hydrographic conditions. CDOM fluorescence at peak-T (Ex/Em, 280/350 nm), 19 characteristic of protein-like materials, decayed at a 1 st order rate constant (k T ) of 0.28 ± 20 0.13 day -1 (average ± SD). k T covaried (R 2 = 0.86, p<0.0002) with the rate constant of the 21 bulk DOC (k DOC ), but the protein-like materials degraded 72 ± 23% faster than DOC. 22Therefore, this study confirms that the CDOM fluorescence at peak-T can be used as a 23 proxy to a DOM fraction significantly more labile than the bulk bioavailable DOC. In 24 parallel with the decay of DOC and protein-like fluorescence, an increase in CDOM 25 fluorescence at peak-M (Ex/Em, 320/410 nm) during the course of the incubations verified 26 the production of marine humic-like substances as a by product of the microbial 27 metabolism. CDOM fluorescence at peak-M built up at a production rate (k M ) of 0.06 ± 28 0.01 day -1 (average ± SD) in the Ría de Vigo. Furthermore, the slope of the linear 29 regression between k DOC and k M (R 2 = 0.64, p< 0.001) revealed that the formation of marine 30 humic-like substances occurred at about one fifth of the rate of net DOC consumption. 31 32 Keywords: DOC, bioavailable, refractory, rate constant, fluorescence spectroscopy 33 has also been identified as a by-product of in situ microbial degradation processes (Nieto-52 Cid et al. 2006; Yamashita and Tanoue 2008). These studies suggest that the protein-and 53 humic-like fluorescence could be used to study labile and refractory DOM in the marine 54 environment. However, quantitative relationships between these variables are still lacking. 55 The coastal upwelling area of the Ría de Vigo (NW Iberian Peninsula) produces and 56 processes large amounts of DOC (Álvarez-Salgado et al. 2001), and is therefore an 57 3 appropriate area to establish if a quantitative relationship between fluorescence 58 spectroscopy measurements and the bioavailability and rate constant of DOC exists. 59 Complementing the study by Lønborg et al. (2009b) on the kinetics and C: N: P molar 60 ratios of DOM degradation in the Ría de Vigo, we show here new insights on the dynamics 61 of the consumption of labile and the production of refractory DOM based on fluorescence 62 spectroscopy measurements during the course of the same experiments. 63 64 2. Material and methods 65 2.

Turnover time of fluorescent dissolved organic matter in the dark global ocean

“…It has been reported that the turnover of these fluorophores in the surface ocean is on a timescale of days 6,28 , but this long-term decline in tyrosine-like fluorescence in the dark global ocean, coupled to water mass ageing, has never been reported. We can hypothesize that a minor fraction of the tyrosine-like fluorescence is processed on the scale of centuries, whereas the bulk of the signal has a turnover time on the order of days to weeks.…”

Linkages among fluorescent dissolved organic matter, dissolved amino acids and lignin-derived phenols in a river-influenced ocean margin

“…In addition, relationships between the relative contribution (%) of protein-like PARAFAC components in total PARAFAC components and the biodegradable fraction (%) of dissolved organic carbon (DOC) were found in freshwater environments (Balcarczyk et al, 2009;Fellman et al, 2009;Hood et al, 2009). A correlation between degradation rates of proteinlike fluorescence intensity and DOC was also observed in coastal environments (Lønborg et al, 2010). Since carbon-normalized yields of amino acids are known to be useful molecular indicators of biodegradable DOM (Davis and Benner, 2007;Benner and Kaiser, 2011), the linkage between bioavailable protein-like components and amino acids in DOM has been assumed based on empirical evidence.…”

Warming increases carbon and nutrient fluxes from sediments in streams across land use

“…The calibrated values of fluorescence intensities at excitation/emission = 275 nm/240 nm and 350 nm/480 nm were recorded as protein-like and humic-like fluorospores (Coble, 1996;Stolpe et al, 2010). Relative to the humic-like fluorospore, the intensity of the protein-like fluorospore is generally higher in labile DOC sources (e.g., wastewater; Hudson et al, 2007) and positively correlated with DOC bioavailability (Balcarczyk et al, 2009;Lønborg et al, 2010). So, the ratio of protein-like to the humic-like fluorospore (P/H) was calculated here as an index for organic carbon lability.…”