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

TLDR: In this paper, 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.

About: This article is published in Marine Chemistry.The article was published on 2009-02-20 and is currently open access. It has received 120 citations till now. The article focuses on the topics: Dissolved organic carbon.

Figures

Table 2 Matrix of the correlation coefficient (R2) of the significant (p< 0.05) linear regressions between DOM bioavailability and hydrological data from Loch Creran. n.s. – not significant.

Table 1 Significant regressions between BDOM and DOM, Inorganic nutrients (DIN, DIP) and degradation constants at 14ºC (k–DOC, k–DON and k–DOP) obtained by fitting the exponential degradation of DOC, DON and DOP with time. Slope, incept, and standard error are values found by Model II regression. R2 = coefficient of determination, p = significant levels and n.s. – not significant.

Table 3 Degradation constants obtained by fitting the exponential degradation of DOC, DON and DOP with time at varying temperature (T, °C) for DOC, DON and DOP ± standard error; R2 = coefficient of

Frequently asked questions

Q1. What is the effect of low temperatures on the DOM pool?

Low temperatures have been shown to both alter rates and availability of organic matter 5 mineralization, as the ability of an organism to sequester substrate declines at low temperature6 (Nedwell, 1999). 

Q2. What is the impact of photochemical processes on DOM bioavailability?

16 Photochemical processes can lead to both reduced and enhanced DOM bioavailability, with 17 the impact probably depending on the source and chemical composition of the DOM (Tranvik and18 Bertilsson, 2001). 

Q3. Why did the bacterial community have to use the BDOM produced in situ?

Since their incubations were closed to new production, they forced the bacterial community to 2 use the BDOM produced in situ prior to these experiments. 

Q4. What is the effect of low temperature on bacterial community composition in the NW Mediterranean Sea?

Seasonal changes in bacterioplankton nutrient limitation and their effects on 21 bacterial community composition in the NW Mediterranean Sea. 

Q5. What is the stoichiometry of the BDOM degraded in Loch?

The stoichiometry of BDOM degraded within Loch Creran exhibits 5 an average C:N:P molar ratio of 236: 38: 1, with the exported BDOM being more C and N rich, with 6 a C:N:P molar ratio of 581: 59: 1. 

Q6. What is the effect of temperature on the decay rates of DOM in Loch Creran?

The decay rates of DOM in Loch Creran could have been further influenced by temperature, 12 as previous studies show inhibition of bacterial growth at low temperatures, probably due to low 13 extra–cellular enzymatic hydrolysis rates (Kirchman and Rich, 1997). 

Q7. How many times were the DOM samples collected?

These were conducted four times throughout the season (28-Jul, 8-Sep-2006 19 and 16-Jan, 16-May-2007) with duplicate bottles at each temperature to test if changing temperature 20 would influence the bioavailability and decay rates of DOM. 

Q8. What is the origin intercept of the relationship between DON and DOP?

12 Furthermore, the origin intercept of the relationship between DON and DOP shows that 3.4 ± 0.9 13 µmol L–1 of DON would remain when DOP is completely depleted. 

Q9. What is the lability of the DOM pool?

It should be noted that using this method, the lability of BDOM is a function of the time 3 steps being employed to measure reactivity. 

Q10. What is the reason for the high C:N:P ratios of BDOM?

High C:N:P ratios of BDOM may 12 either be due to plankton release of C–rich labile compounds such as mono and polysaccharides13 under in situ N– and/or P–depleted conditions (Williams, 1995; Fajon et al., 1999) or/and in-situ14 preferential degradation of the N– and/or P–rich compounds (Hopkinson et al., 1997; 2002).