Quantification of biodegradable dissolved organic carbon in the ocean

Abstract:

[Objective] Refractory dissolved organic carbon (RDOC) is the main component of marine dissolved organic carbon (DOC) pool, which persists in the ocean for thousands of years, and is an important form of marine carbon sequestration. However, there is no consistent protocol for RDOC quantification. RDOC can be quantified by measuring the amount of biodegraded dissolved organic carbon (BDOC). [Methods] We performed quality control experiments to evaluate crucial steps during BDOC quantification, such as the effect of membrane and filtration methods on DOC contamination, and the effect of incubation volume and dilution on DOC utilization. [Results] Results show that (1) GF/F, GF-75, 0.2-μm polytetrafluoroethylene, 0.2-μm polycarbonate membranes and 0.2-μm polytetrafluoroethylene filter did not induce DOC contamination; the performance of vacuum and gravity filtration were relatively contamination-free and more stable than on-line filtration; (2) incubation ranged 30 mL to 480 mL (area-to-volume ratios:1.64-0.67 cm^-1) showed no significant difference in terms of bacterial growth rate and DOC utilization; and (3) dilution had obvious effects on bacterial growth rate, biomass accumulation, and the amount of the DOC used. [Conclusion] Taken together, it is recommended to use the vacuum filtration and non-diluted incubation in BDOC bioassay; and the commonly used filter membranes and incubation volume may not affect BDOC quantification. Furthermore, we proposed a protocol for measuring RDOC based on this work.