Underestimation of nutrient fluxes due to possible bacterial activity during a core incubation experiment

• Published in: Journal of oceanography Vol. 71; no. 3; pp. 263 - 270
• Main Authors: Abe, Kazuo, Tsujino, Mutsumi, Kazama, Takehiro, Nakagawa, Norihisa, Abo, Katsuyuki
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Japan 01.06.2015; Springer Nature B.V
• Subjects: Bacteria; Diffusion; Earth and Environmental Science; Earth Sciences; Freshwater & Marine Ecology; Nutrients; Oceanography; Original Article; Nutrients; Core incubation; Benthic flux; Sediment–water interface; Western Seto Inland Sea
• ISSN: 0916-8370; 1573-868X
• DOI: 10.1007/s10872-015-0285-5

Examinations of sediment core incubation and calculations of diffusive nutrient fluxes based on the difference between the nutrient concentration in pore water and that in the overlying water were carried out to evaluate the benthic fluxes of nutrients such as phosphate (PO 4 ), ammonium (NH 4 ), and silicic acid [Si(OH) 4 ] from the sediment–water interface. Test surface-sediment samples were collected in the western area of the Seto Inland Sea in October 2013 and January 2014. They were incubated onboard the ship for intervals of approximately 40–90 h, and changes in the concentrations of nutrients in the overlying water with incubation time were monitored. Furthermore, in order to inhibit bacterial activity, sodium azide (NaN 3 ) was added to the overlying water of another incubation system, whereupon nutrient concentrations in the overlying water were observed to increase linearly with incubation time. On the other hand, when NaN 3 was not added, a linear increase was observed in the Si(OH) 4 concentration but not in those of PO 4 and NH 4 . The calculated diffusive fluxes generally agreed with those obtained from core incubation with the addition of NaN 3 . These findings suggest that the elution of PO 4 and NH 4 from the sediment–water interface during a core incubation experiment can be affected by bacterial activity, which could potentially lead to the underestimation of benthic fluxes. Therefore, great care should be taken when carrying out incubations of surface sediment, and they should be performed along with calculations of diffusive fluxes.