Effect of bacterial activity on nutrient regeneration and release from bottom sediments
The effect of bacterial activity of surface sediment layer on nutrient regeneration and release from bottom sediment should be an important factor in estimating nutrient fluxes. In this study, core incubation experiments were conducted to investigate the bacterial activity in a shallow coastal area, Shido Bay, the Seto Inland Sea, from May to September 2016. High nutrient upward fluxes were observed in a high temperature period. Sodium azide (NaN3) was added to the overlying water of the core incubation experiment system to inhibit bacterial activity. The results of adding NaN3 showed that the bacteria could not only regenerate nutrients but also assimilate nutrients in the bottom sediments. Moreover, bacteria in the superficial layer, the top 2–3 mm layer of surface sediment (SL), markedly assimilated NH4 and PO4, although they did not assimilate Si(OH)4. Judging from these results, we concluded that the upward nutrient fluxes were fundamentally regulated by temperature, which affected the physicochemical processes and bacterial activity, because our previous study showed that the nutrient fluxes were scarcely affected by the activities of microphytobenthos, which were active only during winter when sufficient light penetrated to the seafloor.
KeywordsSurface sediments Superficial layer Nutrient flux Shido Bay The Seto Inland Sea
We gratefully acknowledge the generous assistance of Mr. Koji Kishimoto, captain of the R/V Calanus III, and the students of the Biological and Chemical Oceanography Laboratory, Kagawa University, during the field study. We would like to thank Mr. Dennis Murphy, the United Graduate School of Agricultural Sciences, Ehime University, for his help with the English in the manuscript. This study was funded by JSPS KAKENHI (Grant no. JP26281009).
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