MEPS 571:65-81 (2017)  -  DOI: https://doi.org/10.3354/meps12135

ABSTRACT: Benthic foraminifera were investigated to determine their vertical distribution, nitrate storage, and potential denitrification in the Yellow Sea (YS) and the East China Sea (ECS). The phytodetritus content and freshness as well as sediment redox conditions were key factors determining the vertical distribution of foraminifera in sediments of the YS and the ECS. The intracellular nitrate (ICNO₃) concentrations of Nonionella stella, Hanzawaia nipponica, Bolivina robusta, Cancris auriculus, and Globobulimina pacifica ranged from 3 to 114 mM, which in some cases was several hundred-fold more than the pore water nitrate (PWNO₃) concentrations. The genus Hanzawaia was for the first time reported to store ICNO₃ (316 ± 73 pmol ind.^-1; 11 ± 3 mM). The significant correlation between the ICNO₃ concentration and foraminiferal abundance (Pearson correlation: r = 0.401, p < 0.01, n = 60) suggested that foraminifera may have an important role in nitrate storage in the sediments. The foraminiferal intracellular nitrate (FINO₃) pool ranged from 9 to 74% of the ICNO₃ pool in sediments, indicating that nitrate may be stored by other sediment organisms (e.g. diatoms). The chlorophyll a concentration, chloroplastic pigment equivalents (CPE), and chlorophyll a:phaeopigment ratio were all significantly positively correlated with the ICNO₃ concentration (Pearson correlation: r = 0.563, 0.603, and 0.457, respectively; p < 0.01; n = 60), indicating that phytodetritus (e.g. diatoms) might also contribute to sedimentary ICNO₃. Potential foraminiferal denitrification rates ranged from 9 to 92 µmol m^-2 d^-1 in the YS and the ECS, indicating that benthic foraminifera might play a role in sedimentary denitrification.

KEY WORDS: Live benthic foraminifera · Vertical distribution · Intracellular nitrate · Potential denitrification · Yellow Sea · East China Sea