Benthic N2 production rates (denitrification, anammox), sediment characteristics and silicate in coastal sediments of the Vistula Estuary and the Bay of Gdansk during 3 seasons (winter, sping, summer)@en

Sediment samples for measuring N2 production rates and for the characterization of the sediment system were taken in three seasons (winter, spring, summer) from sand and mud sediments of the Vistula Estuary and the open Bay of Gdansk at the Polish coast, Southern Baltic Sea. Sediment was sampled with a HAPS bottom corer (coarse sand), a Multicorer and a Boxcorer (fine sand, mud). Porosity was analyzed both from sediment slices and from entire core subsamples, which means that sediment in a sampling core (heights 15-20 cm, iD 2.3 cm) was mixed and sub sampled, assuming vertical homogeneity; sediment was dried overnight at 105°C and calculations followed Burdige (2006). Sediment organic matter content was analyzed as loss on ignition (LOI), for which dried sediment was combusted at 550°C for 4h. Sediment permeability was measured from pooled surface sediments (~1-2 cm homogeneous surface layer) with a permeameter cell following the constant head method for laminar flow of water through granular soil; calculations were derived from Darcy's Law. The oxygen penetration depth (OPD) was determined by manual (EMB 77, AL 449) and automated (EMB 123) profiling at bottom water temperature, electrode tip 100 µm: EMB 123, AL 449 (mud) and 250 µm: EMB 77, AL 449 (sand), EMB 123 (VE05, VE49). Denitrification rates were measured with the revised isotope pairing technique (r-IPT; Risgaard-Petersen et al. 2003, 2004) that accounts for the potential contribution of anammox (anaerobic ammonium oxidation) to total N2 production. Incubations were done in acrylic cores (heights 15-20 cm, iD 2.3 cm) in a concentration series of 30, 60, 90, 120 µM 15NO3- (n=3, EMB 77, AL 449) and 40 (n=4), 80 (n=4), 120 (n=12) µM 15NO3- for 3-5h at in situ bottom water temperature and darkness. In the presence of significant advective pore water flow, an advective incubation design was used. Dw gives denitrification of nitrate from the water column; Dn gives denitrification of nitrate from sediment nitrification (coupled nitrification-denitrification). If no contribution of anammox to total N2 production was found, columns hold a zero (0). The sediment silicate content (ASi =amorphous, biogenic Si (Na2CO3-extractable), Ca-Si = easily available Si (CaCl2-extractable), Ox-Si = oxide-bound Si (extractable by acid oxalate)) was analyzed from the top sediment layer.用于测定N₂生成速率并表征沉积物系统的沉积物样品，于三个季节（冬季、春季、夏季）采自波罗的海南部波兰沿岸的维斯瓦河口（Vistula Estuary）与格但斯克外海（Bay of Gdansk）的砂质、泥质沉积物。沉积物采样分别采用HAPS底质取样器（HAPS bottom corer，适用于粗砂）、多管取样器（Multicorer）与箱式取样器（Boxcorer，适用于细砂、泥质沉积物）。 孔隙度分析涵盖沉积物切片与完整岩芯分样两种方式：具体操作为将高度15~20 cm、内径2.3 cm的采样岩芯内沉积物充分混匀后分样，假设沉积物垂向均一；随后将沉积物置于105℃下烘干过夜，计算方法参照Burdige（2006）的标准。 沉积物有机质含量通过烧失量法（LOI，loss on ignition）测定，具体步骤为将烘干后的沉积物置于550℃高温下灼烧4小时。 沉积物渗透性采用渗透池法，针对颗粒土壤中水流的层流运移采用恒水头法，对混合后的表层沉积物（~1~2 cm厚的均质表层）进行测定，计算依据达西定律（Darcy's Law）。 氧渗透深度（OPD，oxygen penetration depth）在原位底温条件下，通过手动（EMB 77、AL 449）与自动化（EMB 123）剖面扫描法测定，电极尖端规格匹配不同沉积物类型与站位：100 μm适配EMB 123、AL 449（泥质沉积物）及EMB 123（VE05、VE49站位）；250 μm适配EMB 77、AL 449（砂质沉积物）。 反硝化速率采用修正同位素配对技术（r-IPT，revised isotope pairing technique；Risgaard-Petersen et al. 2003, 2004）测定，该方法可考量厌氧氨氧化（anammox，anaerobic ammonium oxidation）对总N₂生成的潜在贡献。培养实验采用高度15~20 cm、内径2.3 cm的亚克力岩芯进行，设置两组¹⁵NO₃⁻浓度梯度：其一为30、60、90、120 μM（n=3，对应EMB 77、AL 449实验），其二为40（n=4）、80（n=4）、120（n=12）μM，培养时长3~5小时，实验条件为原位底温与黑暗环境。当存在显著孔隙水对流流动时，则采用对流培养方案。 其中，Dw代表水体来源硝酸盐的反硝化作用，Dn代表沉积物硝化-反硝化耦合过程中沉积物内源硝酸盐的反硝化作用。若未检测到厌氧氨氧化对总N₂生成的贡献，则对应数据列的取值为0。 沉积物硅质组分（ASi：无定形生物硅，即Na₂CO₃可提取态硅；Ca-Si：易利用态硅，即CaCl₂可提取态硅；Ox-Si：氧化物结合态硅，即草酸可提取态硅）通过表层沉积物样品进行分析测定。