Benthic N2 production rates, Si cycling and environmental characteristics from the Öre estuary on the Swedish coast@en

Sediment samples for measuring N2 production and for the characterization of the sediment system were taken in spring and summer 2015 in the Öre Estuary at the Swedish coast of the Quark Strait, northern Baltic Sea. Sediment was sampled with a HAPS bottom corer (sand) and with a GEMINI twin corer (mud). The grain size of the sand sediment was analyzed via wet sieving from the sediment layers 0-1, 1-2, 2-3 cm (spring campaign) and 0-0.5, 0.5-1.0, 1.0-1.5 cm (summer campaign); due to vertical homogeneity, these surface sediments were subsequently pooled and the sediment type was classified after Wentworth (1922). Porosity and water content were analyzed both from sediment slices and from entire core subsamples, which means that sediment in a sampling core (heights 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 Darcie's Law. The oxygen penetration depth (OPD) was determined by manual (spring) and automated (summer) profiling at bottom water temperature (electrode tip 100 µm). 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 20 cm, iD 2.3 cm) in a concentration series of 30, 60, 90, 120 µM 15NO3- (n=3) for 4-5h at in situ bottom water temperature and darkness. 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).2015年春季与夏季，在波罗的海北部夸克海峡（Quark Strait）瑞典沿岸的厄勒河口（Öre Estuary）采集了用于测定N₂产生量及表征沉积物系统的沉积物样品。沉积物采样分别采用HAPS底泥采样器（HAPS bottom corer）采集砂质沉积物，以及GEMINI双管采样器（GEMINI twin corer）采集泥质沉积物。针对砂质沉积物，分别对春季航次的0-1、1-2、2-3 cm层位，与夏季航次的0-0.5、0.5-1.0、1.0-1.5 cm层位采用湿筛法（wet sieving）开展粒度分析；鉴于表层沉积物垂向均一性良好，后续将对应层位合并，并依据温特沃思（Wentworth, 1922）的沉积物分类标准完成类型判定。孔隙度与含水量的分析分别通过沉积物切片与完整岩芯子样开展：将内径2.3 cm、柱高20 cm的采样岩芯内沉积物充分混匀后分取子样，该操作基于垂向均一性假设；样品于105℃下烘干过夜，计算方法遵循伯迪奇（Burdige, 2006）的标准流程。沉积物有机质含量采用烧失量（LOI, Loss on Ignition）法测定，将烘干后的沉积物置于550℃下灼烧4小时。沉积物渗透率则针对合并后的表层沉积物（约1-2 cm的均一表层层位），采用渗透池装置（permeameter cell），依据层流条件下水体通过颗粒土壤的常水头法开展测定，计算依据达西定律（Darcy's Law）。氧渗透深度（OPD, Oxygen Penetration Depth）通过原位底温条件下的手动（春季航次）与自动（夏季航次）剖面法测定，所用电极尖端直径为100 µm。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，该方法可量化厌氧氨氧化（anammox, anaerobic ammonium oxidation）对总N₂产生量的潜在贡献。培养实验采用内径2.3 cm、柱高20 cm的亚克力岩芯（acrylic cores），设置30、60、90、120 µM的¹⁵NO₃⁻浓度梯度（每组n=3），在原位底温与黑暗条件下培养4-5小时。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，源自沉积物硝化作用产生的硝酸盐的反硝化作用。若未检测到厌氧氨氧化对总N₂产生量的贡献，则对应数据列取值为0。