Surface greenhouse gas fluxes, partial pressures and hydrochemistry at Teno river in northern Fennoscandia

Study area Teno river (Finnish: Tenojoki, Norwegian: Tana, Northern Sámi: Deatnu) at the border between Norway and Finland (70.092°N, 27.959°E) Boreal river flowing into the Arctic Ocean Pristine ecosystem mostly unaffected by industry, damming or other human influences Strahler order at measurement locations ranged between 1 and 5 Measurement overview Measurements were conducted for fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) using different chamber setups, and for respective partial pressures, and hydrochemistry in August 2023, June 2024, and September 2024 at various stages of river discharge (Table 1). Table 1: Overview of measurements in the river channel and at banks, which refer to the transitional area bordering the river channel. Measurements Target Chamber type Time CO2 and CH4 fluxes, partial pressures, hydrochemistry River channel Floating chambers August 2023 CO2 and CH4 fluxes, substrate type, vegetation coverage, sediment analysis Banks Static chambers August 2023 CO2, CH4 and N2O fluxes, partial pressures, hydrochemistry River channel Anchored chambers August 2023, June and September 2024 CO2 fluxes Banks Static chambers June and September 2024 Greenhouse gas flux measurements Greenhouse gas fluxes were determined from chamber measurements conducted at the water surface and at adjacent banks. Mole fractions of CO2, CH4 and N2O within the chamber headspace were measured from a boat, from the shore or at confluences with tributaries, with different greenhouse gas analyzers (portable and laboratory analyzers), at different sites and sections of the river all indicated in the dataset. Water-air and soil-air fluxes were derived from changes of mole fractions over time using linear regressions. The atmospheric pressure was measured with an RM Young barometric pressure sensor or a Multilogger Thermo-hygro barometer. Ambient temperatures were determined with a WTW multiprobe or the Multilogger Thermo-hygro barometer. For terrestrial measurements at banks, the substrate type and percentage of vegetation coverage at the measurement location were visually determined. Furthermore, about 300 g of the top three centimeters of the sediment were sampled and analyzed for water content, pH, electrical conductivity and grain size. Partial pressure measurements Partial pressures of CO2, CH4 and N2O were measured at 5-10 cm depth below the water surface in-situ using an equilibrator connected to a portable greenhouse gas analyzer (LI-7810, LI-COR) or in-lab using gas chromatography after water samples were collected. Detection limits for the gas chromatograph were 200 ppm for CO2, 1 ppm for CH4, and 0.4 ppm for N2O. Continuous CO2 and CH4 partial pressure measurements conducted in August 2023 were averaged and assigned to individual flux measurements, but are also published here as a 1 Hz timeseries. Hydrochemical measurements Measurements of water temperature and specific conductivity, pH, turbidity, chlorophyll, phycocyanin, fluorescent dissolved organic matter (fDOM), and dissolved oxygen (DO) were conducted at approximately 10 cm below the water surface with an EXO2 Multiparameter Sonde (YSI) equipped with a wiper to clean the sensors once an hour. Besides, electric conductivity (EC) at the water surface was measured with an EC meter (WTW pH/cond 340i). Chloride, phosphate and nitrate were measured using ion chromatography (Dionex ICS-2100, Thermo Scientific). Dissolved organic carbon (DOC) and dissolved nitrogen (DN) concentrations were measured with a TOC analyzer (TOC-VCPH, Shimadzu). Corresponding detection limits are given in Table 2. If values were below the detection limits, they were set to zero. Wavelength-specific UV-absorbance at 254 nm (SUVA254) was determined from spectral absorbance measured with a spectrophotometer (UV-1800, Shimadzu) divided by the DOC concentration. The chromophoric dissolved organic matter (CDOM) content was derived from adsorption at 350 nm. Table 2: Detection limits of DOC, TN, chloride, phosphate and nitrate. Analysis Detection limit (mg/L) DOC 0.1 TN 0.3636 Chloride 0.13 Phosphate 0.19 Nitrate 0.16研究区域 特诺河（芬兰语：Tenojoki，挪威语：Tana，北萨米语：Deatnu）坐落于挪威与芬兰边境地带（北纬70.092°，东经27.959°），为注入北冰洋的寒温带河流。该流域为原始生态系统，基本未受工业活动、筑坝工程或其他人类活动干扰。测量点位的斯特拉勒级数（Strahler order）介于1至5之间。 ## 测量概况 本数据集于2023年8月、2024年6月及2024年9月开展，针对不同河流径流阶段（见表1），采用多种箱式布设装置测定了二氧化碳（CO₂）、甲烷（CH₄）和一氧化二氮（N₂O）的气体通量，并同步测定了相关气体分压及水化学参数。 表1 河道及河岸（指毗邻河道的过渡区域）测量概况 | 测量目标 | 布设区域 | 箱式类型 | 测量时段 | |---------|----------|----------|----------| | CO₂与CH₄通量、气体分压及水化学参数 | 河道 | 浮动式箱式装置 | 2023年8月 | | CO₂与CH₄通量、底质类型、植被覆盖度及沉积物分析 | 河岸 | 固定式箱式装置 | 2023年8月 | | CO₂、CH₄与N₂O通量、气体分压及水化学参数 | 河道 | 锚定式箱式装置 | 2023年8月、2024年6月及9月 | | CO₂通量 | 河岸 | 固定式箱式装置 | 2024年6月及9月 | ## 温室气体通量测量 温室气体通量通过水面及毗邻河岸的箱式测定获得。借助便携式与实验室型温室气体分析仪，于河道不同点位、河段及支流汇流处，从船上、岸边现场测定了箱头顶空层内CO₂、CH₄及N₂O的摩尔分数。水面-大气与土壤-大气通量通过摩尔分数随时间的变化，经线性回归计算得到。 大气压力采用RM Young气压传感器或Multilogger温湿气压计测定；环境温度通过WTW多参数探头或Multilogger温湿气压计获取。针对河岸的陆地测量，采用目视法确定测量点位的底质类型及植被覆盖百分比。此外，采集约300g表层3cm沉积物样品，分析其含水率、pH值、电导率及粒径组成。 ## 气体分压测量 CO₂、CH₄及N₂O的分压采用两种方式测定：一是将平衡器连接至便携式温室气体分析仪（LI-7810，LI-COR公司），于水面下5~10cm原位测定；二是采集水样后，在实验室通过气相色谱法测定。气相色谱仪的检出限为：CO₂ 200 ppm、CH₄ 1 ppm、N₂O 0.4 ppm。2023年8月开展的连续CO₂与CH₄分压监测数据经平均后匹配至各通量测量结果，同时以1Hz时序数据形式随本数据集一同发布。 ## 水化学测量 采用搭载自动刮洗传感器装置（每小时清洁一次）的EXO2多参数水质探头（YSI公司），于水面下约10cm处测定水温、比电导率、pH值、浊度、叶绿素、藻蓝蛋白、荧光性溶解有机质（fDOM）及溶解氧（DO）。 此外，采用电导率仪（WTW pH/cond 340i）测定水面电导率（EC）；采用离子色谱仪（Dionex ICS-2100，赛默飞世尔科技公司）测定氯离子、磷酸盐及硝酸盐浓度；采用总有机碳分析仪（TOC-VCPH，岛津公司）测定溶解有机碳（DOC）与溶解态氮（DN）浓度。各参数的检出限详见表2。若测量值低于检出限，则记为0。采用紫外-可见分光光度计（UV-1800，岛津公司）测定254nm波长处的紫外吸光度，除以DOC浓度得到特定波长吸光度（SUVA₂₅₄）；通过350nm处的吸光度推算发色性溶解有机质（CDOM）含量。 表2 DOC、总氮（TN）、氯离子、磷酸盐及硝酸盐的检出限 | 分析物 | 检出限（mg/L） | |-------|--------------| | DOC | 0.1 | | TN | 0.3636 | | 氯离子 | 0.13 | | 磷酸盐 | 0.19 | | 硝酸盐 | 0.16 |