CO2, CH4, and H2O flux data and associated environmental variables for the BBC collapse scar for 2004

This data set contains flux measurements for the transect from the center of the BBC collapse scar (0m) into the surrounding fire scar (30m) of the Survey Line Fire (burned in June-July 2001).
We measured CO2, H2O and CH4 fluxes every one to two weeks throughout the growing season of 2004. We measured fluxes at permanent plots established from the center of the bog into the surrounding burn at 0, 6, 12, 18, 24, and 30 m on the east and west side of the transect. Flux measurements on either side of the transect were treated as replicates. CO2 and H2O fluxes were measured using a Li-840 infrared gas analyzer (Licor Inc., Lincoln, NB, USA). The IRGA was calibrated before each trip to the field using a span of 400 ppm and a zero of N2 gas. We logged data every 0.5 seconds for 2 min. To account for measurement variability, we conducted two measurements in succession at each location, after flushing the chamber for accumulated CO2 and H2O. For the flux measurements, we built plexiglass chambers with pipe insulation bases with dimensions of 61 x 61 x 30.5 cm, 61 x 61 x 61 cm, or 61 x 61 x 122 cm. The shorter chambers were used in the collapse portion of the transect. Chambers included fans for air circulation, inlet and outlet ports for CO2 measurements, or just outlet ports for CH4 measurements (Carroll and Crill 1997). We placed chambers directly on the soil surface and used pipe insulation and plastic sheeting to make a solid seal during the measurement. To estimate the volume for each chamber measurement, we measured the distance to the soil surface from a 6 cm grid suspended 30 cm above each plot, the surface area was then used to calculate the chamber volume for each measurement. Dark measurements were used to determine CO2 derived from soil and root respiration (ecosystem respiration) using a two-layer cloth shroud with a reflective surface to exclude solar radiation. To estimate net ecosystem exchange (NEE) of CO2, we conducted chamber measurements of plant and soil respiration and plant uptake. NEE data are not reported as NEEmax (NEE at PAR greater then 1000 umol m-2 s-1) as PAR only once surpassed 1000 umol m-2 s-1 during field measurement trips in 2004. Smoke from wildfires through July and August reduced PAR and likely influenced relationships between PAR and NEE. After experimenting with different incubation lengths, we conducted 40 min methane flux measurements to compensate for low flux rates and large chambers. Syringe samples were taken after deploying the chamber and at 8 min intervals, yielding 6 gas samples. We analyzed gas samples using a Varian CP-3800 gas chromatograph with a flame ionization detector (Varian Inc., Palo Alto, CA, USA). We calibrated the GC before each use using standard gases (CH4: 99.9 and 1020 ppb; CO2: 284 and 10195 ppm). We calculated CO2, H2O and CH4 flux rates using linear regressions of gas concentrations over time. We excluded all data sets that did not exhibit initial linear fluxes (r2 < 0.9).

本数据集包含2001年6-7月发生的Survey Line野火（Survey Line Fire）的通量观测数据，样带覆盖从BBC塌陷坑中心（0m处）延伸至周边火烧迹地（30m处）的区域。
2004年整个生长季内，我们每1-2周开展一次CO₂、H₂O及CH₄通量观测。观测样地设置于样带东西两侧，从泥炭沼泽中心向周边火烧区域依次布设0、6、12、18、24、30m共6个永久样点，样带两侧的观测数据作为重复样本进行处理。
CO₂与H₂O通量采用Li-840型红外气体分析仪（infrared gas analyzer, IRGA，Licor公司，美国内布拉斯加州林肯市）进行测定。每次野外采样前，均使用400ppm标准气作为跨度校准气、高纯氮气作为零点校准气对红外气体分析仪完成校准。数据采集频率为每0.5秒记录1次，单次观测时长为2分钟。为控制测量变异，每次观测前先对箱室进行吹扫以排出累积的CO₂与H₂O，随后在每个样点连续开展两次重复测量。
本次观测使用的有机玻璃箱室搭配管道保温基座，尺寸分为61×61×30.5cm、61×61×61cm及61×61×122cm三种。样带塌陷区域使用高度较低的短尺寸箱室。箱室配备空气循环风扇，其中CO₂测量用箱室带有进、排气端口，CH₄测量用箱室仅配备排气端口（参考Carroll与Crill, 1997）。观测时将箱室直接放置于土壤表面，使用管道保温材料与塑料薄膜进行密封以保证气密性。
为估算每次观测的箱室体积，我们在每个样点上方30cm处架设6cm间距的网格标尺，测量网格至土壤表面的垂直距离，结合样地面积计算得到单次观测的箱室体积。
采用带有反射面的双层布罩遮挡太阳光以排除辐射干扰，开展暗态测量以估算土壤与根系呼吸产生的CO₂（即生态系统呼吸）。为估算CO₂的净生态系统交换量（Net Ecosystem Exchange, NEE），我们同步开展了植物与土壤呼吸以及植物光合固碳的箱室观测。由于2004年野外观测期间仅出现过1次光合有效辐射（Photosynthetically Active Radiation, PAR）超过1000μmol·m⁻²·s⁻¹的情况，因此未报告NEEmax（即PAR大于1000μmol·m⁻²·s⁻¹时的NEE）。2004年7-8月的野火烟雾降低了PAR水平，可能干扰了PAR与NEE之间的响应关系。
针对甲烷通量速率较低且箱室尺寸较大的情况，在对比了不同培养时长后，我们采用40分钟的甲烷通量观测时长。箱室部署后，每隔8分钟采集1次气样，共获取6个气体样品。采用Varian CP-3800型气相色谱仪搭配火焰离子化检测器（Varian公司，美国加利福尼亚州帕洛阿尔托市）对气体样品进行分析。每次使用气相色谱仪前，均使用标准气体完成校准（CH₄标准气浓度分别为99.9ppb与1020ppb；CO₂标准气浓度分别为284ppm与10195ppm）。
我们通过气体浓度随时间变化的线性回归方法计算CO₂、H₂O及CH₄的通量速率，并剔除所有初始阶段线性相关性不足（决定系数r²<0.9）的数据集。