Air sampling methodology for determination of methane concentration on the periphery and in buoys in a shallow lake

Data shows the temporal variation in atmospheric methane (CH4) concentrations over two consecutive periods of about 15 days each in seasonal fieldworks during four years (April 2011 - March 2015) in a shallow lake, “La Barrancosa”. Also, contain wind speed and direction data for the total study period provided by the National Weather Service (SMN), Weather Station of Benito Juárez. Four sampling stations were located in the lake: two on buoys near the center of the lake and two located at the west – south-southwest of the lake (peripherals). Time-integrated air samples were collected by vacuum vessels equipped with air intake restrictors (IR) (Gere and Gratton 2010). The different technical issues that must be considered for the validation of the sampling methodology are detailed (analysis of the tightness of the vessels and good operation of the shutoff valve and assembly and calibration of the IR). The air samples were analyzed for CH4 concentration by gas chromatography (CG Agilent 7890A). Linear regressions for AM in the air samples from the periphery (AMP) and in those collected within the lake (AMB) were performed using Origin Lab 6.0 software. Pearson correlation analyses (R) to examine the representativeness of AMP regarding CH4 diffusive fluxes at the water - air interface (Fusé et al., 2016) and year-to-year differences of the means of AM (ANOVA, Fisher’s LSD Test) were performed using Infostat Statistical Software. The wind rose was elaborated with WRPLOT View 7.0.0. The results highlight the use of a simple and low-cost methodology to estimate the behavior of CH4 emissions from a shallow lake by measuring peripherals atmospheric CH4 concentrations, which could be easily extrapolated to the simultaneous study of several lakes.

本数据集涵盖2011年4月至2015年3月四年间，在浅水湖泊“拉班坎索萨（La Barrancosa）”开展的季节性野外考察中，两个各持续约15天的连续观测时段内的大气甲烷（CH₄）浓度时间变化数据。同时包含研究全周期的风速与风向数据，数据由国家气象局（National Weather Service, SMN）贝尼托华雷斯气象站提供。该湖泊共设置4个采样站位：2个布设于湖中心附近的浮标上，另外2个位于湖泊西-南西南方向的外围区域。研究采用配备进气限流器（IR）的真空容器采集时间积分型空气样品（Gere与Gratton，2010）。本文详细说明了采样方法验证需考量的各类技术细节，包括容器密封性检测、截止阀运行性能校验，以及进气限流器的组装与校准。空气样品中的甲烷浓度采用气相色谱法（CG Agilent 7890A）进行分析。研究使用OriginLab 6.0软件，分别对外围空气样品中的大气甲烷（AMP）与湖内空气样品中的大气甲烷（AMB）开展线性回归分析。采用Infostat统计软件完成两项统计分析：一是皮尔逊相关分析（R），用于验证外围大气甲烷浓度对水-气界面甲烷扩散通量的代表性（Fusé等，2016）；二是针对大气甲烷平均浓度的年际差异，开展方差分析（ANOVA）与费舍尔最小显著差异检验（Fisher’s LSD Test）。此外，采用WRPLOT View 7.0.0软件绘制研究区风玫瑰图。本研究结果证实，通过监测外围大气甲烷浓度，可采用简便且低成本的方法估算浅水湖泊的甲烷排放特征，该方法可便捷推广至多湖泊的同步研究工作。