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.