Chamber-based Soil Methane Flux Measurement B41H-2824 Liukang Xu*, Richard Vath, Johnathan McCoy LI-COR Biosciences, Lincoln, Nebraska USA;

Introduction Results: The soil at our field site is a Sharpsburg silty clay loam Example of time serial CH4 concentration: With a LI-8100-104 In the literature, datasets for methane oxidation rate in soil are (Typic Argiudall) and the ground cover is primarily fescues chamber (chamber volume of 4013 cm3 and soil area of 318 limited due to the lack of high accuracy and precision methane (Festuca spp.) with a mean vegetation height of approximately 5 cm2), linear regression coefficients were normally higher than -2 -1 analyzers and automated measurement systems. Recently, LI- cm. From the 4-chamber CH4 flux data, two patterns in seasonal 0.9 when the CH4 flux was higher than 0.1 nmol m s . see the COR developed a methane analyzer (LI-7810, LI-COR variation of CH4 flux were observed, which are illustrated below two examples below. Biosciences) which can be used for chamber-based soil CH4 using the datasets from Chamber #1 and #2 as examples. 1960 1972 flux measurements. We integrated this methane analyzer into Pattern 1. From Chamber #1 and #3, the soil was a CH4 source in -1 -1 dCH4/dt=0.277 ppb s dCH4/dt = -0.027 ppb s -2 -1 2 an automated soil CO2 flux system (LI-8100A/8150). Field soil the summer with a rate of up to 2.8 nmol m s even when the R =0.999 R2=0.962 1950 Flux = 1.97 nmol m-2s-1 1970 Flux = - 0.201 nmol m-2s-1 CO2 and CH4 flux measurements were conducted at LI-COR’s soil moisture was dropped to 0.2 (v/v). The high emission rate at field station from early September, 2018 to the end of our field site was unexpected. Additional work is needed to 1940 1968 (ppb) November, 2018. In this report, we first describe some key determine why the high rate of emission occurred over this 4

CH 1930 1966 Deadband Deadband specifications of the analyzer, then preliminary field soil CH4 grassland. After DOY 300, the soil became a CH4 sink with a typical -2 -1 flux data will be reported. rate of -0.2 nmol m s . 1920 1964 Chamber #1 1910 1962 LI-7810 Key Specs 30 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 C) o 25 Time (s) Time (s) Range Precision @ 5s 20 Accuracy 15 CH4: 0.1-50 ppm ≈0.25 ppb 2 ppb@ 2000 ppb,25 °C 10 Based on our seasonal long- CO : 1-10000 ppm ( Temp Soil 2 ≈1.5 ppm 1.5 % @ 300-700 ppm, 25 °C 5 term methane flux data, we H2O: 0.100-60 ppt 0 ≈20 ppm 1.5 % @ 0.5-60 ppt,25 °C 2000 feel confident that this -1 0.4 dCH4/dt = - 0.0066 ppb s 2 0.3 configuration of a closed 1999 R =0.720 A CH analyzer (LI-7810) was integrated into 4 Flux = - 0.051 nmol m-2s-1 Field setup: 4 0.2 chamber system can resolve a 1998 chamber multiplexed system (LI-8100A/8150 system, outlet of 0.1 minimum flux as low as 0.05 Soil Moisture(v/v) Soil

(ppb) 1997 LI-8100 AIU). Soil temperature and moisture at each chamber 0.0 -2 -1 4

) nmol m s . See an example to CH Deadband -1 at the depth of 5 cm were also measured. The clocks of the LI- s 1996 -2 3 the right. Over the two 8100A and the LI-7810 were synchronized by a computer at 2 minutes observation, chamber 1995 the field station. 1 CH4 concentration decreased 1994 0 20 40 60 80 100 120 140 Flux (nmol m (nmol Flux 4 by approximately 0.79 ppb Time (s)

CH 0 (0.0066X120=0.792 ppb). 250 260 270 280 290 300 310 320 330 This is about 3 times the precision of this CH analyzer (~0.25 DOY (Day of Year) 4 Chamber 4 ppb). This should give us enough confidence in the slope LI-7810 Chamber 3 Pattern 2: From Chamber #2 and #4, except for a brief duration estimation using linear or exponential regression. (DOY 281-283), the soil was a CH4 sink with a typical rate of -0.2 LI-8100A/8150 nmol m-2s-1 . The maximum rate was around -0.35 nmol m-2s-1 . Conclusions 1. Depending on the location, the silty clay loam soil with Chamber 2 This rate was expected and consistent with published rates (e.g. Ueyama, at al. AFM 2015). fescues vegetation at the Lincoln Nebraska can be a CH4 source or sink in the summertime. The emission rate can be Chamber #2 -2 -1 35 ashigh as 2.8nmol m s . 30 C) Chamber 1 o 25 2. After DOY 300, the soil is a CH4 sink with a typical rate of – 20 -2 -1 15 0.2 nmol m s . 10 CH flux calculation: 5 3. With our current instrument setup (LI-8100A/8150+LI-

4 ( Temp Soil 0 -5 7810), the minimum detect methane flux is approximately () -2 -1 퐹 = 0.4 0.05 nmol m s . 0.3 References -2 -1 0.2 Where: FCH4; soil CH4 flux (mol m s ) Ueyama M., et al., 2015. Methane uptake in a temperate forest 3 0.1

V: chamber volume (m ) (v/v) Moisture Soil 0.0 soil using continuous closed-chamber measurement. Agricultural )

P: atmospheric pressure (Pa) -1 s and Forest Meteorology. 213:1-9 -1 -2 Wo: initial water vapor mole fraction (mol mol ) 0.0 R: gas constant Acknowledgement: The initial principles and some portions of the new -0.2 S: soil area (m2) technology presented herein were developed in part based on the grant from

Fluxm (nmol the MONITOR Program by the U.S. Department of Energy Advanced Research 4 T: chamber temperature (K) -0.4 CH Projects Agency - Energy (ARPA-E), under award number DE-AR0000537. -1 -1 : rate of CH4 change (mol mol s ) 250 260 270 280 290 300 310 320 330 *Contact information: [email protected] DOY (Day of Year)