Estimating Surface CO 2 Flux Based on Soil Concentration Profile

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1 Britih Journal of Environment & Climate Change 7(4): , 217; Article no.bjecc ISSN: Etimating Surface CO 2 Flux Baed on Soil Concentration Profile Salmawati 1*, K. Saaki 1 and S. Yuichi 1 1 Department of Earth Reource Engineering, Faculty of Engineering, Kyuhu Univerity, 744 Motooka, Nihi-ku, Fukuoka , Japan. Author contribution Thi work wa carried out in collaboration between all author. Firt author performed the meaurement at the field, data analyi and drafted the manucript. Second author checked the conitency of the data, proofread, and managed the flow of the drafted manucript. The third author helped in etting experimental and field work. All author have read and approved the final manucript. Article Information DOI: /BJECC/217/38328 Original Reearch Article Received 2 nd September 217 Accepted 24 th November 217 Publihed 16 th December 217 ABSTRACT Aim: To etimate the urface CO 2 flux derived from CO 2 concentration profile and to validate the reult by previou data of urface CO 2 flux obtained from the meaurement uing cloe-chamber method. Study Deign: The meaurement of oil CO 2 concentration profile, oil propertie, and oil temperature wa carried out to etimate urface CO 2 flux uing the derived model of ma balance equation. The reult were ubequently compared with meaurement of urface CO 2 flux uing cloe-chamber method. Place and Duration of Study: INAS field located in Ito Campu of Kyuhu Univerity (Japan) from November 215 to March 216. Methodology: CO 2 ga wa ampled in four different depth to analyze it concentration within the oil layer. Soil temperature wa monitored throughout the meaurement and oil propertie uch a denity, poroity and moiture content were meaured a well to etimate the diffuion rate. Derived from ma balance equation, the urface CO 2 flux wa etimated. It wa validated uing the previou meaurement data of urface CO 2 flux uing cloe-chamber method that had been conducted formerly at the ame location. Reult: A total of even meaurement of oil CO 2 concentration profile howed that the CO 2 concentration increaed with oil depth and it wa fitted with logarithmic trend (R 2 =.981 in average). A range of CO 2 concentration value wa meaured at each depth, i.e., 13 to 87 ppm at.1 m depth; 25 to 18 ppm at.2 m depth; 42 to 132 ppm at.3 m depth; and *Correponding author: almawati@mine.kyuhu-u.ac.jp;

2 58 to 165 ppm at 1. m depth. High CO 2 concentration in.1 m oil depth indicated high urface CO 2 flux. Concluion: Soil CO 2 concentration in INAS field increaed following a logarithmic trend. Baed upon thi trend, an equation to etimate the urface CO 2 flux wa propoed uing derived model from ma balance equation and ga diffuion model. The etimated urface CO 2 flux wa compared and howed a good agreement with meaured one. The equation preented herein i potentially uitable to etimate the urface CO 2 flux. Keyword: CO 2 concentration profile; logarithmic trend; urface CO 2 flux; cloe-chamber method; INAS field. 1. INTRODUCTION Carbon dioxide (CO 2 ) emiion from oil i one of the important parameter contribute to the carbon cycle on the Earth becaue oil i the bigget carbon pool in terretrial land [1]. It contribute around three-quarter of the CO 2 total ecoytem repiration [2]. Emitted CO 2 can be etimated by meauring it flux on the oil urface or in thi paper defined a urface CO 2 flux. CO 2 flux from the oil i determined by two major procee [3] including the generation of CO 2 within the oil, and it tranport in the oil and the emiion to the atmophere. The ource of the oil CO 2 production i primarily originated from root repiration, decompoition of organic matter, atmopheric infiltration, magmatic degaing, or the metamorphoi or diolution of carbonate [4]. On the other hand, it tranport to the urface i controlled by everal factor uch a phyical propertie of the tranport media (oil), climate condition (temperature, rainfall, wind peed, etc), and many other factor. Neverthele, both the oil temperature and oil water content are reported to be the key factor acting upon urface CO 2 flux [3,5]. The former parameter i the interet of thi work. Some tudie have hown that oil CO 2 concentration increae with depth [7-1]. Turcu et al. (25) carried out a laboratory experiment and howed that the CO 2 concentration increaed linearly with depth. Tang et al. (23) continuouly meaured the CO 2 ga concentration at an oak-gra avanna and found that it linearly increaed with the depth, up to 16 cm. An experimental tudy of nowpack by alo howed the ame trend [11]. In thi cae, the concentration profile increaed linearly up to 1.-m depth. Davidon et al. (26) howed that CO 2 ga concentration exponentially increaed with depth, having varying trend, depending on eaonally enitive parameter uch a oil temperature and moiture content [12]. The different fitting trend oberved in the oil ga concentration with depth affect the governed model ued to etimate the urface CO 2 flux. Therefore, in thi work, we meaured oil CO 2 concentration profile in order to etimate urface CO 2 flux uing derived model baed on ma balance equation. 2. STUDY LOCATION AND MEASURE- MENT METHODS 2.1 Field Location The field meaurement of CO 2 concentration profile were carried out at INAS tet field (Fig. 1). Thi i located on the wet ide of the Ito Campu of Kyuhu Univerity. It ha an altitude of 74 m above ea level. It i currently covered by gra, having no tree around. The oil layer i up to 3. m thick [13]. The official webite of the Japan Meteorological Agency (JMA) provide hitorical weather data. Weather data from 2 to 216 how that the annual mean temperature wa 17.4 C, while the maximum and minimum monthly temperature were around 32.6 C in Augut and 3.7 C in January, repectively. The monthly average temperature in 215 ranged from 7.6 C in February to 27.4 C in Augut with an annual mean temperature of 17.3 C. Fig. 2 how that the daily maximum and minimum temperature meaured during the eight day undertaken during thi tudy, a well their value recorded at the Fukuoka Station (World Meteorological Obervation Station ID:4787; N, E). The highet and lowet monthly precipitation amount were mm in Augut and 42.5 mm in February, repectively. Total precipitation wa mm year-1 throughout the year, including light nowfall. At the INAS tet field, two borehole of 113 m and 1.5 m in depth were drilled in 21, a well a three hole of 19.5 m in depth to monitor CO 2 releae [14]. The oil CO 2 concentration ranged from around 4 ppm at the urface to thouand of ppm in the hallow oil layer. The location elected for monitoring in thi tudy wa about 2 m in the ditance from the 1.5-m well. 215

3 Fig. 1. Location of INAS field. (a) a map howing the context of the INAS field location on Kyuhu Iland, Japan; (b) location of the INAS field on Ito Campu of Kyuhu Univerity (red circle); (c) field condition and borehole location at the INAS field (red circle); and (d) image howing CO 2 ampling uing an air pump and ga bag 4 3 Temperature ( o C) 2 1 Aug'16 Jul'16 Jun'16 May'16 Apr'16 Mar'16 Feb'16 Jan'16 Dec'15 Nov'15 Oct'15 Sep'15 Aug'15 Jul'15-1 Daily maximum temperature Daily minimum temperature Meaurement time Fig. 2. Seven day of field meaurement of CO 2 concentration profile at the INAS tet field, along with daily maximum and minimum temperature 2.2 Field Meaurement of Soil CO 2 Concentration Profile Soil CO 2 ga concentration and it flux are required to quantify CO 2 emiion from the ground urface to the atmophere. CO 2 concentration profile in the oil were meaured at the INAS tet field. A borehole, 1 cm in diameter wa drilled to carry out the meaurement of the oil CO 2. A vertical caing pipe wa fitted within the well and four vinyl tube, 1 mm in diameter, were connected to the 216

4 ampling hole, perpendicular to the inner wall of the pipe at depth of.1,.2,.3 and 1. m from the urface (Fig. 3). Soil gae were ampled into a 1. l ga bag at thee four level uing an air pump having a low uction peed of le than 1 cc -1 to prevent convection flow within the oil. The oil gae were analyzed in the laboratory uing a CO 2 ga analyzer (LI-84A; Li-Cor, Lincoln, NE, USA). In thi tudy, we aumed that the CO 2 concentration from the ga bag wa treated a the average value of oil ga at each depth. 2.3 Model of Surface CO 2 Flux and CO 2 Diffuion Coefficient of the Soil CO 2 concentration in a given oil layer i dependent the ma balance between the CO 2 produced within the layer and the CO 2 diffued into it from other layer. If we aume C (mol m - 3 ) i the oil CO 2 ga concentration at time t (h) and depth z (m), S (mol m -3 h -1 ) i the CO 2 production in the oil and F (mol m -2 h -1 ) i the oil CO 2 flux, then a 1-dimenional CO 2 ma balance can be expreed a Eq. (1). C F t z z S( z) (1) where C t i the unteady term for CO 2 concentration in the oil. In thi tudy, a teady tate ituation wa aumed. Soil depth (z) i defined a poitive, in a downward from the urface. F z 2 z D C z 2 (2) D (m 2 h -1 ) i the ga diffuion coefficient in the oil, which i a function of the oil propertie, and i expreed in term of the effective ga diffuion coefficient, (-), given in Eq. (3), and it variation with temperature and preure, a defined in Eq. (4) [15]. D D (3) a 1.75 T P D D a a T P (4) Thu, D a (m 2.h -1 ) i the diffuion coefficient in free air and D a i the value under tandard condition, 5.4 ẋ 1-2 m 2 h -1 for CO 2 at tandard temperature and preure (T = K; P = 11.3kPa). T (K) i oil temperature, while P i aumed to be equivalent to P, until 1 m oil depth. The CO 2 diffuion coefficient i one of the major parameter ued to etimate the ga flux in the oil. It i determined by the phyical propertie of the oil, uch a it dry denity, poroity, waterfilled poroity and ga-filled poroity. In thi tudy, we etimated the diffuion coefficient uing Moldrup et al., (1997), a written below. Thi model of diffuion rate wa the bet fitted with meaurement reult compared to other model [16] m* *m = 3 for unditurbed oil and m = 6 for diturbed oil 3 (5) where (m 3 m -3 ) i oil poroity and (m 3 m -3 ) i the volumetric water content. Thi model of diffuion rate wa found to uit bet our meaurement reult comparatively to other available model [16]. With the knowledge that the poroity refer to the void pore in the oil capable of being filled with water (and/or ga), it can be conjectured that a high poroity medium with lower moiture content will reult in high ga diffuivity compared to higher moiture content with ame poroity or lower poroity medium with ame moiture content condition (Fig. 4). 2.4 Soil Phyical Propertie of the Field In the field, oil were ampled from the urface a well a from within borehole to determine their denity, moiture content, and poroity. Moiture content wa meaured by heating the oil in an oven at 15 o C for 24 hour. Dry denity wa calculated baed on dry weight and oil volume. Soil poroity wa etimated from the dry denity uing Eq. (6). d 1 (6) p where (m 3 m -3 ) i oil poroity and i evaluated uing dry denity, d (kg m -3 ) and the particle denity for a mineral oil ( p = 256 kg m -3 ). 217

5 Fig. 3. Field meaurement method of oil CO 2 concentration profile uing a ga pump and ga bag at INAS tet field, and laboratory meaurement with a CO 2 analyzer Ga diffuion coefficient, D (m 2.h -1 ) Moiture content, (m 3.m -3 ) Poroity = 45.% Poroity = 4.% Poroity = 36.7% Poroity = 3.% Fig. 4. The effect of moiture content and oil poroity on the ga diffuion coefficient, a calculated by the model of Moldrup et al. (1997) Table 1. Phyical propertie of the oil at INAS field during meaurement Parameter Symbol Unit Soil* Dry denity d Kg m (162) Moiture content m 3 m (.124) Poroity m 3 m (.367) *range (average value) 3. RESULTS AND DISCUSSION In the field, meaurement of oil CO 2 concentration were carried out from November 215 to March 216 (Fig. 2). The CO 2 concentration profile up to 1. m depth followed a logarithmic trend with R 2 =.981 on average (Table 2) and wa generalized in Eq.7. A range of value wa meaured at each depth, i.e., from 13 to 87 ppm at.1 m depth; 25 to 18 ppm at.2 m depth; 42 to 132 ppm at.3 m depth; and 58 to 165 ppm at 1. m depth. ln C z y a z z (7) o where a,y and z were coefficient etimated by the logarithmic regreion. Baed on Eq. 2, the urface CO 2 flux could be etimated uing Eq. 8, 218

6 1 F Da (8) z CO 2 concentration profile for the INAS field are hown in Fig. 5. The oil repiration changed eaonally a a function of the oil temperature, affecting thereby the CO 2 concentration profile [17,18]. High CO 2 concentration in the near urface (up to.3 m depth) wa oberved in November 215, when oil temperature wa till high (17 o C on average), and alo in March 216, when the growing eaon began [19]. The lowet CO 2 concentration wa recorded in February, preumably becaue of the decreae in the microbial activity or root repiration, a oil temperature wa minimal (daily mean temperature wa 7.4 o C on average in February, while daily total precipitation wa at it lowet, about 3. mm on average). Evidently, the high CO 2 concentration hint at a higher ga production concurrently with a low diffuion rate [2, 21]. Baed on Eq. 8 and the value of a and z from logarithmic regreion of oil CO 2 concentration profile, the etimated urface CO 2 flux wa hown in Table 2. The urface CO 2 flux wa found higher when oil concentration wa higher a well, epecially in.1m oil depth. High CO 2 concentration in.1 m oil depth indicated high urface CO 2 flux becaue mot of the urface CO 2 ga flux wa delivered from the hallow urface, 76.3% of it motly from to 15 cm oil depth [21] and more than 75% of it wa originated from 2 cm oil depth [22]. We ued meaured urface CO 2 flux to validate the etimated one. Surface CO 2 flux at INAS field had been meaured uing cloe-chamber method (Fig. 6). A hemipherical chamber, 1 cm in radiu, wa placed on the oil urface to trap the CO 2 emitted. Before tarting the meaurement, the chamber wa opened to the air for 4 minute to clear it. Then, the chamber wa placed on the oil urface for 5 minute. The ga inide the chamber wa pumped and circulated uing a vinyl tube, 1 mm in diameter, connected to an air pump and a ga analyzer to meaure the CO 2 concentration. The ga wa allowed to flow back to the chamber to enure the chamber' internal preure remained contant and to prevent ga diffuion. The urface CO 2 flux wa calculated baed on the rate of the CO 2 ga increae inide the chamber, having a volume of 29 ml and a contact urface area of 314 cm 2, a defined in Eq. (9). V dc F c (9) A dt where, F (mol m -2 h -1 ) i the urface CO 2 flux, (mol m -3 ) i the CO 2 concentration in the chamber, V (m 3 ) i the volume of the chamber, A i the urface area (m 2 ) covered by the chamber, and t (h) i time. Soil depth (m) CO 2 concentration (ppm) /16/215 (17.3) 12/8/215 (1.) 12/22/215 (9.) 1/7/216 (6.9) 2/4/216 (6.) 2/18/216 (11.) 3/3/216 (1.3) Fig. 5. Soil CO 2 concentration profile at INAS tet field. The meaurement date and urface temperature are given in parenthee Table 2. The value of a, z and etimated urface CO 2 flux uing Eq. 8 Meaurement time a (mol m -3 ) z (m) Surface flux, F (mol m -2 h -1 ) 16-Nov Dec Dec Jan Feb Feb Mar

7 Fig. 6. Surface CO 2 flux meaurement uing the cloe-chamber method in the field Surface CO 2 ga flux, F (mol.m -2.h -1 ) Etimated urface CO 2 flux Meaured urface CO 2 flux Surface temperature, T ( o C) Fig. 7. Etimated and meaured urface CO 2 flux with oil temperature (filled triangle are the etimated urface CO 2 flux derived from oil CO 2 concentration profile; open circle are the meaured urface CO 2 flux while filled circle repreent the one that meaured with the ame condition of oil CO 2 concentration profile) From the 13 data meaurement at the field uing cloe-chamber method (Fig. 6). It wa ranged from.97 to.186 mol m -2 h -1 with mean value of.6±.3 mol m -2 h -1 againt increaing temperature from 6 C to 29.6 C (mean value of 17.4±.5 C). Thee reult howed a imilar range in available literature [23]. In contrat, W. Kao & K.Chang (29) and Pingintha et al. (21) reported oil CO 2 flux having a lower value to our [24,16]. Uing the imilar condition by conidering oil temperature, we compared etimated urface CO 2 flux with meaured one, a hown in Fig. 7. Our reult concluded that etimated urface CO 2 flux uing derived equation of logarithmic trend of oil CO 2 concentration profile, a written in Eq. 8, wa acceptable in the INAS field. 4. CONCLUSIONS Soil CO 2 concentration wa meaured in four different depth to etimate urface CO 2 flux in INAS field. The meaurement reult revealed that oil CO 2 concentration increaed with oil depth following the logarithmic trend with R 2 = 22

8 .981. Baed on ma balance equation with ome aumption and uing Moldrup et al., (1997) diffuion rate model to etimate the ga diffuion coefficient, an equation to etimate the urface CO 2 flux wa propoed. Etimated urface CO 2 flux wa compared and howed a good agreement with meaurement reult of urface CO 2 flux uing cloe-chamber method. The equation preented herein i potentially uitable to etimate the urface CO 2 flux. Alo, thi work highlighted that high CO 2 concentration in oil, epecially in.1 m depth, could indicate high urface CO 2 flux. ACKNOWLEDGEMENT The author would like to thank the Sumitomo Foundation (Tokyo, Japan) and the Arai Science and Technology Foundation (Tokyo, Japan) for the financial upport. COMPETING INTERESTS Author have declared that no competing interet exit. REFERENCES 1. Le Quéré C, et al. Global carbon budget 216. Earth Sytem Science Data Dicuion. 216;1 3. DOI: /ed Law B, Kelliher F, Baldocchi D, Anthoni P, Irvine J, Moore D, Van Tuyl S. Spatial and temporal variation in repiration in a young ponderoa pine foret during a ummer drought. Agriculture and Foret Meteorology. 21; Loiy C, Cohen G, Laveuf C, Le Roux O, Delaplace P, Caroline M, Garcia B. The CO 2 -Vadoe Project: Dynamic of the natural CO 2 in carbonate vadoe zone. International Journal of Greenhoue Ga Control. 213; Heiligmann M, Stix J, William Jone G, Lollar BS, Garzon G. Dital degaing of radon and carbon dioxide on Galera volcano, Colombia: Journal of Volcanology and Geothermal Reearch. 1997;77(1-4): Davidon E, Belk E, Boone R. Soil water content and temperature a independent or confounded factor controlling oil repiration in a temperate mixed hardwood foret. Global Change Biology. 1998;4: Pumpanen J, et al. Seaonal dynamic of autotrophic repiration in boreal foret oil etimated by continuou chamber meaurement. Boreal Environment Reearch. 215;2: Bekele A, Kellman L, Beltrami H. Soil Profile CO 2 concentration in foreted and clear cut ite in Nova Scotia, Canada. Foret Ecology and Management. 27;242: DOI: 1.116/j.foreco Billing SA, Richter DD, Yarie J. Soil carbon dioxide fluxe and profile concentration in two boreal foret. Canadian Journal of Foret Reearch- Revue Canadienne De Recherche Foretiere. 1998;28: DOI: /cjfr Turcu VE, Jone SB, Or D. Continuou oil carbon dioxide and oxygen meaurement and etimation of gradient-baed gaeou flux. Vadoe Zone Journal. 25;4: DOI: /vzj Wang YY, Hu CS, Ming H, Zhang YM, Li XX, Dong WX, Oenema O. Concentration profile of CH 4, CO 2 and N 2 O in oil of a wheat-maize rotation ecoytem in North China Plain, meaured weekly over a whole year. Agriculture, Ecoytem and Environment. 213;164: DOI: 1.116/j.agee Mariko S, Bekku Y, Koizumi H. Efflux of carbon dioxide from now-covered foret floor. Ecological Reearch. 1994;9: DOI: 1.17/BF Davidon EA, Savage KE, Trumbore SE, Borken W. Vertical partitioning of CO 2 production within a temperate foret oil. Global Change Biology. 26;12: DOI: /j x 13. Suanto V, Saaki K, Sugai Y, Yamahiro T. Mixing ga migration in fractured rock through unaturated and water-aturated layer : Reult of a pneumatic ga injection tet. Energy Procedia. 213;37: DOI: 1.116/j.egypro Suanto V, Saaki K, Sugai Y, Kawaaki W. Field tet tudy on leakage monitoring at a geological CO2 torage ite uing hydrogen a a tracer. International Journal of Greenhoue Ga Control. 216;5: DOI: 1.116/j.ijggc Pritchard DT, Currie JA. Diffuion of coefficient of carbon dioxide, nitrou oxide, 221

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