# Researches on the Variations of Greenhouse Gas Exchange Flux at Water Surface Nearby the Small Hydropower Station of Qingshui River, Guizhou

Lei Han, Xuyin Yuan, Jizhou Li, Yun Zhao, Zhijie Ma, Jing Qin

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Lei Han, Xuyin Yuan, Jizhou Li, Yun Zhao, Zhijie Ma, et al.. Researches on the Variations of Greenhouse Gas Exchange Flux at Water Surface Nearby the Small Hydropower Station of Qingshui River, Guizhou. 9th International Conference on Computer and Computing Technologies in Agriculture (CCTA), Sep 2015, Beijing, China. pp.539-547, 10.1007/978-3-319-48354-2_55. hal-01614211

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Researches on the Variations of Greenhouse Gas Exchange Flux at
Water Surface nearby the Small Hydropower Station of Qingshui
River, Guizhou

Lei Han¹, Xuyin Yuan¹,*, Jizhou Li¹, Yun Zhao², Zhijie Ma², Jing Qin²

1.College of Environment, Hohai University, Nanjing 210098, Jiangsu, China

2.China Institute of Water Resource and Hydropower Research, Beijing100044,
China

**Abstract:** Greenhouse gas(GHG) emission from water surface nearby the small hydropower station is a rising problem of concern. This paper studied the daytime changes of GHG flux of Fujiang hydropower station (FJHPS) and Xiasi hydropower station(XSHPS) located on Qingshui river in Guizhou by the static float chamber sampling and the gas chromatography analysis method in Autumn. Data showed, the fluxes of CO₂, CH₄ and N₂O ranged from -43 to 72, -23 to 15 and -0.016 to 0.13mmol·(m²·d)⁻¹, respectively. Overall, the GHG fluxes in the downstream of the station were slightly higher than the upstream, which manifested the downstream released more GHGs. The CO₂ exchange fluxes in FJHPS were higher than XSHPS, while CH₄ and N₂O fluxes showed a reverse situation. The fluxes of GHG had a positive correlation with DO and pH. Compared with other lakes and reservoirs, smaller releasing rates of GHG were existed in the small hydropower station.

**Key Words:** Greenhouse Gas; Small hydropower station; Water surface; Qingshui River

# 1 Introduction

The major greenhouse gas concentrations in the atmosphere have reached the highest point since data was recorded at 2011, with average 390.9 ppm, 1813 ppb and 324.2 ppb for CO2, CH4 and N2O respectively and increased by 40%, 159% and 20% comparing with the period of Industrial Revolution based on the World Meteorological Organization[1]. The continuous increase of atmospheric greenhouse gas concentrations and the consequent global warming raises attentions to greenhouse gases produced by the running hydropower station.

Previous studies have shown that the rapid increase of greenhouse gas concentration is closely related to human activities, of which, reservoir is considered to be an important source of greenhouse gas emission. It is estimated that the CO2 exchange flux of world's freshwater reservoirs through accounts for 4% of total anthropogenic CO2 exchange flux[2]. For a long time, the hydropower has been considered a clean, carbon-free energy and gets extensive development[3]. However, some literatures have reported that the reservoir is likely to be an emission source of greenhouse gas[4,5], so the greenhouse gases release from the reservoir has become a controversial problem.

The GHG emissions from reservoir (CO2, CH4) is mainly caused due to the mineralization of organic matter[4,5]which originate from the reservoir water and sediments. The existing researches have

**Acknowledgment.** This study was financially supported by the International Technology Cooperation and Exchange Fund from the Chinese Ministry of Science and Technology (2012DFA60830) and the National Natural Science Foundation of China (41372354).
showed that their exchange processes are closely related to reservoir age, soil properties of flooded ar-
ea, vegetation coverage and regional climate conditions[6,7,8]. The static floating box technology was
used to observe the GHG variations of Dongting Lake, Poyang Lake, Dianchi Lake and the Three
Georges Reservoir by Chen et al. (2006)[9]. But the data of greenhouse gas emission in small reservoirs
is lacked. In addition, as an important greenhouse gas, the warming potential of N₂O is about 310
times(Jain, 2000)[10] than that of CO₂, so it needs to be paid more attention in small reservoirs.

This paper studies the GHG variations in water surface nearby two small hydropower stations in Qingshui river, Guizhou province. Then we link the climatic conditions, water chemical parameters and GHG fluxes to discuss their potential relationships. These results will promote a better understanding of GHG exchange fluxes in the water surface areas of small hydropower stations.

**2 Materials and Methods**

**2.1 Sampling locations**

Qingshui river is located in the Guizhou province, southwest China, which is 459km long and cov-
er 17,145 square kilometers in the watershed. Duyun and Kaili are two major cities in this watershed. In
this study, GHGs were collected at the water surfaces of upstream and downstream of Fujiang hydro-
power station (weak human activity) and Xiasi hydropower station (strong human activity). Locations
of the study site were shown in Figure 1.

<figure><img src="image_2.png" /><figcaption>Fig. 1 Location of the sapling sites</figcaption></figure>

**2.2 Greenhouse gas collection and detection**

GHGs were collected at water surface of two small river reservoir, in a daytime of the Autumn,
with the static float chamber[11]. The collection times ranged from 09:00 am to 17:00 pm with one hour
interval. The gas samples were extracted by a 30ml plastic syringe, and quickly transferred to a vacu-
um-sealed glass vial. Four parallel samples were collected at one time. After collection, samples were quickly returned to the laboratory, and detected within 48 hours. Agilent 7890 A gas chromatograph was used for the simultaneous determination of GHGs.

## 2.3 Calculation of GHG exchange flux

Based on the average concentration of four samples and the background values of local atmosphere, the CO₂, CH₄ and N₂O exchange fluxes were calculated. The calculation formula was as follows:

$$F = (F1 \times F2 \times V \times \Delta c) / (F3 \times S \times \Delta t)$$

Where F represents the gas exchange flux [mg·(m²·d)⁻¹]. F₁ is the unit conversion factor between ppm and µg·m⁻³. F₂ is the conversion factor between min and d. V(m³) represents the volume of air in the floating container. S is the superficial area of water surface inside the floating container. F₃ is the unit conversion factor between µg and mg. Δc/Δt(10⁶·min⁻¹) implies the slope of the greenhouse gas concentration versus time during the observation time, which were calculated in each time period. If the exchange flux is positive, it indicates the waterbody release GHGs into the atmosphere. The negative value of exchange flux represents the waterbody absorption from the atmosphere. In this study, the gas concentration calculated by the above formula was divided by the molar mass of each gas, and the unit mg·(m²·d)⁻¹ was transformed into unit mmol·(m²·d)⁻¹.

## 2.4 Environmental parameters monitoring

The on-site monitoring of relevant environmental parameters were carried out at the same time of GHG collection. A SX-751 portable multi-parameter water quality monitor was used to measure water quality parameters temperature, DO and pH.

# 3 Results and Discussions

## 3.1 Variations of GHG exchange flux in FJHPS and XSHPS

### 3.1.1 CO₂ exchange fluxes

Monitoring results in XSHPS showed that CO₂ exchange fluxes in the downstream water surface was higher than the upstream water surface(most values>0), which indicated that XSHPS was a carbon source of CO₂. For FJHPS, CO₂ exchange fluxes appeared positive or negative values at different times. The CO₂ exchange fluxes ranged from -43.15mmol·(m²·d)⁻¹ to 71.17mmol·(m²·d)⁻¹, with the range of -43.15 to 37.25mmol·(m²·d)⁻¹ and -39.21 to 71.17mmol·(m²·d)⁻¹ for the upstream water surface and downstream water surface respectively. Obviously, concentrations of CO₂ released in FJHPS were larger than XSHPS. This is because that FJHPS has run to generate electric power, which stirs water by turbines and releases the dissolved CO₂ in water[12]. A part of water without disturbance directly ran into river channel in the downstream over the rubber dam. This process can release dissolved CO₂ in water again. But XSHPS, has not yet run which doesn't disturb water to release CO₂.

### 3.1.2 CH₄ exchange fluxes

In the downstream water surface of FJHPS, the concentrations of CH₄ exchange flux changed slightly, which ranged from -2.43 mmol·(m²·d)⁻¹ to 0.94 mmol·(m²·d)⁻¹. The maximum concentrations of exchange fluxes in the upstream water surface and the downstream water surface were 0.94 mmol·(m²·d)⁻¹ and 0.72 mmol·(m²·d)⁻¹, respectively. In XSHPS, the changes of exchange fluxes fluctuated significantly, which ranged from -22.63 mmol·(m²·d)⁻¹ to 14.71 mmol·(m²·d)⁻¹ with a maximum
in the noon. Friedl et al. have found that warm water can further promote the generation of CH₄ at the water surface [13]. It is obvious that the CH₄ exchange flux in XSHPS was greater than FJHPS. XSHPS has deeper waterbody, submerging more vegetation in the shore. When all the plants decay, they produce more CH₄ [14]. Meanwhile, XSHPS is located in the center of Xiasi Town, domestic sewage can directly enter into the reservoir and led to release more methane gas in waterbody [15].

<figure><img src="image_3.png" /><figcaption>Fig. 2 Day time variations of CO₂, CH₄ and N₂O flux in FJHPS and XSHPS (a) Variations of CO₂ emission fluxes (b) Variations of CH₄ emission fluxes (c) Variations of N₂O emission fluxes.</figcaption></figure>

### 3.1.3 N₂O exchange fluxes

The N₂O exchange fluxes in both hydropower stations were small, which ranged from -0.016 to 0.133mmol·(m²·d)⁻¹. In FJHPS, the N₂O exchange fluxes ranged from 0.016 to 0.015mmol·(m²·d)⁻¹, which were obviously smaller than those in XSHPS. The main cause is that XSHPS is located in Xiasi Town, where waterbody receives domestic sewage with high nitrogen. And the amount of N₂O is closely related to TN[16] in the waterbody.

## 3.2 Correlation analysis between water chemical parameters and GHG fluxes
Water temperature, dissolved oxygen and pH were selected as three water chemical parameters to study their correlations with GHG fluxes.

Water temperature can not only directly affect the gas exchange flux by changing the speed of gas molecule diffusion and solubility in water, but also indirectly affect geochemical process of GHG by changing the metabolic activity of microorganisms in water[17]. In addition, the water temperature can affect photosynthesis and respiration of aquatic plants, resulting in variations of CO₂ exchange flux[18]. The average temperature in both areas respectively was 17.75°C and 18.5°C. No correlations between the water temperature and greenhouse gas exchange flux were showed in the studied area (Table 1). It was indicated the water temperature was not a major affecting factor in Autumn.

The concentration of DO determines the ways and products of organic matter degradation in water. In the cycle of carbon, organic matters mainly generate CO₂ in aerobic environment and CH₄ in anaerobic condition. In the nitrogen cycle, organic matters exercise the aerobic nitrification and anaerobic denitrification[19]. Correlation analyses showed the DO had a good positive correlation with three parameters, which implied high DO can promote the release of GHGs in waterbody.

The pH value is another important chemical parameter of waterbody, which can affect the release of CO₂ in the reservoir by changing the carbonate balance. It is a significant factor affecting the produce and release of CO₂ and CH₄, which has close relationships with the decomposition of organic matter, microbial activity and biological metabolic activity in waterbody[20]. Results indicated that correlations between pH and GHGs in FJHPS had better positive correlation than in XSHPS(Table 1). It can be explained that the pH value of waterbody in XSHPS is disturbed by organic matter from sewage.

<table><caption>Table 1 Correlation coefficients between the fluxes of CO₂, CH₄, N₂O and the environmental factor Temperature, DO and pH in waterbody of small hydropower stations in Qingshui River.</caption><thead><tr><th rowspan="2">Item</th><th colspan="3">Fujiang hydropower station</th><th colspan="3">Xiasi hydropower station</th></tr><tr><th>CO₂</th><th>CH₄</th><th>N₂O</th><th>CO₂</th><th>CH₄</th><th>N₂O</th></tr></thead><tbody><tr><td>Temperature</td><td>-0.078</td><td>0.057</td><td>0.192</td><td>-0.173</td><td>-0.076</td><td>-0.010</td></tr><tr><td>DO</td><td>0.428</td><td>0.414</td><td>0.557*</td><td>0.331</td><td>0.307</td><td>0.377</td></tr><tr><td>pH</td><td>0.506*</td><td>0.274</td><td>0.495</td><td>0.257</td><td>0.162</td><td>0.102</td></tr></tbody></table>

<table><caption>Table 2 Range of greenhouse gas fluxes from the studied area and other areas. (mmol/m²·d⁻¹)</caption><thead><tr><th>Name</th><th>Temperature Zone</th><th>CO₂</th><th>CH₄</th><th>N₂O</th><th>References</th></tr></thead><tbody><tr><td>Lokka Lake</td><td>Frigid zone</td><td>11.23-73.44</td><td>0.328-7.430</td><td>-0.500-5.797</td><td>21</td></tr><tr><td>Kevätön Lake</td><td>Frigid zone</td><td>-1.81-25.06</td><td>0.276-12.096</td><td>-1.702-0.440</td><td>22</td></tr><tr><td>Arrow Lake</td><td>Temperate</td><td>13.82-25.92</td><td>0.216-0.665</td><td>-0.023-0.079</td><td>20</td></tr><tr><td>Cabonga Lake</td><td>Temperate</td><td>5.01-78.62</td><td>0.190-3.370</td><td>-0.390-6.099</td><td>6</td></tr></tbody></table>

<footnote>*Significant correlation at the 0.05 level (bilateral); **. Significant correlation at the 0.01 level (bilateral)</footnote>
<table><tr><td>Maotiao River</td><td>Subtropics</td><td>-9.77</td><td>nd</td><td>nd</td><td>23</td></tr><tr><td>Donghu Lake</td><td>Subtropics</td><td>-31.97-87.26</td><td>0.086-8.294</td><td>nd</td><td>16</td></tr><tr><td>Qingshui River</td><td>Subtropics</td><td>-43-72</td><td>-23-15</td><td>-0.016-0.13</td><td>This study</td></tr><tr><td>Curua-Una Lake</td><td>Tropical</td><td>7.5-227.27</td><td>0.125-42.5</td><td>nd</td><td>24</td></tr><tr><td>Petit Saut Lake</td><td>Tropical</td><td>13.18-238.64</td><td>0.313-237.5</td><td>nd</td><td>25</td></tr></table>

Note: nd is not detected

### 3.3 Comparisons of GHGs in the study area and other areas

The GHG flux data summarized in Table 2 were obtained from literatures of different areas. We found that GHG fluxes of tropical lakes or reservoirs of were significantly higher than the other temperature Zone. CO₂ fluxes of frigid zone and temperate were relatively lower. And the CO₂ flux ranges in our studied hydropower stations changed from -43 to 72 mmol·(m²·d)⁻¹, which was similar with those of frigid and temperate reservoirs. The values of CH₄ flux ranged from -23 to 15 mmol·(m²·d)⁻¹, significantly larger than those of other lakes or reservoirs. But the N₂O fluxes ranged from -16 to 130 µmol·(m²·d)⁻¹, which were significantly lower than those of other lakes or reservoirs. Therefore, we can conclude the running of small hydropower station only promote the rising of CH₄ flux, but slightly affect the CO₂ and N₂O fluxes.

## 4 Conclusions

The fluxes of greenhouse gas (CO₂, CH₄ and N₂O) fluctuate at the water surface of small hydropower stations Qingshui river of Guizhou province in Autumn, during a daytime continuous monitoring. On the whole, the GHG fluxes at the downstream water surface of hydropower station are slightly higher than the upstream water surface, manifesting the more GHG releases at downstream waterbody. The turbine rotating can significantly influence the CO₂ exchange fluxes of waterbody nearby hydropower stations. The domestic sewage and submerged plants can result in decomposition of organic matter to release more CH₄ and N₂O. Through the correlation analysis, the dissolved oxygen and pH influences apparently the GHG in Autumn. The running of small hydropower station only influences obviously the CH₄ fluxes, and therefore can be considered as an effective way to clean energy utilization.
References

[1] Administration C M. 2012. Greenhouse gases status of China atmospheric [J].China Greenhouse Gas Bulletin, 12(1):38-41.

[2] Stlouis V L, Kelly C A, Duchemin E, et al. 2000. Reservoir surfaces as sources of greenhouse gases to the atmosphere: A global estimate [J]. Bioscience, 50(9): 766-775.

[3] Victor D G. 1998. Strategies for cutting carbon [J]. Nature, 395(6705): 837-838.

[4] Kelly C A, Rudd J W, Stlouis V L, et al. 1994. Turning attention to reservoir surfaces, a neglected area in greenhouse studies [J]. Eos, Transactions American Geophysical Union, 75(29): 332-333.

[5] Macintyre S, Wanninkhof R, Chanton J. 1995. Trace gas exchange across the air-water interface in freshwater and coastal marine environments [J]. Biogenic trace gases: Measuring emissions from soil and water, 52-97.

[6] Louisv L S, Kelly C A, Duchemin É, et al. 2000. Reservoir Surfaces as Sources of Greenhouse Gases to the Atmosphere: A Global Estimate Reservoirs[J]. BioScience, 50(9): 766-775.

[7] Abril G, Gu rin F, Richard S, et al. 2005. Carbon dioxide and methane emissions and the carbon budget of a 10 - year old tropical reservoir (Petit Saut, French Guiana) [J]. Global biogeochemical cycles, 19(4): GB4007, doi:10.1029/2005GB002457.

[8] Roland F, Vidal L O, Pacheco F S, et al. 2010. Variability of carbon dioxide flux from tropical (Cerrado) hydroelectric reservoirs [J]. Aquatic Sciences, 72(3): 283-293.

[9] Chen Y G, Li C H, et al. 2006. Carbon dioxide flux on the water-air interface of the eight lakes in China in winter [J]. Ecological Environment, 15(4): 665-669.

[10] Jain A K, Briegleb B P, Minschwaner K, et al. 2000. Radiative forcings and global warming potentials of 39 greenhouse gases [J]. Journal of Geophysical Research: Atmospheres, 105(D16): 20773-20790.

[11] Lambert M, Frchette J-L. 2005. Analytical techniques for measuring fluxes of CO₂ and CH₄ from hydroelectric reservoirs and natural water bodies [M]. Greenhouse Gas Emissions—Fluxes and Processes. Springer. 37-60.

[12] Kemenes A, Forsberg B R, Melack J M. 2011. CO₂ emissions from a tropical hydroelectric reservoir (Balbina, Brazil) [J]. Journal of Geophysical Research: Biogeosciences (2005–2012), 116(G3): 206-216.

[13] Friedl G, West A. 2002. Disrupting biogeochemical cycles-Consequences of damming [J]. Aquatic Sciences, 64(1): 55-65.

[14] Huntington T, Aiken G. 2009. Export of Dissolved Organic Carbon From the Penobscot River Basin in North-Central Maine; proceedings of the AGU Spring Meeting Abstracts, [C].

[15] Daelman M R, Van Voorthuizen E M, Van Dongen U G, et al. 2012. Methane emission during municipal wastewater treatment [J]. Water research, 46(11): 3657-3670.

[16] Xing Y P, Xie P, Yang H, et al. 2005. Methane and carbon dioxide fluxes from a shallow hypereutrophic subtropical Lake in China [J]. Atmospheric Environment, 39(30): 5532-5540.

[17] Singh S, Kulshreshtha K, Agnihotri S. 2000. Seasonal dynamics of methane emission from wetlands [J]. Chemosphere-Global Change Science, 2(1): 39-46.

[18] Patra P K, Lal S, Venkataramani S, et al. 1999. Seasonal and spatial variability in N₂O distribution in the Arabian Sea [J]. Deep Sea Research Part I, 46(3): 529-543.

[19] Huttunen J T, Vaisanen T, Hellsten S K, et al. 2006. Methane fluxes at the sediment-water interface in some boreal lakes and reservoirs [J]. Boreal environment research, 11(1): 27-34.

[20] Krumbein W E. 1979. Photolithotropic and chemoorganotrophic activity of bacteria and algae as related to beachrock formation and degradation (Gulf of Aqaba, Sinai) [J]. Geomicrobiology Journal, 1(2): 139-203.

[21] Huttunen J, Mntynen K, Alm J, et al. 1999. Pelagic methane emissions from three boreal lakes with different trophy; proceedings of the Proceedings of 4th Finnish Conference of Environmental Science, Tampere, Finland, [C].

[22] Huttunen J T, Alm J, Liikanen A, et al. 2003. Fluxes of methane, carbon dioxide and nitrous oxide in boreal lakes and potential anthropogenic effects on the aquatic greenhouse gas emissions [J]. Chemosphere, 52(3): 609-621.
[23] Wang F, Wang B, Liu C-Q, et al. 2011. Carbon dioxide emission from surface water in cascade reservoirs–river system on the Maotiao River, southwest of China [J]. Atmospheric Environment, 45(23): 3827-3834.

[24] Duchemin E, Lucotte M, Queiroz A, et al. 2000. Greenhouse gases emissions from a 21 years old tropical hydroelectric reservoir, representativity for large scale and long term estimation [J]. Veranlundgen Int Vereinigung Theor Angew Limnol, 27(1391).

[25] Galy - Lacaux C, Delmas R, Jambert C, et al. 1997. Gaseous emissions and oxygen consumption in hydroelectric dams: A case study in French Guyana [J]. Global Biogeochemical Cycles, 11(4): 471-483.