Data Gas

Chinese Science Bulletin

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Springer

Influences of the degradation of swamp and alpine

meadows on CO2 emission during growing season

on the Qinghai-Tibet Plateau

WANG JunFeng1, WANG GenXu1,2, WANG YiBo1 & LI YuanShou3

1

College of Earth and Environment Sciences, Lanzhou University, Lanzhou 730000, China;

2

Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China;

3

Cold and Arid Regions Environment and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China

CO2 emission fluxes of two types of ecosystem, swamp meadow and alpine meadow, in the Fenghuo-

shan region of the Qinghai-Tibet Plateau were studied by the static chamber-portable infrared chro-

matographic method. The results showed that there was large difference in the CO2 emission fluxes

between the two ecosystems and in the same ecosystem of different degradation degrees. CO2 emis-

sion flux of the swamp meadow gradually decreased with increasing degradation degree, while that of

the alpine meadow gradually increased with increasing degradation degree except in May. The CO2

emission flux of undegraded swamp meadow was 65.1% 80.3% higher than that of undegraded alpine

meadow; and the CO2 emission flux of moderately degraded swamp meadow was 22.1% 67.5% higher

than that of alpine meadow; but the CO2 emission flux of severely degraded alpine meadow was

14.3% 29.5% higher than that of swamp meadow. The soil moisture content and temperature in the

upper 5 cm soil layer and above-ground biomass were significantly correlated with the CO2 emission

fluxes and regarded as the main environment factors to control the CO2 emission.

Qinghai-Tibet Plateau, Fenghuoshan, swamp meadow, alpine meadow, CO2, emission flux, degradation

zone to the climatic changes of the Asian monsoon re-

CO2, as one of the most important greenhouse gases

gion[2,3]; hence, the global warming will inevitably affect

leading to global warming, can absorb the infrared ray

the evolution of the plateau s ecosystem and carbon cy-

reflected from the Earth s surface, store the energy in the

clic processes. Swamp and alpine meadow grasslands

atmosphere, and thereby warm the Earth surface. Ac-

are two major ecosystems of the Qinghai-Tibet Plateau,

cording to the prediction of global climate model, as the

and based on the analyses of satellite images acquired

CO2 concentration in the atmosphere is doubled, the

during the 1985 1987 and 1999 2000 periods, it has

Earth s surface temperature in the high-altitude region at

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north latitude will increase by 3 5 [1]. Climate warm- been found that under the influence of global warming

and human activities, the two ecosystems have been

ing will lead to massive CO2 emission from soil and in

gradually degraded and the degradation is tending to

turn accelerate the global warming, thus forming a vi-

aggravate in recent years[4 6]. Furthermore, owing to the

cious circle. The Qinghai-Tibet Plateau is regarded as

the Earth s third pole and the highest unique territorial

Received December 21, 2006; accepted June 1, 2007

unit in the world, and its ecosystems and natural envi- doi: 10.1007/s11434-007-0343-5

ronment have inherent fragility and instability. The

Corresponding author (email: **********@*****.***.**)

Supported by the National Natural Science Foundation of China (Grant No.

Qinghai-Tibet Plateau, located in the central part of the 90511003) and the Hundred Talent Scholar Foundation, Chinese Academy of Sci-

troposphere in the mid-latitude westerlies, is a sensitive ences (2004)

www.scichina.com www.springerlink.com Chinese Science Bulletin September 2007 vol. 52 no. 18 2565-2574

unique growing environment of the swamp meadow and ence of 200 300 m. The rocks on the mountaintops are

alpine meadow, the characteristics of CO2 emission from bare, mountain ridges are gentle, natural mountain

surface are also different from other ecosystems. Lin et slopes are steep in upper part but gentle in lower part,

al.[7] studied the CO2 emission from the surface of the and intermountain gullies are well developed but are

active layer of permafrost at Wudaoliang of the plateau experiencing intense denudation. The region s topogra-

and found that CO2 emission had an obvious daily phy is generally characterized by flat top and gentle

changes, and the surface of the dry and cold active layer slope, wide valleys and short gullies. The region is lo-

was a CO2 emission source. Wu et al.[8] observed and cated in the plateau-continental climatic zone, its climate

investigated the CO2 emission of Kobresia humilis eco- is cold and dry and freezing period extents from Sep-

system in the Haibei region of the plateau and recorded tember to April of next year. According to the weather

a CO2 emission flux as high as 917.89 mg m 2 h 1. data observed at a temporary meteorological station in

Zhao et al.[9] studied the CO2 concentration distribution Fenghuoshan region in the 1970s, mean annual tem-

perature is 5.3, extreme maximum temperature

in the permafrost active layer of the swamp meadow

ecosystem near the Beiluhe in winter and spring seasons 24.7, extreme minimum temperature 38.5, mean

and found that the CO2 concentration in soil exhibited an annual precipitation 269.7 mm, mean annual evapora-

upper-low and lower-high distribution pattern and the tion 1477.9 mm, mean relative humidity 55%, maximum

soil CO2 had an evident occlusive effect in the freezing wind speed 31 m s 1, prevailing wind direction is west

period of active layer. However, no study has been re-

and the largest number of thunderstorm days is 47.8

ported as to the influences of the degradation of swamp

days per year.

and alpine meadows of the Qinghai-Tibet Plateau on the

The locations of the sample plots of swamp meadow

CO2 emission. The Qinghai-Tibet Plateau has a swamp and alpine meadows are as follows: the sample plot of

meadow and alpine meadow area of 700035 km2; it is the former is at 34 43.816 N and 92 53.506 E, with an

the largest natural grassland zone of China and one of elevation of 4778 m; the sample plot of the latter is at

the largest in the world. Therefore, long-term monitoring 34 43.682 N and 92 53.697 E, with an elevation of 4766

and study of the dynamics of CO2 emission fluxes of the m. All these sample plots are located in permafrost re-

plateau s swamp and alpine meadows of different deg- gion, mean permafrost thickness varies between 70 and

radation degrees have quite important significance to 120 m and mean active layer depths is 1.2 2.5 m. Main

protect the stability of soil carbon pool and slow down

vegetation communities in the swamp meadow region

the global warming. In addition, it also helps to deter-

include Stipa aliena, Kobresia tibetica, Festucasp, Carex

mine the contribution of the carbon emission of the pla-

atrofusca and Leontopodium leontopodioides etc, while

teau s swamp and alpine meadow ecosystems to the

those in the alpine meadow region include Kobresia

carbon emission at regional or even global levels.

pygmaea, K. humilis, K. capilifolia, etc.

The research contents of this study mainly include the

1.2 Experiment layout

following two aspects: (1) CO2 emission characteristics

According to the evaluation criteria of different degrada-

of swamp and alpine meadows of different degradation

tion degrees of alpine ecosystem[10], three types of un-

degrees on the Qinghai-Tibet Plateau; (2) The relation of

CO2 emission fluxes of swamp and alpine meadows of degraded (SL>79%), moderately degraded (SL=79%

different degradation degrees to environment factors 30%) and severely degraded (SL

such as atmospheric temperature, biomass, soil tem- were selected respectively in the swamp meadow and

perature and soil moisture. alpine meadow regions, and there were three replica-

tions for each type.

1 Material and methods 1.3 Collection and analysis of gas samples

1.1 Geographic location of study region and envi- Gas samples were collected by static chamber method.

ronmental features The chamber consists of chamber body (above-ground

The Fenghuoshan district in the interior of the Qinghai- part) and base (subsurface part). The former is made of

Tibet Plateau was selected as the study region with an organic glass, and a 3 cm thick thermal insulating foam

organic glass is bound to the outer wall of the chamber

elevation of 4600 4800 m and relative height differ-

2566 WANG JunFeng et al. Chinese Science Bulletin September 2007 vol. 52 no. 18 2565-2574

ARTICLES

and then is covered with white rainproof cloth to avoid into the density values of CO2 using the measured at-

mospheric pressure and temperature data.

solar radiation; otherwise, the temperature of the cham-

According to the daily changes of CO2 emission

ber may increase and thereby affect the measurement

results. According to the studying results by Du et al.[11], fluxes obtained by the experiments, as shown in Figures

sampling chamber should select a moderate size and the 1 and 2, 9:00 11:00 a.m. is the main time interval for

experiments should be conducted between 9:00 a.m. CO2 emission. The emitted CO2 fluxes occupy about

and 11:00 a.m., in such a case, the microenvironmental 78% 87% of the accumulated emission flux of a day,

disturbance in the chamber is smallest. The mid-size hence the mean daily emission rate of CO2 can be cal-

chamber is shaped like a square, the length of each side culated by eq. (1):

is 40 cm, its top has gas-collecting tube and thermometer, 273.15 P M

Qt = 1440

and two small fans with 12 VDC power supply are in- Ta 101325 22.41

stalled inside the chamber (to make the gas in the

1000 V dC

(mg m 2 d 1 ),

(1)

chamber uniform), and the bottom of the chamber has an

A dt

opening (which is fitted onto the bottom surface). The

where Qt is the CO2 emission flux from soil at t time

base of the chamber is made of stainless steel and is like

(mg m 2 d 1), V is the volume of the chamber (m3), P

a tetrahedron (40 cm 40 cm 10 cm). Its upper end

is atmospheric pressure (105 Pa), 22.41 is the molar

has a water trough. One month prior to the experiments,

volume under standard condition (temperature is 273.15

the base of the chamber was buried in soil and tamped

K and atmospheric pressure is 1.013 105 Pa) (L mol 1),

its outside with wet soil. During the experiment period,

M is the molar mass of determined gas (g mol 1), 1000

soil disturbance should be avoided so as not to affect the

is the coefficient to convert m3 into L, 1440 is the coef-

measurement results. For the collection of samples, wa-

ficient to convert the min into d, dC/dt is the straight-

ter is added to the sealed trough at the base to seal the

line slope to reflect the CO2 concentration changes

gas path between the base and chamber body to cut off

the free exchange of gas outside the chamber.

The land surface CO2 contents at various sampling

sites were directly and automatically measured using

American 7001P portable infrared CO2 gas analyzer.

The measuring range of the instruments is 0 10000

L L 1, response time 1 s, resolution 1 L L 1 and an-

nual deviation 20 L L 1. Prior to the experiment, the

instrument was strictly calibrated using standard CO2

gas, and the instrument itself has the zero-setting func-

tion.

During the growing season of vegetation (May Figure 1 Mean daily changes of CO2 emission flux of swamp meadow

during growing period.

September) on the Qinghai-Tibet Plateau, samples were

collected once every three days and the determinations

were made between 9:00 a.m. 11:00 a.m. At the same

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time, the daily changes were determined once a month

and the determinations were conducted at 2 h interval.

Prior to the experiment, clean water was added to the

water trough at the bottom, in the experiment process

the infrared CO2 gas analyzer was connected to the gas-

collecting tube and the chamber body was placed in the

water trough at the bottom, each determination lasted for

30 min and the data were recorded once every 10 min.

The determined results are expressed as the volumetric Figure 2 Mean daily changes of CO2 emission flux of alpine meadow

concentration of CO2 ( L L 1), they can be converted during growing period.

WANG JunFeng et al. Chinese Science Bulletin September 2007 vol. 52 no. 18-256*-****-****

Qinghai-Tibet Plateau were figured out.

with time in the determination: the positive value indi-

cates emission and negative value indicates absorption,

2 Results and discussion

dC is the increment of CO2 concentration at t time in-

terval in the chamber ( L L 1), and A is the area of de-

Experiments and observations were conducted in the

termined soil (m2).

growing season of the plateau s vegetation from May to

1.4 Determination of environment factors September of 2006, with emphasis placed on the tempo-

ral-spatial changes of CO2 emission fluxes of the two

Geothermometer was used to determine the soil tem-

major terrestrial ecosystems, swamp meadow and alpine

perature at the depths of 5, 10, 15, 20 and 25 cm of ac-

meadow. The experimental and studying results showed

tive layer and they were measured once every 3 h. Port-

that there was large difference in the CO2 emission

able TDR was used to measure soil moisture contents at

fluxes between the two ecosystems and for the same

the depths of 5, 10, 15, 20 and 25 cm of active layer.

ecosystem of different degradation degrees.

Thawed depth of active layer was determined by meas-

uring pin method. Soil samples were collected by strati- 2.1 Biomass changes of swamp and alpine meadows

fied sampling method using auger to observe soil profile. and the physiochemical properties of their underlying

Biomass of swamp meadow and alpine meadow of dif- soils

ferent degradation degrees were measured at the end of

The above-ground biomass and below-ground biomass

every month respectively.

of the swamp and alpine meadow grasslands of different

1.5 Vegetation investigation degradation degrees were determined at the end of every

month. By the end of the experiments, the samples of

The distribution area of vegetation of different degrada-

underlying soils of the swamp and alpine meadow

tion degrees in the experiment region was measured and

samples were collected. Under the support of ERDAS, grasslands of three different degradation degrees were

collected and analyzed. The measured and analytical

IMAGE and ARC/INFO softwares, the 1999 2000

results are presented in Tables 1 and 2, respectively.

remote sensing TM data were processed with 1:100000

It can be seen from Table 1 that there was a signifi-

topographic map as a basis. Then according to the re-

cant difference in biomass between different degradation

mote sensing mark bank consisting of 11 types and 246

d egrees of swamp meadow and alpine meadow

mark points, which was established based on field in-

(ANOVA, P 0.68, regression analysis, P0.42, regression analysis, P0.61, regres-

sion analysis, P 0.80, regression

soil moisture content in the upper 5 cm soil layer, analysis, P 0.47, regression analysis,

regression equations that soil moisture content and soil

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P 0.32, regression analysis, P

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