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Environmental Management ISSN 0364-152XVolume 52Number 2 Environmental Management (2013)52:441-449DOI 10.1007/s00267-013-0107-8
Impacts of Dung Combustion on theCarbon Cycle of Alpine Grassland of theNorth Tibetan Plateau
Zengrang Xu, Shengkui Cheng, LinZhen, Ying Pan, Xianzhou Zhang, JunxiWu, Xiuping Zou & G. C. Dhruba Bijaya
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Impacts of Dung Combustion on the Carbon Cycle of AlpineGrassland of the North Tibetan Plateau
Zengrang Xu • Shengkui Cheng • Lin Zhen •
Ying Pan • Xianzhou Zhang • Junxi Wu •
Xiuping Zou • G. C. Dhruba Bijaya
Received: 22 March 2012 / Accepted: 7 June 2013 / Published online: 25 June 2013
� Springer Science+Business Media New York 2013
Abstract Alpine grassland of Tibet is a frangible eco-
system in terms of carbon (C) emission. Yak dung is an
important resident energy with about 80 % of yak dung
combusted for energy in the north Tibetan plateau. This
paper investigated the impact of dung combustion on the C
cycle of the alpine grassland ecosystem in north Tibet,
China. During the growing season of 2011, from a field
survey and household questionnaires, the main impacts of
dung collection for fuel on the C cycle of the ecosystem
were identified. (1) The C sequestration and storage
capacity, including the dung-derived C stored in soil and C
captured by vegetation, decreased. The net primary pro-
duction decreased remarkably because of the reduction of
dung returned to soil. (2) In a given period, more C was
emitted to the atmosphere in the dung combustion situation
than that in the dung returned to soil situation. (3) The
energy grazing alpine meadow ecosystem changed into a
net C source, and the net biome production of the eco-
system dropped to -15.18 g C/m2 year in the dung com-
bustion situation, 42.95 g C/m2 year less than that in the
dung returned situation. To reduce the CO2 emission
derived from dung use, the proportion of dung combustion
should be reduced and alternative renewable energy such
as solar, wind, or hydro energy should be advocated, which
is suitable for, and accessible to, the north Tibetan plateau.
Keywords Dung � Renewable energy � Carbon budget �Grazing � Alpine grassland ecosystem � Tibet
Introduction
Carbon (C) exchanges between the atmosphere, land, and
ocean play an important role in regulating the global C cycle.
Of the 7–8 Gigaton (Gt) of C emitted annually by burning
fossil fuels and removing forest, only*3 Gt C appears in the
atmosphere and 2 Gt C is dissolved in the ocean, which
leaves 2–3 Gt C to be absorbed by terrestrial ecosystems
globally (Grace 2004). Grass ecosystems may be responsible
for[20 % of total terrestrial C. The net C exchange of ter-
restrial ecosystems is the balance between uptake (photo-
synthesis) and loss (respiration, etc.). One of the indicators for
C budget is net ecosystem productivity (NEP = NPP - Rs),
where NPP is the net primary production, and Rs is the soil
heterotroph respiration rate (Steffen and others 1998). The
other indicator for C budget is net biome production (NBP)
(Shimizu and others 2009). Some studies presented that the
NBP better represents the net C exchange at larger spatial and
temporal scales because it integrates disturbance such as fires
and grazing into the accounting system (Steffen and others
1998; Grace 2004; Running 2008). Shimizu and others
(2009) presented a framework of C budget in grasslands
which includes C input through manure application and C
output through grazing as well as NEP. This budget is esti-
mated using the following equation: NBP = NEP ? C
import (manure application) - C export (grazing).
Z. Xu (&) � S. Cheng � L. Zhen � Y. Pan � X. Zhang �J. Wu � G. C. D. Bijaya
Institute of Geographic Science and Natural Resources Research,
Chinese Academy of Sciences, Datun Road A11,
Beijing 100101, China
e-mail: [email protected]
X. Zou
Institute of Policy and Management, Chinese Academy
of Sciences, Zhongguancun Beiyitiao Alley15,
Beijing 100190, China
123
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DOI 10.1007/s00267-013-0107-8
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There are two factors influencing the C cycling and C
budget of grassland on the Tibetan plateau. The first one is
a continuous rise in air temperatures on the plateau over the
last several decades and the high thermal sensitivity mak-
ing the plateau a potential C emission source (Wang and
others 2002). Under this condition, the C budget can be
measured with NEP, which is mainly influenced by eco-
physiological determinations such as temperature and
moisture. There is still much uncertainty on the NEP of
grassland on the Tibetan plateau. The CO2 emissions from
the grassland soils of the Qinghai–Tibetan plateau reached
1.27 Pg C/year (1P = 1 9 1015) (Wang and others 2002),
which was more than the NPP of the plateau (Chen and
others 2012), suggesting the plateau is a C source. The
annual Rs of alpine steppe on the Qinghai–Tibetan plateau
was 79.6 g C/m2 year and NPP was 92.5 g C/m2 year, so
the alpine steppe is a C sink (Pei and others 2009). The
Kobresia humilis alpine meadow in the northeastern
Qinghai–Tibetan plateau is a C source, with C release of
663.0 g C/m2 year, while the NPP is 464.4 g C/m2 year
(Zhang and others 2003).
The second factor to influence the C cycling of the
grassland on the plateau is the disturbance from excessive
human activities such as overgrazing and the heavy use of
dung-dependent energy, which drive an increase in C
emission. Grazing significantly influences the C budget
(Falkowski and others 2000; Fang and others 2010; Wang
and others 2008). Improving grazing intensity increases C
emission while simultaneously reducing the C sink on the
Tibetan plateau (Scurlock and Hall 1998). Dung manage-
ment obviously affects the C budget in grazing grassland
(Janzen and others 1998; Cao and others 2004). Dung
combustion is currently a popular usage pattern in the north
Tibetan plateau. There is competition for using dung either
as fertilizer or fuels in pastoral areas in Tibet (Cai 2003). It
is claimed that the dung should remain on the ground to be
returned as fertilizer. Removing dung from grassland at a
high intensity disturbs material recycling, causes soil
infertility and depresses primary production in the long
term (Shimizu and others 2009; He and others 2009a).
Others argue that dung combustion for energy originated
from *1,200 years ago on the Tibetan plateau and is the
kind of resource usage pattern that adapts to the alpine
environment (Li and others 2003).
The influences of dung combustion on C cycling in the
alpine grassland still lack scientific understanding. There-
fore, this study compared the dung combustion situation
with that of dung returned to soil to investigate the impact
of dung combustion on the C cycle of the alpine grassland
ecosystem in the north Tibetan plateau and measured the C
budget with the NBP. This study aims to support decision
making on dung use optimization and C sequestration
capacity enhancement.
Materials and Methods
Study Area
Damxung County is located in the north Tibetan plateau
with a mean altitude of 4,200 m (Fig. 1). It is characterized
by an alpine semi-dry temperate monsoon climate, with an
annual mean temperature of 1.7 �C, a frost-free period of
62 days, an annual evaporation of 1,996 mm and an annual
precipitation of 459.6 mm (Zhang and others 2009). Nat-
ural grassland in Damxung County covers 682,000 ha,
which accounts for 68 % of the land. Alpine meadow
accounts for 64.1 % of the natural grassland (Li 2000).
There were 560,000 livestock including cattle, sheep,
goats, and horses in Damxung County at the end of 2009.
Yaks (Bos grunniens Linnaeus) account for 40 % of the
total livestock.
Methodology
Primary Production and Soil Respiration Based on a Plot
Survey
A plot survey was conducted near the grassland manage-
ment station of Damxung County during the growing
season of 2011. The sample plot (N30�29052.3500,E91�03054.0600, 4,320 m a.s.l) was 6 9 18 m2. The vege-
tation community was Kobresia pygmaea, Stipa purpurea
alpine meadow, 6–10 cm high, with 30–50 % coverage.
The dominant species were Kobresia pygmaea C.
B. Clarke, Stipa purpurea Griseb, Stipa capillacea Keng,
and Carex montis-everestii Kukenth, and the soil texture
was dark felty soil. There were two treatments for the
vegetation survey and the soil respiration (Rs) survey. One
was that dung remained on the ground and was returned to
soil (DB); the other was that dung was collected and sub-
sequently combusted for energy (DC). Six dung patches of
25 cm diameter were set up in the plots of DB treatment
before the growing season (early April 2011) and each had
1 kg of fresh yak dung applied to simulate the situation of
DB. There were six 0.5 9 0.5 m2 replications for mea-
suring aboveground NPP remaining on the ground (rAN-
PP) in each of the two treatments in mid-September. In the
Rs plots, six polyvinyl chloride (PVC) collars (20 cm inside
diameter, 6 cm height) were inserted 3 cm into the soil,
three in each treatment (Fig. 2).
ANPP is the sum of the rANPP at the end of the growing
season and the grass intake by livestock during the growing
season [Eq. 1, which is adapted from Erb and others
(2009)]. The rANPP includes the living plants and the dead
standing and surface litter of the current year. The samples
of rANPP were oven-dried at 65 �C until a constant weight
was achieved, then the dry material of rANPP was weighed
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with an electronic balance (YP-B Electronic Balance,
Guangzheng Co., Ltd., Shanghai, China). The C content in
total dry material of grass was 0.45, and was also measured
in the north Tibetan alpine grassland (Zhang and others
2004).
ANPP ¼ rANPPþ hANPP ¼ rANPPþ Gi � tg=365: ð1Þ
Here rANPP is the ANPP remaining on the ground, hANPP
is the harvested or grazed ANPP, Gi is the grass intake by
yak per year, 365 is the number of days in a year, and tg is
the growing season, which is 150 days in Damxung County
(Fu and others 2011).
The belowground NPP (BNPP) is calculated by the ratio
(r = BNPP/ANPP). The total NPP is the sum of ANPP and
BNPP [Eq. 2, adapted from Klumpp and others (2007)].
r is applied as 2.4 in this study, referenced from Yan and
others (2005) studied in the Tibetan plateau
NPP ¼ ANPPþ BNPP ¼ ANPPþ ANPP� r: ð2Þ
The annual soil respiration (Rs) can be calculated by
Eq. 3, which is adapted from Wang and others (2010). The
daily soil respiration rate was measured by a Li-8100 soil
CO2 Flux system (LI-COR Inc., Lincoln, NE, USA) at six
intervals during the growing season of 2011 (July 23, July
30, August 6, August 26, September 7, and September 17)
in both treatments. To obtain an average daily soil
respiration, measurements were made between 8:00 and
11:00. Living plants inside the soil collars were clipped at
the soil surface 1 day before each measurement
Rs ¼ Fm;gtg=ð1� RwÞ; ð3Þ
where Fm,g is the mean daily soil respiration rate during the
growing season, tg is the growing season, and Rw is the
contribution of non-growing season soil respiration to total
annual soil respiration. The Rw is 3.48–6.84 % in meadows
of north China (Wang and others 2010), and thus was
applied as 5 % in this study.
Estimation of Yak Intake and Excretion Based
on Household Interview
A total of 36 household questionnaires were recovered in
Damxung County during the growing season in 2011 to
acquire the number of times a yak excretes per day (t) and
the dung combustion daily in the growing season (Deg) and
non-growing season (Den). A total of 48 fresh samples of
dung were collected from the rangeland of the households
to find out the average dry material (dM) of a dung patch.
Fig. 1 The study area in
Damxung County
3.0m
0.5m
3.0m DC
DB
Vegetation plot (0.5×0.5m2)
Respiration plot (d=0.2m)
Dung plot (d=0.25m)
Fig. 2 Location of the treatments of dung returned to soil (DB) and
dung combusted for energy (DC)
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After desiccating at 65 �C for 48 h, the dried dung samples
were weighed with an electronic balance. The C content in
dry material of dung (c) is analyzed in the lab from the
dung samples. Yak excretion (Dt) can be calculated by
Eq. 4, which is adapted from Soussana and others (2007)
and Zhang and others (2003)
Dt ¼ dM� t � c� 365� s; ð4Þ
where Dt is the yak excretion in g C/m2 year, dM is the
mean dry material (dM) of a dung patch in gram, t is the
yak excretion times per day, c is % C content in total dry
material of yak dung, and s is the stock ratio. The s applied
is that 2 ha of alpine meadow can sustain a yak annually
according to references Yang (1995) and Miller (2005).
Equations 5 and 6 are deduced according to the survey
to estimate the amount and proportion of dung combustion.
The dung combusted annually in households was calcu-
lated by Eq. 5. The proportion of dung combustion in total
dung excretion can be estimated by Eq. 6
De ¼ Deg � tg þ Den � ð365� tgÞ; ð5Þ
Cr ¼ De=Dt: ð6Þ
Here De is dung combusted annually. Deg and Den refer to
the amount of dung combusted per day in the growing
season (mid-April to mid-September) and non-growing
season, respectively. Cr is the dung combustion ratio in the
total dung excretion. tg is the growing season.
The dung heterotrophic respiration is the part of dung
decomposed into the atmosphere according to Eq. (7) from
Shimizu and others (2009)
Rd ¼ ðDt � DeÞ � rRd; ð7Þ
where Rd is the dung heterotrophic respiration in g C/m2 year,
and the rRd is the % dung released into the atmosphere
from the dung remaining on the ground. The annual rRd of
yak dung in the Tibetan plateau is 30 % (Jiang and Zhou
2006).
As for the yak intake, there is a relationship between
grass intake and excretion according to the digest efficient
of herbivorous animals [Eq. 8, which was referenced from
Feng and others (2005)]
Gi ¼ Dt=ð1� dÞ; ð8Þ
where Gi is grass intake by livestock in g C/m2 year, and
d is the digest ratio of forage. The d of yak in Tibet was
applied as 70 % according to the experiment by Yan and
others (2003).
Carbon Budget
The C cycle of grassland ecosystems refers to C trans-
forming and recycling among the atmosphere, soil, plants,
and herbivorous animals. Plants capture atmospheric CO2
via photosynthesis. Live plants are eaten by livestock.
Standing dead material, litter, and dung are decomposed
into atmospheric C or stored in soil as organic matter.
Adapted from Schulze and others (2000) and Shimizu and
others (2009), a framework for the C budget of a grazing
grassland in the context of dung combustion is presented in
this study (Fig. 3).
The C budget NBP can be calculated by adding the C
import (dung excretion) to NEP, while subtracting the C
export (grazing intake, dung combusted, and dung respi-
ration) from the NEP
NBP ¼ NPP� Rs � Gi þ Dt � De � Rd; ð9Þ
where NPP is net primary production, Rs is soil respiration,
Gi is grazing intake, Dt is livestock excretion, De is dung
combusted, and Rd is dung decomposition. Eq. 9 was
adapted from Shimizu and others (2009).
Statistical Analysis
The rANPP and Fm,g in each treatment was normally dis-
tributed according to the Kolmogorov–Smirnov test. The
mean differences of rANPP, Fm,g between the DB and DC
treatments were analyzed with the paired sample t test.
Equation 10, which taken from Norusis (2008), was used to
calculate the statistic parameter
Fig. 3 Framework of C cycling in terms of dung combustion in the
alpine grassland ecosystem. Note (1) the framework of C cycling was
adapted from Schulze and others (2000) and Shimizu and others
(2009) to describe the C budget in the energy grazing grassland
ecosystem in the north Tibetan plateau. (2) NBP is applied to measure
the C budget. NBP = NEP - Gi ? Dt - De -Rd, where
NEP = NPP - Rs, and NPP = GPP - Ra. (3) GPP is the photosyn-
thetic rate, NPP is the net primary production, NEP is the net
ecosystem production, NBP is the net biome production. Ra is the
plants’ autotrophy respiration rate, RLitter,Root is the heterotrophy
respiration of litter and roots, RSOC is the heterotrophy respiration of
soil organic carbon, and RDung (Rd) is the heterotrophy respiration of
dung. The soil heterotrophic respiration (Rs) = RLitter,Root ? RSOC
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t ¼�dffiffiffiffiffiffiffiffiffi
s2=np ; ð10Þ
where �d is the mean difference between samples of the two
treatments, s2 is the sample variance, n is the sample size,
and t is a paired sample t test parameter with n - 1 degrees
of freedom.
After calculating the parameter, whether the t calculated
is larger than the t looked up in the table of t threshold in
different confidence level can be determined. If the t cal-
culated is bigger than the t looked up from the table under
the confidence level of 0.05, the null hypothesis will be
rejected for the paired sample t test and there is a statisti-
cally significant mean difference between the two paired
samples.
Results
Primary Production and Soil Respiration
There was a significant difference at the confidence level of
0.05 in the rANPP between DB (M = 89.03 g C/m2 year)
and DC (M = 74.91 g C/m2 year) treatments, for
t = 4.60 [ t (0.05) (Fig. 4; Table 1). The grass intake by
yak reached 34.13 g C/m2 year, so the total ANPP can be
calculated as 88.94 and 103.06 g C/m2 year in the DC and
DB treatments, respectively (Eq. 1). The total NPP
including ANPP and BNPP (Eq. 2) of the alpine meadow
was 302.38 and 350.41 g C/m2 year in the DC and DB
treatments, respectively (Table 3). As an organic fertilizer,
yak dung returned to soil enhances the NPP by improving
the soil fertility and, by contrast, primary production suf-
fers from dung removal from the ecosystem.
There was not a significant difference at the confidence
level of 0.05 in the average daily Fm,g between DB
(M = 1.87 g C/m2 day) and DC (M = 1.80 g C/m2 day)
treatments, for t = 0.86 \ t (0.05) (Fig. 5; Table 1). The
average annual Rs reached 295.67 and 284.67 g C/m2 year
in the DB and DC treatments, respectively (Table 3). The
results suggest that the impact of dung on the soil respi-
ration is uncertain.
Yak Intake, Excretion, and Dung Combustion
The grass intake by yak can reach 34.13 g C/m2 year as
calculated by Eq. 8. Yak in the north Tibetan plateau intake
consume an average of 6.17 kg grass in dry material (dM)
daily. The dung excreted per meter square annually is
10.24 g C according to Eq. 4. The mean dry material of a
dung patch is 295.3 g and the excreta times per yak daily is
6.26 (Table 2), so a yak excretes 1.85 kg dung (dM) each
day according to these estimates. The C content of dry
dung is 30.34 % according to the in-lab analysis of dung
samples.
Yak dung combustion as fuels emits much CO2 directly
into the atmosphere. There was an average of 32.9 yaks per
household (Table 2), so yaks excreted 22,225 kg of dry
material dung per household per year. The daily average
yak dung combusted for energy per household is 35.80 and
60.42 kg in the growing and non-growing season, respec-
tively, and the dung combusted as fuels annually per
household is 18,359.4 kg (calculated by Eq. 5). 82.6 % of
yak dung excreted is combusted for energy, thus only a
small part is returned to soil. The dung combustion ratio
(Cr) is 82.6 % and 0, and the dung combusted is 8.46 g C/
m2 year, 0 according to Eq. 6 in the DC and DB situations,
respectively.
The amount of C emission from dung respiration was
small for the little dung remaining on the ground in the
dung combustion situation. In the situation of dung
returned to soil, all the dung remains on the rangeland and
there is 10.24 g/m2 year of dung-derived C to be decom-
posed slowly by the process of respiration. In the dung
combustion situation, only 1.78 g/m2 year of dung-derived
C will be decomposed. The dung respiration (Rd) is 0.53
and 3.07 g C/m2 year in the DC and DB situations,
respectively, according to Eq. 7.
Carbon Budget
Compared with the dung returned situation, the alpine
grassland ecosystem changed into a net C source measured
with NBP (calculated by Eq. 9) in the dung combusted
situation. Stock rate and the associated indicators such as
livestock intake and excretion had no significant difference
between the dung combustion and dung returned situations,
while the dung combustion proportion is significantly dif-
ferent (Figs. 6, 7).
Fig. 4 Aboveground net primary production remainder (rANPP) at
the end of the growing season in the treatments of dung returned (DB)
and dung combusted (DC) in the alpine meadow
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In the dung returned situation, the dung-derived C emis-
sion was 3.07 g C/m2 year all from the dung respiration
process, while the dung-derived C returned to soil reached
7.17 g C/m2 year. The C stored in vegetation as NPP was
350.41 g C/m2 year, and the NBP was 27.77 g C/m2 year
(Table 3), therefore the alpine meadow ecosystem is a dis-
tinct C sink.
In thedung combusted situation,mostdung (Cr = 82.6 %,
De = 8.46 g C/m2 year) was combusted for energy. Dung
combustion resulted in a huge C emission into the atmosphere.
Dung-derived C emission including dung combusted and dung
respiration reached 8.99 g C/m2 year, 5.92 g C/m2 year more
than that in the dung returned situation. Correspondingly,
very little C was returned to soil (Ds = 1.25 g C/m2 year).
The NPP was only 302.38 g C/m2 year, which was
48.03 g C/m2 year less than in the dung returned situation. The
energy grazing alpine meadow ecosystem is an obvious C
source as the NBP is -15.18 g C/m2 year, 42.95 g C/m2 year
less than in the dung returned situation.
Discussion
Primary Production and Soil Respiration
The mean of NPP in the dung returned situation is more than
that in the dung combusted situation according to this study,
which justified the opinion that organic fertilizer can
improve soil quality and increase primary production. About
80–95 % of the nutrition ingested by cattle can return to soil
via dung, which improves the content of organic C, N, P, and
K in soil (Janzen and others 1998; Shimizu and others 2009;
He and others 2009b; Wu and Liu 2010).
There was no significant difference in Rs between the
dung returned and dung combusted situation in this study.
Although the influence of manure application on soil res-
piration was not obvious (Shimizu and others 2009), the
effect on root respiration should not be ignored (Lee and
others 2007; Lin and others 2009). In the situation of dung
returned, the increased soil respiration is mainly due to an
increase in root respiration and dung heterotrophic respi-
ration. The influencing mechanism of dung on the respi-
ration of soil organic C should be explored further.
Yak Intake, Excretion, and Dung Combustion
Estimation of yak intake, excretion, and dung combustion
in this study were consistent with other research. A yak
Table 1 Paired samples test of the rANPP, and the daily soil respiration rate during the growing season between the dung returned and dung
combusted treatments
Treatments rANPP* Fm,g t from look-up table
Mean Std. deviation t Mean Std. deviation t df t (0.05)
DB 89.03 7.64 4.6 1.87 0.66 0.86 5 2.57
DC 74.91 5.78 1.80 0.51
DB, dung returned; DC, dung combusted; rANPP, ANPP remaining on the ground; Fm,g, mean daily soil respiration rate during growing season;
t, t calculated in the t test; t (0.05), t threshold in confidence level of 0.05 (two-tailed); df, degree of freedom
* Significant difference in confidence level of 0.05
Fig. 5 Daily soil respiration rate (Fm,g) during the growing season in
2011 in the treatments of dung returned (DB) and dung combusted
(DC) in the alpine grassland
Table 2 Yak dung usage at a household level in Damxung County in
2011
Item N Minimum Maximum Mean ± std.
deviation
Population (person) 36 3 9 5.61 ± 1.66
Yak in stock
(capita)
35 0 125 32.91 ± 24.25
Yak excreta times
(day)
34 5 7 6.26 ± 0.57
Yak dung patch
(g dM)
48 162 642 295.30 ± 133.24
Dung combusted in
growing season
(kg/day)
36 25 55 35.80 ± 7.82
Dung combusted in
non-growing
season (kg/day)
36 45 85 60.42 ± 11.43
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intakes 6.17 kg grass in dry material (dM), and excretes
1.85 kg dung (dM) daily according to this study. Yak
intake was 3.07–8.43 kg (dM) and excretion was
1.68–2.22 kg dung (dM) daily in the Qinghai–Tibetan
alpine grassland (Zhao 2011). As an important fuel for
cooking and heating, dung currently accounts for *80 %
of the resident energy in pasture areas of the north Tibetan
plateau. An average of 3.96 ton of dung is combusted
annually as fuels per person according to this investigation.
An average of 4–5 ton of dung are consumed as fuel
annually per person in the pastoral area of Tibet (Li and
others 2003). There is a obviously decline trend of dung
combustion in Tibetan plateau for the increase of conser-
vation awareness and the alternative energy for dung. The
dung proportion in energy mix being over 80 % in north
Tibetan plateau in 2010, will drop to 40 % in the end of
2015, for the 50 % of dung used in pastoral area in Tibet
will be substituted with renewable energy according to the
Plant103.06
Livestock Dung10.24
34.13
7.17
CO2 in atmosphere
Live roots173.14
Dead roots74.20
Soil organic carbon
42.36
CO
2 inatm
osphere
295.67
31.84
Unit: g C/m2.yr
3.07
CO
2 inatm
osphere
Grazing intake Excretion
Dung respiration
Dung returned to soil
Soil respiration
Autotrophy respiration
Respiration & Carbon losses off site
Fig. 6 The C cycle of the
alpine grassland ecosystem in
the dung returned situation
Plant88.94
LivestockDung10.24
34.13
1.25
CO2 in atmosphere
Live roots149.41
Dead roots64.03
Soil organic carbon
36.56
CO
2 inatm
osphere
8.46
284.67
27.48
Unit: g C/m2.yr
0.53
CO
2 inatm
osphere
Grazing intake Excretion
Dung respiration
Dung returned to soil
Soil respiration
Autotrophy respiration
Respiration & Carbon losses off site
Dung combusted
Fig. 7 The C cycle of the
alpine grassland ecosystem in
the dung combusted situation.
Note the ratio of live to dead
roots is 7:3. The decomposition
rate of dead root is 42.9 %
according to Zhang and others
(2003) in alpine meadows of the
northeastern Qinghai–Tibetan
plateau
Table 3 Influence of dung combustion on C sequestration and storage capacity of alpine meadows (g C/m2 year)
Dung utilization Cr NPP Rs Gi Dt De Rd Ds NBP
Dung returned 0 350.41 295.67 34.13 10.24 0.00 3.07 7.17 27.77
Dung combustion 0.83 302.38 284.67 34.13 10.24 8.46 0.53 1.25 -15.18
NPP is net primary production, Rs is soil respiration, Gi is livestock intake during grazing, Dt is yak excretion, De is dung combusted as fuels, Cr
is the ratio of De/Dt, Rd is dung heterotrophic respiration, and Ds is the dung returned to soil. All the indicators are measured by the unit of g C/
m2 year
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Plan of Energy Alternatives to Firewood and Dung in
Tibet.1
Attention should also be paid to the spatial distribution
of dung by maintaining livestock mobility in Tibetan
grasslands. In recent decades, the traditional extensive
grazing management system has been altered and the
livestock mobility has decreased (Miller 2005). Grassland
is now being allocated to groups of herders, which con-
strains livestock in fenced enclosures, and rotation grazing
among different rangelands, as occurred before the 1980s,
no longer occurs. Grassland is degraded faster than before
and the dung is distributed more unevenly. The pooling of
livestock into larger herds on shared pastures and the
reestablishing of the common property regime institutions
would disperse the grazing pressure and distribute dung
more evenly.
Carbon Budget
Ecosystems may change from a C sink into a source if
disturbance is integrated into the C budget (Running 2008).
By integrating grazing, especially the dung combustion,
into the C budget framework, the grassland ecosystem in
the north Tibetan plateau is a noticeable C source. Dung
combustion decreases the C storage capacity while it
increases the C emission. Besides countermeasures, such as
restoration of the grassland degraded on the Tibetan pla-
teau (Scurlock and Hall 1998; Wang and others 2002),
applied to increase the C sink, the application of dung
management is presented as another important option to
reduce C emission in this study.
It is time to make a decision to decrease the proportion
of dung combusted to reduce C emission in the Tibetan
plateau. Gongtang town in Damxung County has a regu-
lation that the ceiling of dung consumption per household
is 15 kg/day. In fact, the effect of the regulation is far
below local government expectation as the average dung
combustion is triple the regulation ceiling according to this
household interview. It is a time-consuming task to collect
dung and herdsmen would prefer alternative energy sour-
ces. Thanks to the high potential for renewable energy
resources in the north Tibetan plateau such as solar, wind,
and small hydro, some alternative energy sources to dung
have been demonstrated since 2006. Solar energy is pop-
ularizing in the north Tibetan plateau. If a solar cooker and
a passive solar house (100 m2) can substitute 2.26 and
5.80 ton, respectively, of dung combustion annually (Luo
and Liu 2009) then 25,376 ton of dung combustion in
Damxung County can be substituted by solar energy
annually, as there were 8,662 solar cookers installed and
1,000 passive solar house built in the county in the end of
2010. According to the Plan of Energy Alternatives to
Firewood and Dung in Tibet (see footnote 1), 50 % of dung
could be substituted by solar energy and electricity from
small hydro and wind schemes in the pastoral area in the
north Tibetan plateau via increased investment in the
electricity grid, advancing technology innovation in solar
energy and wind electricity and an allowance given to
herdsmen directly for using new energy.
Conclusion
Compared with the dung return to soil situation, dung
collection for energy combustion changes C cycling in the
grazing alpine grassland ecosystem. The main impacts of
dung combustion on the C cycle of the alpine grassland
ecosystem are (1) the C sequestration and storage capacity,
including the dung-derived C returned to soil and C cap-
tured by vegetation, decreased remarkably. The NPP
decreased remarkably because of the reduction of dung
returned to soil. (2) During a given period, more C is
emitted to the atmosphere in the dung combustion than in
the dung returned to soil situation. (3) The NBP of the
alpine meadow ecosystem dropped to -15.18 g C/m2 year
in the dung combustion situation, 42.95 g C/m2 year less
than that in the dung returned situation, which showed that
the energy grazing alpine meadow ecosystem changed into
a net C source. To prevent the grassland from deterioration
and reduce C emission, it is necessary to lessen dung
combustion, while increasing the dung returning to soil to
maintain soil fertility. Renewable energy including solar,
wind, and hydro power should be developed to substitute
dung combustion in the future.
Acknowledgments The authors are grateful for the constructive and
valuable comments from the anonymous reviewers. Financial support
from the Strategic Leading Scientific & Technology Project (B) from
the Chinese Academy of Sciences (CAS): Interactions among earth
surface in the modern Qinghai-Tibet plateau (Grant Number:
XDB03030000), the Basic Work of the National Ministry of Science
and Technology: Scientific Survey on the upper-reaches of Mekong
River and Grand Shangri-La Area (Grant Number: 2008FY110300),
and the Knowledge Innovation Program of IGSNRR, CAS: Impacts
of dung combustion on the carbon cycle of alpine grassland of the
north Tibetan plateau (Grant number: 201003016) was greatly
appreciated.
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