Impacts of Dung Combustion on the Carbon Cycle of Alpine Grassland of the North Tibetan Plateaue

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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

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Environmental Management (2013) 52:441–449

DOI 10.1007/s00267-013-0107-8

Author's personal copy

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

442 Environmental Management (2013) 52:441–449

123


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)

Environmental Management (2013) 52:441–449 443

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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


123


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


123


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


123


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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