Symposium no. 61
Paper no. 1857
Presentation: oral
Pedosphere, global changes and environmental
quality of soil
ZHAO Qiguo
Institute of Soil Science, Chinese Academy of Science, P.O. Box 821. Nanjing 210008,
China
Abstract
With development of modern geoscience, particularly of environmental sciences,
the contemporary soil science is undergoing great changes in both research contents and
scope. Soil is not only a certain substance or a certain independent natural historical
body, but also a spheric layer with peculiar structure and functions in the earth system.
From the viewpoint of the geo-biosphere system of the earth, soil science does not only
deal with the soil substances per se, but also more importantly with the relationship
between soil, the other spheres and the human survivorship environment in view of the
pedosphere. This is the new orientation of soil science today and will affect profoundly
the studies on the human survivorship environment and global changes. To throw more
light on this subject, the present paper intends to address the conception of pedosphere
and its role in global changes and environmental quality of soil. Also addressed are
series of environmental issues in China and their relations to the global change.
Moreover, research orientation and priorities are discussed in the field of pedosphere for
agriculture and environment.
Keywords: pedosphere, global change, environmental quality
Conception and Connotation of Pedosphere
Pedosphere is the overburden layer composed of soils covering the land and the
bottom of shallow water, looking like a membrane of the earth, somewhat like biomembrane of an organism. As an important component of geosphere, its lies on the
interface of lithosphere with atmosphere, hydrosphere and biosphere and is both the
supporter of all these spheres and the products of their long-term interaction. As early as
in 1932, Mattson stated that soil is the product of the interaction among lithosphere,
atmosphere, hydrosphere and biosphere and generalized the connotation of pdedosphere
from the viewpoint of material cycling (Mattson, 1932). Based on the current
knowledge, the principal conception of pedosphere includes the following 6 points
(Zhao, 1991).
Perpetual material cycling and energy exchange. The pedosphere is the important
interface where the most intense interaction occurs between biotic and non-biotic
substances. Different from any surface sediment and weathering substances of rock, soil
provides not only growth medium and surroundings to vegetation, but also habitat to
microbes. It interacts with other spheres through perpetual material cycling and energy
exchange.
The most alive and vital sphere As an interface and interaction layer in the
geosphere system, the pedosphere functions in sustaining, regulating and controlling
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various material cycling and flows. Owing to its inherent properties of soil fertility, the
pedosphere is one of the most active and vital spheres in the geospheric systems.
Interactions with environmen. The pedosphere per se is an important component of
the environment. It, on one hand, contributes positively to the environment with its
purificational functions. On the other hand, it also exerts a negative impact on the
environment e.g. through its deterioration and/ or destruction.
Memory module and gene base. As a memory block, the pedosphere stores
information pertaining to soil forming processes, soil properties, the past and present
influences on the soil body from atmosphere, hydropshere, biosphere and lithosphere.
By reading this information it possible to distinguish old soil changes from new ones
and to predict future changes off the pedosphere.
Temporal and spatial variations. The spatial characteristics of pedosphere displays
itself inform of variation in thickness and type of different soils over the land, while
temporal characteristics in form of soil forming ages, ranging from 1×103 to 1×106
years. The interactions amongst pedosphere and other geospheres are abstracted in
Figure 1. With relation to biosphere, the pedosphere sustains and regulates the
biological processes through providing nutrients, water and suitable physical conditions
or exerting adverse constraints for growth. At the ecosystem level the pedosphere
determines the distribution and succession of natural vegetation together with climate.
As for the atomsphere, pedosphere affects the chemical composition and hydrothermal
equilibrium of atmosphere by absorbing O2 and releasing CO2, CH4, H2S, N2O etc.,
which have significant impacts on global atomospheric changes (Lal et al., 1995). As
hydrosphere is concerned, the pedosphere influences participation of precipitation over
land, water bodies and into soils. As well as that, it changes the behaviors, balances,
differentiation, transphormation and compostion of chemical elements in hydropshere.
The pedosphere protects the lithosphere, the skin of the earth, against various external
forces and exchanges with it in geological circulation.
Composition of fauna,
flora, microorganism
and organic matter
Biosphere
Atmosphere
Absorbing
O2
Biological
process
Releasing
house gases
Pedosphere
Biomass,
water & nutrition
Biosphere
Cycling of biological nutrition
Exchanges of trace gases
between atmosphere and other spheres
Earth
skin
Cycling &
Balance, cycling,
balance
Hydrospheretransformation
of water
of water
Geological
Cycling
Lithosphere
Cycling of metals &micro-elements
Minerals and inorganic composition
Composition,properties and structure of materials
Physical-chemical-biological
(Surface nature and characteristics of soil colloids)
Research
Orientation
Hydrosphere
Properties and composition of water
Cycling and balance of materials
Composition, properties and
structure of materials
Composition of atmosphere
and soil gases
Cycling and balance of materials
(Water, heat and energy)
(material cycling, energy flow and balance)
1. Pedosphere and earth life; 2. Pedosphere and human survivorship condition;
3. Pedosphere and natural environment; 4. Pedosphere and global soil changes;
5. Composition and characteristics of Pedosphere
Figure 1 Position, connotation, functions and research orientation of pedosphere.
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Based of the pedospheric conception, the physical, chemical and biological
processes, their intensities and mechanisms of translocation and transformation of
materials in the pedosphere and their and the interactions and impacts and with other
geospheres are much concerned. The final targets of the research work on pedospheric
scale are to sustain agriculture and protect the environment for human beings and life on
earth.
Role of Pedosphere in Global Changes
Global changes refer to changes in global environmental components that are vital
to human surial, such as greenhouse effect, formation of holes in the ozone layer,
diminution of forests, depletion of bio-diversity, degradation of land (desertification)
and deficiency in water resources. Substantially, these changes result from the
interactions among the various geospheres and the interactions between mankind and
the spheres.
The pedosphere affects global soil changes by exchanging substances with other
spheres. For example, absorption, translocation and exchange of nutrient elements
between the pedosphere and the biosphere affect the composition and decomposition of
litter when land use systems degrade from tropical rainforest to tropical monsoon forest
and to savanna. Formation of soil and its characteristics are mainly influenced by the
migration and material cyclings between the pedosphere and lithosphere. For example,
in southern China, the elements, B, Mn, Co, Pb, Ti, Zn and Zr are leached more than
accumulated, whereas the elements, Ba, Cr and Ni, are resversely accumulated. Water
movement transports chemical elements and sediments from the pedosphere into
hydrosphere. It is estimated that annual runoff on the continents amounts to 37x1015 L,
carrying away 4.0x108 t of chemical compounds from the land and indicating a
significant influence on environmental changes. Between the pedosphere and the
atmosphere exchanges of macro and trace gases occur. Through N fixation,
photosynthesis and precipitation, some gases and elements depose into soil, while
through organic matter decomposition and transformation of C, N and S, soil emits
some trace gases into the atmosphere, generating the greenhouse effect, which exerts an
impact on global climate.
The pedosphere triggers global soil changes through temporal and spatial evolution
of the global soil cover, such as changes in soil forming processes and soil properties.
For example, when formation of soil resources proceeds in the stable natural
environment, changes in water, gas and heat regime are relatively steady and the
resources utilization is in good state. Whereas under erosion conditions, the epipedon is
being lost and soil fertility is decreasing. Under accumulation environment, e.g., being
frequently overlaid by volcanic products, the soils are always in their infancy.
The pedosphere causes global soil changes and affects the survival environment
due to the strong disturbances of human activities on pedosphere. Indiscriminate
clearing of forests, accelerated soil erosion, overgrazing and over-cultivation and
expansion of cities have changed the land structure. Irrational exploitation and poor
management of soil resources and over-cultivation of steep slope cause various soil
degradations such as soil erosion, sandification, formation of bogs, salinization, decline
in soil fertility, consequently affecting the whole survival environment of mankind.
Land uses change from wet lands such as exploitation of paddy fields, swamps and
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lakes into upland cultivation. These changes generate trace gases such as CO2, N2O and
H2S, which have exerted impact on global temperature rising.
Environmental Problems Confronting China and their Relation to Global Changes
As a country with a territorial area of 9.6 million km2 and population of 1.3 billion,
China plays an important role in global environment changes. Comparing the
environmental problems in China and in the world, a clear picture can be drawn. As
given in Table 1, the emission of CO2 in China reached 6.2×108 t C, accounting for
10.7% of the total amount in the world and being ranked in the third position.
Meanwhile, the emission of CH4 amounted to 2.6×107 t, about 4.7% of the global total.
During the fifth period of “Five-Year-Plan”, the felling rate of trees was as high as 1.34
million ha y-1, about 1/5 of the world average of 7.05 million ha y-1. Upland accounts for
69% of the national area of China, higher than the average 61% of the world. Chinese
water resources account for 1/4 of the worlds total, while the average amount per capita
is only about 6% of the world average. Soil erosion by water in China has reached 5.0×
109 t y-1, about 8.3% of the world total.
Table 1 Comparison of global environment problem (Yie, 1992).
Globe
Trace gas
Forest
CO2 (million t)
CH4 (million t)
CFCl3 (1000 t)
CF2Cl3 (1000 t)
Area (1000 ha)
Felling rate
(1000 ha y-1)
Desertification Upland area
(million ha)
Percentage (%)
Water resource Annual runoff
(108 m3)
Runoff per capita
(m3 y-1)
Soil erosion
Erosion loss
(100 million t y-1)
Soil flowing into the sea
(100 million t y-1)
5800
553
280.8
368.4
418342
0
7046
3257
China
619.72
26.12
9.50
15.5
170,000
China/Globe
(%)
10.7
4.7
3
4
4
1342
19
315
10
61
468000
69
27115
6
10800
2600
24
600
50
8.3
240
20
8.3
*: The felling rate during the forth “Five-Year Plan”
Recent researches also revealed that in the past years, the climate in China was
becoming drier and warmer; with the drastic increase in population and the increased
human activity, the surface runoff increased, and the natural vegetation and cultivated
land area decreased. Consequently, soil fertility depletion, desertification and other land
degradation become more and more serious; and the area per capita of farmland,
grassland and forestland is much lower than the world average. It is estimated that,
when Chinese population reaches 1.3 billion, the cultivated land area would decrease by
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about 2×107 ha. The net reduction in farmland would be 1.0×107 excluding the newly
reclaimed farmland (Zhao and Liu, 1990). Besides, the decertified area would expand
from 1.76×105 km2 to 2.51×105 km2 (Zhu, 1990), the water-eroded area from 1.5×106
million km2 to 1.7×106 km2, and 1.7×107 ha of farmland would be threatened by
salinization. The forest area would decrease by 15%, grassland by 20% and the hay
yield per unit area by 30% (Yie, 1992). All these indicate that China is playing a
decisive role in the global environment (air, vegetation, soil, water, etc.) changes.
Environmental Quality of Soil in ASIA
Continuous urbanization and industrialization demand land. Urbanization and
industrialization have proceeded rapidly in many parts of Asia during the last decades.
For example, Agriculture-Forestry-Fisheries, Mining and Manufacturing Industries, and
Social Overhead Capital and Services in Korea comprised 36.6%, 16.3% and 47.1%,
respectively, of GNP in the early 1960s, whereas the proportions changed to 10.9%,
32.8% and 56.0% in the late 1980s. More than two-thirds of Koreans now live in cities
with populations over 200,000. The rapid industrialization and urbanization have
resulted in environmental problems especially in the most densely populated areas and
adversely affect regional and global environmental quality. In China, nearly 0.15
million ha of cultivated land declined each year recently in China due to the building of
housing/industrial estates, the construction of roads, reservoirs and recreation grounds.
In the southeastern part of Saitama Prefecture in Japan, cultivated land decreased 44%
of the total during a period from 1970 to 1988. This will be further aggravated in
developing areas where industrial development is progressing rapidly compared with
developed areas.
Rapid industrial development has resulted in soil pollution, which becomes a
serious problem in China and other Asian countries in the last two to three decades.
This is particular concern around the major cities and large industrial enterprises where
wastewater, industrial and mining wastes, vehicle exhausts and agricultural chemicals
are often discharged onto land. More than 30 industrial districts amounting to an area
more than 5.0×105 ha have been polluted due to irrigation with wastewater and 7.2×1010 t
of tailing and slag had accumulated in 75 industrial cities up to 1980 in mainland China.
In Hong Kong about 2.0×104 t day-1 of solid and semi-solid wastes were produced in
1994. The amount of wastes generated rises as the population and its affluence
increases. Municipal wastes include wastes from household, commercial, industrial and
construction sources. By the year 2001 daily municipal waste output is projected to be
some 1.67×107 t. In Taiwan up to 80% of soil pollution has resulted from the discharge
of wastewater from chemical plants and metal surface treatment plants in the industrial
parks. Sewage sludge is a by-product of wastewater treatment. Nearly 10 million t were
generated annually from wastewater treatment plants in China. The quantity of sewage
sludge is very likely to increase greatly in the near future. The waste will be mainly
disposed in landfills. Analyses of landfill soils contaminated with leachate have shown
elevated levels of heavy metals. Land application and recycling of sewage sludge and
other organic manure or composts has escalated great concern over the environmental
impact and agricultural sustainability.
Soil pollution by waste-derived heavy metal has been discovered in many Asian
countries. Heavy metal contents in the soils from areas around metal mining sites,
smelters and landfills for industrial wastes were generally higher than those from the
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agricultural areas. In South Korea Cd contaminated-rice paddy soils and brown rice has
been found around Zn mining sites. Rice paddy soils polluted with As was also
discovered. Concentrations of As in the rice paddy soils around the As mining sites
were in the range of 6.7-701.3 mg kg-1 with an average of 11.1 mg kg-1.
Besides agricultural soil, roadside soils are contaminated with Pb and possibly
other metals such as Zn, Ni, and Cu associated with motor vehicles . In Hong Kong the
industrial area had the highest Pb concentration, followed by industrial/residential area,
rural area and country park area, while the agricultural area had the lowest
concentration. In urban soil of Tokyo city concentrations of Cd and Pb increase 0.05
and 0.55 mg kg-1 on average annually.
Soil is fundamental to most land -based plant or animal production systems. Any
soil contamination is extremely serious because the contaminant or its breakdown
products may accumulate in food products ultimately for human consumption. There is
currently much activity in determining the causes and effects of heavy metal additions
on the quality of the agricultural environment. A major concern about the contamination
of agricultural soils is the uptake of pollutants by vegetable crops and its consequences
for human health. For example, in Hong Kong two common local cabbages (Brassica
chinensis and Brassica parachinensis) approached or exceeded the maximum permitted
Cd concentration (0.05 mg kg-1). The elevated Cd contents in these vegetables may
cause a potential health risk if used for human consumption. Some soils contaminated
with Cd have been designated for remediation in Taiwan.
In addition to inorganic metal pollutants, organic micropollutants such as pesticides
and their residues, PCBs, PAHs, petroleum chemicals and dioxins may also cause a
potential risk of health. Pesticide use has been credited as one of the major contributors
to modern agricultural production. For instance, a recent survey has establelished that
about 3,500 to 4,000 t of pesticide active ingredients are applied annually in New
Zealand. Pesticide has progressed from persistent and highly toxic chemicals such as
arsenate through the era of DDT and other persistent but less toxic organichlorines to
the present era which includes herbicides, and fungicides that are generally less
persistent but more specific in their activity than their predecessors. There has been a
lack of information concerning trace pollutants particularly the organic micropollutants
in the terrestrial environment. Investigation into contamination by trace organic
pollutants is urgently required.
Following entry into the soil environment, metal, non-metal and organic pollutants
undergo rapid interactions with both the solid and solution phases. Some of the
interactions include physical, chemical and biological reactions such as filtration,
dilution, decomposition, transformation and adsorption-description processes. Soil can
act as a contaminant source for surface water and groundwater as well as to agricultural
products once contamination exceeds a threshold value. Examples of these include the
impact of nitrate leaching from grazed grass/legume pastures and rice paddy soils on
groundwater quality and eutrophication of surface waters through the movement of soil
particulate enriched with phosphorus (P) as a result of P fertilizer use. It has been
reported that in the Tome River of Japan water concentration of total N increased from
1 mg L-1 in the 1970's to 2 mg L-1 in the 1980's and to 3 mg L-1 in the 1990's, and the
increasing trend has existed in upstream water.
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Urbanization and industrialization as well as soil-plant production system produce a
large quantity of greenhouse gases. Atmospheric concentrations of SO2, NOX and O3
have been shown to cause direct damage to natural ecosystems and crops, as well as
having heath effects in large urban areas. Due to high economic growth, emissions of
SO2 in Asia are expected to be rapidly increase from about 34 million in 1990 to about
110 million by 2020 when no control measures are taken. In fact in many parts of Asia
the concentrations of SO2 may already reach hazardous levels. It is also found that
concentrations of toxic metals such as Ni, Hg, Cd and Pb are much higher in urban air
than those in uncontaminated air in Japan. The atmospheric deposition and damage to
ecosystem and human health are associated with soil types and land use.
Soils are frequently the recipients of numerous pollutants associated with
agricultural production. Soils are often the interface between human activities and the
hydrosphere and the atmosphere in the environment, and serve as a source or sink for
various constituents in water and air. Both point and non-point source pollution may
result in contaminated soils. Contaminated soils will continually be discovered and will
continue to occur. We should protect our soil environment from accelerating
contamination. Most countries in Asia have not accumulated much data on soil
contamination considering the extent of industrialization and urbanization. It is now
time to treat the soil environment as a matter of both national and international concern.
There is an urgent need to conduct a more comprehensive survey on the pollution of the
soil environment. It is necessary to develop a local regulation guideline for
contaminated soil classification and investigations with consideration of local
conditions. It is important to enforce regulatory measures to minimize contaminating
activities and also to ensure that with the increase in industrial activities there is a
greater recognition of the need for soil preservation and for maintaining a quality
environment. Research related to soil environment management should be developed
further and related to future preservation of global environments.
Orientation and Contents of Study on Pedosphere
As described above, with the expansion of the scope of human activities and
development of science, soil science is also developing and expanding from the study
on soil per se to the study on pedosphere and its relations with other spheres in the earth
system. In this sense, the orientation and contents of the study on pedosphere will be
completely in conformity with soil science for agriculture and the environment.
Considering future development of the geospheric system, the study on pedosphere is
orientated towards composition and properties of the pedospheric substances, material
cycling and energy flow and its influence on the environment of human survival.
Taking N cycling as an example (Figure 2), it is important to understand the
mechanism, pathways and quantity evaluation of N loss, the forms and stability
mechanism of organic N and the chemical characteristics and fertility of paddy soil so
as to achieve sustainable agriculture. From environmental viewpoint the emission
mechanism of CO2, CH4 and N2O to atmosphere, the N translocation to water, the
memory module and environment information and the chemical behavior of pollutants
in soil itself must have to be focus. The relationships between pedosphere and the other
geosphere are the bases to take countermeasures to tackle the problems related to
agriculture and the environment. As to the relationships among pedosphere, agriculture
and the environment, there are 7 hot research spots: 1) soil and global changes; 2) soil
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degradation and its prevention and restoration; 3) soil pollution and its prevention; 4)
soil quality and its assessment; 5) soil and agriculture environment; 6) characteristics of
urban and suburb soil and human health; 7) application of and research into new
technology and methods. Among them focuses must be given to soil degradation, soil
quality and soil pollution in China.
Figure 2 Orientation and contents on pedosphere taken N cycling as an example.
Fe
rti
lity
Material cycling
in
Pedosphere
Agriculture
ial
ter nt
Ma veme
mo
1. The mechanism, pathways
and quantity evaluation
of N loss
2. The forms and stability
mechanism of organic N
3. Chemical characteristics
and fertility of paddy soil
Sustainable
development
1. Emission mechanism of
CO2,CH4 and N2O
2. N translocation to water
3. Memory module and
environment information
4. Chemical behavior of
pollutants in soil
Environment
Soil Quality
1. Counter measures to reduce
1. Counter measures to reduce the
Should be emphasized:
N gaseous loss
emission of CO2, CH4 and N2O
2. The efficiency
of organic
N
2. Control
translocation
Impact
on agriculture,
environment
and the
human
healthof N to
3. Fertility and fertilization of
water
Research topics:
paddy soil
3. Measures to control
Main soil types ( especially organic/inorganic
cultivated soil)pollutants
Evolution
Evaluation
Reconstruction
Regularity
and
Mechanism
Standard
Indexes
Technology
and
Measures
Soil degradations should be studied from spatial and temporal variation, formation
mechanism and adjustment measures from different scales such as large scale with
remote sensing and GIS methodology and small scale with stationary observation and
simulation (Figure 3). The regional problems are different in China. Desertification is
the priority in Western China. Salinization is the key problem on Huanhuaihai Plateau
of Northern China. Swampification exists in the Northeastern China while in
Northwestern China soil erosion is most serious. In Southern China acidification and
depletion in soil fertility are of high concern. In the fast-growing economy region,
pollution is enlarging and threatening.
Figure 3 Hot research spots of research on soil degradation in China.
With respect to soil quality, emphasis should be given to the impact of changes in
soil quality on the environment and human health (Figure 4). The studies should aim at
understanding the driving forces and mechanisms of soil quality evolution (changes), a
Soil Degradation
Spatial & temporal
variation
Formation
mechanism
Adjustment
measures
Method: Information from R. S. technology
Stationary simulating prediction
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Soil degradation problems
In the west: Desertification
In the Huahuaihai: Salinization
In the North-east: Swampification In the North-west: Soil erosion
In the South-west & in the South-east: Acidation
In the South: Decline in soil fertility
In the fast-growing-economy region: Pollution
17th WCSS, 14-21 August 2002, Thailand
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base on which an index system assessing can be constructed to evaluate and compare
the soil quality and functions of main soil types. Final, technology and measures have to
be identified to tackle the problems of specific soils and restore the functions and
productivity of the soils.
Figure 4 Hot research spots on soil quality in China.
Research on soil pollution esp. In the developed and industrial regions, includes
those on organic pollution in soil and water, inorganic pollution (N, P) in soil and water,
heavy metal pollution in soil and water, radioactive pollution in soil and water and there
impacts on food chain and human health (Figure 5). The objectives are to identify the
genetic classes, determine pollutant formation regularity and find the methods and
measures to prevent the harms of the pollutants either from industrial sewage, solid
waste, fertilizer and pesticides or from settlement of inhabitants.
Soil Pollution
Genetic Class
Formation Regularity
Prevention Method
Developed and Industrial Region
Industry Sewage
Solid Waste
Fertilizer & Pesticide Settlement
1. Organic Pollution in Soil and Water
2. Inorganic Pollution (N, P) in Soil and Water
3. Heavy metal Pollution in Soil and Water
4. Radioactive Pollution in Soil and Water
5. Impact on Food Chain and Human Health
Figure 5 Hot research spots on soil pollution.
In conclusion, the study on pedosphere is still at its initial stage. However, it will
possibly substitute soil science or became a new branch of soil science in the future, and
will play an important role in the study of global soil changes and global environment
changes. This is a topic that is worthwhile for soil sciences all over the world especially
in Asia to ponder and explore.
References
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Lal, R., J. Kimble, E. Levine and C. Whitman. 1995. World soils and greenhouse effect:
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and Global Change. CRC Press, Inc. USA.
Shi, D.M. 1990. The loss of water and soil in China, pp. 207-205. In G.Z. Sun et al.
(eds.). The Natural Disasters in China. Beijing (in Chinese).
Yie, D.Z. 1992. Pre-study on Global Changes in China. Meteorology Press.
Zhao, Q.G. 1991. Study on material cycling in pedosphere and development of soil
science. Soil 23(1):1-3 (in Chinese).
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Zhao, Q.G. 1991. Global soil change. Progress in Soil Science 19(5):16-20 (in Chinese).
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