Urban soils store more carbon than natural soils. The study analyzed carbon stocks in 118 cities worldwide and found urban soil carbon stocks were typically 3-5 times higher than background natural soils. Larger and older cities tended to have lower average carbon levels in topsoils. However, substantial carbon and nitrogen were found stored deeper in urban subsoils and cultural layers, highlighting the importance of these "hidden" stocks. Urban soils accumulate carbon at a rate of about 20-30 kg of carbon per square meter per century as the soils grow upward by around 50 centimeters per century through inputs from surrounding areas, in-city redistribution, and transformations from activities like sealing and compaction.

1. Urban soils as hotspots of
anthropogenic carbon
accumulation
Viacheslav Vasenev,1
Yakov Kuzyakov2
& Ivan
Vasenev3
1
RUDN University, Moscow; 2
George-August University, Goettingen; 3
RTSAU, Moscow
Global Symposium on soil organic carbon-2017

2. Urbanization – global tendency
 World population will exceed 9 billion people by 2050 (FAO, 2013)
 More than 70% of world population will live in cities by then

3. Urbanization
Traditionally urbanization
was related to negative
environmental impacts
 Recently the potential of
urban areas to provide
important soil functions and
services is highlighted
Natural and agricultural
landscapes
Green zonesBuild-up areas

4. Driving factors behind urban soil’s
formation and transformation
Slope terracing «Urban heat island» Plant species introduction
Wastes and landfills Soil sealing Soil construction
Indirect anthropogenic
influence
Direct anthropogenic
influence

5. Why soil carbon? Soil
functions
 Protection of
humans and
environment
 Biomass
production
 General reservoir
 Physical basis of
human activities
 Source of raw
materials
 Geogenic and
cultural heritage
Blum, 2005
 Water and
nutrient cycling
 Ground water
protection
 Basis for
organisms’ life
 Land for
settlements
 Land for
agriculture
 Deposition of raw
materials
…
BBodSchG, 1998
 Nutrient
cycling
 Water
filtering and
buffering
 Biodiversity
and habitat
 Resistance
and
resilience
 Physical
stability and
support
Andrews et al, 2004
!!! 30 to 50% of distinguished soil functions are
directly or indirectly related to soil carbon

6. ESs’ categories (TEEB, 2010)ESs’ categories (TEEB, 2010)
!!! 25 to 40% of distinguished ecosystem services
are directly or indirectly related to soil carbon
Food
Water
 Raw materials
Genetic
resources
Medical
resources
Ornamental
resources
Provisioning
Air quality regulation
Climate regulation
Moderation of
extreme events
Regulation of water
flows
Water treatment
Erosion prevention
Maintenance of soil
fertility
Regulating
•Aesthetic
information
•Opportunities
for recreation
and tourism
•Inspiration of
culture, art
and design
•Spiritual
experience
Cultural
Habitat
Maintenance of life cycles of migratory species
Maintenance of genetic diversity
Why soil carbon? Ecosystem
services (ES)

7. Aim of the review study
 To analyze the global pattern of C
stocks in urban soils as compared to
their natural ones
 To analyze factors of intra- and inter-
city variability of C stocks
 To compare profile distribution of C
forms stored in urban soils, compared to
natural ones
 To propose the main mechanisms of C
accumulation in urban soils
 To estimate C accumulation time in
urban soils

8. Materials and methods
118 cities 770 values SOC, SIC and BC stocks 5
depths

9. Global patterns of C stocks in urban soils
Urban SOC stocks are usually greater than those of
natural soils
 Urban soils in cold and temperate climate often store
more SOC than those in tropical and arid climates

10. Inter-city variability in SOC stocks
Generally, the larger is a city
(in terms of extent and
population) the less are
average topsoil SOC stocks
The largest urban SOC
stocks are related to cultural
layers of medieval cities

11. Intra-city variability in SOC stocksIntra-city variability in SOC stocks
Public and residential areas usually stored more SOC than
all the other functional zones with the maximal
contribution from subsoils and cultural layers

12. ““Hidden” C and N stocks in urban subsoilsHidden” C and N stocks in urban subsoils
Substantial amounts of SOC, SIC and N have been
sequestered in the subsoils, cultural layers and
sealed soils, underlining the importance of these
‘hidden’ stocks for C assessments.

13. Profile distribution of C and N stocksProfile distribution of C and N stocks

14. Mechanism of C accumulationMechanism of C accumulation
1) C inputs from
suburban-areas
(e.g. transfer of
food, wood and raw
materials);
2) C provisioning and
redistribution
inside the city (e.g.
xenobiotics, soot
and charcoal);
3) in situ
transformations
(e.g. sealing, over-
compaction and
water-logging)

15. C accumulation rate in urban soilsC accumulation rate in urban soils
Urban soils
growth rate
~ 50 cm/
century
Carbon
accumulatio
n in urban
soils
~ 20-30
kg C m-2
per century

16. Conclusions
 The estimated C stocks in the investigated urban soils
generally were up to 3-5 times higher than in background
natural soils
 SOC and BC stocks in the analyzed urban soils often
positively correlated with city latitude
 City size and age were the main factors explaining inter-city
variability of soil C stocks
 Intra-city variability of soil C stocks was dominated by their
functional zoning
 Large stocks of SOC and SIC are located in subsoils (below
30 cm) and cultural layers (below 100 cm) of sealed soils
 Urban soils grow upward by about 50 cm per century,
corresponding to C accumulation rate of 20-30 kg C m-2
per
century

17. Thank you for attention !

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