Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
A workshop in support of the Thematic Strategy for Soil Protection
Common Criteria for Risk Area Identification in the Soil Framework Directive
BGR, Hannover, 25 April 2007
Soil Erosion
Dick Thompson on behalf of:
Bob Jones
National Soil Resources Institute
Cranfield University UK
Contributors: Christine Le Bas, Josef Kozak
Advisors: Olaf Düwel, Dominique King
Soil Erosion – points to be covered
¾ Definitions, types, causes and
consequences of soil erosion
¾ Identifying areas at risk
¾ Conclusions
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Definition of Soil Erosion
‘Soil erosion is the wearing away of the land surface
by physical forces such as rainfall, flowing water, wind,
ice, temperature change, gravity or other natural or
anthropogenic agents that abrade, detach and remove
soil or geological material from one point on the
earth's surface to be deposited elsewhere’.
Soil erosion is normally a natural process occurring
over geological timescales; but where (and when) the
natural rate has been significantly increased by
anthropogenic activity accelerated soil erosion
becomes a process of degradation and thus an
identifiable threat to soil.
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Types of erosion
- Water
- Wind
- Tillage
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Water erosion
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Water erosion
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Water erosion
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Wind erosion
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Tillage erosion
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Characteristics of soil erosion
• Variable in intensity, scale & nature
• Episodic – very often event-driven
• Leads to conversion of soil into
sediment
• Driven by nature as well as man
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Drivers
Natural factors
Water Rain-splash dislodges soil particles
that initially fly through the air (saltation)
Rain-flow, Rill-wash cause overland flow
Slope wash, Sheet wash cause overland flow
Wave motion in streams, rivers and lakes
cause slumping of bank material
Wind Wind velocity dislodges loose soil particles that
become airborne until velocity reduces
Anthropogenic factors, such as:Human/climate-induced changes in soil – loss of
organic carbon, structure
Tillage and other mechanical influences
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Surface capping
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Livestock
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Compaction (heavy machinery)
Topsoil / Subsoil
junction
Topsoil
(normal structure)
Dense, compacted layer with lack of soil structure
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Consequences of Soil Erosion
On-site
¾ Removal/redistribution of soil
¾ Loss of productivity
¾ Reduction of soil functional capacity
Off-site
¾ Silting of lakes, reservoirs and
river courses
¾ Diffuse pollution of soil and water by
contaminants and nutrients
¾ Destruction of habitats
¾ Damage to property & infrastructure
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Identification of areas at risk
Approaches
1. Empirical - on-site measurement;
2. Modelling – calibrated with real data;
3. Combination of 1 and 2 above.
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Measuring Soil Erosion
1. Measure soil loss from plots [ field scale] or larger
areas (resource intensive and requires long term
commitment)
2. Expert judgement/field observation of soil loss
from a field, hillslope, river basin or catchment,
or other spatial unit (e.g. administrative unit)
3. Measure suspended sediment in rivers, lakes
[catchment scale]
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Weather station
Carcassonne Site
Collector
Weather station
Sediment traps in place
Pipe from collectors
General site view
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
We have insufficient field data and the required
monitoring networks do not currently exist so:
The assessment of erosion at European scale is
only feasible by using mathematical models
Most models attempt to combine:
1. Inherent soil erodibility & landscape
(eg slope characteristics for water erosion) - vulnerability
2. Drivers & degree of protection provided by
vegetation or crops - risk
Advise note:
Soil losses estimated from computer models need validation
- we need a monitoring network
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Common Criteria
Natural
Anthropogenic
Parent material/soil:
particle size (sand, silt content),
Tillage-cultivation practices
susceptibility to crusting, aggregate
stability
Topography:
slope gradient, length and form
Land levelling, terrace
construction
Climate:
precipitation, evapotranspiration,
Climate change?
temperature, wind speed & direction
Vegetation/Land cover:
natural or climax
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
Land Use/Land cover:
arable, grassland/pasture, forest,
semi-natural vegetation
Land management: cropping
systems, irrigation, grazing
intensity
‘Soil Erosion’
Rainfall
Soil
DATA
Sources
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
Temperature
‘Soil Erosion’
Pan-European Soil Erosion Risk Assessment
PESERA
Estimated soil loss
by rill and inter-rill
(water) erosion
Accelerated erosion by running water has been
identified as one of the most severe threats to soil in Europe.
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Two critical questions – limits?
¾ What is an ‘accelerated’ rate of erosion?
¾ Is there a ‘tolerable rate’ of soil erosion?
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Some figures
Average rates
1- 20 t/ha/yr for Europe
Extreme events
Storms can erode 50-100+ t/ha/single event
Natural erosion rates:
Recent study (Wilkinson and McElroy, 2007)
Avg rate for 542million years (Phanerozoic) = 0.42 t/ha/yr
Avg rate in Pliocene (most erosive period) = 1.36 t/ha/yr
Current riverine flux to global oceans
= 1.78 t/ha/yr
Erosion from present day farmland
= 6.36 t/ha/yr
Tolerable erosion rates :
< 1 t/ha/yr as a precaution
1.5 t/ha/yr might be acceptable ~ Pliocene = 1.4 t/ha/yr
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Summary and conclusions
¾ Soil erosion is a significant problem in Europe
¾ It is expected to increase under climate change
¾ Water erosion is the most widespread form
¾ It is right that the SFD covers its control
¾ Tolerable erosion rates - policy process to decide
[but] soil loss >1 t/ha/yr = accelerated over natural
rate
¾ Soil erosion should be monitored through a
network of fully instrumented measuring sites
should be established across Europe
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’
Thank you!
Danke schön!
Workshop on Common Criteria for Risk Area Identification in
the Soil Framework Directive, BGR, Hannover, 25 April 2007
‘Soil Erosion’