Download Mechanisms of soil erosion as affected by climatatic and

Mechanisms of soil erosion as
affected by climatic and management
factors
Helena Soinne
23.4.2009
Helsinki University Centre for Environment
MTT Research Finland
Mechanisms of soil erosion as
affected by climatic and
management factors
Helena Soinne
23.4.2009
Helsinki University Centre for Environment
MTT Agrifood Research Finland
Presentation outline
Erosion
How and what?
Erosion control
Soil structure
Aggregates
Management
Climate
Erosion and climate change
To sum up...
Aims
Helena Soinne
23.4.2009
Erosion
Transport of soil constituents by natural forces primarily
water and wind
Natural process
Sedimentation of eroded material forms the parent material
of many present day agricultural soils
Translocation of eroded colloidal material leads to
development of illuvial sub surface horizons
Human activity (agriculture) accelerates
- Problems in water quality
Helena Soinne
23.4.2009
Water erosion
Erosion can be connected to radical
changes in landscape
Heavy rains, steep slope
Massive loss of fertile soil,
agricultural importance
Rare in Finland
Photo by UH, Environmental Soil Science
Erosion of agricultural fields
Removal of soil material is
evidenced by turbid drain water,
colloid-size particles
Helena Soinne
23.4.2009
Colloidal material
Continuum of particle size ranges, 1 nm - 1µm
Fine clay, Fe- and Al-oxides, organic macromolecules,
bacteria and viruses
Small particles are chemically active
Mobilised colloids act as carriers for
Pesticides
Phosphorus
Heavy metals
Environmental
importance
Non-polar organic compounds
Helena Soinne
23.4.2009
Soil erosion
Erosion is controlled by
Rainfall intensity and runoff
- Impact of raindrops can break down soil aggregates
- Runoff water detaches and transports soil material
Slope gradient and length
- accumulation of runoff
- velocity
Vegetation
Soil erodibility
Helena Soinne
23.4.2009
Soil erosion
Photo by UH, Environmental Soil Science
Photo by Tommi Peltovuori
Erodibility = the ease by which soil particles are detached by
rain or by the running water
Structurally unstable soils may disperse in water into basic
particles i.e. sand, silt and clay
Stability of soil aggregates – most important property governing soil
erodibility
Helena Soinne
23.4.2009
Erosion control
Eroded material carrying contaminants and nutrients
poses a threat to the receiving ecosystems
(eutrophication)
Suggested measures to decrease these threats:
- Buffer strips
Aim to protect the waterways
- Constructed wetlands
Erosion is a sign of structural imbalance in the soil
Sealing and blocking of pores– infiltration and oxygen
exchange becomes difficult
Permanent loss of soil and nutrients
Erosion control should aim to keep the soil
and nutrients in the field
Helena Soinne
23.4.2009
Erosion control on the field
Effect of raindrops should be diminished
vegetation cover
minimal tillage
Surface runoff should be diminished
Enhancing infiltrability
Increasing surface storage
Aggregate stability should be increased
Helena Soinne
23.4.2009
Soil Structure - aggregates
Micro-aggregates
<250 µm
Clay-size particles bonded together by cementing agents
(organic molecules, calcium carbonate, amorphous Al and
Fe oxides, disordered aluminosilicates)
Dense, high internal strength
Macro-aggregates
>250 µm
Combinations of micro-aggregates
Held together by roots and fungae
Aggregates of different size classes have different stability
Helena Soinne
23.4.2009
Soil structure - aggregate destabilisation
Disintegration of macro-aggregates into microaggregates
Wetting action: breakdown caused by compression of
entrapped air during wetting or by differential swelling
Water drop impact
Dispersion of clay into the solution (micro-aggregates)
Diffusion in wet soil
High ionic strength – less dispersion
Helena Soinne
23.4.2009
Soil structure - aggregates
Factors affecting aggregate stability
Internal:
- Ionic strength
+
- Clay mineralogy
and content
+-
- Organic matter
+ (-)
- Fe and Al oxides
+
External:
- Age
+
- Biological factors
+
- Agricultural management + - Climate
Helena Soinne
+23.4.2009
Structure and management
Effect of management on soil structure:
Tillage
- Brake up natural aggregates, new surfaces for colloid
detachment
- Increase / decrease infiltration
Vegetation cover
- Dissipate raindrop energy, reduce wetting rate
- Roots
Organic matter amendments
- increase in biological activity
Fertilisers
- Increase in ionic strength
Helena Soinne
23.4.2009
Structure and climate
Wetting and drying
Drying is driving force for aggregation (micro-aggregates)
Cycles decrease macro-aggregate stability ?
- Effect is influenced by wetting rate and soil water content
Freezing and thawing
Freezing resembles drying – Traditionally frost has been
considered to increase aggregate stability in clay soils
Cycles: results showing decrease and increase in macroaggregate stability have been reported (water content)
Spring: weak structure and high runoff
- Soil saturated, snow melting, vegetative cover minimal
Helena Soinne
23.4.2009
Erosion and climate change
The erosion rates are expected to increase if precipitation
becomes more intense and frequent (ClimSoil 2008)
Frozen soil under snow cover stays intact However:
Photo taken on March 18th in 2007
by Tommi Peltovuori
Helena Soinne
23.4.2009
Erosion and climate change
In the Boreal zone, increasing winter temperatures may
further increase the potential for erosion
Less snow cover
Run-off volumes higher
Duration of soil frost
is shorter
Freeze-thaw cycles
Erosion throughout the year?
Importance of erosion control
Photo taken on March 18th in 2007
by Tommi Peltovuori
Helena Soinne
23.4.2009
To sum up….
Climate change
Heavier rains
Winter rains
Mobilisation of colloids
Milder winters
Transport of nutrients
- Freeze-thaw cycles
Soil structure is essential in erosion control
Stabilisation of different aggregate size fractions is due to
different mechanisms (micro- and macro-aggregates)
- Management should have positive effect on aggregates in
all size classes
Climate change - changes in temporal distribution of
precipitation
- Challenge for soil management
Helena Soinne
23.4.2009
Aims
To characterise (quality) the eroded material
Variation between land-use types, "no-erosion -field"?
Seasonal variation
To get knowledge that helps in predicting the environmental risk
caused by erosion and to find management practises that
reduce the potential for erosion
To identify mechanisms behind the detachment of soil particles
from the soil
Environmental conditions that increase the instability of aggregates
Conditions where high potential for erosion
To identify problematic circumstances typical for certain
management-type
Helena Soinne
23.4.2009
Thank you!
Helsinki University Centre for Environment
MTT Agrifood Research Finland