multiscale variability of soil aggregate stability

Multiscale variability of soil aggregate stability: implications

for rangeland hydrology and erosion

Mike DuniwayJeff HerrickKen Spaeth

Nichole BargerJustin Van Zee Jayne Belnap

Why soil aggregate stability?

•

Soil surface characteristics control capture and retention of water and nutrients

•

Soil aggregate stability is related to soil erodibility & infiltration capacity, both of which are:–

highly variable

in space and time

–

difficult to measure

“…“… soil aggregate stability soil aggregate stability …… has been demonstrated to have a has been demonstrated to have a strong relationship with interrill erosionstrong relationship with interrill erosion”” (Blackburn & Pierson, 1994)(Blackburn & Pierson, 1994)

Soil stability kit(2) Immerse in dI water.(2) Immerse in dI water.

(3) Record slaking in 1(3) Record slaking in 1stst

5 min.5 min.

(4) Wet sieve 5x.(4) Wet sieve 5x.

(5) Rate sample on a(5) Rate sample on a

scale from 1 to 6.scale from 1 to 6.

(1) Collect 6(1) Collect 6--8 mm8 mm--diameterdiameter sample from surface and 20sample from surface and 20--

25mm depth (1 sample/sieve). 25mm depth (1 sample/sieve). Herrick et. al 2001. Catena 44: 27-35.

Soil stability kit: interpretation

Stability class

Criteria for assignment to stability class (for Standard Characterization)a

1

50 % of structural integrity lost within 5 seconds of insertion in water.

2

50 % of structural integrity lost 5 - 30 seconds.

3

50 % of structural integrity lost 30 - 300 seconds after insertion OR <10% of soil remains on sieve after 5 dipping cycles.

4

10 - 25% of soil remains after 5 dipping cycles.

5


6


Soil erosionSoil erosion:: high values high values indicate lower indicate lower erodibilityerodibility

Water infiltrationWater infiltration: : high values high values may be associated with may be associated with higher infiltration rates.higher infiltration rates.

Relatively static factors that affect aggregate stability

Regional climate

SOM (stable fraction, turnover

time >15 yrs)Soil texture

Mineralogy


Mean Annual Precipitation (mm)150 200 250 300 350 400 450

Soil

Stab

ility

Cla

ss

0

1

2

3

4

5

6

r = 0.247p = 0.055

Regional climate

NRCS NRI Data from 2003-06


Mean Annual Precipitation (mm)

200 250 300 350 400 450

Soil

Stab

ility

Cla

ss(N

o C

anop

y)

1

2

3

4

5

6

r = 0.623p = 0.041

Regional climate



% Silt0 10 20 30 40 50 60

Soil

Stab

ility

Cla

ss

0

1

2

3

4

5

6

r = 0.254p = 0.049

Soil texture



% OM0.0 0.5 1.0 1.5 2.0 2.5 3.0

Soil

Stab

ility

Cla

ss

0

1

2

3

4

5

6

r = 0.349p = 0.006

SOM (stable fraction,

turnover time >15 yrs)


Dynamic factors that affect aggregate stability

Annual, inter annual climate variability

SOM (active fraction, 1-2 yr

turnover)Plant biomass/

production

Plant communitycomposition

Bare ground & canopy cover

Soil biota, Biological soil crusts

Disturbance

Dynamic factors that affect aggregate stability

% Bare Ground0 20 40 60 80 100

0

1

2

3

4

5

6

r = 0.477p < 0.001

% Canopy Cover0 20 40 60 80 100

Soil

Stab

ility

Cla

ss

0

1

2

3

4

5

6

r = 0.500p < 0.001


How do we look at in context of hydrology and erosion?

•

Auto correlated with many other plot attributes at larger scales

•

Falsely conclude not important for predicting site hydrology and erosion characteristics

Static + Dynamic Axis

-3 -2 -1 0 1 2 3

Soil

Stab

ility

Axi

s

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Canonical Corr = 0.650

p< 0.001


•

Disturbance & Patchiness

Distance (m)

0-5 5-15 > 40

Soil

Stab

ility

Rat

ing

0

1

2

3

4

5

6

Crown and Ditch Two Track



Protected

Soil

Stab

ility

Rat

ing

0

1

2

3

4

5

6

7

Unprotected

•

Protected vs. Unprotected–

Protected not important for raindrop impact

–

Protected often not important for overland flow

•

Site average not always reflective of importance


•

Non-linear response

Soil Stability Class

1 2 3 4 5 6 7

Sedi

men

t (g

m-2

)

10-1

100

101

102

103

104

10 min30 min

R2 = 0.58p = 0.002

R2 = 0.41p = 0.014


•

Ideal for heterogeneous systems?

•

Incorporate spatial distribution of: –

Soil stability measures

–

Vegetation measures–

Other soil & site properties

•

With:–

Multiscale runoff and erosion measures


•

And…………incorporate field data in spatially explicit analysis

Questions?

multiscale variability of soil aggregate stability

Documents