Spatial variability in soil biogeochemistry and biodiversity in periglacial landscapes of the McMurdo Dry Valleys, Antarctica.

Jeb BarrettRoss Virginia

Dartmouth College

Diana Wall

Colorado State University

Spatial variability in soil biogeochemistry and biodiversitySpatial variability in soil biogeochemistry and biodiversity

Questions:Questions:What are the appropriate scales for studying spatial What are the appropriate scales for studying spatial variability in soil ecosystems? variability in soil ecosystems?

What are the opportunities for predictive modeling and What are the opportunities for predictive modeling and mapping?mapping?

Is there opportunity to use polygons as a unit for scaling soil Is there opportunity to use polygons as a unit for scaling soil biology and biogeochemistry?biology and biogeochemistry?

Is the spatial heterogeneity in soil biota and chemistry Is the spatial heterogeneity in soil biota and chemistry linked to the process of polygon and soil development?linked to the process of polygon and soil development?

Patterned ground formations near Commonwealth Glacier, Taylor Valley.

Importance of understanding spatial patterning

-Scaling issues

-Inferring mechanism from spatial correlations

Dry Valley Soil Ecology: Life in the active layerDry Valley Soil Ecology: Life in the active layer

Vertical distribution of organic matter, salts and biota.Vertical distribution of organic matter, salts and biota.Nematodes -Powers et al. 1996Nematodes -Powers et al. 1996Soil chemistry - Burkins et al. 2001, Barrett unpublishedSoil chemistry - Burkins et al. 2001, Barrett unpublished

Horizontal distribution of biodiversity and biogeochemistryHorizontal distribution of biodiversity and biogeochemistrySampling design/stratificationSampling design/stratificationInfluence of polygons on biota and biogeochemistryInfluence of polygons on biota and biogeochemistryVariation among multiple scalesVariation among multiple scalesPredicative soil habitat modeling (Spatial?) Predicative soil habitat modeling (Spatial?)

Algal mats and moss beds

Lithic environments Invertebrates

Antarctic Soil EcosystemsAntarctic Soil Ecosystems

0.3 m

13C (‰)

1

5N

(‰

)

Fryxell - Ross Sea drift 12-20 KY

Hoare - Ross Sea drift 12-20 KY

Taylor-Bonney drift 75-98 KY

Mummy - Taylor III drift 200-210 KY

Source Materials:

EDOM: Endolithic derived organic matter.

LDOM: Lacustrine derived organic matter

MDOM: Marine derived organic matter SDOM: Soil microalgae derived organic matter.

Burkins et al. 2000, Barrett et al. in preparation

Stable isotope composition of Dry Valley soils

-25

-20

-15

-10

-5

0

5

10

15

-35 -30 -25 -20 -15 -10

MDOM

LDOM

EDOM

SDOM

Beacon Valley -Taylor IV drift 2-8 MY

Life in the active layer: Vertical distribution of soil biota

Re-plotted from Powers et al. 1996

0

5

10

15

20

25

30

0 200 400 600 800 1000 1200

# of live organisms per

soil depth

Soil Organic Carbon (%)

0

5

10

15

20

25

30

0.00 0.01 0.02 0.03 0.04 0.05

Extractable NO3- (PPM-N)

0

5

10

15

20

25

30

0.00 0.01 0.10 1.0 10 100 1000 10000

So

il d

epth

cm

Fryxell Hoare

Bonney Beacon

Life in the active layer: vertical distribution of soil organic carbon and nitrate

Burkins et al. 2000 and

Barrett and Virginia unpublished

Scaling Units

• Valleys

• Lake basins

• Patterned ground formations

Polygons

Polygons

Nested Experimental DesignNested Experimental Design

Taylor ValleyTaylor Valley3 Lake Basins3 Lake Basins

FryxellFryxellHoareHoareBonneyBonney

3 Polygon clusters per basin3 Polygon clusters per basin

3 Adjacent polygons per cluster3 Adjacent polygons per cluster

1 transect per polygon. Samples collected at:1 transect per polygon. Samples collected at:0, 0.2, 0.4, 0.6, 0.8, 1, 2, 4, and ~6 m from cracks0, 0.2, 0.4, 0.6, 0.8, 1, 2, 4, and ~6 m from cracks

Barrett et al. 2004. Ecology

soil organic carbon

y = 0.01x + 0.18

R 2 = 0.790.00

0.05

0.10

0.15

0.20

0.25

0.30

0 1 2 3 4 5 6

total soil nitrogen

y = 0.002x + 0.026

R 2 = 0.91

0.00

0.01

0.02

0.03

0.04

0.05

0 1 2 3 4 5 6

distance from polygon edge (m)

(g kg-1) (g kg-1)

> >

Soil biogeochemical properties Soil biogeochemical properties

in Taylor Valley sand-wedge polygonsin Taylor Valley sand-wedge polygons

Barrett et al. 2004. Ecology

soil mositure

0.00

0.30

0.60

0.90

1.20

1.50

1.80

0 1 2 3 4 5 6

Soil conductivity

y = 454.42x0.13

R2 = 0.68

0

200

400

600

800

1000

0 1 2 3 4 5 6

distance from polygon edge (m)

(% by weight) (S cm-1)

> >

Soil biogeochemical properties Soil biogeochemical properties

in Taylor Valley sand-wedge polygonsin Taylor Valley sand-wedge polygons

Barrett et al. 2004. Ecology

S. lindsayae, live

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6

Mortality (dead/ living)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 1 2 3 4 5 6

distance from polygon edge (m)

Scottnema Eudorylaimus

Ind

ivid

ual

s kg

-1 (

OD

WE

)

distance from polygon edge (m)

Soil nematode communitiesSoil nematode communities

in Taylor Valley sand-wedge polygonsin Taylor Valley sand-wedge polygons

Barrett et al. 2004. Ecology

Polygons cracks are unfavorable habitats

Low organic matter, low salt, high moisture and chlorophyll a content.

Mechanical disturbance?

Scaling Units?

• Valleys

• Hydrological basins

• Polygons

Proportion of 2

contributed by landscape scales

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

pH E.C. soil

water

SIC TN SOC Chl.a Eudor. Scott.

par

tial

r 2

basin polygon

VARIABILITY IN SOIL PROPERTIES OVER NESTED SCALES WITHIN TAYLOR VALLEY

Barrett et al. 2004. Ecology

Dry Valley Spatial Variability

• Polygons influence soil biogeochemisty and biodiversity , but …

• biogeochemcial properties vary most at scales> 10 km(among lake basins).

Mechanism?Till provenance?

Surface age?

Microclimaterelative humiditysoil moisture

0

2000

4000

6000

8000

Beacon Arena Wright Victoria Taylor

Upper

MiddleLower

soil salinity (uS cm-1)

0.00

0.25

0.50

0.75

Beacon Arena Wright Victoria Taylor

soil organic carbon (g kg-1)

0

1000

2000

3000

4000

5000

Beacon Arena Wright Victoria Taylor

Scottnema (#'s kg soil-1)

Broader scales?Broader scales?

data from Courtright et al. 2001 and Barrett and Virginia unpublished data.

NA NA

NA NA

Logistic Regression Probability Models

P is the probability of an outcome (0,1)

log(P)ixi iixiiiiixiii … +

for example:In a survey of 500 samples collected from the DV’s

log(P of Scottnema)soil water) + 2.1(pH) – 0.003 (E.C.) +

p = 0.0001, R2 = 0.75

0.0

0.2

0.4

0.6

0.8

1.0

6 7 8 9 10soil pH

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1

soil organic C (g C kg-1)

Scottnema

Eudorylaimus

Multi-taxa communities

NS

Logistic Probability Models

ConclusionsConclusions

Strong scale-dependant links between spatial patterns of Strong scale-dependant links between spatial patterns of biodiversity and biogeochemistry.biodiversity and biogeochemistry.

Soil biology and biogeochemical properties vary over Soil biology and biogeochemical properties vary over multiple scales associated with:multiple scales associated with:

• continuous spatial gradients across polygonscontinuous spatial gradients across polygons

• discontinuous variability among basins discontinuous variability among basins

What do we (soil scientists) have to gain from understanding biodiversity in the dry valleys?

What do we (ecologists) have to gain from understanding periglacial dynamics?

Mechanisms?Polygon development

SortingMechanical disturbance

GeographicMicroclimateTill age and provenance

Barrett, J. E., D. H. Wall, R. A. Virginia, A. N. Parsons, L. E. Powers, and M. B. Burkins. 2004. Biogeochemical parameters and constraints on the structure of soil biodiversity. Ecology 85: In press.