in situ soil moisture representation robert w. scott illinois state water survey institute of...

In Situ Soil Moisture Representation

Robert W. Scott

Illinois State Water Survey

Institute of Natural Resource SustainabilityUniversity of Illinois at Urbana-Champaign

Workshop on Soil Moisture and Soil Temperature Monitoring in the U.S. Climate Reference Network, Oak Ridge TN, March 3-5, 2009

Climate and soil moisture/temperatu

re observations sites

• Illinois Climate Network (ICN) -- sites were co-located with/near neutron probe site

* ICN -- no nearby neutron probe site

▲ neutron probe site only

Neutron probe sites were decommissioned between 2004-2008.

All ICN sites have various soil temperature sensors and soil moisture capacitance sensors.

Source: Illinois State Water Survey

(1989 - present)Air temperaturePrecipitation Relative humidityWind speed and directionSolar radiationSoil temperature under sod (10, 20 cm; Campbell thermistors)

(1993 – present)Barometric pressure

(1996 - present)Soil temperature profiler (5 cm &

every 10 cm, surface-100 cm; thermocouples)

(2002 - present)Surface water table (well)Soil moisture (5, 10, 20, 50, 100, 150 cm; thermistors in Hydra probe)

(2004 - present)Bare soil temperature (10 cm; Campbell thermistor)

Dew point temperaturePotential evapotranspirationPest degree-days (31 pests)

Growing degree-days (2 crops)

Observed data

Computed data

Illinois Climate Network

Illinois Soil Moisture Network

Neutron probe data, 1983-2004 (through 2008 at 8 sites) - Troxler (twice monthly -- growing season, monthly -- fallow season)

Capacitance probe data, ~2002-present - Stevens-Vitel, Hydra A (connected to ICN data stream with hourly polling)

Illinois Climate Network

Data management

Most sensors polled every 10 secondsHourly averages, standard deviationsHourly max/min values with time stampsDaily averages, max/min with time stamps

Data download: hourly or once a day via internet or telephone Automated QC Tables/maps updated daily on web

Contact:Bob ScottEmail: rwscott1@illinois.edu

Web site:http://www.isws.illinois.edu/warm/Update scheduled for June 2009.

ISWS suggested use of these

data:

Departures from normal…….

0 - 6 inch Soil Layer 6 - 20 inch Soil Layer

20 - 40 inch Soil Layer 40 - 72 inch Soil Layer

100

100

100

100

100

100

100

100

100

100

75

75

7575

75

75

125

125

125

125

125

125

125

125

125

125

125

125

150

150

150

150

150

150

150

150

175

175

175

ISWS suggested use of these data:

…….and monthly change.

Location Jan 1 Change Jan 1 Change Jan 1 Change 0 – 6 from 6 – 20 from 20 – 40 from (inches) Dec 1 (%) (inches) Dec 1 (%) (inches) Dec 1 (%)

Freeport (NW) 2.1 -5 5.1 0 7.5 0 DeKalb (NE) 2.2 1 5.5 4 7.7 3 Monmouth (W) 1.9 8 4.9 14 7.5 7 East Peoria (C) 2.2 7 5.4 3 7.9 2 Stelle (E) 2.0 21 5.2 8 7.8 13 Champaign (E) 2.1 16 5.3 5 7.4 4 Bondville (E) 2.3 34 5.4 11 7.8 2 Perry (WSW) 2.3 8 5.1 7 7.5 4 Springfield (WSW) 2.2 26 5.0 20 7.5 6 Brownstown (ESE) 2.1 -3 5.2 1 7.4 1 Olney (ESE) 2.2 22 5.3 21 7.9 8 Belleville (SW) 2.1 15 5.2 11 7.8 3 Carbondale (SW) 2.3 7 5.3 5 7.9 2Ina (SE) 2.1 43 5.2 6 7.2 4 Fairfield (SE) 1.7 11 5.2 3 7.7 -2 Dixon Springs (SE) 2.3 4 5.4 1 7.9 1

If these soil moisture data are to be used as “representative” of the “general area” where sites are

located, are there other variables we need to consider to obtain the

highest quality data?

"Things that make you go ‘Hmmmm...’" A. Hall

Volumetric soil moisture at 10 cm and 150 cm under sod, corn, and soybeans at Bondville IL, using Stevens-Vitel capacitance probes, June 2005 – April 2006.

Certain aspects of ISWS historic neutron probe data collections

• Initial siting of neutron probe locations were coincident with climate sites, and installed concurrent with three other new/enhanced data monitoring networks (1981).

• Most criteria (climate sites) involved accessibility (vehicles, power, communications), longevity (public property), and security.

• No documented soil moisture protocols (e.g. topography – surface slope, distances from: different vegetation covers [crop fields, trees, etc.], buildings, roadways, field tiles, land use).

• Extensive travel was required for manual data every two or four weeks, concomitant with three other ISWS network data sets on the same 2- to 3-day, pre- and post-precipitation event, data runs.

• All sites under grass, with sod types ranging from well-manicured lawn grasses in public areas to infrequently mowed, thick-matted sod at remote sites in agricultural regions, creating root zone differences.

DeKalb IL ICN site

When comparing soil moisture data collected under sod to adjacent areas…..

…..does it matter if the data are collected over a well manicured lawn-type sod with a definite slope…..

Bondville IL ICN site

…..or if the sod is a thick matted variety on a surface with no apparent slope?

Soil Moisture Under Sod Experiment (SMUSE)• Eight sites chosen at random at Bondville IL for twice weekly neutron

probe observations, every 20 cm from the surface to 2 m, across a 5.9 hectare sodded field (Aug 2006 – Sep 2007).

• Two additional sites were selected within 1 meter of one site above to serve as a cluster observation site.

• Data were collected similarly at the historic Bondville neutron probe soil moisture location.

• A surface terrain elevation analysis was conducted to consider the impacts attributable to surface slope/ponding potential.

• The near-surface water table was monitored.

• Soil property heterogeneity (soil porosity, bulk density, soil color) was evaluated by trenching adjacent to soil moisture tubes and extracting soil cores.

Neutron probe equipment

Aerial photograph of the Bondville Environmental and Atmospheric Research Site (BEARS), showing soil type boundaries (NCSS, NRCS, USDA) and neutron probe monitoring sites during SMUSE.

Drummer - Silty clay loam Flanagan - Silt loamElburn - Silt loam

ICN

Looking west at the Bondville ICN site

CRN

Looking south

Historic neutron probe location

Looking east

Looking north

Surface terrain elevations (m, MSL) across the BEARS research site. Neutron probe locations during SMUSE, the ICN tower and shallow ground water well, and the historic soil moisture location (B71) are included.

120 125 130 135 140 145 150 155 160 165 170

Distance (m)

55

60

65

70

75

80

85

90

95

100D

ista

nce

(m

)

B61

B67

Terrain elevations (m) at Sites B61 and B67

150 155 160 165 170 175 180 185 190 195

Distance (m )

70

75

80

85

90

95

100

105

110

115

Dis

tan

ce (

m)

B68

Topography at B-68 Transect

Hydrograph of the water table at the Bondville IL, ICN site during SMUSE.

0

0.5

1

1.5

2

2.5

3

Aug-06

Sep Oct Nov Dec Jan-07

Feb Mar Apr May Jun Jul Aug Sep

Dep

th t

o w

ater

bel

ow

lan

d s

urf

ace

(m)

Trenching activities

Soil color analysis

Site B68

Site B67

Sites with very low surface slope profiles had thicker A horizons and yellower subsoils, features diagnostic of being wetter than other soil profiles with greater surface slopes.

LevelBulk

density Porosity LevelBulk

density Porosity LevelBulk

density Porosity LevelBulk

density PorositySite (cm) (g/cm3) (%) Site (cm) (g/cm3) (%) Site (cm) (g/cm3) (%) Site (cm) (g/cm3) (%)

B61 20 1.22 54.0 B64 20 1.38 48.0 B66 20 1.23 53.7 B67 20 1.20 54.940 1.15 56.5 40 1.35 49.1 40 1.28 51.8 40 1.22 53.960 1.26 52.4 60 1.40 47.1 60 1.32 50.3 60 1.36 48.880 1.43 46.2 80 1.49 43.7 80 1.37 48.2 80 1.38 48.0100 1.41 46.9 100 1.43 46.1 100 1.40 47.4 100 1.45 45.3120 1.40 47.1 120 1.46 44.9 120 1.44 45.7 120 1.44 45.7140 1.38 47.8 140 1.53 42.3 140 1.48 44.2 140 1.42 46.4160 1.44 45.6 160 1.13 57.4 160 1.42 46.3 160 1.38 48.0180 NA NA 180 NA NA 180 NA NA 180 NA NA200 NA NA 200 NA NA 200 NA NA 200 NA NA

B62 20 1.49 43.8 B63 20 1.23 53.7 B65 20 1.25 52.7 B68 20 1.17 55.840 1.26 52.6 40 1.30 50.8 40 1.29 51.2 40 1.24 53.360 1.41 46.7 60 1.41 46.7 60 1.32 50.2 60 1.34 49.480 1.25 52.7 80 1.35 49.0 80 1.76 33.5 80 1.46 44.7100 1.41 46.9 100 1.45 45.1 100 1.72 35.1 100 1.66 37.4120 1.51 42.9 120 1.73 34.5 120 1.44 45.6 120 1.63 38.6140 1.59 40.0 140 1.66 37.5 140 1.45 45.4 140 1.81 31.8160 1.69 36.2 160 1.68 36.4 160 1.42 46.6 160 1.60 39.5180 1.69 36.2 180 1.73 34.8 180 NA NA 180 1.63 38.6200 1.74 34.2 200 1.81 34.8 200 NA NA 200 1.73 34.6

Average soil core attributes at each sampling level.

Low sloped terrainsites

High sloped terrainsites

Volumetric soil moisture at 8 neutron probe sites and the historic soil moisture

location (B71) at 0-30 cm and precipitation totals between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

) prec

B61

B62

B63

B64

B65

B66

B67

B68

B71

a

Volumetric soil moisture at 8 neutron probe sites and the historic soil moisture location (B71) at 30-90 cm and

precipitation totals between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

)

prec

B61

B62

B63

B64

B65

B66

B67

B68

B71

b

Volumetric soil moisture at 8 neutron probe sites and the historic soil moisture location (B71) at 90-170 cm and

precipitation totals between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

) prec

B61

B62

B63

B64

B65

B66

B67

B68

B71

c

Volumetric soil moisture at 8 neutron probe sites and the historic soil moisture location (B71) at 170-200 cm and

precipitation totals between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

) prec

B61

B62

B63

B64

B65

B66

B67

B68

B71

d

Volumetric soil moisture (percent) at 3 clustered sites and the historic soil moisture location (B71) at 90-170 cm and

precipitation (cm) between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

)

prec

B66N

B66

B66S

B71

c

Volumetric soil moisture (percent) at 3 clustered sites and the historic soil moisture location (B71) at 170-200 cm and precipitation (cm) between sampling dates during SMUSE.

15

20

25

30

35

40

45

50

55

8/8/

2006

9/8/

2006

10/8

/200

6

11/8

/200

6

12/8

/200

6

1/8/

2007

2/8/

2007

3/8/

2007

4/8/

2007

5/8/

2007

6/8/

2007

7/8/

2007

8/8/

2007

9/8/

2007

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

0

1

2

3

4

5

6

7

8

Inte

r-sa

mp

ling

pre

cip

itat

ion

(cm

)

prec

B66N

B66

B66S

B71

d

0

5

10

15

20

25

30

35

40

45

50

0-30 cm 30-90 cm 90-170 cm 170-200 cmObservation depth

Vo

lum

etri

c so

il m

ois

ture

(p

erce

nt)

B64 B66 B67 B61 B65 B63 B68 B62 B71

Average volumetric soil moisture at nine sites during SMUSE. Earth tones are sites with the lowest surface terrain slopes; blue columns have higher slopes. The long-term Bondville site (black)

has the highest terrain slope.

The Soil Moisture Under Sod Experiment was conducted across a 5.9 hectare sodded field in east-central Illinois to increase understanding of soil moisture variability in a small area under seemingly uniform conditions.

• strong, intra-site, temporal consistencies in volumetric soil moisture at all levels

• increasing inter-site soil moisture variability with depth, ranging from ±3% near the surface year-round to ±6% in winter and ±10% during the growing season in the deepest layer

• a seemingly strong connection in deeper layers at sites with low surface terrain slope and high soil moisture content, and vice versa

• a noticeable level of mottling was observed visually and in soil cores, indicative of heterogeneity in the soils’ processing of moisture

• data from the clustered group of stations (separated by 1 m), revealed larger than expected inter-site soil moisture variability

Summary of SMUSE results

Conclusion

• Without a measure of soil profiling, a true representative level of soil moisture may go undefined.

– an apparent water lens observed in the 140-160 cm layer at one site– a very large seasonal fluctuation of water at two sites, possessing low

soil porosity, perhaps allowing the height of the local water table to seasonally move closer to the surface than at other sites

– continuously high soil moisture with low temporal variability at two sites, possessing high porosity, perhaps allowing more water volume to be stored permanently in the middle layers

– conflicting results observed in the clustered site data– soil conditions below 2 m is unknown; its impact on soil moisture above

is similarly unknown

Protocols to consider for new/enhanced soil moisture site installations

• Site selection to be placed within the major surface cover of area• Soil core analyses at sufficient locations to define soil attributes• A localized surface terrain analysis to define ponding potential• Climatology of local water table variability• Summary of the local land use (distance from: impervious surfaces

– runoff, use of irrigation systems, and tilling practices, etc.)• Local field tiling network, nearby drainage construction

Hourly soil moisture (capacitance and neutron probe) observations at 10 cm of depth, temperature, and precipitation at

the Bondville ICN monitoring site during SMUSE.

8/1/

06 1

0:00

AM

8/13

/06

4:00

PM

8/25

/06

10:0

0 PM

9/7/

06 4

:00

AM

9/19

/06

10:0

0 AM

10/1

/06

4:00

PM

10/1

3/06

10:

00 P

M

10/2

6/06

4:0

0 AM

11/7

/06

10:0

0 AM

11/1

9/06

4:0

0 PM

12/1

/06

10:0

0 PM

12/1

4/06

4:0

0 AM

12/2

6/06

10:

00 A

M

1/7/

07 4

:00

PM

1/19

/07

10:0

0 PM

2/1/

07 4

:00

AM

2/13

/07

10:0

0 AM

2/25

/07

4:00

PM

3/9/

07 1

0:00

PM

3/22

/07

4:00

AM

4/3/

07 1

0:00

AM

4/15

/07

4:00

PM

4/27

/07

10:0

0 PM

5/10

/07

4:00

AM

5/22

/07

10:0

0 AM

6/3/

07 4

:00

PM

6/15

/07

10:0

0 PM

6/28

/07

4:00

AM

7/10

/07

10:0

0 AM

7/22

/07

4:00

PM

8/3/

07 1

0:00

PM

8/16

/07

4:00

AM

8/28

/07

10:0

0 AM

9/9/

07 4

:00

PM

9/21

/07

10:0

0 PM

0

5

10

15

20

25

30

35

40

45

50

-4

0

4

8

12

16

20

24

28

32

36

capacitance probe neutron probe temperature (C) precipitation (cm)

Vo

lum

etri

c w

ater

co

nte

nt

(per

cen

t)

Te

mp

(C

) /

pre

cip

ita

tio

n (

cm

)

Thank you.

Web site: http://www.isws.illinois.edu/warm/