in situ soil moisture representation robert w. scott illinois state water survey institute of...
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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: [email protected]
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
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2006
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/200
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/200
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/200
6
1/8/
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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
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2006
9/8/
2006
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/200
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/200
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/200
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Vo
lum
etri
c so
il m
ois
ture
(p
erce
nt)
0
1
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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
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/200
6
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/200
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/200
6
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Vo
lum
etri
c so
il m
ois
ture
(p
erce
nt)
0
1
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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
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2006
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/200
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Vo
lum
etri
c so
il m
ois
ture
(p
erce
nt)
0
1
2
3
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5
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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.
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20
25
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45
50
55
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2006
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/200
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Vo
lum
etri
c so
il m
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ture
(p
erce
nt)
0
1
2
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5
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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
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55
8/8/
2006
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2006
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/200
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/200
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etri
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il m
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(p
erce
nt)
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r-sa
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pre
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itat
ion
(cm
)
prec
B66N
B66
B66S
B71
d
0
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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
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0 AM
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/07
4:00
PM
3/9/
07 1
0:00
PM
3/22
/07
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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
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0 AM
9/9/
07 4
:00
PM
9/21
/07
10:0
0 PM
0
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-4
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36
capacitance probe neutron probe temperature (C) precipitation (cm)
Vo
lum
etri
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ater
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nte
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cen
t)
Te
mp
(C
) /
pre
cip
ita
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n (
cm
)
