1. In Situ Soil Moisture Representation Robert W. Scott Illinois State Water Survey Institute of Natural Resource Sustainability University 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

2. Climate and soil moisture/temperature 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

3. (1989 - present) Air temperature Precipitation Relative humidity Wind speed and direction Solar radiation Soil 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 temperature Potential evapotranspiration Pest degree-days (31 pests) Growing degree-days (2 crops) Observed data Computed data Illinois Climate Network

4. 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 seconds Hourly averages, standard deviations Hourly max/min values with time stamps Daily 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 Scott Email: rwscott1@illinois.edu Web site: http://www.isws.illinois.edu/warm/ Update scheduled for June 2009.

5. ISWS suggested use of these data: Departures from normal…….

6. 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 2 Ina (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

7. 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

8. 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.

9. 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.

10. 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…..

11. Bondville IL ICN site …..or if the sod is a thick matted variety on a surface with no apparent slope?

12. 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.

13. Neutron probe equipment

14. 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 loam Elburn - Silt loam ICN

15. Looking west at the Bondville ICN site CRN

16. Looking south Historic neutron probe location

17. Looking east

18. Looking north

19. 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.

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

23. Trenching activities

24. Soil color analysis

25. Site B68

26. 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.

27. Level Bulk density PorosityLevel Bulk density PorosityLevel Bulk density PorosityLevel Bulk density Porosity Site(cm) (g/cm3) (%)Site(cm) (g/cm3) (%)Site(cm) (g/cm3) (%)Site(cm) (g/cm3) (%) B61201.2254.0B64201.3848.0B66201.2353.7B67201.2054.9 401.1556.5401.3549.1401.2851.8401.2253.9 601.2652.4601.4047.1601.3250.3601.3648.8 801.4346.2801.4943.7801.3748.2801.3848.0 1001.4146.91001.4346.11001.4047.41001.4545.3 1201.4047.11201.4644.91201.4445.71201.4445.7 1401.3847.81401.5342.31401.4844.21401.4246.4 1601.4445.61601.1357.41601.4246.31601.3848.0 180NA 180NA 180NA 180NA 200NA 200NA 200NA 200NA B62201.4943.8B63201.2353.7B65201.2552.7B68201.1755.8 401.2652.6401.3050.8401.2951.2401.2453.3 601.4146.7601.4146.7601.3250.2601.3449.4 801.2552.7801.3549.0801.7633.5801.4644.7 1001.4146.91001.4545.11001.7235.11001.6637.4 1201.5142.91201.7334.51201.4445.61201.6338.6 1401.5940.01401.6637.51401.4545.41401.8131.8 1601.6936.21601.6836.41601.4246.61601.6039.5 1801.6936.21801.7334.8180NA 1801.6338.6 2001.7434.22001.8134.8200NA 2001.7334.6 Average soil core attributes at each sampling level. Low sloped terrain sites High sloped terrain sites

28. 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.

29. 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.

30. 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.

31. 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.

32. 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.

33. 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.

34. 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.

35. 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

36. 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

37. 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

38. Hourly soil moisture (capacitance and neutron probe) observations at 10 cm of depth, temperature, and precipitation at the Bondville ICN monitoring site during SMUSE.

39. Thank you. Web site: http://www.isws.illinois.edu/warm/http://www.isws.illinois.edu/warm/