| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00210A(See Project History for COL00210) | |
| Title | Characterizing Mass and Energy Transport at Different Scales |
| Investigator(s) | Butters, G; |
| Department | Soil and Crop Sciences |
| Objectives | 1) To develop an improved understanding of the fundamental physical properties and processes governing mass and energy transport, and the biogeochemical interactions these mediate. 2) To develop and evaluate instrumentation and methods of analysis for characterizing mass and energy transport in soils at different scales. |
| Approach | Soil hydraulic properties are key inputs to nearly all management and modeling scenarios of unsaturated soil water flow yet measurement of these fundamental properties is tedious and often inaccurate. A continuous flow method for rapid and accurate measurement of K(h) and water retention, including hysteresis, has been successfully developed at Colorado State University and tested in several soils. The method employs simultaneous tensiometry, air pressure, and water flow measurements that allows for both direct and inverse analysis of hydraulic properties of variably saturated natural or re-packed porous material. Because the continuous flow method is very rapid, accurate, and repeatable, this approach is ideally suited for fundamental investigations of temporal variation and scale effects in water flow properties. Causes of temporal changes in hydraulic properties open to study include root-growth, microbial activity, changes in irrigation water quality, freeze-thaw, and soil disturbance/reconsolidation. |
| Keywords | Soil hydraulic properties, Hydraulic conductivity, moisture retention, soil water hysteresis, inverse analysis, parameter identification, continuous flow method |
| Progress Reports | |
| 2005 | In as much as soil hydraulic properties are critical to nearly all environmental, management and modeling scenarios of water flow in soil, the fundamental characterization of hydraulic properties is an on-going area of basic research. Using soils of contrasting texture and structure from widely varying climates, repeated measurements of hydraulic conductivity and moisture retention functions are being used to evaluate non-equilibrium and non-constant hysteresis effects. Results from several soils show that, except in single grained sands, parameters characterizing hysteresis are not constant as is typically assumed but instead depend on the water content where a reversal from draining to wetting occurs. Studies also continue on the affect of changes in water quality on hydraulic conductivity and moisture retention of soils in southeastern Colorado. In addition to the fundamental characteristics of hydraulic properties, temporal variation of hydraulic functions due to plant root and microbial growth is also under evaluation in on-going laboratory and greenhouse studies. In the case of microbial impacts, field cores from an LTER site are subjected to nutrient and temperature conditions designed to enhance or suppress microbial activity while the hydraulic properties are monitored over several months. For root-growth impacts, the hydraulic properties of re-packed soil columns (0.15 m diameter by 0.15 m high) are being monitored through growth, death, and re-growth stages of Blue grama grass. In field research, monitoring of fire-induced water repellency in the Hayman fire area concluded. Three years after the fire, the soils in the study area no longer exhibit enhanced repellency. In fact, non-burned soils in the area are now typically more repellent than the burned soils. Soil organic material and fungal hyphae that lend repellency to the soil are yet to re-establish in the burned soil while the fire induced repellency has degraded. Over the three years of monitoring, no statistical difference in water repellency was found between the hydro-mulch BAER treatment and the non-treated burned soil. |
| 2006 | In on-going laboratory and greenhouse studies, research continues on the temporal variation of hydraulic functions due to plant root and microbial growth. In the case of microbial impacts, field cores from an LTER site have been exposed for over one year to nutrient and temperature conditions designed to enhance or suppress microbial activity. We found that, in general, the impact of microbial growth on hydraulic conductivity and moisture retention is subtle while maintaining soils at water contents near field capacity, even with high nutrient conditions. Elevating water contents to near saturation, however, results in large reductions in the hydraulic conductivity suggesting biomass plugging of pores. We speculate that the lower water content conditions limit diffusion supply of nutrients to microbial colonies. For root-growth impacts, the hydraulic properties of re-packed soil columns (0.15 m diameter by 0 .15 m high) continue to be monitored through growth, death, and re-growth stages of Blue grama grass. After several months of growth, soil hydraulic conductivity and water retention of the planted columns were not significantly different from non-planted control columns. We hypothesize that root mass decomposition during a prolonged death phase (on-going) will open pores for water flow and retention and at that point difference will be observed between planted and non-planted soils. Estimation of methane gas flux into soil is a new research area for this project. In cooperation with scientists in biology and mathematics, we are developing a rapid (<30 minute), in-situ, chamber based technique to simultaneously measure methane gas diffusion and degradation in soil. The analysis is made possible through refined analytical solutions to the governing equation for methane diffusion and degradation. We have successfully tested the approach against numerical simulations and with field measurements in on a grassland site in eastern Colorado. |
| Impact | |
| 2005 | Investigations into the fundamentals of soil water flow improve our understanding of processes and enable improvements to predictive models of field scale water and chemical transport. Temporal variation in hydraulic properties due to root growth, decay, and regrowth are poorly understood but needed to improve management and prediction of water movement in soils under reclamation or during the growing season. Studies regarding water quality effects on hydraulic properties is targeted to growers in southeastern Colorado. Results indicate that due to the high calcite and gypsum concentrations typical of the area, changes in water quality will have minimal impact on soil hydraulic properties and infiltration. In the fire affected soil research, the benefits of hydro-mulching did not include accelerated recovery of soil wettability and hence, as the hydro-mulch thins, the exposed soil will still be susceptible to enhanced run-off. |
| 2006 | Estimation of methane flux into soil is an area of interest and importance to a wide array of scientists. As a greenhouse gas, soil uptake of methane could be an important component of carbon budgeting in climate change modeling. The methane flux measurement approach developed here can easily be applied to assess methane uptake as a function of, for example, landscape position, land use, soil management, or soil amendments such as biosolids. In the research investigating fundamental soil hydraulic properties, temporal variation in hydraulic properties due to microbial activity and root growth, decay, and regrowth are poorly understood. These naturally occurring processes are largely ignored in models of soil water movement, even over multiple season time scales. These investigations into the fundamentals of soil water flow improve our understanding of processes and enable improvements to predictive models of field scale water and chemical transport. |
| Publications | |
| 2005 |
Barbarick, K.A., Ippolito, J.A., Butters, G.L., and Sorge, G.M. 2005. An Infiltration Exercise for Introductory Soil Science. J. Nat. Resour. Life Sci. Educ., 34:72-76. Butters, G.L., Shilito, R., and Huber, D. 2005. Effect of Root Growth on Soil Hydraulic Properties. ASA National Meetings, Salt Lake City,UT, Nov. 6-10. Butters, G.L., Stromberger, M.E., and Huber, D. 2005. Effect of Microbial Growth on Soil Hydraulic Properties. ASA National Meetings, Salt Lake City,UT, Nov. 6-10. |