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Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/16/2011 Publication Date: 12/8/2011 Citation: Green, T.R., Erskine, R.H. 2011. Measurement and inference of profile soil-water dynamics at different hillslope positions in a semi-arid agricultural watershed. Water Resources Research. VOL.47, W00H15, 15 p. Interpretive Summary: Water contents in soil profiles vary in relation to terrain, soil and plant characteristics. The objectives of this study are to quantify dynamic soil-water content over a range of slope positions, infer soil profile water fluxes, and identify locations most likely influenced by multidimensional flow. The 56-ha watershed lies mostly within a dryland (rainfed) wheat field in semi-arid eastern Colorado. Capacitance sensors were used to infer soil-water content for approximately 8 years at 18 landscape positions. Based on previous research, sensor measurements were corrected for temperature effects before inferring soil water content. We analyzed changes in soil-water content at each sensor to infer the dynamics of water flux at different depths and landscape positions. At summit positions, vertical processes appear to control profile soil-water dynamics. At down-slope positions, infrequent overland flow events and unsaturated subsurface lateral flow appear to influence soil-water dynamics. Crop water use accounts for much of the variability in soil water, while soil hydraulic properties and near-surface hydrology affect soil-water variability across landscape positions within each management zone. The observed patterns exhibit the joint effects of short-term hydrology and long-term soil development. These quantitative methods improve our understanding of dominant soil hydrological processes and may aid future land management decisions. Technical Abstract: Dynamics of profile soil water vary in relation to terrain, soil and plant characteristics. The objectives of this study are to quantify dynamic soil-water content over a range of slope positions, infer soil profile water fluxes, and identify locations most likely influenced by multidimensional flow. The instrumented 56-ha watershed lies mostly within a dryland (rainfed) wheat field in semi-arid eastern Colorado. Dielectric capacitance sensors were used to infer hourly soil-water content for approximately 8 years (minus missing data) at 18 landscape positions and four or more depths. Based on previous research, sensor measurements (resonant frequency) were rescaled to estimate soil permittivity, then corrected for temperature effects on bulk electrical conductivity before inferring soil water content. Using a mass-conservation method, we analyzed multi-temporal changes in soil-water content at each sensor to infer the dynamics of water flux at different depths and landscape positions. At summit positions, vertical processes appear to control profile soil-water dynamics. At down-slope positions, infrequent overland flow events and unsaturated subsurface lateral flow appear to influence soil-water dynamics. Crop water use accounts for much of the variability in soil water between transects that are either cropped or fallow in alternating years, while soil hydraulic properties and near-surface hydrology affect soil-water variability across landscape positions within each management zone. The observed space-time patterns exhibit the joint effects of short-term hydrology and long-term soil development. Quantitative methods of analyzing soil-water patterns in space and time improve our understanding of dominant soil hydrological processes and may aid future land management decisions. |
