The Use of Subsurface Temperature Fluctuations to Estimate Plant Water Use
Soil, Water & Environmental Science
AdvisorFerre, Ty P.A.
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PublisherThe University of Arizona.
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AbstractIrrigation agriculture is the largest use of water (~80%) in the United States ('Irrigation and Water Use', 2016) A combination of irrigation and precipitation infiltrates through the Earth's subsurface and represents the primary inputs to an agricultural field's groundwater system. This water propagates down from the surface, with some of it recharging the underlying groundwater storage as return flow. The difference between the amount of irrigation water applied and the return flow to the aquifer, represents the consumptive use of the system. The alterations in the quality and distribution of water from groundwater pumping and irrigation places greater emphasis on the need to understand the connection between agricultural consumption and subsurface groundwater flux. Temperature fluctuations in the Earth's shallow subsurface are mainly governed by spatial and temporal variations in temperature at the ground surface (Hatch et al., 2006). These temperature signals at depth are primarily controlled by advection, dispersion, and thermal conduction. It has been shown for streambeds that when temperature propagates through the subsurface, it is a nonlinear function of fluid velocity, the frequency of the surface temperature variations, and the sediment and fluid thermal properties (Stallman, 1965). This information has been useful for understanding fluxes for saturated conditions such as in stream systems, but has not yet been applied to understand consumptive use in unsaturated conditions such as in agricultural systems. Temperature propagation in unsaturated conditions is different than saturated conditions due to changes in soil and thermal properties. Previous models have had difficulty estimating groundwater fluxes for some unsaturated conditions. This study experiments with the possibility of using a combination of MATLAB and HYDRUS 1D to infer unsaturated groundwater fluxes, saturated hydraulic conductivity, and saturated water content. One application of this type of flux estimation could be the inference of root water uptake and the consumptive use of an agricultural system. The method is designed to calculate root water uptake under steady-state conditions; and therefore might have limitations for quantifying consumptive use in field applications.It is beneficial to research the consumptive use in agricultural systems in order to gain understanding of the effects of irrigation on the total flux in groundwater storage. Other applications of consumptive use include: site specific farm efficiency and crop use parameters, nonpoint source pollution to estimate nutrient fluxes, irrigation efficiency, soil salinization, waste isolation, and slope stability.
Degree ProgramGraduate College
Soil, Water and Environmental Science