UConn CE 320 - Solute Transport in Soils and Salinity

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Solute Transport in Soils and SalinitySolute Transport in SoilsSlide 3Mechanisms for Solute Transport in SoilSlide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Hydrodynamic dispersionSlide 14Effect of scale and heterogeneityThe Convection-Dispersion Equation (CDE)Slide 17Slide 18Slide 19Column Break Through Curve (BTC) ExperimentsSlide 21Slide 22BTC’s - Piston DisplacementBTC’s - Longitudinal DispersionSlide 25Slide 26BTC’s - Adsorption and ExclusionSlide 28CDE in the fieldWater and solute movement in unsaturated soilSlide 31Analytical Solutions for the CDESlide 33Slide 34Slide 35Transport parameter estimationSalt balance and salinitySOIL SALINITYSlide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Other effects of salinitySlide 50Resident vs. Flux ConcentrationsSlide 52CE/ENVE 320 – Vadose Zone Hydrology/Soil PhysicsCE/ENVE 320 – Vadose Zone Hydrology/Soil PhysicsSpring 2004Spring 2004Copyright © Markus Tuller and Dani Or 2002-2004Copyright © Markus Tuller and Dani Or 2002-2004Solute Transport in Soils and Salinity16Hillel, pp. 243-254Copyright© Markus Tuller and Dani Or2002-2004Solute Transport in SoilsThe transport of soluble chemicals in soils is very important The transport of soluble chemicals in soils is very important for a range environmental and agricultural issues.for a range environmental and agricultural issues. Typical sources of contamination?Typical sources of contamination?•Large amounts of water-soluble chemicals are applied for Large amounts of water-soluble chemicals are applied for agricultural, industrial, construction, and transportation with the agricultural, industrial, construction, and transportation with the intent of using them in uppermost soil zone (e.g., fertilizers, salts intent of using them in uppermost soil zone (e.g., fertilizers, salts on roads).on roads).•In many cases these chemicals are transported to greater depths In many cases these chemicals are transported to greater depths (beyond the root zone), which not only makes them ineffective for (beyond the root zone), which not only makes them ineffective for their original intended use, but leads to contamination of natural their original intended use, but leads to contamination of natural resources (drinking water) and the environment.resources (drinking water) and the environment.•Accidental releases of chemicals (leaky tanks, landfills, chemical Accidental releases of chemicals (leaky tanks, landfills, chemical pits, etc.) resulting contaminant plumes that migrate through soils.pits, etc.) resulting contaminant plumes that migrate through soils.Copyright© Markus Tuller and Dani Or2002-2004Solute Transport in Soils•The transport of solutes through The transport of solutes through porous media is coupled with the porous media is coupled with the flow of water. The convective flow of water. The convective streams of flowing soil water streams of flowing soil water carry salts and other carry salts and other constituents.constituents.•Self-diffusion of constituents in Self-diffusion of constituents in the liquid phase is another the liquid phase is another mechanism of transport in soils.mechanism of transport in soils.•Solutes interact with the soil Solutes interact with the soil matrix through adsorption and matrix through adsorption and desorption, they may precipitate desorption, they may precipitate whenever their solubility is whenever their solubility is exceeded, and they may react exceeded, and they may react among themselves.among themselves.Copyright© Markus Tuller and Dani Or2002-2004Mechanisms for Solute Transport in Soil Convective transport is the passive transport of dissolved Convective transport is the passive transport of dissolved constituents with the flowing water. In this case, water and the constituents with the flowing water. In this case, water and the solutes move at the same average rate: solutes move at the same average rate: Convective Transport (JConvective Transport (Jcc):): dxdHhKccJJwcDarcy VelocityJJcc is the solute flux is the solute fluxc is the volume averaged solute concentrationc is the volume averaged solute concentrationJJww is the water flux density or Darcy velocity is the water flux density or Darcy velocityThe water flux density JThe water flux density Jww represents the flow velocity averaged over represents the flow velocity averaged over an entire cross sectional area.an entire cross sectional area.tAVJwCopyright© Markus Tuller and Dani Or2002-2004Mechanisms for Solute Transport in Soil Because convection occurs in the liquid phase only, we use the Because convection occurs in the liquid phase only, we use the mean apparent velocity or pore water velocity (v) to estimate mean apparent velocity or pore water velocity (v) to estimate solute travel or arrival times:solute travel or arrival times:Convective Transport (JConvective Transport (Jcc) - Continued:) - Continued:Therefore solute flux may also be characterized as: Therefore solute flux may also be characterized as: wwJvthatNoteJv cvJcCopyright© Markus Tuller and Dani Or2002-2004Mechanisms for Solute Transport in Soil The annual drainage rate below a rooting zone is 0.5 m/yr and the The annual drainage rate below a rooting zone is 0.5 m/yr and the average water content between the bottom of the rooting zone and average water content between the bottom of the rooting zone and the water table located 10 m below is 0.2 mthe water table located 10 m below is 0.2 m33/m/m33..Find the time required to transport nitrate from the bottom of the root Find the time required to transport nitrate from the bottom of the root zone to ground water.zone to ground water.Convective Transport (JConvective Transport (Jcc) - Example:) - Example:1.1.First we calculate pore water velocity according to:First we calculate pore water velocity according to:yr/m5.22.05.0Jvw2.2.The time required for nitrates to reach the groundwater by The time required for nitrates to reach the groundwater by convective transport is simply:convective transport is simply:yrs45.210vLt What happens in practice with heterogeneous pathways?What happens in practice with heterogeneous pathways?Copyright© Markus Tuller and Dani Or2002-2004Mechanisms for Solute Transport in Soil Diffusive transport is a spontaneous process resulting from random Diffusive transport is a spontaneous process


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UConn CE 320 - Solute Transport in Soils and Salinity

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