Advective flow

It is assumed that of this 5000 m3/h deposited, 2000 m3/h or 40% is buried (yielding the advective flow rate in Table 1.5.1), 2000 m3/h or 40% is resuspended (as discussed later) and the remaining 20% is mineralized organic matter. The organic carbon balance is thus only approximate. 

The two flux equations of importance to subsurface transport are Darcy s law for the advective flow of water and other liquids and Fick s law for the diffusive flow of molecules and gases. These laws are independently discussed below. 

FIGURE 10.6 Relationship between advection flow and diffusive recovery. 

The advective flow of the mobile phases or the steepness of concentration gradients within the phases ... 

Hansel CM, Benner SG, Neiss J, Dohnalkova A, Kukkadapu RK, Fendorf S (2003) Secondary mineralization pathways induced by dissimilatory iron reduction of ferrihydrite under advective flow. Geochim Cosmochim Acta 67 2977-2992... 

As continuing sedimentation increases the depth of a sedimentary layer relative to the seafloor, the overlying pressure increases because of the increased weight of the additional particles. The increased pressure leads to particle compaction if the pore waters can escape upward. Under these conditions, sedimentation generates an upward advective flow of pore water. This flow has the potential to transport solutes. 

Dispersion will be discussed in the subsequent section. At this point we only mention that dispersion always occurs in fluids with a distinct direction of advective flow. It originates from the velocity difference between adjacent streamlines. This effect is called velocity shear. 

Although dispersion can be described by the same law as diffusion, its nature is different. Dispersion is the result of the velocity shear, that is, of the velocity difference between adjacent streamlines in an advective flow. Due to turbulent exchange perpendicular to the direction of flow, water parcels continuously change the streamline along which they move. Since these streamlines move at different speeds, each water parcel has its own individual history of speed and thus its individual mean velocity. 

The attenuation strongly decreases with increasing length of the characteristic period t. Particularly, for periods t that are smaller than the mean advective flow time rw, the signal of the concentration variation is practically absent atxw. 

The attenuation decreases from the Natural Regime to Pump Regime II. This is consistent with (1), since the mean advective flow time rw is smallest for Pump Regime II. A short advective flow time increases the change of the oscillations to reach the well. 

The time lag of the oscillation increases with increasing period t and approaches (but does not surpass) the advective flow time, tw. 

In surface waters advective currents often dominate the transport of toxicants, and they can be estimated from hydrodynamic models or current measurements. In many cases advective flow can be approximated by the volume of water exchanged per unit... 

Solutes also moved through the weathering environment along with the advective flow of water. In this case, the solute flux is the product of the solute concentration and the flux density of water i.e.. 

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