Abstract
Gas exchange between the Earth subsurface and the atmosphere is an
important mechanism, affecting hydrological, agricultural and
environmental processes. From a hydrological aspect, water vapor
transport is the most important process related to Earth-atmosphere gas
exchange. In respect to agriculture, gas transport in the upper soil
profile is important for soil aeration. From an environmental aspect,
emission of volatile radionuclides, such as 3H, 14C and Rd from
radioactive waste disposal facilities; volatile organic components from
industrial sources and Rn from natural sources, all found in the upper
vadose zone, can greatly affect public health when emissions occur in
populated areas. Thus, it is vital to better understand gas exchange
processes between the Earth's upper crust and atmosphere. Four major
mechanisms are known to transfer gases between ground surface and
atmosphere: (1) Diffusion; (2) Pressure gradients between ground pores
and atmosphere due to changes in barometric pressure; (3) Density-driven
gas flow in respond to thermal gradients in the ground; and (4) Winds
above the ground surface. Herein, the wind ventilation mechanism is
studied. Whereas the wind's impact on ground ventilation was explored in
several studies, the physical mechanisms governing this process were
hardly quantified or characterized. In this work the physical properties
of fracture ventilation due to wind blowing along land surface were
explored and quantified. Both field measurements and Hele-Shaw
experiments under controlled conditions in the laboratory were used to
study this process. It was found that winds in the range of 0.3 m/s
result in fracture ventilation down to a depth of 0.2 m. As wind
velocity increases, the depth of the ventilation inside the fracture
increases respectively, in a linear manner. In addition, the fracture
aperture also affects the depth of ventilation, which grows as fracture
aperture increases. For the maximal examined aperture of 2 cm and wind
velocity of 1.25 m/s, fracture ventilation was deeper than 0.45 m. This
study sheds new light on fracture ventilation, showing that moderate
winds may increase evaporation and gas exchange between fractured media
and the atmosphere. Even though wind impact is limited to the top 0.5 m
below the ground surface, it is an important process as most of the
biological activities, as well as important hydrological processes occur
in this region. Wind effect should be considered when modeling mass and
energy balances between the Earth upper crust and atmosphere.
Original language | English GB |
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Journal | Geophysical Research Abstracts |
Volume | 31 |
State | Published - 1 Dec 2011 |
Keywords
- 1818 HYDROLOGY / Evapotranspiration
- 1843 HYDROLOGY / Land/atmosphere interactions
- 1875 HYDROLOGY / Vadose zone