Vegetal interception

Evapotranspiration (ET) is the collective term for land surface evaporation and plant transpiration, which are difficult to isolate in practice. Transpiration refers to the process in which water is transported through plants and returned to the atmosphere through pores in the leaves called stomata, and is distinct from direct evaporation of intercepted precipitation from leaf surfaces. Some land surface processes and the roles of vegetation in the water and energy balances are illustrated in Fig. 6-5. Due to... 

Subsurface runoff. When precipitation hits the land surface, the vast majority does not go directly into the network of streams and rivers in fact, it may be cycled several times before ever reaching a river and the ocean. Instead, most precipitation that is not intercepted by the vegetation canopy and re-evaporated infiltrates into the soil, where it may reside as soil moisture, percolate down to ground-water, or be transpired by plants. 

Radioactive aerosols are intercepted by vegetation either by mechanical trapping of dry particulate matter or in the rainfall which wets the vegetation. 

Webster and Shaw (1996) showed the importance of vegetative density on effectiveness of the filter strip. In the first years of strip establishment, total herbicide losses from no-till doublecrop soybeans were similar with and without filter strips, while metolachlor and metribuzin losses were reduced as much as 90% with the more established, denser filter strips in the third year. Both fresh and thatch switchgrass residue in vegetative filter strips can intercept and sorb herbicides (Mersie et al., 2006). 

Whether fallout is by washout or dry deposition, a certain fraction of the deposited activity is intercepted by foliage. Foliar deposition, followed by uptake by grazing animals, is an important pathway into food chains. The leaf area of herbage eaten by cattle and sheep is large. Also, animals eat herbage as it is, whereas humans usually wash leaf vegetables and discard outer leaves, pods and husks. 

Interception and retention of radioactive aerosols by vegetation. Atmospheric Environment, 4, 57-78. 

Hoffman, F.O., Garton, C.T., Huckabee, J.W. Lucas, D.M. (1982) Interception and retention of technetium by vegetation and soil. Journal of Environmental Quality, 11,134-40. 

Miller, C.W. (1980) An analysis of measured values for the fraction of a radioactive aerosol intercepted by vegetation. Health Physics, 38, 705-12. 

Simmonds, J.R. Linsley, G.S. (1982) Parameters for modelling the interception and retention of deposits from atmosphere by grain and leafy vegetables. Health Physics, 43, 679-81. 

Gosse, G., Varlet-Grancher, C., Bonhomme, R., Chartier, M., Allirand, J.M., and Lemaire, G., Production maximale de matiere seche et rayonnement intercepte par un couvert vegetal, Agronomie, 6, 47-56, 1986. 

Perhaps the earliest account is an entry in the log of Columbus during his fourth voyage to the New World. In July 1502, off Yucatan, he intercepted a coastwise canoe loaded with products of agricultural commerce. Among them was cacao, one of the many unique vegetable legacies from the Americas (23). 

One more valuable piece of information can be extracted from Figure 1. The intercept of the extrapolated line on the ordinate gives the amount of substrate "b" at zero time. The difference between this point and the total firmness gives the amount of substrate "a at zero time. Table HI lists the proportion of total firmness of the raw vegetable supplied by substrate "b" (16). 

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