<br />003\)8~
<br />
<br />
<br />SECCION IV - GEOHIDROLOCiA
<br />
<br />83
<br />
<br />,,+"'>:2:,::'.<........ . ..;;
<br />
<br />.
<br />
<br />Ground water low in dissolved solids is indicated by such phreatophytes
<br />as ash, cottonwood, aspen, and willow. Wherever these plants grow it is safe
<br />to assume that the groundwater is potable and probaly suitable for most uses.
<br />
<br />PHREATOPHYTES AS CONSUMERS OF GROUND WATER
<br />
<br />:,'...... ;"" ;.:.)f/;.
<br />.Of.: ;;:>t..
<br />''<:';/':.::>. ..;.
<br />X:"..,\. .j':::l
<br />...,.(,.:.(:;:\..."
<br />
<br />, ";;";';';[;;~:"')
<br />"...".:..,,::,:k;f,:;{::
<br />';,:{, ';.i';i;i',;;,:"::;,\; 0':>"
<br />...~< .' ... . ,,"
<br />,,;':,e,:.;" ......,."
<br />
<br />;>:,-,",;.:' .>< ',,'"
<br />.<:.}. ,.
<br />
<br />
<br />Elt
<br />.....\;.t:y*% ,:;"
<br />''.~t);!;;t;~; ':'" '" 0',';
<br />;;;:11[~..'<i.'" ~~~[~."
<br />"""" >"..",? \~:t.i~l~ ~
<br />::; ;;
<br />..:
<br />.{'.
<br />;g.;':'; ''''
<br />
<br />".;'<:
<br />:d.:
<br />
<br />'.:;7:...''-...
<br />..,:':} /',<./",. 1;~
<br />
<br />:/:::;j'~;':;;';':j;" .; ....
<br />; .. ....,..... . .Y".;.; ., .. ...n ,,; f;~~{~j~g;:;/t{,
<br />...).;',;"c;>':'.i' ...;.....;.;..:.:''.:..':';.....:(:C:;:;,.:~"....\. :";;i'~;; :i........:;:::, .'>:.~,::.:; ..:"i:: ..'?..:,,',...;:~;:;;;<;'~,\..:;.~; ;,E .;:r;; :
<br />>,.....,.........).:...:,.>.,.., ....,.. ......>..,;........... ./>>.,..}.>....C,:~t~.r?:\f:\'>.':;..,(i':;' .. ;i}'
<br />"'::'<":"'2"'1 'tf~"l>;'::) '>"/;':.;;'.: .,.; . ",.\/ ..' ,
<br />>.:iC;:;;;';;'s< '.. ; ;8).;;" ,'<;"~~f;': ;;"< ;s<;;;";;: ;;;s,</ ..... . ;
<br />.' ...........;./..... '" .....'.' ...... ...,.... ....,.;......,..:;;:,:.. .............<.;...',.,./;,:;;:;c...,.'..;\:;;,;... ;;..,..::>>....:; ...;...'...,;.... ....'......;... .............,.,.,.'t.. ';......1.', .'.,
<br />
<br />As consumers of ground water, phreatophytes are becoming more and more
<br />important to the water economy of the desert and semidesert regions of the
<br />United States, and it is belived that this situation exists to some extent in
<br />all arid regions of the world. Phreatophytes are important in the arid regions
<br />of the United States for several reasons: (1) Large quantities of ground water
<br />are involved. Extensive areas of phreatophytes having a high rate of water con-
<br />sumption result in an annual draft on the ground~water reservoir amounting
<br />to millions of acre.feet. (2) Much of this water is virtually wasted, Most
<br />phreatophytes have a low economic or cultural valne, and so the water nsed
<br />by them does not have a high beneficial nse, (3) The usable, readily available
<br />water supplies, particularly the flow of streams, are depleted, (4) The water
<br />wasted is available for salvage. Whatever amonnt is salvaged may be regard.
<br />ed as 'new water", for it has not previously been utilized by man, (5) Phreato'
<br />phytes may also cause flooding and sediment deposition in river flood plaius,
<br />The annual rate of water consumption varies with the plant species and
<br />with variable factors that control or affect the growth of the species, Three
<br />factors that stand out in affecting tbe rate are: depth to the water table, climatic
<br />conditions, and density of growth.
<br />The relationship between water use, depth to the water table, and temperat.
<br />ure is shown in figure 3 for saltgrass, With reference to depth to the water
<br />table, the rate of use is greatest where the water lies at shallow depth and
<br />decreases as the depth to water increases. In the case of saltgrass growing in
<br />tanks this is shown conclusively in figure 3 A at five localities in the western
<br />United States, for depths up to 5. feet. It has been demonstrated, by tank experi.
<br />ments, for saltcedar and batamote up to depths of 7 feet (Gatewood, Robinson,
<br />Colby, and others, 1940, p, 137) and for cottonwood experimentally to a depth
<br />of 4,7 feet and inferentially to a depth of 12 feet (Muckel and Blaney, 1945),
<br />Specific data for depths greater than -theseare lacking, but it has been observed
<br />that, as the depth to water increases, phreatophyte growth becomes progressiv.
<br />ely less dense and vigorous, the plants diminishes in size until finally the
<br />species ceases to exist altogether. It seems logical to attribute this decrease in
<br />density, vigor, and size to decreased water consumption.
<br />The rate of ns" of ground water by phreatophytes is affected in one WilY
<br />or another by the various elements of climate; temperature, humidity, winq
<br />
<br />,i:',
<br />
<br />:;:...
<br />';\2'
<br />
<br />:e
<br />
<br />':.,
<br />.,..::;,,'.'.,
<br />,.:'
<br />
<br />;;;':{
<br />
<br />."~, ~" ,;
<br />
<br />,
<br />
<br />,...;,
<br />
|