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<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 />