EDAPUIC OR f<OIT. FACTORS: CIIEynCAT. 



199 



On low shores the sweeping advance of natural vegetative and soil 

 changes ("sweetening of the soil") affords a great number of sociological 

 problems, whose vast practical significance have not received the 

 recognition and consideration which they deserve, especially in the 

 regions about the mouths of such great rivers as the Po, Ebro, Rhine 

 and Mississippi. 



The saline soils on the shores of the large inland lakes are also rich 

 in sulphates. Thus the salt crust on the shore of Lake Jugar Kul near 

 Chiwa, in Transcaspia, according to Paulsen (1911), contains NaCl 

 79.9 per cent; MgS04 21.5 per cent; and Na2S04 1.6 per cent. The soil 

 is overgrown with SaUcomia herbacea. 



On the strands and in many of the playas of the Great Salt Lake 

 region, Utah, the concentration of salts often exceeds the limits of 

 toleration of vascular plants. SaUcomia rubra and S. utahensis are 

 commonly found in soil containing 2 to 3 per cent of salt. In areas 

 subject to summer desiccation they may be found in soil bearing as high 

 as 6.5 per cent. Suaeda ereda grows best in soils of 1.5 to 2.0 per cent 

 of alkali but has been found in soil with concentrations of 3.3 per cent. 

 Distichlis generally favors soils of about 1 per cent but has been found 

 in those carrying 2.6 per cent. Allenrolfea occidentalis is common on 

 barren salt flats, growing in 1 to 1.5 per cent salt. Being a perennial it 

 will grow in dryer soils. By far the commonest association is that of 

 grease wood and shad scale (Sarcobofus vermiculatus and Atriplex 

 confertifolia). It occurs on rather mildly saline plains where the salt 

 content amounts to about 0.8 per cent. This varies, however, widely, 

 and it grows abundantly in lower concentrations (0.2 to 0.4 per cent) 

 and also in sHghtly higher concentrations (1.1 per cent). 



The following table shows the analysis of soils taken from repre- 

 sentative plant associations: 



Table 18. — Salt Content in the Soils of Various Halophytic Plant 



Associations Near Great Salt Lake, Utah, July, 1929 



(After Flowers) 



Association 



NaCl 



NaaCOa 



NaHCO; 



Na^SO, 



Total 



SaUcomia rubra 



Suaeda erecla 



Distichlis spicala 



Allenrolfea occidentalis 



5.81 

 2.60 

 2.21 

 1.20 



0.005 

 0.005 

 0.053 

 0.005 



0.05 

 0.672 

 0.141 

 0.08 



0.401 

 Trace 

 Trace 

 0.112 



G.26 

 3.31 

 2.60 

 1.39 



The relation of the depth of the ground-water level to the per- 

 centage of NaCl in the soil within the basin of the Great Salt Lake has 

 led to the following generaUzation (determinations during July) : 



