1923) 



YOUNG — NOTES ON THE PHYSIOGRAPHY OF NORTH DAKOTA 387 



Where the lakes have an outlet, either permanently or at times 

 of high water only, as in the case of Arrowhead and Jim Lakes, 

 already mentioned, the salts washed into the lakes by run-off 

 from the drainage area are carried out by the outflow. In the 

 case of lakes which are completely land-locked but yet are not 

 markedly alkaline, it is probable that acids carried in by run-off 

 from humus-covered areas, neutralize the alkalies in the water 

 and largely precipitate them in the form of insoluble salts. The 

 presence of organisms in the water, especially animals, may play 

 a small part in reducing alkalinity through the production of 

 carbon dioxide. 



With reference to their chemical character it is not possible to 

 make any definite classification of the lakes. They range all 

 the way from those of a distinctly freshwater type, with low aikali- 

 nities, to exceedingly brackish waters with total carbonate 

 alkalinities running up to 2000 ppm. and more. 



But little attention has been paid to physical features, such as 

 temperature, turbidity, and color, in most cases. Where the 

 lakes are shallow there is little temperature difference between 

 surface and bottom, and the summer temperature frequently 

 runs up to 25° C. or more, especially near shore. In the deeper 

 lakes several degrees difference may exist between surface and 

 bottom. The determinations, however, in most of the lakes are 

 too few to permit of any generalizations. 



The larger plants comprise chiefly Ruppia maritima, which 

 occurs abundantly in practically all the lakes of the region; 

 Potamogeton, M yriophyllum , Ceratophyllum and Chara, all of 

 which are common in fresh water; while Juncus, Carex, and 

 Scirpus are abundant in the shallower parts of all but the more 

 alkaline lakes. 



The location of each lake is indicated on the accompanying 

 map (pi. 20). In considering the various lakes, no definite 

 classification can be made, either in the character of the water, 

 or in the nature of shores and bottom. Several of the freshwater 

 lakes, especially such as are merely expansions of a river, are 

 very shallow, largely overgrown with rushes and sedges, and with 

 muddy bottoms. Others, such as Spiritwood and Wood Lake, 

 have, in part, rocky, steeply sloping shores with comparatively 



