Effects of Turbidity 47 



water. In contradistinction, ponds that received runoff from sizeable feed 

 lots or barnyards were usually clear of silt turbidity. Apparently, organic 

 decay reduces the Brownian movements of the soil particles, probably 

 through the neutralization of electrical charges. 



Although hay or fresh green vegetation introduced into a pond or lake 

 caused a clearing of the silty water, the fresh green vegetation was the 

 more effective of the two. Commercial fertilizers containing super- 

 phosphate produced a good neutralizing agent involving phosphoric acid, 

 and nitrate compounds also increased precipitation of soil particles. 



Any acid or other agent that ionizes in water or causes other compounds 

 to ionize will bring about a release of positive ions that will neutralize the 

 negative charges of the minute soil particles. If a sufficient number of 

 positive ions are released, all of the negative charges will be neutralized, 

 allowing complete precipitation of the soil particles. The continued 

 presence of such a buffer will result in the continuous precipitation of 

 colloidal soil particles. ^"^ 



Colloidal clay particles are not limited to Oklahoma soils, and are 

 probably found in greater or lesser amounts in many states. 



In order to discover the direct effect of montomorillonite (hydrous 

 aluminum siHcate) clay turbidity on fishes, Wallen ^^ made a series of 

 experiments exposing fishes to turbidities as high as 225,000 ppm. A total 

 of 16 common species was used. Most individuals of species exposed to 

 more than 100,000 ppm turbidity had their opercular cavities and gill 

 filaments clogged with clay particles, but some behavioral reactions were 

 noted in common fishes within the range of 20,000 to 100,000 ppm. How- 

 ever, very few turbidities resulting from natural conditions have been 

 recorded that exceeded the lowest lethal turbidity in these experiments. 

 Maximum natural turbidities for several streams in Oregon and Idaho were 

 between 137 and 395 ppm ^^; maximum for the Rio Grande was 14,800 

 ppm. Although Whitewood Creek (South Dakota) was polluted at the 

 rate of 48,400 ppm ^ and Coyote Creek (Oregon) ^i at 38,000 ppm, these 

 turbidities were not from natural causes but rather from mining opera- 

 tions. It must be concluded that natural turbidities are seldom if ever 

 directly lethal to fishes. 



While high turbidities from soil particles may not be lethal to fishes, 

 turbid waters may affect their growth rates. Growth of largemouth bass 

 was considerably reduced in Oklahoma ponds that were turbid.^ The 

 effect on growth of red-ears and bluegills was similar but less pronounced. 

 Turbidity also affected the success of reproduction, particularly of large- 

 mouth bass. It was also shown that the volume of basic food in clear 

 ponds was approximately 8 times greater than in ponds of intermediate 

 turbidities (average turbidities 40 to 90 ppm) and 12.8 times greater tlian 

 in the muddiest ponds (average turbidities 110 to 205 ppm). These studies 



