by lowering nutrient levels, either by improving sewage treatment or by 

 discharging the effluent elsewhere. Conditions that are likely to en- 

 hance the growth of Cladophora are: decreasing turbidity; smoothing 

 flows and reducing temperature extremes via flow regulation; and any 

 increase in hardness or in phosphate levels. 



Whitton (15) concludes his review as follows: 



It is reasonable to assume that Cladophora played a relatively 

 minor role in aquatic communities before the activities of man 

 led to widespread nutrient enrichment. Certainly it is hard to 

 imagine a situation where massive growths could develop in flow- 

 ing waters without man's activities. , . Cladophora as a genus is 

 favored by high light intensities, high water turbulence, high 

 nutrient levels, high pH values, hard waters. Not all species 

 share all these characters, but C. glomerata , the species which 

 has increased the most as a response of man's activities, is 

 the organism which combines all these characters within a 

 single species. 



Unfortunately, we have no record of the Yellowstone's algal flora 

 before civilization came to the Yellowstone Valley. But we do know 

 that Cladophora glomerata now plays a dominant role in the river. And 

 from Whitton' s closing remarks it is possible that it came to assume 

 that position through cultural enrichment. If this is so, then the 

 nutrient contributions of man are pervasive throughout the drainage 

 because C. glomerata is abundant the length of the river (Table 3), 



Nevertheless, there is considerable evidence that naturally high 

 background nutrient levels exist in the upper river above Laurel. Auto- 

 trophic index (AI) levels reported by Stadnyk (12) indicate eutrophic 

 conditions from Corwin Springs downriver to Laurel, The maximum average 

 monthly AI at Corwin Springs (296) indicates moderate eutrophication 



■20- 



