LAKE EUTROPHICATION AND PRODUCTIVITY 



early in the process of deterioration 

 of a number of European lakes. Thus, 

 it seemed to be a distinct harbinger 

 of pollutional deterioration. 



Eutrophication — The problem is 

 that sewage treated ("purified") by 

 normal processes is relatively rich in 

 nutrients, especially phosphate. As 

 a result, when the effluent is put into 

 a lake, it acts as a plant fertilizer and 

 stimulates the growth of algae. While 

 some increase in biological production 

 may be favorable, overproduction of 

 algae results in water of low trans- 

 parency; large quantities of decaying 

 algae also produce bad odor prob- 

 lems. In such lakes, dissolved oxygen 

 may be exhausted from the deep wa- 

 ter by decomposition, and this elimi- 

 nates many desirable species of fish 

 (whitefish, trout, salmon). These con- 

 ditions interfere with most uses of a 

 lake — recreational, water supply, and 

 fisheries. As long as the sewage is 

 well treated, human health problems 

 are not dominant, but some individ- 

 uals are sensitive to algae and develop 

 skin rashes or nausea when they are 

 in contact with the lake. 



This effect of pollution, often called 

 eutrophication, is common around 

 the world. It is well documented by 

 many studies. Lake Washington was 

 thus exhibiting perfectly normal be- 

 havior when its increase in the abun- 

 dance of algae began. 



Public Action — Public concern 

 over the sewerage situation had been 

 growing in the entire Seattle metro- 

 politan area. In 1955, the Mayor of 

 Seattle appointed a Metropolitan 

 Problems Advisory Committee to 

 study sewerage conditions, among 

 other things. The obvious beginning 

 of deterioration of Lake Washington 

 and the rather clear-cut predictions 

 that could be made about its future 

 condition gave focus to public con- 

 cern. At the same time, it was recog- 

 nized that unsatisfactory conditions 

 also existed in Puget Sound and that 

 a broadly based, coordinated program 

 was necessary. 



As a result of the Committee's ac- 

 tion, a campaign was organized by 



public-minded citizens' groups to de- 

 velop a governmental organization 

 to handle the problem (Municipality 

 of Metropolitan Seattle, or "Metro"). 

 An active informational campaign 

 was carried out, mostly using infor- 

 mation about the actual deterioration 

 of Lake Washington and predictions 

 about its future. 



After a certain amount of difficulty, 

 Metro was passed on the second vote 

 in 1958. A project of sewage diver- 

 sion from the lake was started in 

 1963 and completed in 196S. The 

 total cost of Metro to date is about 

 $145 million, of which about $85 

 million is attributable to the Lake 

 Washington part of the project. 



Results of Diversion of Sewage — 

 With the first diversion of about a 

 third of the sewage, deterioration of 

 Lake Washington slowed, and further 

 diversions were promptly followed by 

 more improvement as measured by 

 increased transparency of the water 

 and decreased amounts of phos- 

 phorus and algae. During late sum- 



mer of 1969, the deep-water oxygen 

 conditions were more favorable than 

 in 1933, phosphate was nearly down 

 to the concentrations seen in 1950, 

 and summer transparency was two- 

 and-a-half times as great as in 1963. 

 (See Figure VIII-16) 



It is important to realize that action 

 was taken before the lake had de- 

 teriorated very far, relative to the 

 well-known problem lakes in Europe 

 and the Midwest of this country. 

 The condition of the lake changed 

 conspicuously enough that there was 

 no doubt about its reality, but action 

 was taken early in the process. 



Generalizations from the Lake 

 Washington Experience 



It is clear that Lake Washington 

 responded promptly and sensitively 

 to both increases and decreases in 

 nutrient input. Lake Washington 

 should not be regarded as unusual; 

 many lakes are similar enough in 

 their chemical characteristics that 



Figure VIII-16 — TRANSPARENCY MEASUREMENTS IN LAKE WASHINGTON 



The graph shows observations of transparency made in Lake Washington from 

 1950 to 1971. The measurements are made with a Secchi disc, a 20-centimeter 

 white disc that is lowered into the water until it disappears from view. 



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