LAKE EUTROPHICATION AND PRODUCTIVITY 



5. Role of lake sediments in the 

 cycling and storage of chemical 

 substances; 



6. The precise residence time of 

 water in each lake basin; 



7. Utilization and cycling of nu- 

 trients by biota; 



8. Population dynamics of various 

 communities; 



9. Energy budget; 



10. Water budget. 



Without more complete information 

 in these areas, the eutrophication of 

 the Great Lakes cannot be effectively 

 controlled. 



Importance of Scale in the 

 Design of Great Lakes Studies 



The matter of transferability of 

 information and experiences derived 

 from studies of small to large lakes 

 requires careful evaluation before a 

 Great Lakes eutrophication program 

 is established. Although the funda- 

 mental processes of aquatic systems, 

 whether large or small, are basically 

 the same, the mechanisms controlling 

 these processes and the rates may 

 vary importantly with water-body 

 size. In the size-series of water bodies 

 from small lakes to oceans, the Great 

 Lakes represent the mesoscale aquatic 

 system. The lakes are subject to 

 essentially the same physical, chemi- 

 cal, biological, meteorological, and 

 geological conditions as the oceans 

 and they possess both lacustrine and 

 oceanic characteristics. Nevertheless, 

 a direct transfer of information from 

 small lakes to these large lakes is 

 difficult for a number of reasons. 

 Some characteristics that make the 

 Great Lakes uniquely different from 

 small lakes are: 



1. Visible effects of Coriolis force 

 on water circulation; 



2. Distribution of upwelling and 

 sinking according to relation- 



ship of current streamlines and 

 the shore; 



3. Discrete water masses which 

 maintain distinct limnological 

 characteristics; 



4. Modifying effect on weather; 



5. Large water volume in propor- 

 tion to area of water surface 

 and lake bottom; 



6. Existence of a wide range of 

 industrial and urban complexes, 

 land uses, shore development, 

 and water uses in the 295,000 

 square miles of drainage basin; 



7. Each of the five lakes differs 

 in size, morphometry, and lim- 

 nological characteristics, but 

 they are interconnected, result- 

 ing in a flow-through or down- 

 stream effect; 



8. Residence time for water in a 

 lake basin may exceed 100 

 years. 



Scale, then, becomes an important 

 factor in designing studies on the 

 Great Lakes. Two ways to meet some 

 of the inherent difficulties are: (a) 

 extrapolation of experience from 

 small to large lakes, including labo- 

 ratory-type studies as well as studies 

 from scale enclosures (plastic bags, 

 cylinders, etc.) and the experience 

 gained from intermediate-size lakes; 

 and (b) development of appropriate 

 mathematical models (black-box mod- 

 els, hydrodynamic models, produc- 

 tivity models, etc.). Transfer from 

 physical models (small lakes) could be 

 facilitated by developing some kinds 

 of transfer coefficients, analogous to 

 Reynold's numbers. 



Plans for Action 



It becomes apparent that water- 

 resource problems of the Great Lakes 

 are large, diverse, and urgent. There 

 is general agreement among scien- 

 tists, engineers, political scientists, 



and socio-economists that the most 

 fruitful approach to the solution of 

 these problems is a direct study of 

 the lakes through use of systems- 

 analysis techniques and a well-de- 

 signed program of data collection and 

 analysis. There is also basic agree- 

 ment that an effective program to 

 control Great Lakes eutrophication 

 must place primary emphasis on con- 

 trolling nutrients and pollutants at 

 source of entry and secondary em- 

 phasis on measures to ameliorate the 

 effects of these substances after en- 

 tering the lakes. 



Modeling Efforts — Several organi- 

 zations and research teams are devel- 

 oping a set of linked systems-modeling 

 studies that will use simulation as a 

 research tool in conjunction with the 

 study of the Great Lakes. The long- 

 range objective of this effort is to 

 construct a region-wide comprehen- 

 sive model. Initial efforts are directed 

 toward a water-quality model on a 

 regional scale, a water-quality sub- 

 system model for one or more sub- 

 regions within the Great Lakes basin, 

 and a regional economic-growth 

 model. These efforts are too new to 

 have produced tangible results, but 

 this kind of thinking dominates pres- 

 ent Great Lakes investigations. The 

 organizations offering leadership in 

 this approach are: the Great Lakes 

 Basin Commission, with emphasis on 

 regional models; the Council on Eco- 

 nomic Growth, Technology and Pub- 

 lic Policy of the Committee on In- 

 stitutional Cooperation (CIC), with 

 emphasis on water-quantity and 

 water-quality models; the University 

 of Michigan Sea Grant Program, with 

 emphasis on comprehensive modeling 

 of a subregion (Grand Traverse Bay); 

 and the University of Wisconsin Sea 

 Grant Program, with emphasis on 

 modeling of Green Bay. 



Data Collection and Systems Anal- 

 ysis — Two field-data collection pro- 

 grams and related systems-analysis 

 efforts that are under serious con- 

 sideration will serve as examples of 

 current thinking on Great Lakes in- 

 vestigations. The first is a materials- 



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