A. Municipal Wastewater 



Nitrogen can be fixed directly from the atmos- 

 phere by biological life. But phosphorus is a more 

 readily controllable nutrient. In the Great Lakes 

 the dominant source of nutrients, especially phos- 

 phorous, is municipal wastewater, mainly sewage. 

 A Federal Water Pollution Control Agency survey 

 has shown that 75 per cent of the phosphorus 

 added to Lake Erie annually comes from munic- 

 ipal wastewater. Moreover, about 66 per cent of 

 the phosphorus is associated with detergents. 

 Approximately two-thirds of this nutrient is re- 

 tained in the lake, principally by incorporation in 

 bottom sediments. 



Needless to say, the effects of municipal waste- 

 water discharges have drastically effected the aging 

 of the Great Lakes, Lake Erie in particular. There 

 can be no doubt that the discharge of domestic 

 sewage has been a predominating contributor to 

 the deterioration of water quality, not only 

 because of nutrients but also because of bacterial 

 and organic contamination. 



Whereas eutrophication is measured on a geo- 

 logical time scale under natural conditions, acceler- 

 ated eutrophication resulting from man's activities 

 is evident in a single lifetime. 



B. Sedimentation 



The preceding discussion identified municipal 

 wastewater as the principal source of nutrients in 

 the Great Lakes.^* Sedimentation, including silts, 

 erosion and agricultural runoff, dead biological 

 life, and wastewater residues, is the second most 

 important source of nutrients. 



As silts and erosion runoff flow into a lake, 

 nutrients are dissolved and are available for biolog- 

 ical utilization. Land use practices, especially land 

 area development practices in urban as well as 

 agricultural areas, have contributed to the prob- 

 lem. If measures are not undertaken to control this 

 nutrient source, accelerated eutrophication will be 

 rapid, second only to municipal wastewater 

 effects. 



C. Agricultural Runoff 



Agricultural runoff is also a significant source 

 of nutrients entering the Great Lakes. It is 



comprised of eroded soil, leached salts and ferti- 

 lizers, and excess fertilizer. Measures to alleviate 

 some nutrient contribution from agricultural run- 

 off include land management techniques (contour 

 plowing, for example), judicious fertilizer applica- 

 tion, and where possible, controlled water addi- 

 tion. Because treatment cannot be appUed to point 

 sources, it is difficult to control nutrients in 

 agricultural runoff. This problem is a major one in 

 terms of accelerated eutrophication of the Great 

 Lakes. 



^"L. R. Webber and D. E. Ebich, "The Soil and Lake 

 Eutrophication," ft-oceedmgs. Tenth Conference on Great 

 Lakes Research, ibid., pp. 404-412, 1967. 



Figure 12. Eutrophication is a natural, long- 

 term process of lake aging. However man-made 

 accelerated eutrophication through pollution 

 may transform a lake into a swamp within a 

 lifetime. (Department of the Interior photo) 



Other contributors to eutrophication having a 

 lesser but still significant impact are: 



— Industrial wastewater 



— Combined storm sewage 



— Urban land drainage 



— Dredging 



— Tributary inflow. 



Still others have been identified but having a low 

 impact are: 



*- Watercraft wastes 



— Oil discharges 



— Thermal discharges 



— Waterfowl 



— Subsurface disposal 



— Atmospheric quality deterioration. 



III-44 



