Corps of Engineers, 1977; Flemer and Heinle, 1974; Hydroscience, 1975; Jaworski, 

 1981; Jensen, 1976; Kuo et al., 1975; Laniak, 1979; Lippson and Lippson, 1979; 

 Pheiffer et al., 1972; Roberts et al., 1975; Schubel, 1972; Sullivan et al., 1977; Tsai, 

 1975; Williamson, 1972). It would be inappropriate to detail all of these here; 

 summary comments will be presented instead. Fortunately, much information has 

 been synthesized in the last decade, so that highly useful analyses exist. These and 

 several unusual specific cases will be reviewed. 



An ambitious effort has been made to review all of the useful field data from the 

 total Chesapeake Bay since 1913-1916, when the first were obtained ( Heinle et al., in 

 press). This review demonstrates the great difficulties inherent in such an effort. 

 Records are lost; analytic techniques have been revolutionized; very few studies are 

 sustained for decades; computerized sets are often incompatible, etc. It is possible to 

 provide the following summary, however: 



• The various portions of a large estuary differ fundamentally in components and 

 processes related to nutrients and cannot be successfully lumped together under a 

 single criterion or set of standards. 



• The inherent variability of the estuarine system in response to rainfall, tempera- 

 ture, storms, and other factors vastly complicates interpretation of long-term 

 data. 



• Water quality in much of the total Chesapeake system has changed in recent 

 decades because of increased nutrient enrichment. 



• In the upper and middle Chesapeake Bay proper, and in several tributaries, 

 nutrient content and algal concentrations have increased and light penetration 

 has decreased. 



• In some tributaries, available oxygen in deeper waters has been reduced, and 

 annual variations in concentrations of oxygen are now more extreme. 



• The lower Bay has been little affected, although the effects of enrichment have 

 progressed down the main stem and tributaries over time. 



• If concentration of Chlorophyll-a is used as the best available, albeit imperfect, 

 gross indicator of threat from nutrient enrichment, the following guidelines can 

 be stated for the Chesapeake Bay system: 



1) Estuarine waters of salinity less than 8 to 12 percent are moderately en- 

 riched if they have summer chlorophyll levels of 30 to 60 ugl l 1 ; they are 

 highly enriched, with potential of damage, if summer levels exceed 60 



Mg/r'. 



2) Waters of salinity higher than 8 to 1 2 percent are moderately enriched at 

 20 to 40 jug/ 1" in summer, and highly enriched at levels above 40 jug/ 1~'. 



• The quality of algal populations may be as important as quantity, and each may 

 at times be an objective in management. 



• Reduction of nutrient input in the Potomac system has been demonstrated to be 

 effective in improving the lower river and upper estuary. 



• Either nitrogen or phosphorus may control production ratio in various areas of 

 lower salinity, but nitrogen appears to dominate the mid- and lower Bay. 



• The Bay has indeed been affected, but not yet to a critical degree except in some 

 tributaries. 



• Demographic projections and the present evidence of undesired effects are 

 portents of possible serious future losses of quality and usefulness of parts of the 

 Chesapeake Bay system. 



A different, recent, brief summary has emphasized the very great role of sediments 

 in the nutrient sequence in the Chesapeake Bay and other estuaries (Bertine et al., 

 1980). 



Much of the nutrient entering the system becomes associated with the sediment 

 and is deposited but may be regenerated from that sink at later dates. The processes 

 involved are partially understood and include sediment deposition, biological 

 activity in the sediment, resuspension, and interface transport. In the Chesapeake, 



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