The Chesapeake was subjected to the effects of Tropical Storm Agnes in June of 

 1972. The storm, which had been of hurricane strength before it reached the Mid- 

 Atlantic region, was obviously not a human activity, but it is relevant because it 

 affected pollutants and revealed fundamental patterns of pollutant behavior and 

 effects. Average basin rainfall over a 3-day period was in excess of 1 2 cm (5 in), with 

 approximately one-third of the area receiving 30 cm (12 in) and isolated locations 

 recording 46 cm ( 18 in) (Chesapeake Research Consortium, 1976). Theeffects of this 

 100- to 200-year storm event were dramatic, and observations were exceptionally 

 thorough because the scientific community and, later, the management agencies 

 recognized the importance of the event and arranged for extensive detailed observa- 

 tion. The Virginia Institute of Marine Science, the Chesapeake Biological Labora- 

 tory of the University of Maryland, and Chesapeake Bay Institute of the Johns 

 Hopkins University were especially prompt and effective in their research, and the 

 Corps of Engineers provided essential financial assistance. Highlights of observa- 

 tions include: 



• The dominating Susquehanna had 7-day flows 15.5 times greater than normal, 

 peaking at 1 ,130,000 cfs. The James flowed at as much as 24.4 times normal and 

 the Potomac at 19.7 times normal. 



• The Susquehanna debouched more sediment in 10 days than during the preceding 

 10, perhaps 25 or more, years, about 31 million metric tons against an annual 

 average of one-half to one million tons. 



• Dissolved nitrates and nitrite were 2 to 3 times normal in the northern half, but 

 little affected downstream. Phosphate remained near normal. The nutrients were 

 rapidly lost to the sediments. 



• Trace metal and pesticide concentrations were not drastically changed. Oil input 

 was substantial. 



• Soft-shell clams, oysters, and some aquatic plants suffered heavy mortalities. Fin- 

 fish, crabs, and hard clams were relatively unaffected. 



• Bacterial contamination forced temporary closure of the Chesapeake Bay and its 

 tributaries to the harvest of shellfish, but reopening was possible within weeks or 

 a few months. 



• The entire biological community was disrupted, but most effects had disappeared 

 after 2 years. 



• The Chesapeake Bay ecosystem demonstrated great resilience to this extreme 

 natural event. 



• The storm increased heterotrophic activity in parts of the Bay, reduced phyto- 

 plankton in the upper Bay but stimulated greater production in the lower Bay, 

 raised nitrogen in the lower estuary, moderated algal production in some areas by 

 shading, and was followed by reduction in dissolved oxygen concentration 

 (Chesapeake Research Consortium, 1976). 



The studies are detailed in the last-named reference by a large number of authors 

 who cannot be individually credited here. They provided a remarkable record and 

 achieved important advances in estuarine science. 



An artificially constructed waterway, the Chesapeake and Delaware Canal, was 

 dug in 1829, converted from a locked sequence to a sea-level canal in 1927, and 

 enlarged from 8 by 75 m to 10 by 135 m (27 by 250 ft to 35 by 450 ft) in the period 

 between 1958 and 1972. In 1974, nearly 11,000 vessels carrying 12,400,000 tons 

 transited the canal. Concern over the possible environmental effects of enlargement, 

 including possible diversion of large volumes at periods of low flow, resulted in 

 extensive research and analysis of the hydrologic patterns created and of effects on 

 the biota (Cronin, 1977). It was concluded that the physical hydrography, chemical 

 environment, and biotic populations of the canal and areas of approach had been 

 substantially altered. Long-term net transport from the Chesapeake was estimated 

 to increase from 900 to about 2,450 cfs in a highly complicated hydrologic sequence 

 with eastward and westward maximum flows of about 48,800 and 37,900 cfs. A new 



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