NOAA PROFESSIONAL PAPER 11 



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NOTE: Zero time of rate-of-depletion graph should be positioned over date of occurrence of 3 ml/I . 



FIGURE 16-4 — Oxygen depletion alert guide for New York Bight Shows days required for dissolved oxygen concentration to decrease from 

 typical annual minimum of 3 ml/I to critical level of 2 ml/I at four rates of depletion. 



decline to the critical D.O. level of 2 ml/1 can be predicted 

 from the observed rate of decline. Depending on the rate 

 of decline, there are 10 to 40 days in which to issue a 

 warning that certain marine organisms will be subjected 

 to stress and that mortalities are likely. Both the duration 

 and severity of the potential oxygen-depletion event can 

 be evaluated against the typical autumn date for the break- 

 down of the pycnocline (density stratification) — mid-Sep- 

 tember to end of October — or any observation of other 

 environmental conditions contributing to D.O. concen- 

 trations in bottom waters. 



This method of predicting any severe depletion in D.O. 

 offers a reasonable likelihood of success. As models of 

 carbon, oxygen, and nitrogen (C/O/N) cycles in the Bight 

 are developed and refined, more reliable predictive ap- 

 proaches can be applied. 



RECOMMENDATIONS 



Severe oxygen depletion in bottom waters of the New 

 York Bight in 1976, especially off the New Jersey coast. 



was determined to have been caused from anomalous nat- 

 ural events, and probably will occur again. The phenom- 

 enon apparently cannot be controlled, but some reduction 

 in its severity might be achieved by reducing the input of 

 wastes and other substances from human activities. The 

 intensive field investigations and study of the 1976 event 

 revealed shortcomings in the data collected and research 

 conducted before this event. It is clear that our under- 

 standing of dynamic processes in coastal waters must be 

 improved, particularly the following: 



1) development of the pycnocline — its timing, char- 

 acteristics, and influence on ecosystem functions; 



2) occurrence of large phytoplankton blooms — their 

 relation to oceanic and climatic conditions; and 



3) functions of the ecosystem — as they relate to C/O/ 

 N cycles and inputs to coastal waters from human 

 activities. 



In the light of these needs, as they relate to D.O. depletion 

 and possible mass mortalities, and to improve our under- 

 standing about and management of coastal waters, certain 

 recommendations are made and discussed. 



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