CHAPTER 15 



important. During August-September 1976 the concen- 

 trations of dissolved organic carbon were exceptionally 

 high — "extraordinarily high" concentrations in the Apex 

 relative to other coastal areas (ch. 4) and about 12 times 

 the POC concentrations averaged over the oxygen deple- 

 tion zone. Atwood et ai. (ch. 4) present some evidence 

 that dissolved organic carbon may have contributed sig- 

 nificantly to oxygen depletion in 1976. 



CONCLUSIONS 



While human activities are very important sources of 

 nitrogen and carbon loadings to the Bight, the quantities 

 of some natural loadings have not yet been estimated. The 

 natural contributions of carbon and nitrogen from along- 

 shelf transport, shelf onwelling, and sediment regenera- 

 tion could be major, but estimates are not available. 



While the bulk of these anthropogenic loadings enter 

 the Bight through the Sandy Hook/Rockaway Point tran- 

 sect, nitrogenous loadings from the New Jersey coast are 

 more than 20 percent of those from the transect. These 

 sources largely from sewage treatment plant outfalls ail 

 along the New Jersey coast, may well have contributed 

 to the nearshore oxygen depletion events in the past — 

 particularly in 1968, 1971. 1974, and 1977 (fig. 15-1). It 

 is not yet possible to link quantitatively the particular 

 sources of nutrients and carbon to their roles in depleting 

 oxygen from Bight waters. 



Other contributors to this report have developed an 

 entirely plausible hypothesis for the severe oxygen deple- 

 tion in 1976. This hypothesis implies that the anthropo- 

 genic loadings of carbon and plant nutrients contribute to 

 oxygen depletion of the inner Bight, but have not been 

 the major cause of anoxia, even in 1976 when physical 

 conditions favored oxygen depletion. However prepon- 

 derant the anthropogenic loadings, the resulting summer 

 phytoplankton blooms and detritus are actively grazed 

 upon and dispersed widely while still in surface water. The 

 particulate carbon falling into the bottom layer does not 

 become concentrated enough to cause anoxia. The hy- 

 pothesis invokes C. tripos, which bloomed in 1976 inde- 

 pendently of known anthropogenic stimuli, as a mecha- 

 nism for accumulating beneath the pycnocline unusually 

 large quantities of carbon. Because C. tripos is seldom 

 eaten, essentially all this biomass respires actively until 

 death when the labile fractions of the cells are oxidized 

 making Ceratium a very effective agent for oxygen deple- 

 tion. This hypothesis is consistent with the extended du- 

 ration of stratification, probable physical concentration of 

 C. tripos, and increased residence time of New Jersey 

 coastal bottom water, all of which contributed to oxygen 

 depletion in 1976. 



This hypothesis seems entirely consistent with realistic 

 ranges of the loadings and processes involved. However, 



the realistic ranges are great for oxidation rates of POC 

 and DOC in bottom waters. If sinking rates of nanno- 

 plankton and detritus are toward the high end of presently 

 realistic values and if substantial quantities of this material 

 are not incorporated in planktonic food webs before being 

 oxidized, this fraction of POC would be more significant 

 than the hypothesis allows. Also, despite the overwhelm- 

 ing concentrations of DOC, there seems to be very little 

 quantitative evidence about its sources or oxidation rates. 

 Turnover rates would not need to be very large to make 

 DOC more significant than has been presumed. Substan- 

 tially more precise and systematic evaluations are needed 

 to determine the relative significance of nutrient and car- 

 bon loadings to oxygen depletion. Mathematical models 

 of carbon/oxygen/nutrient dynamics in the Bight are being 

 developed to refine the assessments in this volume. 



The extent of human contributions to this coastal eu- 

 trophication and seasonal oxygen depletion remains ar- 

 guable. Annual variation in the degree of oxygen deple- 

 tion is pronounced. Reductions in any significant, relatively 

 constant BOD loading would, on the average, reduce the 

 likelihood of anoxic events. Consequently, curbs on hu- 

 man waste loadings would reduce BOD in bottom waters 

 of the inner Bight and, hence, the probability and severity 

 of benthic mortalities. Other alternatives to the same ends 

 are not obvious to me. 



ACKNOWLEDGMENTS 



The MESA New York Bight Project staff contributed 

 ideas and useful criticism, particularly Paul Eisen, who 

 developed another estimate of atmospheric nitrogen load- 

 ing. 



REFERENCES 



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Bascom. W., 1974b. Letter re Woodwell (1974), Sa. Am. 231 (5):8-9. 



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PP 

 Bowman, M. J., and Wunderlich. L. D.. 1977. Hydrographic Properties, 



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331 



