CHAPTER 10 



18. At stations outside the Apex, adjacent to the New 

 Jersey coast and in the oxygen-depleted area, the euphotic 

 layer occupied the entire water column. At these stations 

 the typical vertical profile, with the highest productivity 

 at or near the surface, was not seen. Instead, the simulated 

 in-situ and photosynthetic capacity primary productivity 

 of these stations was maximal below the pycnocline. 



19. Phytoplankton above the pycnocline appeared 

 healthy, based on high productivity, high assimilation 

 numbers, and high photosynthetic efficiencies. 



20. Phytoplankton below the pycnocline appeared less 

 healthy, based on low chlorophyll/phaeopigment ratios, 

 low assimilation numbers, and low photosynthetic effi- 

 ciencies. 



21. The percent of photoassimilated carbon released as 

 dissolved organic matter from phytoplankton was 7 to 34 

 percent and was highest where total primary productivity 

 and DOC were highest, suggesting that phytoplankton 

 release of dissolved extracellular products may be con- 

 tributing significantly to the total DOC pool. 



22. Total plankton respiration rates generally were high, 

 up to 25 ml 0;/mVh or on an integral basis 5.9 g C/m-/d 

 assuming an RQ of 1. 



23. Total plankton respiration rates generally were high- 

 est at or near the surface and decreased with depth except 

 on the periphery of the oxygen-depleted area where rates 

 were highest at or below the pycnocline. 



24. In the oxygen-depleted area, total plankton respi- 

 ration rates above the pycnocline were low, 2 to 5 ml O,/ 

 mVh, or on an integral basis 0.2-0.3 g C/m-/d, assuming 

 an RQ of 1. No measureable aerobic metabolism occurred 

 below the pycnocline. 



25. During June 1977, a "normal" summer, total plank- 

 ton respiration rates measured were equivalent to about 

 2 g C/m-/d oxidized and were several times higher than 

 the rates measured in the oxygen-depleted area during 

 August-September 1976. 



I 26. Aerobic measurements of seabed oxygen consump- 

 tion could not be made under in situ oxygen conditions 

 in the oxygen-depleted area. However, within and im- 

 mediately surrounding the oxygen-depleted area, high 

 rates of oxygen uptake (up to 37 ml OJm-lh) were meas- 

 ured, suggesting that additional organic loading of the 

 seabed occurred in the vicinity of the oxygen-depleted 

 area during 1976. 



27. Rates of seabed oxygen consumption appeared to 

 be higher around the periphery of the oxygen-depleted 

 area during August-September 1976 than during June 

 1977. Rates of seabed oxygen consumption during June 

 1977 in the area of former oxygen depletion were com- 

 parable to rates measured in surrounding areas. Away 

 from the oxygen-depleted area no differences among the 

 summers of 1975, 1976, and 1977 were readily apparent. 



28. The contribution of the seabed to total oxygen con- 



sumption rates (water column plus seabed) was unusually 

 high (>10%) around the periphery of the oxygen-deleted 

 area, further supporting the idea that additional organic 

 loading to the seabed took place during 1976. 



29. The relatively greater contribution of the seabed to 

 total (water plus seabed) oxygen uptake on the periphery 

 of the oxygen-depleted area in 1976 was due to the com- 

 bination of higher rates of seabed oxygen consumption 

 and relatively lower rates of total plankton respiration 

 compared with June 1977. 



30. Our measurements of an average oxygen consump- 

 tion rate below the pycnocline (includes bottom 9.4 m of 

 water plus seabed) was 3.7 ml 0,/mVh. This measurement 

 appears to support the net oxygen utilization rate estimate 

 of 4.0 ml 0,/mVh derived by Han et al. (ch. 8) for May- 

 June 1976. 



31. Estimated rates of anaerobic metabolism for the 

 subpycnocline waters of the oxygen-depleted area were 

 based on observed phosphate concentrations and found 

 to be slightly lower than aerobic rates of water column 

 carbon mineralization for the subpycnocline water at sta- 

 tions adjacent to the oxygen-depleted area. 



32. The large increase in bacterial numbers and biomass 

 and different morphology of bacteria in the subpycnocline 

 waters of the oxygen-depleted area suggest the presence 

 of additional labile organic material and its probable an- 

 aerobic decomposition. 



33. The logical sources of organic carbon, which could 

 provide the organic material necessary to account for the 

 estimated anaerobic metabolism and for the maintenance 

 of low D.O., include decaying benthic macrofaunal bio- 

 mass, DOC, and primary productivity. Decaying benthic 

 macrofauna can account for only about 50 percent of the 

 estimated anaerobic metabolism. The DOC pool is diffi- 

 cult to evaluate because of scarcity of information and 

 lack of understanding of the dynamic interactions among 

 bacteria, DOC and POC pools, and phytoplankton. Pri- 

 mary production appears to be the most likely major sup- 

 ply of labile organic carbon, based on observed produc- 

 tivity to respiration ratios. 



34. Primary productivity and respiration were uncou- 

 pled both vertically and horizontally as evidenced by P/R 

 ratios above and below the pycnocline and over the New 

 Jersey shelf. 



35. Based on measurements of DIN and DOC for the 

 entire water column in the Verrazano Narrows a DIN/ 

 DON ratio of 0.7:1 was estimated (assumed atomic com- 

 position ratio of 106C:16N). Thus the area actually stim- 

 ulated by human nitrogen loading could be double pre- 

 vious estimates which considered only DIN. 



36. Wastes (including inorganic and organic nitrogen) 

 from the New York metropolitan area are normally super- 

 imposed upon the natural organic loading of the New York 

 Bight. These compounds may affect the system well be- 



259 



