CHAPTER 10 



mate of anaerobic metabolism) in the vicinity of the oxy- 

 gen-depleted area (fig. K>-13). On the average, the seabed 

 consumed an amount of carbon equivalent to about 20 

 percent of the carbon photoassimilated throughout the 

 water column per day. The seabed and water below the 

 pycnocline together consumed a quantity of carbon equiv- 

 alent to 57 percent of the carbon photosynthesized each 

 day. This suggests that large fluxes of oxidizable organic 

 carbon must have been supplied to subpycnocline waters 

 daily. In fact, at stations in and adjacent to the oxygen- 

 depleted area (photosynthetic capacity profile fig. 10-9A. 

 stations 200 and 213) large increases in both netplankton 

 and nannoplankton and in POC were observed in the pyc- 

 nocline and below where PAR intensity was low. The 

 assimilation numbers (productivity per unit biomass-chlo- 

 rophyll a) for the pycnocline and subpycnocline phyto- 

 plankton were low (fig. 10-7), and, in general, respiration 

 greatly exceeded photosynthesis (table 10-2). 



EXPANDED APEX HYPOTHESIS 



Production (P) and respiration (R) ultimately balance 

 one another since stoichiometrically the oxygen produced 

 during photosynthesis should balance the oxygen con- 

 sumed during respiration and mineralization of the newly 

 photosynthesized carbon. However, very often production 

 and respiration are uncoupled over time and space (both 

 vertically and horizontally). For instance we know that P/ 

 R ratios are much greater than 1 during the spring bloom, 

 while following the bloom they are much less than 1. Our 

 data (table 10-2) demonstrate the vertical uncoupling of 

 photosynthesis and mineralization where P/R ratios above 

 the pycnocline are considerably greater than 1 while those 

 below are considerably less than 1. The large quantities 

 of decaying organic carbon in Ceratium tripos transported 

 to the subpycnocline waters of the New York Bight during 

 1976 further exacerbated the uncoupling of production 

 and consumption activities above and below the pycnoc- 

 line, respectively. Horizontally, additional organic carbon 

 as sewage discharged to the Apex represents a BOD load, 

 (i.e., not a source of photosynthetic oxygen) and will sup- 

 port more respiration. Because of temporal and spatial 

 partitioning of organic carbon and oxygen sources as de- 

 scribed above, we believe that the eutrophic effects of 

 riverborne, sewage-derived nutrients (including organic 

 components) may actually occur over a larger area than 

 the estimated affected area, based on the stimulatory ef- 

 fects of inorganic nutrients alone (sans nutrient regener- 

 ation) on primary production (Garside et al. 1976). 



Water column mineralization probably supplies the 

 major portion of nitrogen-nutrients required by assimi- 

 lating phytoplankton in the New York Bight. Garside et 

 al. (1976) indicated that during the summer 120 t of dis- 

 solved inorganic nitrogen (ammonium, nitrate, nitrite) are 



discharged into the Bight Apex. These authors estimated 

 that the sewage-derived nitrogen (inorganic) would be 

 assimilated by phytoplankton in a 257 km- area of the 

 Apex during summer. If we consider the large quantities 

 of daily and annual primary productivity measured in the 

 lower Hudson-Raritan estuary — 6 to 8 g C/m-/d at summer 

 maximum, 750 to 1053 g C/m-/yr (O'Reilly et al. 1976)— 

 and the high concentration of phytoplankton biomass 

 transported out of the estuary into the Apex (Duedall et 

 al. 1976; Parker et al. 1976) then much more nitrogen as 

 organic N will be transported from the estuary into the 

 Bight during summer. Furthermore, the dissolved organic 

 nitrogen (DON) contributed by sewage effluent could 

 double the estimate of nitrogen loading based solely on 

 ammonium, nitrate, and nitrite. 



Mueller et al. (1976) estimated that (average) 209 t of 

 inorganic nitrogen (ammonium -i- nitrate -i- nitrite) and 

 130 t of organic nitrogen are transported into the Apex 

 each day. Subtracting the Mueller et al. (1976) estimates 

 of barged nitrogen via dredge materials (because the 

 barged material might be expected to be derived from 

 wastewater and gauged and nongauged runoff already 

 counted in riverborne output) results in 172 t N/d of dis- 

 solved inorganic nitrogen (DIN) and 104 t N/d of DON 

 transported to the Apex. Ultimately, barged nitrogen is 

 also added to the Apex but not as part of the river flow. 

 This estimate of DIN is slightly greater than the Garside 

 et al. (1976) estimate of total DIN (160 t N/d before es- 

 tuarine phytoplankton uptake is subtracted). 



Few measurements of the relative proportions of DIN 

 to DON are available for marine waters receiving sewage 

 effluent. The data presented by Epply et al. (1972), col- 

 lected near coastal sewage outfalls off California indicate 

 that the average water column concentrations of nitrate 

 plus ammonium are 1.2 times (by atomic weight) the con- 

 centration of DON. Using the Mueller et al. data above. 

 the ratio of DIN to DON in estuarine effluent is 1.7:1. At 

 the time of our cruise, we measured an average of 33.2 

 \iMl\ of DIN for the entire water column under the Ver- 

 razano Bridge at station 69. The average water column 

 concentration of DOC was 4 mg C/1. If we assume an 

 atomic composition ratio of 106C:16N, then this repre- 

 sents 50.3 |xM/l of DON, or a DIN/DON ratio of 0.7; 1. 

 The area actually stimulated by human nitrogen loading 

 could be double the previous estimates (Garside et al. 

 1976) if the DON pool is biologically labile and not re- 

 fractory to heterotrophic bacteria in the water column. 

 Litchfield et al. (in press) show that substantial hetero- 

 trophic activity and mineralization of organic nitrogen 

 compounds do occur with the sediment bacteria in New 

 York Bight. This activity also extends upward into the 

 water column as well (C. D. Litchfield, personal com- 

 munication). 



Both Ryther and Dunstan (1971) and Garside et al. 



257 



