CHAPTER 4 



be seen, the organic carbon in marsh water in 1976 gen- 

 erally was equal to or lower than 1975, so there is no 

 evidence of exceptional marsh output for 1976 unless flow 

 rates out of the marshes were exceptional in 1976 as com- 

 pared to 1975. 



The impact of this organic carbon on oxygen distribution 

 in the Bight should be considered. A somewhat simplified 

 stoichiometric relationship for primary productivity and 

 organic breakdown has been established (Redfield et al. 

 1963), and can be written: 



[(CH^O.oft (NH,),6 H^POJ + 138 O^ ?± 106 CO, + 

 16 HNO3 + H3PO4 + 122 H2O. 



where the term in brackets represents an average chemical 

 composition for marine phytoplankton. It is the product 

 of analysis of elements in plankton and of nutrients in 

 seawater and was intended as an average picture for the 

 oceanic environment. If a semienclosed coastal system can 

 be considered in equilibrium, these same ratios can hold. 

 Analysis of TransX data (Sharp et al. 1979) indicates that 

 sometimes Middle Atlantic coastal bottom waters do show 

 the predicted molar ratios of fluxes of phosphate, D.O., 

 and organic carbon. Therefore, it is possible to evaluate 

 the impact of the measured organic carbon on bottom 

 water D.O., using the idealized ratio of 138 moles of oxy- 

 gen to 106 moles of carbon. We can postulate the D.O. 

 for a starting point by using the concentration that would 

 be in equilibrium with the atmosphere if there were no 

 biological oxygen utilization. Bottom water salinity in the 

 New York shelf region is about 32.75"/fH^„ and the tem- 

 perature is about 9.6° C. The salinity is the average from 

 chapters 2 and 5; temperature is an average of June 

 through September for all segments from table 4-5. Using 

 oxygen saturation tables (e.g., Riley and Skirrow 1975), 

 this would give an oxygen content of 6.57 ml/1. With stoi- 

 chiometric equivalence, this amount of oxygen would be 

 used by respirational consumption of 0.225 millimoles C/ 

 1 or 2.70 mg C/1. 



Of course, all organic matter in the water will not be 

 easily broken down by rapid heterotrophic activity. How- 

 ever, organic content greatly in excess of 2.70 mg C/1 may 

 suggest sufficient labile (oxidizable) material to pose a 

 serious oxygen demand that, without oxygen replenish- 

 ment, could hypothetically lead to oxygen depletion. For 

 this consideration, total organic carbon (TOC) should be 

 treated as the cause of the potential oxygen demand, and 

 particulate matter may be less important than dissolved 

 material; Duedall et al. (1977) showed that bacterial ox- 

 idation of dissolved organic matter in sewage sludge occurs 

 before oxidation of particulate matter. This opinion is also 

 based upon the observation that particulates usually make 

 up only 10 to 15 percent of the total organic matter (table 

 4-8) and upon the suspicion that the particulates are not 

 a long-term (months) feature of the water column. The 



water column, not the benthic interface, has been shown 

 to be responsible for the majority of the oxygen demand 

 on an areal basis (Thomas et al. 1976). If an average 

 oceanic DOC value is taken as 0.80 mg C/1 (Sharp 1975) 

 and is viewed as the upper limit of refractory carbon in 

 an oceanic environment, then anything greater than 0.8 

 can be considered labile. By adding 0.80 and 2.70, we get 

 3.50 mg C/1 as an amount sufficient to provide a 100- 

 percent oxygen demand and leave the residual refractory 

 oceanic value. From table 4-8, we can see that many of 

 the samples in the Bight Apex have potential oxygen de- 

 mands sufficient to cause anoxia if the organic degradation 

 were rapid in comparison to oxygen replenishment. More 

 startling is that all the averaged bottom water values (fig. 

 4-15) for the Apex have sufficient DOC to deplete the 

 oxygen present if no oxygen renewal occurs. The bottom 

 waters of the Bight are not physically stagnant and the 

 general circulation is southwestward (Bumpus 1973; ch. 

 7). However, this circulation also develops gyres and areas 

 of very sluggish circulation (ch. 8). Thus, unless a source 

 of oxygen-rich, organic-poor water is postulated, we 

 would expect the water in this region to continue to pose 

 a large oxygen demand until the autumnal breakdown of 

 the thermocline. 



Therefore, from examination of the data acquired dur- 

 ing August-September 1976, it is concluded that DOC 



(1) was not exceptional in the Hudson-Raritan estuary; 



(2) was possibly higher than normal (compared to other 

 coastal areas) in the lower portion of New York Bight; 

 and (3) was extraordinarily high in the Apex. There is no 

 way of knowing whether the high Apex values are unusual 

 as compared to other years. If they are, they could have 

 resulted from the combined effects of the large Ceratium 

 bloom in summer 1976 and the estuarine circulation of 

 the Apex. POC did not show exceptional values in these 

 areas. In the Apex, the organic carbon values are more 

 than sufficient to give a potential oxygen demand that 

 could totally deplete the D.O. in the bottom waters. 



CHEMICAL RESPONSES 



In 1976 oxygen demand loading in the bottom waters 

 of the Bight depleted D.O. levels to near anoxic or anoxic 

 conditions over an area roughly equal to segments A, Jl, 

 J2, Ml, and part of M2. We will now examine how the 

 Bight chemistry changed as a resuU of this depletion by 

 briefly discussing it in the light of other chemical events 

 associated with anoxic development. 



Evidence for nitrate reduction is presented above in the 

 discussion of nutrients where plots of NH^*, NO,", and 

 NO3" versus D.O. are shown for cruise XWCC-11 (fig. 

 4-14). Although there is no clear evidence that NOr was 

 removed from the system as oxygen declined, the peak 



119 



