CHAPTER 15 



Table 15-2. — Estimates of organic carbon loadings to Apex waters 



and inshore of iO fathoms (55 m) during June-August, in metric tons 



per day 



" Modified from Mueller et al. (1976b). 



I- From Garside and Malone (1978). omitting their estimate of m situ 

 primary production not considered an input loading here. 



' This estimate (Garside and Malone 1978) includes particulate organic 

 carbon only. 



"I From Segar and Berberian (1976), omitting in-situ primary produc- 

 tion. 



" Considerable uncertainty exists as to the dissolved fraction of this 

 estimate. (See Segar and Berberian 1976.) 



how quickly these materials fall below the pycnocline and 

 how rapidly they are oxidized. 



An interesting analysis of oxygen dynamics in the Apex 

 concludes that the total carbon respired annually requires 

 an input of 1,690 t C/d, of which 77 percent is produced 

 by in-situ primary production (Garside and Malone 1978). 

 These authors also estimate that 36 percent of the annual 

 Apex carbon load is flushed from the Hudson-Raritan 

 estuary during January and April alone, months when 

 river runoff is exceptionally high, winter diatom blooms 

 occur in part from low grazing pressure (ch. 9, pt. 1), and 

 levels of resuspended organic material from estuarine sed- 

 iments are probably exceptional. The large, short-term 

 loadings in January and April probably fall to the inner 

 Bight sediments to be oxidized over the following year. 



The small cells normally dominating the spring/summer 

 phytoplankton assemblages sink very slowly, and most are 

 probably grazed or dispersed widely before falling below 

 the pycnocline to consume bottom oxygen (ch. 9, pt. 1). 

 However, the intensive summer/autumn zooplankton 

 grazing upon phytoplankton and organic detritus results 

 in zooplankton fecal material falling below the pycnocline 

 and consuming oxygen. Copepods alone assimilate 23 to 

 41 percent of the phytoplankton productivity daily in the 



inner Bight (Malone and Chervin 1979). The extent of 

 grazing by other zooplankton is not known, but copepods 

 probably dominate grazing activity most of the year (Cher- 

 vin, personal communication). Copepod assimilation ef- 

 ficiencies vary greatly, but an average of 70 percent seems 

 reasonable (Conover 1956, 1966; Gaudy 1974; Chervin 

 1978). Given this major copepod grazing plus the addi- 

 tional grazing by other zooplankton (Malone 1976; Cher- 

 vin 1978) and the relatively rapid sinking rates of zoo- 

 plankton fecal material (Wiebe et al. 1976; Elder and 

 Fowler 1977), more than 15 percent of the phytoplankton 

 produced in and carried to the inner Bight probably sinks 

 rapidly below the pycnocline as zooplankton fecal pellets. 



There are as yet no estimates of average carbon loadings 

 to the region of oxygen depletion from offshore waters. 

 However, during April through June 1976 it seems likely 

 that large inshore loadings of carbon as Ceratium tripos 

 were translocated from offshore by onshore bottom water 

 movements (ch. 7, 8, and 9, pt. 1 ). This was an exceptional 

 year because of unusually dense Ceratium concentrations 

 at the least, and the average onshelf flow of nearly 1.5 

 cm/s during May and June 1976 was probably atypical 

 (ch. 7). 



Annual fluctuations in the combined ocean dumping 

 fractions of these carbon and nitrogen loadings are seldom 

 greater than 25 percent, and are generally less. The quan- 

 tities of dumped dredged materials and sewage sludge 

 have increased almost 50 percent since 1960 (Gross 1976). 

 Long-term historical data apparently are not compiled for 

 annual total loadings from treated and untreated domestic 

 wastes, but there is no reason to believe that their annual 

 fluctuations are greater than those of dumped materials. 

 A substantial increasing trend in total domestic waste ef- 

 fluents (treated plus untreated) has occurred since 1936. 

 Total sewage discharges to waters under jurisdiction of 

 the Interstate Sanitation Commission have increased by 

 over 80 percent since 1936. This increase had essentially 

 stabilized by 1970 (A. Mytelka, personal communication). 



Physical and Biochemical Processes 



The proximate cause of oxygen depletion is oxidation 

 of organic matter and chemically reduced species of ni- 

 trogen, primarily by bacteria. In the Bight, marked re- 

 ductions in dissolved oxygen occur only when the water 

 column is stratified, preventing oxygen replenishment 

 from surface waters (ch. 6). Given effective stratification, 

 annual differences in the extent of oxygen depletion in 

 recent years must be due to the combined influences of 

 year-to-year oxygen-demanding loadings beneath the pyc- 

 nocline, physical transport and diffusion of these loadings, 

 and the mass specific rates of oxidation. The physical fea- 

 tures of the Bight are described in other chapters and are 

 summarized in chapter 16. 



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