NO A A PROFESSIONAL PAPER II 



in the estuary during summer. This assessment is shared 

 by O'Connors and Duedall (1975), who estimated that 

 phytopiankton took up only about 34 percent of the total 

 dissolved nitrogen released to the New York area waters 

 in June 1974 before it reached the Bight. Garside et al. 

 (1976) estimated that 120 t of dissolved nitrogen per day 

 enter the Bight via the estuary "during low-flow summer 

 months'" (generally June through September). 



Another estimate of inorganic nitrogen flux to the Bight 

 is based upon short-term measurements of nutrient con- 

 centrations and velocity profiles across the transect from 

 Sandy Hook, N.J., to Rockaway Point, N.Y. (O'Connors 

 and Duedall 1975; Parker 1976; Duedall et al. 1977). This 

 estimate rests on assumptions about the representative- 

 ness of three measured velocity fields and one nutrient 

 concentration field at the transect over different, short- 

 time intervals. Though the assumptions are only partly 

 evaluated, three lines of evidence tend to validate the 

 calculations: 1) the calculated net salt flux yields an esti- 

 mate of the longitudinal coefficient of eddy diffusion, 

 which is comparable to values estimated for other estu- 

 aries; 2) a comparison of current meter records along the 

 transect shows the velocity structure similar in June 1952, 

 May 1958, and August 1959 (Kao 1975; Doyle and Wilson 

 1978); and 3) the estimate of June 1974 estuarine inorganic 

 nitrogen flux to the Bight (58 t/d) is of the same order as 

 the 120 t/d estimated by Garside et al. (1976). 



These estimates of inorganic nitrogen flux do not in- 

 clude estuarine inputs of dissolved and particulate organic 

 nitrogen, probably very important forms of nutrient input 

 to the Bight. Mueller et al. (1976b) estimated that the 

 Hudson-Raritan estuary received from all sources 130 t/ 

 d of organic nitrogen, or 38 percent of all nitrogen inputs. 

 The large quantities of nitrogen flushed to the Bight as 

 phytopiankton (O'Reilly et al. 1976; Parker 1976: Malone 

 1977) and as dissolved organic matter (O'Reilly et al. 

 1976) deserve consideration. This is particularly true, be- 

 cause nitrogen is recycled rapidly in summer. The nitrogen 

 recycling rate above the pycnocline is estimated to be 0.5 

 to 2 days (Malone et al., ch. 9, pt. 1). Hence a significant 

 quantity of organic nitrogen is probably exported to the 

 Bight and mineralized rather quickly before settling below 

 the pycnocline, to be further oxidized or assimilated by 

 phytopiankton. Grazing copepods play an important role 

 in nutrient regeneration (Chervin 1978). Indeed, Garside 

 and Malone (1978) suggest that photosynthesized carbon 

 does not sink below the pycnocline "to any great extent" — 

 within an arc 40 km seaward of the Sandy Hook/Rockaway 

 Point transect during stratified summer seasons. 



A first-order estimate of 1.6 t/d of chlorophyll a is 

 flushed to the Bight via the estuary during summer (Parker 

 1976). This estimate is a refinement of one using the same 

 methodology by Duedall et al. 1977. The proportion of 

 particulate nitrogen to chlorophyll a, by weight, in June 



1975 was rather stable in the estuary and inner Bight and 

 was estimated at 6.8 (N):(Chl a) by Duedall et al. (1978). 

 Thus, the chlorophyll a flux estimate of Parker (1976) 

 implies a flux of about 11 t/d of nitrogen bound as partic- 

 ulate nitrogen, primarily as phytopiankton biomass. Given 

 the rapid cycling of this nitrogen in surface water during 

 summer, and its tendency to remain above the pycnocline 

 (ch. 9, pt. 1), it is likely that most of this nitrogen becomes 

 available rather rapidly and promotes further primary pro- 

 ductivity. 



The June-August daily inputs of nitrogen from the New 

 Jersey coast were calculated from sewage treatment plant 

 flows in summer (New Jersey Department of Environ- 

 mental Protection 1976) assuming 22 mg/l of total nitrogen 

 in the average of primary and secondary effluents (Mueller 

 et al. 1976b). This estimate (8.7 t/d) is only slightly higher 

 than that of Mueller et al. (1976b), but the total summer 

 nitrogenous inputs from the New Jersey coast are more 

 than 20 percent of those from the transect (table 15-1). 



Estimates are not available for nitrogenous releases to 

 the water column by ocean dumping; however, an esti- 

 mated 80 t total N/d is dumped as sewage sludge and 

 dredge material (Mueller et al. 1976b). These authors es- 

 timate that about 60 percent of the nitrogen is in the form 

 of ammonium and the remainder is bound with carbon. 

 It seems likely that most of the ammonium in sewage 

 sludge is released to the water column (O'Connors and 

 Duedall 1975). Some ammonium is apparently released 



Table 15-1. — Estimates of nitrogen loadings to waters inshore of 30 

 fathoms (55 m) during June-August, in metric tons per day 



Modified from Mueller et al. (1976b). 

 ' Estimated from total Kjeldahl nitrogen analyses. 



From Garside et al. (1976). 

 ' From Parker (1976); a refinement of an earlier estimate by Duedall 



et al. (1977). 



Derivations discussed in text. 



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