CHAPTER 4 



vail. Data quality was responsible for only a minor part 

 of this observed variation. However, at low oxygen con- 

 centrations (<1.0 ml/1), where ammonium levels were 

 very high, the few measured nitrate values were low. 



Comparison of 1975 and 1976 nutrient distribution 



There are no apparent causal factors to be found in the 

 nutrient distribution itself that explain the low oxygen 

 concentrations in New York Bight in the summer of 1976. 

 However, the nutrient data exclude several possibilities, 

 such as larger than normal nutrient inputs from the Hud- 

 son River estuary or greatly prolonged or reduced rates 

 of transport of offshore water to the inner shelf region. 

 The outstanding differences in nutrient distributions be- 

 tween 1976 and 1975 are: smaller amounts of nutrients at 

 the shelf break in spring 1976; lower nitrate concentrations 

 over the entire shelf in July 1976 (when the oxygen de- 

 pletion developed); and extraordinarily larger concentra- 

 tions of ammonium and sulfide in the region of the 1976 

 low oxygen concentrations. Taken singly, these observa- 

 tions are not powerful clues to the cause of the oxygen 

 deficiency, but, taken together, they may be significant. 



If the source for water brought onto the shelf by up- 

 welling or other physical processes in 1976 had a deficit 

 of at least 3 jjLg-at NO /I, the resulting smaller concen- 

 trations of nitrate available on the shelf would favor de- 

 velopment of phytoplankton such as Ceratiiim tripos. 

 which can function at lower light and nutrient levels. This 

 might have contributed to Ceratium's domination of the 

 phytoplankton community (ch. 9, pt. 1). The uptake of 

 ammonium accounted for 66 percent of nitrogen uptake 

 in stations collected across the shelf (Conway and Whi- 

 tledge, personal communication). This probably also fa- 

 vors production of dinoflagellates such as Ceratium be- 

 cause of their affinity for ammonium-rich environments. 



The very low nitrate concentrations over the entire shelf 

 in July 1976 (even in bottom waters) probably resulted 

 from renewal processes being slower than usual compared 

 to biological uptake rates. The extraordinarily large con- 

 centrations of ammonium measured off New Jersey in 

 1976 are an order of magnitude larger than pristine oceanic 

 concentrations. Large ammonium concentrations have 

 been measured as high as 150 jig-at/l off marine sewage 

 outfalls (Whitledge, unpublished data), 500 to 1,200 jjig- 

 at/l in the New York Bight sewage sludge dumpsite (Due- 

 dall et al. 1975; Duedall et al. 1977), and somewhat lower 

 in anoxic areas like the Black Sea and Lake Nitinat (Rich- 

 ards et al. 1965). 



The distribution of ammonium off New Jersey suggests 

 its origin is other than Hudson-Raritan discharge. This 

 agrees with the limited range of estuarine influence from 

 the Hudson River found for nutrients (Segar and Berber- 

 ian 1976) and trace metals (Segar and Cantillo 1976). The 

 possibility of heavy organic loading, which decomposes 

 to produce the observed ammonium concentrations, is not 



great since the gradient for dissolved organic carbon in 

 the Hudson-Raritan discharge is small (fig. 4-15). 



The wide area where ammonium concentrations were 

 greater than 5 |i,g-at/l is probably where denitrification 

 processes occurred or where ammonium was not being 

 oxidized to nitrate. These high ammonium concentrations 

 were located where undetectable or minute quantities of 

 oxygen were measured (ch. 2) and in the general locations 

 where hydrogen sulfide was found. 



Off Long Island, the near-bottom concentrations of am- 

 monium were sometimes as high as 3 ixg-at/l in the BNL 

 transect (BNL, unpublished data), and these elevated con- 

 centrations occurred several meters above the bottom. 

 Whether these concentrations originated in the sediments 

 or in an organic layer of decomposing phytoplankton at 

 the sediment interface is not known. The highest concen- 

 trations of sulfide (equivalent to 56.2 (xg-at/1) correspond 

 well with amounts predicted from empirical relationships 

 in anoxic environments where the ratio ammonium:sulfide 

 was equal to 0.319 (Richards et al. 1965). 



DISSOLVED AND PARTICULATE 

 ORGANIC LOADING 



Depletion of D.O. in isolated bottom waters results 

 mostly from oxidation of organic matter. The nutrients 

 discussed above are important to the production of this 

 organic matter, but understanding the distribution of the 

 organic matter itself is important to any comprehension 

 of the causes of depletion. The limited information per- 

 tinent to the summer of 1976 is discussed below. 



During late August and early September 1976, samples 

 for particulate organic carbon (POC) and dissolved or- 

 ganic carbon (DOC) were collected during a National 

 Marine Fisheries Service (NMFS) cruise (fig. 4-16). POC 

 samples were analyzed using a Coleman carbon analyzer. 

 DOC samples were analyzed by the Marine Chemistry 

 Laboratory of the University of Delaware, using a mod- 

 ification (Sharp 1973) of the method of Menzel and Va- 

 carro (1964). This method is inaccurate compared to high 

 temperature combustion methodology (up to 25% lower 

 in deep ocean samples where more refractory carbon com- 

 pounds are found), but in relatively shallow coastal waters 

 the error is probably minimal (Sharp 1973). 



Ideally, interpretation of these data would include com- 

 parison to other measurements in coastal environments; 

 however, little such information exists. Additional un- 

 published data from the University of Delaware, desig- 

 nated NOAA Salt Marsh, and TransX, were utilized. The 

 DOC analytical methods used for these samples were the 

 same as for the NMFS samples, but POC analyses were 

 performed with a modified CHN analyzer (Sharp 1974). 



The 1976 NMFS cruise organic carbon data given in 

 table 4-8 are summarized in table 4-9 by grouping all 



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