CHAPTERS 



STATIONS 



107 105 103 101 99 



I 106i 104 I 102 I 100 I 98 



97 

 96 



95 



93 



94 



L 



100 



25 50 75 100 



DISTANCE OFFSHORE (km) 



125 



150 



FIGURE 4-1 1. — Ammonium aincentriitions April 20 to May 4, 1976. BNL cross-shell transect values in p-g-at'l 



regions of the New Jersey shelf received little input (fig. 

 4-9). The extent of high bottom nitrate concentrations 

 was larger in 1976 than in the previous year, but low 

 oxygen was still observed simultaneously off New Jersey. 

 Winter 1975-76 nitrate concentrations were larger than 

 2 |xg-at/l nearshore, and there was some possible input 

 from the Hudson-Raritan runoff (fig. 4-10). Concentra- 

 tions greater than 0.5 |xg-at/l were present everywhere 

 over the shelf, and bottom concentrations were 2 to 5 |jLg- 

 at nitrate/I. Hudson River stations contained more than 

 20 |xg-at/l. and thus elevated nitrate concentrations in the. 

 Apex. 



Ammonium 



Ammonium concentrations were measured in fewer 

 samples than nitrate because they were measured only 

 when analyses were performed aboard ship. This severely 

 limits our ability to present an overall picture of nitrogen 

 nutrient distributions in 1975 and 1976. The 1976 spring 

 distribution (fig. 4-11) along the BNL transect (fig. 4—4) 

 off the Long Island coast was almost uniform across the 

 shelf and ranged from 0.5 to 2.0 ixg-at/l. 



In early autumn 1976, during the last part of the severe 

 oxygen depletion, ammonium levels were measured along 

 five transects (fig. 4-12). The transects off New Jersey 

 contained very high values near the bottom, especially in 

 transects I and II where values were greater than 20 (xg- 

 at/l. These high bottom concentrations were found in sam- 

 ples that also had little or no oxygen present. 



Transects off the Long Island coast showed lower am- 

 monium values, with a maximum of about 2 |JLg-at/l. Am- 

 monium concentrations (fig. 4-13) show high values near 

 the bottom, centered where the oxygen depletion was pre- 

 sent in the New Jersey shelf. This correlation between low 

 oxygen and high ammonium is shown more clearly in fig- 

 ure 4—14, where bottom ammonium values are plotted 

 against D.O. levels. Below oxygen values of 2.0 ml/1, the 

 ammonium levels increase almost exponentially as the 

 oxygen values declined to zero. Surface ammonium con- 

 centrations in figure 4-13 show no unusual pattern, with 

 typical values 0.5 to 2.0 |xg-at/l. Figure 4-13 also shows 

 evidence of a source of ammonium from Hudson-Raritan 

 discharge. 



Nitrite 



Figure 4-14 shows nitrite concentrations plotted against 

 D.O. in September 1976. Where the oxygen concentration 

 was below 3.0 ml/I, the NO," concentration showed a 

 definite increase, reaching a maximum at about 1.6 ml/1 

 oxygen. Below 1 .6 ml/I of oxygen, the nitrite concentration 

 dropped off again as the NO," was apparently reduced 

 to NHj"^ , as demonstrated in the bottom ammonium plot. 



An expected relationship between oxygen and nitrate 

 concenirations (fig. 4-14) is not so well defined as for 

 ammonium and nitrite. The combination of biological use. 

 advection, and nitrification in oxygenated waters evidently 

 produces a highly variable pattern of nitrate and oxygen 

 distribution in which equilibrium conditions may not pre- 



109 



