NO A A PROFESSIONAL PAPER 11 



as shallow and those below as deep (the summer ther- 

 modine usually is close to the bottom of the photic zone). 

 This is done in figure 4-15, with stations 34, 41, and 109 

 grouped and stations 45, 69, 101, and 102 grouped. Again, 

 there is striking evidence of higher DOC in the Bight Apex 

 than in the estuary. Also striking is the extraordinarily 

 high value for the deep water at station 51 (this station 

 is nearer to the acid dumpsite than to the sewage sludge 

 dumpsite). There is a rather consistent offshore trend of 

 decreasing DOC which needs explanation. 



One reason for the very high values in the Apex may 

 be sludge dumping. That possibility has been explored 

 and shown to be unlikely (Segar and Berberian 1976; 

 Sharp 1976). Segar and Berberian suggest that the high 

 oxygen demand in this area is the result of high produc- 

 tivity supported by nutrients from the estuarine outflow. 

 Another cause of high nutrients that would also explain 

 the decrease of DOC in an offshore trend comes from a 

 mathematical model (Riley 1967). According to Riley, the 

 higher productivity in a shallow coastal region as com- 

 pared to farther offshore is a result of faster exchange 

 between surface and bottom waters. This, when coupled 

 with upwelling, can give a continuous and rapid supply of 



nutrients to the phytoplankton. Resulting higher produc- 

 tivity would ultimately give rise to more organic matter 

 in the water, which soon resides in the DOC pool. Sim- 

 ilarly, Han et al. (ch. 8) show greater upward vertical flux 

 for water in the Apex than in adjacent segments. (See 

 their fig. 8-12.) The strong flow of water to the north in 

 June (ch. 7) could also contribute to the concentration in 

 the Apex. 



Another explanation of the offshore carbon trend is 

 organic input from salt marshes. There are marshes all 

 along the New Jersey coast, and the NOAA Salt Marsh 

 data show output of DOC and POC throughout the year 

 (F.C. Daiber, personal communication). Since a consist- 

 ent data set is available for 1975 and 1976, it is possible 

 to see whether the marsh output of organic carbon was 

 exceptional in the second year. The NOAA Salt Marsh 

 data for the lower Delaware Bay are considered repre- 

 sentative of salt marshes along the New Jersey and Long 

 Island coasts. A more thorough analysis of actual fluxes 

 is being prepared (V. A. Lotrich, personal communica- 

 tion); the values to be considered here are averages of 

 ambient concentrations taken over tidal cycles. Values are 

 given in table 4-9 and are plotted in figure 4-17. As can 



1 1 



10 



9 



8 



7 



o> 

 E 



6h 



5 



4 



3 



2 



1 

 



M 



M 



J J 



MONTHS 



N 



FIGURE 4-17. — Total organic carbon (dissolved and particulate) m waters of a salt marsh on lower Delaware Bay in 1975 and 1976. (NOAA Salt 



Marsh data). 



118 



