variation occurs near the mouth of the Harbor estuary where large flows 

 of fresh water from the rivers enter. The flow of the Hudson and Raritan 

 Rivers varies seasonally from less than 0.6 x 10^ cubic feet to more than 

 1.3 X 10^ cubic feet per day. This flow, in addition to other seasonal 

 variations, affects the physical -chemical properties of the nearshore 

 waters. 



During the winter, in the absence of a thermocline, the waters be- 

 come vertically homogeneous. Waters near the shore are colder and less 

 saline; further offshore, the waters are warmer and more saline. A 

 tongue of warmer ocean water is found along the Hudson Canyon (Home, 

 et al, 1971). Water temperature near the shore reaches a low of around 

 0°C; offshore water fluctuates around 5°C. The salinity varies also from 



31 parts per thousand (0/00) nearshore to 34 0/00 offshore, with lower 

 salinities at the mouth of the Hudson River. During spring, large flows 

 of warmer, fresh water enter the Bight. This water stays on the surface, 

 and establishes the beginning of a thermocline. The temperature differ- 

 ence between surface and bottom temperatures, at this time, is about 4°C. 

 During April, surface temperature varies from a little less than 1°C to 

 over S^C, and salinities vary from 20 0/00 at the Hudson River mouth to 



32 0/00 offshore. 



During the summer, the thermocline becomes pronounced; surface tempera- 

 tures vary between 20 and 25 °C, and bottom temperatures vary from under 

 10°C in the Hudson Canyon to 20°C elsewhere. Temperatures differ 5° to 

 6°C offshore and over the Hudson Canyon. Surface salinity varies from 25 

 0/00 to 32 0/00; the lower values are near the mouth of the river. Bottom 

 salinity varies from 28 0/00 to over 32 0/00 offshore. The difference 

 in salinity between surface and bottom ranges from a maximum of 3 0/00 

 near the mouth of the estuary to a slight value offshore. 



In autumn, the temperature-salinity structure is re-established. The 

 temperature drops and salinity increases as the river flow decreases. 

 The coldest water is again found onshore. Salinities vary from 27 0/00 

 to 33 0/00 and temperatures from 10°C-15°C. Figure 21 illustrates season- 

 al variation in salinity and temperature at two stations in the Bight, 

 measured by Ketchum, et al, (1951). The SHL investigation confirmed 

 Ketchum's results. Low salinity was found in the surface waters moving 

 from New York Harbor to the southwest. 



b. Dissolved Oxygen . Oxygen content is an important measure of 

 seawater's ability to support life. Dissolved oxygen (DO) concentration 

 in the sea varies with temperature, salinity, biological processes, and 

 degree of mixing. 



Oxygen content of the waters in and around the dumping grounds of 

 the Bight varies seasonally. (Fig. 21). Reduction of the DO in bottom 

 waters in this area has been correlated with biochemical oxygen demand 

 (B.O.D.) of the organically rich waste materials. 



54 



