WHOI's studies in 1948-49 showed the oxygen content near the bottom 

 of the dredge disposal grounds to be 61 percent of saturation and 50 per- 

 cent in the sludge disposal area. In July 1964, the WHOI investigation 

 found an oxygen minimum (which is considered normal for summer months) , 

 and in 1969 oxygen content in the sludge dump area had dropped to 27 

 percent of saturation (Ketchura, 1970) . 



Oxygen content of sea water near the bottom, compared to surface 

 concentration, is lower during the summer months; concentration between 

 surface and bottom levels differs from 2 to 13 parts per million (ppm) . 

 These differences diminish with the breakdown of the thermocline in 

 October-November. 



Reduced values of DO in bottom waters were found during summer in 

 both the sewage sludge and dredge spoil disposal areas by the SHL. Ac- 

 cording to the SHL study, DO in the dumping grounds is 2-3 ppm less 

 than in water outside the dump area at the same depth, and the DO level 

 in bottom water over the sewage sludge dump is frequently less than 

 2 ppm from late July to mid-October. This level is insufficient to 

 support life. On the average, dissolved oxygen ranged from 2.0 ppm to 

 15.2 ppm depending on sampling sites, season, and depth. 



Fig. 22 shows the DO content of surface and bottom water for a cross 

 section along both the sewer sludge and the dredge spoils dunqjing sites. 

 The sparcity of data precludes statistically significant conclusions and 

 the quantification of the B.O.D. in the area of the dumping grounds. 



c. Nutrients . In the Bight, concentrations of natural nutrients such 

 as phosphorus and nitrogen vary seasonally. Nitrate-nitrogen concentra- 

 tion in the surface waters is sometimes completely exhausted; small con- 

 centrations of phosphorus are always present. Nitrogen-phosphorus (N:P) 

 ratios fluctuate widely. During summer, vertical mixing provides nutrients 

 to the euphotic zone where there is enough light to permit growth of 

 green plants. In deep offshore waters of an area just east, of the Bight, 

 the N:P ratio was about 12:1 with low seasonal variation at the oxygen- 

 maximum-nutirent-maximum layer (Home et al, 1971, Ketchum et al, 1958). 

 In the dump areas, concentrations are expected to be different. Sewer 

 sludges disposed in the area are rich in certain nutrients. 



Concentrations of phosphorus (ortho, organic meta and total), nitrate, 

 and chlorophyll -a, within this area, were determined in the Bight by SHL. 

 Phosphorus, an essential nutrient in aquatic food chains, is abundant in 

 the sludges, and can serve as a tracer in following the movement of con- 

 taminated water. As expected^ the concentration of phosphorus was higher 

 in the dump area. SHL found concentrations of orthophosphorus up to 

 5.64 micro gram- atom per liter (yg-at/1), while reference levels, outside 

 the dumping grounds, ranged from 0.2-0.9 yg-at/1. 



Nitrogen, as reflected by N:P ratios, and chlorophyll-a concentrations, 

 are greatly affected by phosphorus concentrations. In the oceans, phyto- 

 plankton utilize both phosphates and nitrates and since the content of 



55 



