10-23 



tion) are easily mobilized in solution under reducing conditions but 

 their ultimate fate is burial in the sediment. 



Summary of Controls on Trace Metal Distribution in Long Island Sound 



Sediments 



There are three main sources of trace-metal supply to the 

 sediments of Long Island Sound as stated above: (1) industrially de- 

 rived metal-rich particles from streams draining into harbors and 

 directly into the Sound; (2) sewer outfalls in coastal areas; and (3) 

 atmospherically transported materials. In addition, it is possible to 

 include trace-metal-rich dredge spoils from contaminated harbors and 

 channels as a source analogous to the situation observed in the New York 

 Bight. 



The pattern of trace-metal distribution in the sediments of 

 Long Island Sound follows, to a first approximation, the pattern of 

 grain- size distribution - the trace-metal concentrations are highest, on 

 the average, in the finest grained sediments. But the second order 

 effect related to localized trace-metal inputs from contaminated rivers 

 or from sewer outfalls can also be seen - in particular, the sediments 

 of the western part of the Sound nearest to the highly impacted New York 

 City area around Throgs Neck. Those in the area west of the Housatonic 

 River estuary and those in New Haven Harbor are conspicuously higher in 

 trace metals than surrounding sediments independent of grain size. 



There is evidence from the distribution of energy at the 

 bottom of the Sound (Bokuniewicz, Gebert and Gordon, 1976) that the top 

 few millimeters of the fine-grained, metal-rich sediments, are resuspen- 

 ded and moved around the bottom of the Sound's central basin. This 



process would tend to homogenize the trace-metal concentrations at the 



234 

 sediment-water interface. When considering the Th (24 day half life) 



standing crop distribution in the uppermost part of the sediment column 



in cores collected from different water depths (Aller, Benninger and 



Cochran, 1979) , the time scale of this homogenization process is on the 



order of months. 



