10-9 



The Distribution of Trace Metals in Long Island Sound Sediments 



Horizontal Distribution 



Greig, Reid and Wenzlogg (1977) have recently made a detailed 

 study of the distribution of a number of trace metals (Sb, Cd, Co, Cr, 

 Cu, Pb, Mn, Ni, Ag, Sc, Zn) in the top 4 cm of Long Island Sound sedi- 

 ments using a Smith-Mclntyre grab sampler. The choice of 4 cm was 

 fortuitous since this represents, within plus or minus a centimeter, the 



rapidly reworked portion of the sediments as determined at Yale University 



234 

 using Th (Aller and Cochran, 1976) . Figures 10-5 through 10-7 show 



concentration maps for Cu, Zn and Pb constructed from their data. 



The primary control on the trace-metal concentration is the 

 grain size of the sediment. This can be seen by comparing Figures 10- 

 5 through 10-7 with Figure 10-8 which shows the grain-size distribution 

 in the Sound. The sand rich sediments have the lowest trace-metal 

 content. There is, however, an important second-order effect related to 

 the source of trace metals to coastal waters. Sediments adjacent to 

 Throgs Neck, the Housatonic River and New Haven Harbor are higher in 

 trace metals than other sediments of the same grain size. These three 

 areas are heavily impacted either by sewer outfalls or direct injection 

 of industrial sewage along a contiguous channel (as in the Naugatuck- 

 Housatonic system) . 



Distribution With Depth of Trace Metals in Cores 



A nvimber of cores collected from central Long Island Sound 

 have been analyzed for trace metals as a function of sediment depth 

 (Thomson, Turekian and McCaffrey, 1975) . They show roughly the same 

 patterns for Cu, Zn, Pb and Hg (Figure 10-9) with a homogeneous upper 2 to 

 4 cm zone and a roughly exponential decrease to a depth of about 30 cm. 

 At greater depths there are occasional peaks of high concentrations. 



Thomson, Turekian and McCaffrey (1975) interpreted the dis- 

 tribution patterns of metals to 30 cm as representing a superficial zone 



Text continued on page 10-15 



